The Nattukottai Chettiars (or Nakarattars) of Tamil Nadu, provide an interesting illustration of how these indigenous trading networks were organised and worked. A study of this community during the colonial period shows how its banking and trade activities were deeply embedded in the social organisation of the community. The structures of caste, kinship, and family were oriented towards commercial activity, and business activity was carried out within these social structures.

Many sociological studies of the Indian economy have focused on ‘traditional merchant communities’ or castes such as the Nakarattars. As you have already learned, there is a close connection between the caste system and the economy, in terms of landholding, occupational differentiation, and so on. This is also true in the case of trade and markets. In fact, ‘Vaisyas’ constitute one of the four varnas – an indication of the importance of the merchant and of trade or business in Indian society since ancient times. However, like the other varnas, ‘Vaisya’ is often a status that is claimed or aspired to rather than a fixed identity or social status. Although there are ‘Vaisya’ communities (such as banias in North India), whose traditional occupation has been trade or commerce for a long time, there are some caste groups that have entered into trade. Such groups tend to acquire or claim ‘Vaisya’ status in the process of upward mobility.

To understand the operation of markets in India, both in earlier periods and at present, we can examine how specific arenas of business are controlled by particular communities. One of the reasons for this caste-based specialisation is that trade and commerce often operate through caste and kinship networks, as we have seen in the case of the Nakarattars. Because businessmen are more likely to trust others of their own community or kin group, they tend to do business within such networks rather than with others outside – and this tends to create a caste monopoly within certain areas of business.

The advent of colonialism in India produced major upheavals in the economy, causing disruptions in production, trade, and agriculture. A well-known example is the demise of the handloom industry due to the flooding of the market with cheap manufactured textiles from England. Although pre-colonial India already had a complex monetised economy, most historians consider the colonial period to be the turning point. In the colonial era India began to be more fully linked to the world capitalist economy. Before being colonised by the British, India was a major supplier of manufactured goods to the world market. After colonisation, she became a source of raw materials and agricultural products and a consumer of manufactured goods, both largely for the benefit of industrialising England. At the same time, new groups (especially the Europeans) entered into trade and business, sometimes in alliance with existing merchant communities and in some cases by forcing them out. But rather than completely overturning existing economic institutions, the expansion of the market economy in India provided new opportunities to some merchant communities, which were able to improve their position by re-orienting themselves to changing economic circumstances. In some cases, new communities emerged to take advantage of the economic opportunities provided by colonialism, and continued to hold economic power even after Independence.

A good example of this process is provided by the Marwaris, probably the most widespread and best-known business community in India. Represented by leading industrial families such as the Birlas, the community also includes shopkeepers and small traders in the bazaars of towns throughout the country. The Marwaris became a successful business community only during the colonial period, when they took advantage of new opportunities in colonial cities such as Calcutta and settled throughout the country to carry out trade and moneylending. Like the Nakarattars, the success of the Marwaris rested on their extensive social networks, which created the relations of trust necessary to operate their banking system. Many Marwari families accumulated enough wealth to become moneylenders, and by acting as bankers also helped the commercial expansion of the British in India (Hardgrove 2004). In the late colonial period and after Independence, some Marwari families transformed themselves into modern industrialists, and even today Marwaris control more of India’s industry than any other community. This story of the emergence of a new business community under colonialism, and its transformation from small migrant traders to merchant bankers to industrialists, illustrates the importance of the social context to economic processes.


The growth of capitalism around the world has meant the extension of markets into places and spheres of life that were previously untouched by this system. Commodification occurs when things that were earlier not traded in the market become commodities. For instance, labour or skills become things that can be bought and sold. According to Marx and other critics of capitalism, the process of commodification has negative social effects. The commodification of labour is one example, but there are many other examples in contemporary society. For instance, there is a controversy about the sale of kidneys by the poor to cater to rich patients who need kidney transplants. According to many people, human organs should not become commodities. In earlier times, human beings themselves were bought and sold as slaves, but today it is considered immoral to treat people as commodities. But in modern society, almost everyone accepts the idea that a person’s labour can be bought, or that other services or skills can be provided in exchange for money. This is a situation that is found only in capitalist societies, according to Marx.

In contemporary India, we can observe that things or processes that earlier were not part of market exchange become commodified. For example, traditionally, marriages were arranged by families, but now there are professional marriage bureaus and websites that help people to find brides and grooms for a fee. Another example are the many private institutes that offer courses in ‘personality development’, spoken English, and so on, that teach students (mostly middle class youth) the cultural and social skills required to succeed in the contemporary world. In earlier times, social skills such as good manners and etiquette were imparted mainly through the family. Or we could think of the burgeoning of privately owned schools and colleges and coaching classes as a process of commodification of education.

Another important feature of capitalist society is that consumption becomes more and more important, not just for economic reasons but because it has symbolic meaning. In modern societies, consumption is an important way in which social distinctions are created and communicated. The consumer conveys a message about his or her socioeconomic status or cultural preferences by buying and displaying certain goods, and companies try to sell their goods by appealing to symbols of status or culture. Think of the advertisements that we see every day on television and roadside hoardings, and the meanings that advertisers try to attach to consumer goods in order to sell them.

One of sociology’s founders, Max Weber, was among the first to point out that the goods that people buy and use are closely related to their status in society. He coined the term status symbol to describe this relationship. For example, among the middle class in India today, the brand of cell phone or the model of car that one owns are important markers of socio-economic status. Weber also wrote about how classes and status groups are differentiated on the basis of their lifestyles. Consumption is one aspect of lifestyle, but it also includes the way you decorate your home and the way you dress, your leisure activities, and many other aspects of daily life. Sociologists study consumption patterns and lifestyles because of their cultural and social significance in modern life.

Since the late 1980s, India has entered a new era in its economic history, following the change in economic policy from one of state-led development to liberalisation. This shift also ushered in the era of globalisation, a period in which the world is becoming increasingly interconnected — not only economically but also culturally and politically. The term globalisation includes a number of trends, especially the increase in international movement of commodities, money, information, and people, as well as the development of technology (such as in computers, telecommunications, and transport) and other infrastructure to allow this movement.

A central feature of globalisation is the increasing extension and integration of markets around the world. This integration means that changes in a market in one part of the globe may have a profound impact somewhere else far away. For instance, India’s booming software industry may face a slump if the U.S. economy does badly (as happened after the 9/11 attacks on the World Trade Centre in New York), leading to loss of business and jobs here. The software services industries and business process outsourcing (BPO) industries (such as call centres) are some of the major avenues through which India is getting connected to the global economy. Companies based in India provide low-cost services and labour to customers located in the developed countries of the West. We can say that there is now a global market for Indian software labour and other services.


Under globalisation, not only money and goods, but also people, cultural products, and images circulate rapidly around the world, enter new circuits of exchange, and create new markets. Products, services, or elements of culture that were earlier outside of the market system are drawn into it. An example is the marketing of Indian spirituality and knowledge systems (such as yoga and ayurveda) in the West. The growing market for international tourism also suggests how culture itself may become a commodity. An example is the famous annual fair in Pushkar, Rajasthan, to which pastoralists and traders come from distant places to buy and sell camels and other livestock. While the Pushkar fair continues to be a major social and economic event for local people, it is also marketed internationally as a major tourist attraction. The fair is all the more attractive to tourists because it comes just before a major Hindu religious festival of Kartik Purnima, when pilgrims come to bathe in the holy Pushkar Lake. Thus, Hindu pilgrims, camel traders, and foreign tourists mingle at this event, exchanging not only livestock and money but also cultural symbols and religious merit.

The globalisation of the Indian economy has been due primarily to the policy of liberalisation that was started in the late 1980s. Liberalisation includes a range of policies such as the privatisation of public sector enterprises (selling government-owned companies to private companies); loosening of government regulations on capital, labour, and trade; a reduction in tariffs and import duties so that foreign goods can be imported more easily; and allowing easier access for foreign companies to set up industries in India. Another word for such changes is marketisation, or the use of markets or market-based processes (rather than government regulations or policies) to solve social, political, or economic problems. These include relaxation or removal of economic controls (deregulation), privatisation of industries, and removing government controls over wages and prices. Those who advocate marketisation believe that these steps will promote economic growth and prosperity because private industry is more efficient than government-owned industry.

The changes that have been made under the liberalisation programme have stimulated economic growth and opened up Indian markets to foreign companies. For example, many foreign branded goods are now sold, which were not previously available. Increasing foreign investment is supposed to help economic growth and employment. The privatisation of public companies is supposed to increase their efficiency and reduce the government’s burden of running these companies. However, the impact of liberalisation has been mixed. Many people argue that liberalisation and globalisation have had, or will have, a negative net impact on India – that is, the costs and disadvantages will be more than the advantages and benefits. Some sectors of Indian industry (like software and information technology) or agriculture (like fish or fruit) may benefit from access to a global market, but other sectors (like automobiles, electronics or oilseeds) will lose because they cannot compete with foreign producers.

For example, Indian farmers are now exposed to competition from farmers in other countries because import of agricultural products is allowed. Earlier, Indian agriculture was protected from the world market by support prices and subsidies. Support prices help to ensure a minimum income for farmers because they are the prices at which the government agrees to buy agricultural commodities. Subsidies lower the cost of farming because the government pays part of the price charged for inputs (such as fertilisers or diesel oil). Liberalisation is against this kind of government interference in markets, so support prices and subsidies are reduced or withdrawn. This means that many farmers are not able to make a decent living from agriculture. Similarly, small manufacturers have been exposed to global competition as foreign goods and brands have entered the market, and some have not been able to compete. The privatisation or closing of public sector industries has led to loss of employment in some sectors, and to growth of unorganised sector employment at the expense of the organised sector. This is not good for workers because the organised sector generally offers better paid and more regular or permanent jobs.

In this chapter we have seen that there are many different kinds of markets in contemporary India, from the village haat to the virtual stock exchange. These markets are themselves social institutions, and are connected to other aspects of the social structure, such as caste and class, in various ways. In addition, we have learned that exchange has a social and symbolic significance that goes far beyond its immediate economic purpose. Moreover, the ways in which goods and services are exchanged or circulate is rapidly changing due to the liberalisation of the Indian economy and globalisation. There are many different ways and levels at which goods, services, cultural symbols, money, and so on, circulate — from the local market in a village or town right up to a global trading network such as the Nasdaq. In today’s rapidly changing world, it is important to understand how markets are being constantly transformed, and the broader social and economic consequences of these changes.


In every society, some people have a greater share of valued resources – money, property, education, health, and power – than others. These social resources can be divided into three forms of capital – economic capital in the form of material assets and income; cultural capital such as educational qualifications and status; and social capital in the form of networks of contacts and social associations (Bourdieu 1986). Often, these three forms of capital overlap and one can be converted into the other. For example, a person from a well-off family (economic capital) can afford expensive higher education, and so can acquire cultural or educational capital. Someone with influential relatives and friends (social capital) may – through access to good advice, recommendations or information – manage to get a well-paid job.

Patterns of unequal access to social resources are commonly called social inequality. Some social inequality reflects innate differences between individuals for example, their varying abilities and efforts. Someone may be endowed with exceptional intelligence or talent, or may have worked very hard to achieve their wealth and status. However, by and large, social inequality is not the outcome of innate or ‘natural’ differences between people, but is produced by the society in which they live. Sociologists use the term social stratification to refer to a system by which categories of people in a society are ranked in a hierarchy. This hierarchy then shapes people’s identity and experiences, their relations with others, as well as their access to resources and opportunities. Three key principles help explain social stratification:
1. Social stratification is a characteristic of society, not simply a function of individual differences. Social stratification is a society-wide system that unequally distributes social resources among categories of people. In the most technologically primitive societies – hunting and gathering societies, for instance – little was produced so only rudimentary social stratification could exist. In more technologically advanced societies where people produce a surplus over and above their basic needs, however, social resources are unequally distributed to various social categories regardless of people’s innate individual abilities.
2. Social stratification persists over generations. It is closely linked to the family and to the inheritance of social resources from one generation to the next. A person’s social position is ascribed. That is, children assume the social positions of their parents. Within the caste system, birth dictates occupational opportunities. A Dalit is likely to be confined to traditional occupations such as agricultural labour, scavenging, or leather work, with little chance of being able to get high-paying white-collar or professional work. The ascribed aspect of social inequality is reinforced by the practice of endogamy. That is, marriage is usually restricted to members of the same caste, ruling out the potential for blurring caste lines through intermarriage.
3. Social stratification is supported by patterns of belief, or ideology. No system of social stratification is likely to persist over generations unless it is widely viewed as being either fair or inevitable. The caste system, for example, is justified in terms of the opposition of purity and pollution, with the Brahmins designated as the most superior and Dalits as the most inferior by virtue of their birth and occupation. Not everyone, though, thinks of a system of inequality as legitimate. Typically, people with the greatest social privileges express the strongest support for systems of stratification such as caste and race. Those who have experienced the exploitation and humiliation of being at the bottom of the hierarchy are most likely to challenge it.

Often we discuss social exclusion and discrimination as though they pertain to differential economic resources alone. This however is only partially true. People often face discrimination and exclusion because of their gender, religion, ethnicity, language, caste and disability. Thus, women from a privileged background may face sexual harassment in public places. A middle class professional from a minority religious or ethnic group may find it difficult to get accommodation in a middle class colony even in a metropolitan city. People often harbour prejudices about other social groups. Each of us grows up as a member of a community from which we acquire ideas not just about our ‘community’, our ‘caste’ or ‘class’ our ‘gender’ but also about others. Often these ideas reflect prejudices.

Prejudices refer to pre-conceived opinions or attitudes held by members of one group towards another. The word literally means ‘pre-judgement’, that is, an opinion formed in advance of any familiarity with the subject, before considering any available evidence. A prejudiced person’s preconceived views are often based on hearsay rather than on direct evidence, and are resistant to change even in the face of new information. Prejudice may be either positive or negative. Although the word is generally used for negative pre-judgements, it can also apply to favourable pre-judgement. For example, a person may be prejudiced in favour of members of his/her own caste or group and – without any evidence – believe them to be superior to members of other castes or groups.

Prejudices are often grounded in stereotypes, fixed and inflexible characterisations of a group of people. Stereotypes are often applied to ethnic and racial groups and to women. In a country such as India, which was colonised for a long time, many of these stereotypes are partly colonial creations. Some communities were characterised as ‘martial races’, some others as effeminate or cowardly, yet others as untrustworthy. In both English and Indian fictional writings we often encounter an entire group of people classified as ‘lazy’ or ‘cunning’. It may indeed be true that some individuals are sometimes lazy or cunning, brave or cowardly. But such a general statement is true of individuals in every group. Even for such individuals, it is not true all the time – the same individual may be both lazy and hardworking at different times. Stereotypes fix whole groups into single, homogenous categories; they refuse to recognise the variation across individuals and across contexts or across time. They treat an entire community as though it were a single person with a single all-encompassing trait or characteristic.

If prejudice describes attitudes and opinions, discrimination refers to actual behaviour towards another group or individual. Discrimination can be seen in practices that disqualify members of one group from opportunities open to others, as when a person is refused a job because of their gender or religion. Discrimination can be very hard to prove because it may not be open or explicitly stated. Discriminatory behaviour or practices may be presented as motivated by other, more justifiable, reasons rather than prejudice. For example, the person who is refused a job because of his or her caste may be told that he or she was less qualified than others, and that the selection was done purely on merit.


Social exclusion refers to ways in which individuals may become cut off from full involvement in the wider society. It focuses attention on a broad range of factors that prevent individuals or groups from having opportunities open to the majority of the population. In order to live a full and active life, individuals must not only be able to feed, clothe and house themselves, but should also have access to essential goods and services such as education, health, transportation, insurance, social security, banking and even access to the police or judiciary. Social exclusion is not accidental but systematic – it is the result of structural features of society.

It is important to note that social exclusion is involuntary – that is, exclusion is practiced regardless of the wishes of those who are excluded. For example, rich people are never found sleeping on the pavements or under bridges like thousands of homeless poor people in cities and towns. This does not mean that the rich are being ‘excluded’ from access to pavements and park benches, because they could certainly gain access if they wanted to, but they choose not to. Social exclusion is sometimes wrongly justified by the same logic – it is said that the excluded group itself does not wish to participate. The truth of such an argument is not obvious when exclusion is preventing access to something desirable (as different from something clearly undesirable, like sleeping on the pavement).

Prolonged experience of discriminatory or insulting behaviour often produces a reaction on the part of the excluded who then stop trying for inclusion. For example, ‘upper’ caste Hindu communities have often denied entry into temples for the ‘lower’ castes and specially the Dalits. After decades of such treatment, the Dalits may build their own temple, or convert to another religion like Buddhism, Christianity or Islam. After they do this, they may no longer desire to be included in the Hindu temple or religious events. But this does not mean that social exclusion is not being practiced. The point is that the exclusion occurs regardless of the wishes of the excluded.

India like most societies has been marked by acute practices of social discrimination and exclusion. At different periods of history protest movements arose against caste, gender and religious discrimination. Yet prejudices remain and often, new ones emerge. Thus, legislation alone is unable to transform society or produce lasting social change. A constant social campaign to change awareness and sensitivity is required to break them.

You have already read about the impact of colonialism on Indian society. What discrimination and exclusion mean was brought home to even the most privileged Indians at the hands of the British colonial state. Such experiences were, of course, common to the various socially discriminated groups such as women, dalits and other oppressed castes and tribes. Faced with the humiliation of colonial rule and simultaneously exposed to ideas of democracy and justice, many Indians initiated and participated in a large number of social reform movements.

In this chapter we focus on four such groups who have suffered from serious social inequality and exclusion, namely Dalits or the ex-untouchable castes; adivasis or communities refered to as ‘tribal’; women, and the differently abled. We attempt to look at each of their stories of struggles and achievements in the following sections.

Apart from these four groups, there are two more groups included in this category like transgender and people of third gender group. Information about these groups are given in Box 5.1a.


‘Untouchability’ is an extreme and particularly vicious aspect of the caste system that prescribes stringent social sanctions against members of castes located at the bottom of the purity-pollution scale. Strictly speaking, the ‘untouchable’ castes are outside the caste hierarchy – they are considered to be so ‘impure’ that their mere touch severely pollutes members of all other castes, bringing terrible punishment for the former and forcing the latter to perform elaborate purification rituals. In fact, notions of ‘distance pollution’ existed in many regions of India (particularly in the south) such that even the mere presence or the shadow of an ‘untouchable’ person is considered polluting. Despite the limited literal meaning of the word, the institution of ‘untouchability’ refers not just to the avoidance or prohibition of physical contact but to a much broader set of social sanctions.

It is important to emphasise that the three main dimensions of untouchability – namely, exclusion, humiliation-subordination and exploitation – are all equally important in defining the phenomenon. Although other (i.e., ‘touchable’) low castes are also subjected to subordination and exploitation to some degree, they do not suffer the extreme forms of exclusion reserved for ‘untouchables.’ Dalits experience forms of exclusion that are unique and not practised against other groups – for instance, being prohibited from sharing drinking water sources or participating in collective religious worship, social ceremonies and festivals. At the same time, untouchability may also involve forced inclusion in a subordinated role, such as being compelled to play the drums at a religious event. The performance of publicly visible acts of (self-)humiliation and subordination is an important part of the practice of untouchability. Common instances include the imposition of gestures of deference (such as taking off headgear, carrying footwear in the hand, standing with bowed head, not wearing Moreover, untouchability is almost always associated with economic exploitation clean or ‘bright’ clothes, and so on) as well as routinised abuse and humiliation. of various kinds, most commonly through the imposition of forced, unpaid (or under-paid) labour, or the confiscation of property. Finally, untouchability is a pan-Indian phenomenon, although its specific forms and intensity vary considerably across regions and socio-historical contexts.

The so-called ‘untouchables’ have been referred to collectively by many names over the centuries. Whatever the specific etymology of these names, they are all derogatory and carry a strongly pejorative charge. In fact, many of them continue to be used as forms of abuse even today, although their use is now a criminal offence. Mahatma Gandhi had popularised the term ‘Harijan’ (literally, children of God) in the 1930s to counter the pejorative charge carried by caste names.

However, the ex-untouchable communities and their leaders have coined another term, ‘Dalit’, which is now the generally accepted term for referring to these groups. In Indian languages, the term Dalit literally means ‘downtrodden’ and conveys the sense of an oppressed people. Though it was neither coined by Dr. Ambedkar nor frequently used by him, the term certainly resonates with his philosophy and the movement for empowerment that he led. It received wide currency during the caste riots in Mumbai in the early 1970s. The Dalit Panthers, a radical group that emerged in western India during that time, used the term to assert their identity as part of their struggle for rights and dignity.


Each and every organism can live only for a certain period of time. The period from birth to the natural death of an organism represents its life span. Life spans of a few organisms are given in Figure 1.1. Several other organisms are drawn for which you should find out their life spans and write in the spaces provided. Examine the life spans of organisms represented in the Figure 1.1. Isn’t it both interesting and intriguing to note that it may be as short as a few days or as long as a few thousand years? Between these two extremes are the life spans of most other living organisms. You may note that life spans of organisms are not necessarily correlated with their sizes; the sizes of crows and parrots are not very different yet their life spans show a wide difference. Similarly, a mango tree has a much shorter life span as compared to a peepal tree. Whatever be the life span, death of every individual organism is a certainty, i.e., no individual is immortal, except single-celled organisms. Why do we say there is no natural death in single-celled organisms? Given this reality, have you ever wondered how vast number of plant and animal species have existed on earth for several thousands of years? There must be some processes in living organisms that ensure this continuity. Yes, we are talking about reproduction, something that we take for granted.

Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself. The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death. Reproduction enables the continuity of the species, generation after generation. You will study later in Chapter 5 (Principles of Inheritance and Variation) how genetic variation is created and inherited during reproduction.

There is a large diversity in the biological world and each organism has evolved its own mechanism to multiply and produce offspring. The organism’s habitat, its internal physiology and several other factors are collectively responsible for how it reproduces. Based on whether there is participation of one organism or two in the process of reproduction, it is of two types. When offspring is produced by a single parent with or without the involvement of gamete formation, the reproduction is asexual. When two parents (opposite sex) participate in the reproductive process and also involve fusion of male and female gametes, it is called sexual reproduction.

In this method, a single individual (parent) is capable of producing offspring. As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent. Are these offspring likely to be genetically identical or different? The term clone is used to describe such morphologically and genetically similar individuals.

Let us see how widespread asexual reproduction is, among different groups of organisms. Asexual reproduction is common among single-celled organisms, and in plants and animals with relatively simple organisations. In Protists and Monerans, the organism or the parent cell divides by mitosis into two to give rise to new individuals (Figure1.2). Thus, in these organisms cell division is itself a mode of reproduction.

Many single-celled organisms reproduce by binary fission, where a cell divides into two halves and each rapidly grows into an adult (e.g., Amoeba, Paramecium). In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells). Under unfavourable condition the Amoeba withdraws its pseudopodia and secretes a three-layered hard covering or cyst around itself. This phenomenon is termed as encystation. When favourable conditions return, the encysted Amoeba divides by multiple fission and produces many minute amoeba or pseudopodiospores; the cyst wall bursts out, and the spores are liberated in the surrounding medium to grow up into many amoebae. This phenomenon is known as sporulation.

Members of the Kingdom Fungi and simple plants such as algae reproduce through special asexual reproductive structures (Figure 1.3). The most common of these structures are zoospores that usually are microscopic motile structures. Other common asexual reproductive structures are conidia (Penicillium), buds (Hydra) and gemmules (sponge). You have learnt about vegetative reproduction in plants in Class XI. What do you think – Is vegetative reproduction also a type of asexual reproduction? Why do you say so? Is the term clone applicable to the offspring formed by vegetative reproduction? While in animals and other simple organisms the term asexual is used unambiguously, in plants, the term vegetative reproduction is frequently used. In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offspring (Figure1.4). These structures are called vegetative propagules.


Asexual Reproduction
In this method, a single individual (parent) is capable of producing offspring. As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent. Are these offspring likely to be genetically identical or different? The term clone is used to describe such morphologically and genetically similar individuals.

Let us see how widespread asexual reproduction is, among different groups of organisms. Asexual reproduction is common among single-celled organisms, and in plants and animals with relatively simple organisations. In Protists and Monerans, the organism or the parent cell divides by mitosis into two to give rise to new individuals (Figure1.2). Thus, in these organisms cell division is itself a mode of reproduction.

Many single-celled organisms reproduce by binary fission, where a cell divides into two halves and each rapidly grows into an adult (e.g., Amoeba, Paramecium). In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells). Under unfavourable condition the Amoeba withdraws its pseudopodia and secretes a three-layered hard covering or cyst around itself. This phenomenon is termed as encystation. When favourable conditions return, the encysted Amoeba divides by multiple fission and produces many minute amoeba or pseudopodiospores; the cyst wall bursts out, and the spores are liberated in the surrounding medium to grow up into many amoebae. This phenomenon is known as sporulation.

Members of the Kingdom Fungi and simple plants such as algae reproduce through special asexual reproductive structures (Figure 1.3). The most common of these structures are zoospores that usually are microscopic motile structures. Other common asexual reproductive structures are conidia (Penicillium), buds (Hydra) and gemmules (sponge). You have learnt about vegetative reproduction in plants in Class XI. What do you think – Is vegetative reproduction also a type of asexual reproduction? Why do you say so? Is the term clone applicable to the offspring formed by vegetative reproduction? While in animals and other simple organisms the term asexual is used unambiguously, in plants, the term vegetative reproduction is frequently used. In plants, the units of vegetative propagation such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offspring (Figure1.4). These structures are called vegetative propagules.

Obviously, since the formation of these structures does not involve two parents, the process involved is asexual. In some organisms, if the body breaks into distinct pieces (fragments) each fragment grows into an adult capable of producing offspring (e.g., Hydra). This is also a mode of asexual reproduction called fragmentation. You must have heard about the scourge of the water bodies or about the ‘terror of Bengal’. This is nothing but the aquatic plant ‘water hyacinth’ which is one of the most invasive weeds found growing wherever there is standing water. It drains oxygen from the water, which leads to death of fishes. You will learn more about it in Chapters 13 and 14. You may find it interesting to know that this plant was introduced in India because of its beautiful flowers and shape of leaves. Since it can propagate vegetatively at a phenomenal rate and spread all over the water body in a short period of time, it is very difficult to get rid off them.

Are you aware how plants like potato, sugarcane, banana, ginger, dahlia are cultivated? Have you seen small plants emerging from the buds (called eyes) of the potato tuber, from the rhizomes of banana and ginger? When you carefully try to determine the site of origin of the new plantlets in the plants listed above, you will notice that they invariably arise from the nodes present in the modified stems of these plants. When the nodes come in contact with damp soil or water, they produce roots and new plants. Similarly, adventitious buds arise from the notches present at margins of leaves of Bryophyllum. This ability is fully exploited by gardeners and farmers for commercial propagation of such plants. It is interesting to note that asexual reproduction is the common method of reproduction in organisms that have a relatively simple organisation, like algae and fungi and that they shift to sexual method of reproduction just before the onset of adverse conditions. Find out how sexual reproduction enables these organisms to survive during unfavourable conditions? Why is sexual reproduction favoured under such conditions? Asexual (vegetative) as well as sexual modes of reproduction are exhibited by the higher plants. On the other hand, only sexual mode of reproduction is present in most of the animals.


Are you aware how plants like potato, sugarcane, banana, ginger, dahlia are cultivated? Have you seen small plants emerging from the buds (called eyes) of the potato tuber, from the rhizomes of banana and ginger? When you carefully try to determine the site of origin of the new plantlets in the plants listed above, you will notice that they invariably arise from the nodes present in the modified stems of these plants. When the nodes come in contact with damp soil or water, they produce roots and new plants. Similarly, adventitious buds arise from the notches present at margins of leaves of Bryophyllum. This ability is fully exploited by gardeners and farmers for commercial propagation of such plants. It is interesting to note that asexual reproduction is the common method of reproduction in organisms that have a relatively simple organisation, like algae and fungi and that they shift to sexual method of reproduction just before the onset of adverse conditions. Find out how sexual reproduction enables these organisms to survive during unfavourable conditions? Why is sexual reproduction favoured under such conditions? Asexual (vegetative) as well as sexual modes of reproduction are exhibited by the higher plants. On the other hand, only sexual mode of reproduction is present in most of the animals.

Sexual reproduction involves formation of the male and female gametes, either by the same individual or by different individuals of the opposite sex. These gametes fuse to form the zygote which develops to form the new organism. It is an elaborate, complex and slow process as compared to asexual reproduction. Because of the fusion of male and female gametes, sexual reproduction results in offspring that are not identical to the parents or amongst themselves.

A study of diverse organisms–plants, animals or fungi–show that though they differ so greatly in external morphology, internal structure and physiology, when it comes to sexual mode of reproduction, surprisingly, they share a similar pattern. Let us first discuss what features are common to these diverse organisms. ,All organisms have to reach a certain stage of growth and maturity in their life, before they can reproduce sexually. That period of growth is called the juvenile phase. It is known as vegetative phase in plants. This phase is of variable durations in different organisms. The end of juvenile/vegetative phase which marks the beginning of the reproductive phase can be seen easily in the higher plants when they come to flower. How long does it take for marigold/rice/wheat/coconut/mango plants to come to flower? In some plants, where flowering occurs more than once, what would you call the inter-flowering period – juvenile or mature?

Observe a few trees in your area. Do they flower during the same month year after year? Why do you think the availability of fruits like mango, apple, jackfruit, etc., is seasonal? Are there some plants that flower throughout the year and some others that show seasonal flowering? Plants –the annual and biennial types, show clear cut vegetative, reproductive and senescent phases, but in the perennial species it is very difficult to clearly define these phases. A few plants exhibit unusual flowering phenomenon; some of them such as bamboo species flower only once in their life time, generally after 50-100 years, produce large number of fruits and die. Another plant, Strobilanthus kunthiana (neelakuranji), flowers once in 12 years. As many of you would know, this plant flowered during September-October 2006. Its mass flowering transformed large tracks of hilly areas in Kerala, Karnataka and Tamil Nadu into blue stretches and attracted a large number of tourists. In animals, the juvenile phase is followed by morphological and physiological changes prior to active reproductive behaviour. The reproductive phase is also of variable duration in different organisms.

Among animals, for example birds, do they lay eggs all through the year? Or is it a seasonal phenomenon? What about other animals like frogs and lizards? You will notice that, birds living in nature lay eggs only seasonally. However, birds in captivity (as in poultry farms) can be made to lay eggs throughout the year. In this case, laying eggs is not related to reproduction but is a commercial exploitation for human welfare. The females of placental mammals exhibit cyclical changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase. In non-primate mammals like cows, sheep, rats, deers, dogs, tiger, etc., such cyclical changes during reproduction are called oestrus cycle where as in primates (monkeys, apes, and humans) it is called menstrual cycle. Many mammals, especially those living in natural, wild conditions exhibit such cycles only during favourable seasons in their reproductive phase and are therefore called seasonal breeders. Many other mammals are reproductively active throughout their reproductive phase and hence are called continuous breeders.

That we all grow old (if we live long enough), is something that we recognise. But what is meant by growing old? The end of reproductive phase can be considered as one of the parameters of senescence or old age. There are concomitant changes in the body (like slowing of metabolism, etc.) during this last phase of life span. Old age ultimately leads to death.

In both plants and animals, hormones are responsible for the transitions between the three phases. Interaction between hormones and certain environmental factors regulate the reproductive processes and the associated behavioural expressions of organisms.

Events in sexual reproduction : After attainment of maturity, all sexually reproducing organisms exhibit events and processes that have remarkable fundamental similarity, even though the structures associated with sexual reproduction are indeed very different. The events of sexual reproduction though elaborate and complex, follow a regular sequence. Sexual reproduction is characterised by the fusion (or fertilisation) of the male and female gametes, the formation of zygote and embryogenesis. For convenience these sequential events may be grouped into three distinct stages namely, the pre-fertilisation, fertilisation and the post-fertilisation events.


After their formation, male and female gametes must be physically brought together to facilitate fusion (fertilisation). Have you ever wondered how the gametes meet? In a majority of organisms, male gamete is motile and the female gamete is stationary. Exceptions are a few fungi and algae in which both types of gametes are motile (Figure1.7a). There is a need for a medium through which the male gametes move. In several simple plants like algae, bryophytes and pteridophytes, water is the medium through which this gamete transfer takes place. A large number of the male gametes, however, fail to reach the female gametes. To compensate this loss of male gametes during transport, the number of male gametes produced is several thousand times the number of female gametes produced.

In seed plants, pollen grains are the carriers of male gametes and ovule have the egg. Pollen grains produced in anthers therefore, have to be transferred to the stigma before it can lead to fertilisation (Figure 1.7b). In bisexual, self-fertilising plants, e.g., peas, transfer of pollen grains to the stigma is relatively easy as anthers and stigma are located close to each other; pollen grains soon after they are shed, come in contact with the stigma. But in cross pollinating plants (including dioecious plants), a specialised event called pollination facilitates transfer of pollen grains to the stigma. Pollen grains germinate on the stigma and the pollen tubes carrying the male gametes reach the ovule and discharge male gametes near the egg. In dioecious animals, since male and female gametes are formed in different individuals, the organism must evolve a special mechanism for gamete transfer. Successful transfer and coming together of gametes is essential for the most critical event in sexual reproduction, the fertilisation.

The most vital event of sexual reproduction is perhaps the fusion of gametes. This process called syngamy results in the formation of a diploid zygote. The term fertilisation is also often used for this process. The terms syngamy and fertilisation are frequently used though , interchangeably. What would happen if syngamy does not occur? However, it has to be mentioned here that in some organisms like rotifers, honeybees and even some lizards and birds (turkey), the female gamete undergoes development to form new organisms without fertilisation. This phenomenon is called parthenogenesis. Where does syngamy occur? In most aquatic organisms, such as a majority of algae and fishes as well as amphibians, syngamy occurs in the external medium (water), i.e., outside the body of the organism. This type of gametic fusion is called external fertilisation. Organisms exhibiting external fertilisation show great synchrony between the sexes and release a large number of gametes into the surrounding medium (water) in order to enhance the chances of syngamy. This happens in the bony fishes and frogs where a large number of offspring are produced. A major disadvantage is that the offspring are extremely vulnerable to predators threatening their survival up to adulthood.

In many terrestrial organisms, belonging to fungi, higher animals such as reptiles, birds, mammals and in a majority of plants (bryophytes, pteridophytes, gymnosperms and angiosperms), syngamy occurs inside the body of the organism, hence the process is called internal fertilisation. In all these organisms, egg is formed inside the female body where they fuse with the male gamete. In organisms exhibiting internal fertilisation, the male gamete is motile and has to reach the egg in order to fuse with it. In these even though the number of sperms produced is very large, there is a significant reduction in the number of eggs produced. In seed plants, however, the non-motile male gametes are carried to female gamete by pollen tubes.


In many terrestrial organisms, belonging to fungi, higher animals such as reptiles, birds, mammals and in a majority of plants (bryophytes, pteridophytes, gymnosperms and angiosperms), syngamy occurs inside the body of the organism, hence the process is called internal fertilisation. In all these organisms, egg is formed inside the female body where they fuse with the male gamete. In organisms exhibiting internal fertilisation, the male gamete is motile and has to reach the egg in order to fuse with it. In these even though the number of sperms produced is very large, there is a significant reduction in the number of eggs produced. In seed plants, however, the non-motile male gametes are carried to female gamete by pollen tubes.

Events in sexual reproduction after the formation of zygote are called post-fertilisation events.

Formation of the diploid zygote is universal in all sexually reproducing organisms. In organisms with external fertilisation, zygote is formed in the external medium (usually water), whereas in those exhibiting internal fertilisation, zygote is formed inside the body of the organism.

Further development of the zygote depends on the type of life cycle the organism has and the environment it is exposed to. In organisms belonging to fungi and algae, zygote develops a thick wall that is resistant to dessication and damage. It undergoes a period of rest before germination. In organisms with haplontic life cycle, zygote divides by meiosis to form haploid spores that grow into haploid individuals.

Zygote is the vital link that ensures continuity of species between organisms of one generation and the next. Every sexually reproducing organism, including human beings begin life as a single cell–the zygote.

Embryogenesis refers to the process of development of embryo from the zygote. During embryogenesis, zygote undergoes cell division (mitosis) and cell differentiation. While cell divisions increase the number of cells in the developing embryo; cell differentiation helps groups of cells to undergo certain modifications to form specialised tissues and organs to form an organism. You have studied about the process of cell division and differentiation in the previous class.

Animals are categorised into oviparous and viviparous based on whether the development of the zygote takes place outside the body of the female parent or inside, i.e., whether they lay fertilised/unfertilised eggs or give birth to young ones. In oviparous animals like reptiles and birds, the fertilised eggs covered by hard calcareous shell are laid in a safe place in the environment; after a period of incubation young ones hatch out. On the other hand, in viviparous animals (majority of mammals including human beings), the zygote develops into a young one inside the body of the female organism. After attaining a certain stage of growth, the young ones are delivered out of the body of the female organism. Because of proper embryonic care and protection, the chances of survival of young ones is greater in viviparous organisms.

In flowering plants, the zygote is formed inside the ovule. After fertilisation the sepals, petals and stamens of the flower wither and fall off. Can you name a plant in which the sepals remain attached? The pistil however, remains attached to the plant. The zygote develops into the embryo and the ovules develop into the seed. The ovary develops into the fruit which develops a thick wall called pericarp that is protective in function (Figure 1.8). After dispersal, seeds germinate under favourable conditions to produce new plants.


When once they are shed, pollen grains have to land on the stigma before they lose viability if they have to bring about fertilisation. How long do you think the pollen grains retain viability? The period for which pollen grains remain viable is highly variable and to some extent depends on the prevailing temperature and humidity. In some cereals such as rice and wheat, pollen grains lose viability within 30 minutes of their release, and in some members of Rosaceae, Leguminoseae and Solanaceae, they maintain viability for months. You may have heard of storing semen/sperms of many animals including humans for artificial insemination. It is possible to store pollen grains of a large number of species for years in liquid nitrogen (-196 Celcius). Such stored pollen can be used as pollen banks, similar to seed banks, in crop breeding programmes.

The gynoecium represents the female reproductive part of the flower. The gynoecium may consist of a single pistil (monocarpellary) or may have more than one pistil (multicarpellary). When there are more than one, the pistils may be fused together (syncarpous) (Figure 2.7b) or may be free (apocarpous) (Figure 2.7c). Each pistil has three parts (Figure 2.7a), the stigma, style and ovary. The stigma serves as a landing platform for pollen grains. The style is the elongated slender part beneath the stigma. The basal bulged part of the pistil is the ovary. Inside the ovary is the ovarian cavity (locule). The placenta is located inside the ovarian cavity. Arising from the placenta are the megasporangia, commonly called ovules. The number of ovules in an ovary may be one (wheat, paddy, mango) to many (papaya, water melon, orchids).

The Megasporangium (Ovule) : Let us familiarise ourselves with the structure of a typical angiosperm ovule (Figure 2.7d). The ovule is a small structure attached to the placenta by means of a stalk called funicle. The body of the ovule fuses with funicle in the region called hilum. Thus, hilum represents the junction between ovule and funicle. Each ovule has one or two protective envelopes called integuments. Integuments encircle the nucellus except at the tip where a small opening called the micropyle is organised. Opposite the micropylar end, is the chalaza, representing the basal part of the ovule. Enclosed within the integuments is a mass of cells called the nucellus. Cells of the nucellus have abundant reserve food materials. Located in the nucellus is the embryo sac or female gametophyte. An ovule generally has a single embryo sac formed from a megaspore.

Megasporogenesis: The process of formation of megaspores from the megaspore mother cell is called megasporogenesis. Ovules generally differentiate a single megaspore mother cell (MMC) in the micropylar region of the nucellus. It is a large cell containing dense cytoplasm and a prominent nucleus. The MMC undergoes meiotic division. What is the importance of the MMC undergoing meiosis? Meiosis results in the production of four megaspores (Figure 2.8a).

Female gametophyte: In a majority of flowering plants, one of the megaspores is functional while the other three degenerate. Only the functional megaspore develops into the female gametophyte (embryo sac). This method of embryo sac formation from a single megaspore is termed monosporic development. What will be the ploidy of the cells of the nucellus, MMC, the functional megaspore and female gametophyte?

Let us study formation of the embryo sac in a little more detail. The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. It is of interest to note that these mitotic divisions are strictly free nuclear, that is, nuclear divisions are not followed immediately by cell wall formation. After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac. Observe the distribution of cells inside the embryo sac (Figure 2.8b, c). Six of the eight nuclei are surrounded by cell walls and organised into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell. There is a characteristic distribution of the cells within the embryo sac. Three cells are grouped together at the micropylar end and constitute the egg apparatus. The egg apparatus, in turn, consists of two synergids and one egg cell. The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid. Three cells are at the chalazal end and are called the antipodals. The large central cell, as mentioned earlier, has two polar nuclei. Thus, a typical angiosperm embryo sac, at maturity, though 8-nucleate is 7-celled.


In the preceding sections you have learnt that the male and female gametes in flowering plants are produced in the pollen grain and embryo sac, respectively. As both types of gametes are non-motile, they have to be brought together for fertilisation to occur. How is this achieved? Pollination is the mechanism to achieve this objective. Transfer of pollen grains (shed from the anther) to the stigma of a pistil is termed pollination. Flowering plants have evolved an amazing array of adaptations to achieve pollination. They make use of external agents to achieve pollination.

Kinds of Pollination : Depending on the source of pollen, pollination can be divided into three types.
(i) Autogamy: In this type, pollination is achieved within the same flower. Transfer of pollen grains from the anther to the stigma of the same flower (Figure 2.9a). In a normal flower which opens and exposes the anthers and the stigma, complete autogamy is rather rare. Autogamy in such flowers requires synchrony in pollen release and stigma receptivity and also, the anthers and the stigma should lie close to each other so that self-pollination can occur. Some plants such as Viola (common pansy), Oxalis, and Commelina produce two types of flowers – chasmogamous flowers which are similar to flowers of other species with exposed anthers and stigma, and cleistogamous flowers which do not open at all. In such flowers, the anthers and stigma lie close to each other. When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollen landing on the stigma. Cleistogamous flowers produce assured seed-set even in the absence of pollinators. Do you think that cleistogamy is advantageous or disadvantageous to the plant?
(ii) Geitonogamy – Transfer of pollen grains from the anther to the stigma of another flower of the same plant. Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.
(iii) Xenogamy – Transfer of pollen grains from anther to the stigma of a different plant (Figure 2.9b). This is the only type of pollination which during pollination brings genetically different types of pollen grains to the stigma.

Agents of Pollination : Plants use two abiotic (wind and water) and one biotic (animals) agents to achieve pollination. Majority of plants use biotic agents for pollination. Only a small proportion of plants use abiotic agents. Pollen grains coming in contact with the stigma is a chance factor in both wind and water pollination. To compensate for this uncertainties and associated loss of pollen grains, the flowers produce enormous amount of pollen when compared to the number of ovules available for pollination.

Pollination by wind is more common amongst abiotic pollinations. Wind pollination also requires that the pollen grains are light and non-sticky so that they can be transported in wind currents. They often possess well-exposed stamens (so that the pollens are easily dispersed into wind currents) and large often-feathery stigma to easily trap air-borne pollen grains. Windpollinated flowers often have a single ovule in each ovary and numerous flowers packed into an inflorescence; a familiar example is the corn cob – the tassels you see are nothing but the stigma and style which wave in the wind to trap pollen grains. Wind-pollination is quite common in grasses.

Pollination by water is quite rare in flowering plants and is limited to about 30 genera, mostly monocotyledons. As against this, you would recall that water is a regular mode of transport for the male gametes among the lower plant groups such as algae, bryophytes and pteridophytes. It is believed, particularly for some bryophytes and pteridophytes, that their distribution is limited because of the need for water for the transport of male gametes and fertilisation. Some examples of water pollinated plants are Vallisneria and Hydrilla which grow in fresh water and several marine sea-grasses such as Zostera. Not all aquatic plants use water for pollination. In a majority of aquatic plants such as water hyacinth and water lily, the flowers emerge above the level of water and are pollinated by insects or wind as in most of the land plants. In Vallisneria, the female flower reach the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water. They are carried passively by water currents (Figure 2.11a); some of them eventually reach the female flowers and the stigma. In another group of water pollinated plants such as seagrasses, female flowers remain submerged in water and the pollen grains are released inside the water. Pollen grains in many such species are long, ribbon like and they are carried passively inside the water; some of them reach the stigma and achieve pollination. In most of the water-pollinated species, pollen grains are protected from wetting by a mucilaginous covering. Both wind and water pollinated flowers are not very colourful and do not produce nectar.


Majority of insect-pollinated flowers are large, colourful, fragrant and rich in nectar. When the flowers are small, a number of flowers are clustered into an inflorescence to make them conspicuous. Animals are attracted to flowers by colour and/or fragrance. The flowers pollinated by flies and beetles secrete foul odours to attract these animals. To sustain animal visits, the flowers have to provide rewards to the animals. Nectar and pollen grains are the usual floral rewards. For harvesting the reward(s) from the flower the animal visitor comes in contact with the anthers and the stigma. The body of the animal gets a coating of pollen grains, which are generally sticky in animal pollinated flowers. When the animal carrying pollen on its body comes in contact with the stigma, it brings about pollination.

In some species floral rewards are in providing safe places to lay eggs; an example is that of the tallest flower of Amorphophallus (the flower itself is about 6 feet in height). A similar relationship exists between a species of moth and the plant Yucca where both species – moth and the plant – cannot complete their life cycles without each other. The moth deposits its eggs in the locule of the ovary and the flower, in turn, gets pollinated by the moth. The larvae of the moth come out of the eggs as the seeds start developing.

Outbreeding Devices : Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression. Flowering plants have developed many devices to discourage selfpollination and to encourage cross-pollination. In some species, pollen release and stigma receptivity are not synchronised. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen. In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. Both these devices prevent autogamy. The third device to prevent inbreeding is self-incompatibility. This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil. Another device to prevent self-pollination is the production of unisexual flowers. If both male and female flowers are present on the same plant such as castor and maize (monoecious), it prevents autogamy but not geitonogamy. In several species such as papaya, male and female flowers are present on different plants, that is each plant is either male or female (dioecy). This condition prevents both autogamy and geitonogamy.

Pollen-pistil Interaction : Pollination does not guarantee the transfer of the right type of pollen (compatible pollen of the same species as the stigma). Often, pollen of the wrong type, either from other species or from the same plant (if it is self-incompatible), also land on the stigma. The pistil has the ability to recognise the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible). If it is of the right type, the pistil accepts the pollen and promotes post-pollination events that leads to fertilisation. If the pollen is of the wrong type, the pistil rejects the pollen by preventing pollen germination on the stigma or the pollen tube growth in the style. The ability of the pistil to recognise the pollen followed by its acceptance or rejection is the result of a continuous dialogue between pollen grain and the pistil. This dialogue is mediated by chemical components of the pollen interacting with those of the pistil. It is only in recent years that botanists have been able to identify some of the pollen and pistil components and the interactions leading to the recognition, followed by acceptance or rejection.


Outbreeding Devices : Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression. Flowering plants have developed many devices to discourage selfpollination and to encourage cross-pollination. In some species, pollen release and stigma receptivity are not synchronised. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen. In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. Both these devices prevent autogamy. The third device to prevent inbreeding is self-incompatibility. This is a genetic mechanism and prevents self-pollen (from the same flower or other flowers of the same plant) from fertilising the ovules by inhibiting pollen germination or pollen tube growth in the pistil. Another device to prevent self-pollination is the production of unisexual flowers. If both male and female flowers are present on the same plant such as castor and maize (monoecious), it prevents autogamy but not geitonogamy. In several species such as papaya, male and female flowers are present on different plants, that is each plant is either male or female (dioecy). This condition prevents both autogamy and geitonogamy.

Pollen-pistil Interaction : Pollination does not guarantee the transfer of the right type of pollen (compatible pollen of the same species as the stigma). Often, pollen of the wrong type, either from other species or from the same plant (if it is self-incompatible), also land on the stigma. The pistil has the ability to recognise the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible). If it is of the right type, the pistil accepts the pollen and promotes post-pollination events that leads to fertilisation. If the pollen is of the wrong type, the pistil rejects the pollen by preventing pollen germination on the stigma or the pollen tube growth in the style. The ability of the pistil to recognise the pollen followed by its acceptance or rejection is the result of a continuous dialogue between pollen grain and the pistil. This dialogue is mediated by chemical components of the pollen interacting with those of the pistil. It is only in recent years that botanists have been able to identify some of the pollen and pistil components and the interactions leading to the recognition, followed by acceptance or rejection.

As mentioned earlier, following compatible pollination, the pollen grain germinates on the stigma to produce a pollen tube through one of the germ pores (Figure 2.12a). The contents of the pollen grain move into the pollen tube. Pollen tube grows through the tissues of the stigma and style and reaches the ovary (Figure 2.12b, c). You would recall that in some plants, pollen grains are shed at two-celled condition (a vegetative cell and a generative cell). In such plants, the generative cell divides and forms the two male gametes during the growth of pollen tube in the stigma. In plants which shed pollen in the three-celled condition, pollen tubes carry the two male gametes from the beginning. Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus (Figure 2.12d, e). Many recent studies have shown that filiform apparatus present at the micropylar part of the synergids guides the entry of pollen tube. All these events–from pollen deposition on the stigma until pollen tubes enter the ovule–are together referred to as pollen-pistil interaction. As pointed out earlier, pollen-pistil interaction is a dynamic process involving pollen recognition followed by promotion or inhibition of the pollen. The knowledge gained in this area would help the plant breeder in manipulating pollen-pistil interaction, even in incompatible pollinations, to get desired hybrids.

As you shall learn in the chapter on plant breeding (Chapter 9), a breeder is interested in crossing different species and often genera to combine desirable characters to produce commercially ‘superior’ varieties. Artificial hybridisation is one of the major approaches of crop improvement programme. In such crossing experiments it is important to make sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollen). This is achieved by emasculation and bagging techniques.

If the female parent bears bisexual flowers, removal of anthers from the flower bud before the anther dehisces using a pair of forceps is necessary. This step is referred to as emasculation. Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. This process is called bagging. When the stigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parent are dusted on the stigma, and the flowers are rebagged, and the fruits allowed to develop.

If the female parent produces unisexual flowers, there is no need for emasculation. The female flower buds are bagged before the flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower rebagged.


As ovules mature into seeds, the ovary develops into a fruit, i.e., the transformation of ovules into seeds and ovary into fruit proceeds simultaneously. The wall of the ovary develops into the wall of fruit called pericarp. The fruits may be fleshy as in guava, orange, mango, etc., or may be dry, as in groundnut, and mustard, etc. Many fruits have evolved mechanisms for dispersal of seeds. Recall the classification of fruits and their dispersal mechanisms that you have studied in an earlier class. Is there any relationship between number of ovules in an ovary and the number of seeds present in a fruit?

In most plants, by the time the fruit develops from the ovary, other floral parts degenerate and fall off. However, in a few species such as apple, strawberry, cashew, etc., the thalamus also contributes to fruit formation. Such fruits are called false fruits (Figure 2.15b). Most fruits however develop only from the ovary and are called true fruits. Although in most of the species, fruits are the results of fertilisation, there are a few species in which fruits develop without fertilisation. Such fruits are called parthenocarpic fruits. Banana is one such example. Parthenocarpy can be induced through the application of growth hormones and such fruits are seedless.

Seeds offer several advantages to angiosperms. Firstly, since reproductive processes such as pollination and fertilisation are independent of water, seed formation is more dependable. Also seeds have better adaptive strategies for dispersal to new habitats and help the species to colonise in other areas. As they have sufficient food reserves, young seedlings are nourished until they are capable of photosynthesis on their own. The hard seed coat provides protection to the young embryo. Being products of sexual reproduction, they generate new genetic combinations leading to variations.

Seed is the basis of our agriculture. Dehydration and dormancy of mature seeds are crucial for storage of seeds which can be used as food throughout the year and also to raise crop in the next season. Can you imagine agriculture in the absence of seeds, or in the presence of seeds which germinate straight away soon after formation and cannot be stored? How long do the seeds remain alive after they are dispersed? This period again varies greatly. In a few species the seeds lose viability within a few months. Seeds of a large number of species live for several years. Some seeds can remain alive for hundreds of years. There are several records of very old yet viable seeds. The oldest is that of a lupine, Lupinus arcticus excavated from Arctic Tundra. The seed germinated and flowered after an estimated record of 10,000 years of dormancy. A recent record of 2000 years old viable seed is of the date palm, Phoenix dactylifera discovered during the archeological excavation at King Herod’s palace near the Dead Sea.

Although seeds, in general are the products of fertilisation, a few flowering plants such as some species of Asteraceae and grasses, have evolved a special mechanism, to produce seeds without fertilisation, called apomixis. What is fruit production without fertilisation called? Thus, apomixis is a form of asexual reproduction that mimics sexual reproduction. There are several ways of development of apomictic seeds. In some species, the diploid egg cell is formed without reduction division and develops into the embryo without fertilisation. More often, as in many Citrus and Mango varieties some of the nucellar cells surrounding the embryo sac start dividing, protrude into the embryo sac and develop into the embryos. In such species each ovule contains many embryos. Occurrence of more than one embryo in a seed is referred to as polyembryony.

Hybrid varieties of several of our food and vegetable crops are being extensively cultivated. Cultivation of hybrids has tremendously increased productivity. One of the problems of hybrids is that hybrid seeds have to be produced every year. If the seeds collected from hybrids are sown, the plants in the progeny will segregate and do not maintain hybrid characters. Production of hybrid seeds is costly and hence the cost of hybrid seeds become too expensive for the farmers. If these hybrids are made into apomicts, there is no segregation of characters in the hybrid progeny. Then the farmers can keep on using the hybrid seeds to raise new crop year after year and he does not have to buy hybrid seeds every year. Because of the importance of apomixis in hybrid seed industry, active research is going on in many laboratories around the world to understand the genetics of apomixis and to transfer apomictic genes into hybrid varieties.


Let us take the example of one such
hybridisation experiment carried out by
Mendel where he crossed tall and dwarf pea
plants to study the inheritance of one gene
(Figure 5.2). He collected the seeds produced
as a result of this cross and grew them to
generate plants of the first hybrid generation.
This generation is also called the Filial1
progeny or the F1. Mendel observed that all the F1 progeny plants were tall, like one of its parents; none were dwarf (Figure 5.3). He made similar observations for the other pairs of traits – he found that the F1 always resembled either one of the parents, and that the trait of the other parent was not seen in them.

Mendel then self-pollinated the tall F1 plants and to his surprise found that in the Filial2 generation some of the offspring were ‘dwarf’; the character that was not seen in the F1 generation was now expressed. The proportion of plants that were dwarf were 1/4th of the F2 plants while 3/4th of the F2 plants were tall. The tall and dwarf traits were identical to their parental type and did not show any blending, that is all the offspring were either tall or dwarf, none were of inbetween height (Figure 5.3).

Similar results were obtained with the other traits that he studied: only one of the parental traits was expressed in the F1 generation while at the F2 stage both the traits were expressed in the proportion 3:1. The contrasting traits did not show any blending at either F1 or F2 stage.

Based on these observations, Mendel proposed that something was being stably passed down, unchanged, from parent to offspring through the gametes, over successive generations. He called these things as ‘factors’. Now we call them as genes. Genes, therefore, are the units of inheritance. They contain the information that is required to express a particular trait in an organism. Genes which code for a pair of contrasting traits are known as alleles, i.e., they are slightly different forms of the same gene.

If we use alphabetical symbols for each gene, then the capital letter is used for the trait expressed at the F1 stage and the small alphabet for the other trait. For example, in case of the character of height, T is used for the Tall trait and t for the ‘dwarf’, and T and t are alleles of each other. Hence, in plants the pair of alleles for height would be TT, Tt or tt. Mendel also proposed that in a true breeding, tall or dwarf pea variety the allelic pair of genes for height are identical or homozygous, TT and tt, respectively. TT and tt are called the genotype of the plant while the descriptive terms tall and dwarf are the phenotype. What then would be the phenotype of a plant that had a genotype Tt?

As Mendel found the phenotype of the F1 heterozygote Tt to be exactly like the TT parent in appearance, he proposed that in a pair of dissimilar factors, one dominates the other (as in the F1 ) and hence is called the dominant factor while the other factor is recessive . In this case T (for tallness) is dominant over t (for dwarfness), that is recessive. He observed identical behaviour for all the other characters/trait-pairs that he studied. It is convenient (and logical) to use the capital and lower case of an alphabetical symbol to remember this concept of dominance and recessiveness. (Do not use T for tall and d for dwarf because you will find it difficult to remember whether T and d are alleles of the same gene/character or not). Alleles can be similar as in the case of homozygotes TT and tt or can be dissimilar as in the case of the heterozygote Tt. Since the Tt plant is heterozygous for genes controlling one character (height), it is a monohybrid and the cross between TT and tt is a monohybrid cross.

From the observation that the recessive parental trait is expressed without any blending in the F2 generation, we can infer that, when the tall and dwarf plant produce gametes, by the process of meiosis, the alleles of the parental pair separate or segregate from each other and only one allele is transmitted to a gamete. This segregation of alleles is a random process and so there is a 50 per cent chance of a gamete containing either allele, as has been verified by the results of the crossings. In this way the gametes of the tall TT plants have the allele T and the gametes of the dwarf tt plants have the allele t. During fertilisation the two alleles, T from one parent say, through the pollen, and t from the other parent, then through the egg, are united to produce zygotes that have one T allele and one t allele. In other words the hybrids have Tt. Since these hybrids contain alleles which express contrasting traits, the plants are heterozygous. The production of gametes by the parents, the formation of the zygotes, the F1 and F2 plants can be understood from a diagram called Punnett Square as shown in Figure 5.4. It was developed by a British geneticist, Reginald C. Punnett. It is a graphical representation to calculate the probability of all possible genotypes of offspring in a genetic cross. The possible gametes are written on two sides, usually the top row and left columns. All possible combinations are represented in boxes below in the squares, which generates a square output form.


The mechanism of sex determination has always been a puzzle before the geneticists. The initial clue about the genetic/chromosomal mechanism of sex determination can be traced back to some of the experiments carried out in insects. In fact, the cytological observations made in a number of insects led to the development of the concept of genetic/chromosomal basis of sex-determination. Henking (1891) could trace a specific nuclear structure all through spermatogenesis in a few insects, and it was also observed by him that 50 per cent of the sperm received this structure after spermatogenesis, whereas the other 50 per cent sperm did not receive it. Henking gave a name to this structure as the X body but he could not explain its significance. Further investigations by other scientists led to the conclusion that the ‘X body’ of Henking was in fact a chromosome and that is why it was given the name X-chromosome. It was also observed that in a large number of insects the mechanism of sex determination is of the XO type, i.e., all eggs bear an additional X-chromosome besides the other chromosomes (autosomes). On the other hand, some of the sperms bear the X-chromosome whereas some do not. Eggs fertilised by sperm having an X-chromosome become females and, those fertilised by sperms that do not have an X-chromosome become males. Do you think the number of chromosomes in the male and female are equal? Due to the involvement of the X-chromosome in the determination of sex, it was designated to be the sex chromosome, and the rest of the chromosomes were named as autosomes.Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.

These observations led to the investigation of a number of species to understand the mechanism of sex determination. In a number of other insects and mammals including man, XY type of sex determination is seen where both male and female have same number of chromosomes. Among the males an X-chromosome is present but its counter part is distinctly smaller and called the Y-chromosome. Females, however, have a pair of Xchromosomes. Both males and females bear same number of autosomes. Hence, the males have autosomes plus XY, while female have autosomes plus XX. In human beings and in Drosophila the males have one X and one Y chromosome, whereas females have a pair of X-chromosomes besides autosomes (Figure 5.12 a, b).

In the above description you have studied about two types of sex determining mechanisms, i.e., XO type and XY type. But in both cases males produce two different types of gametes, (a) either with or without X-chromosome or (b) some gametes with X-chromosome and some with Y-chromosome. Such types of sex determination mechanism is designated to be the example of male heterogamety. In some other organisms, e.g., birds, a different mechanism of sex determination is observed (Figure 5.12 c). In this case the total number of chromosome is same in both males and females. But two different types of gametes in terms of the sex chromosomes, are produced by females, i.e., female heterogamety. In order to have a distinction with the mechanism of sex determination described earlier, the two different sex chromosomes of a female bird has been designated to be the Z and W chromosomes. In these organisms the females have one Z and one W chromosome, whereas males have a pair of Z-chromosomes besides the autosomes.

It has already been mentioned that the sex determining mechanism in case of humans is XY type. Out of 23 pairs of chromosomes present, 22 pairs are exactly same in both males and females; these are the autosomes. A pair of X-chromosomes are present in the female, whereas the presence of an X and Y chromosome are determinant of the male characteristic. During spermatogenesis among males, two types of gametes are produced. 50 per cent of the total sperm produced carry the X-chromosome and the rest 50 per cent has Y-chromosome besides the autosomes. Females, however, produce only one type of ovum with an X-chromosome. There is an equal probability of fertilisation of the ovum with the sperm carrying either X or Y chromosome. In case the ovum fertilises with a sperm carrying X-chromosome the zygote develops into a female (XX) and the fertilisation of ovum with Y-chromosome carrying sperm results into a male offspring. Thus, it is evident that it is the genetic makeup of the sperm that determines the sex of the child. It is also evident that in each pregnancy there is always 50 per cent probability of either a male or a female child. It is unfortunate that in our society women are blamed for giving birth to female children and have been ostracised and ill-treated because of this false notion.


Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism. In addition to recombination, mutation is another phenomenon that leads to variation in DNA.

As you will learn in Chapter 6, one DNA helix runs continuously from one end to the other in each chromatid, in a highly supercoiled form. Therefore loss (deletions) or gain (insertion/duplication) of a segment of DNA, result in alteration in chromosomes. Since genes are known to be located on chromosomes, alteration in chromosomes results in abnormalities or aberrations. Chromosomal aberrations are commonly observed in cancer cells.

In addition to the above, mutation also arise due to change in a single base pair of DNA. This is known as point mutation. A classical example of such a mutation is sickle cell anemia. Deletions and insertions of base pairs of DNA, causes frame-shift mutations.

The mechanism of mutation is beyond the scope of this discussion, at this level. However, there are many chemical and physical factors that induce mutations. These are referred to as mutagens. UV radiations can cause mutations in organisms – it is a mutagen.

The idea that disorders are inherited has been prevailing in the human society since long. This was based on the heritability of certain characteristic features in families. After the rediscovery of Mendel’s work the practice of analysing inheritance pattern of traits in human beings began. Since it is evident that control crosses that can be performed in pea plant or some other organisms, are not possible in case of human beings, study of the family history about inheritance of a particular trait provides an alternative. Such an analysis of traits in a several of generations of a family is called the pedigree analysis. In the pedigree analysis the inheritance of a particular trait is represented in the family tree over generations. In human genetics, pedigree study provides a strong tool, which is utilised to trace the inheritance of a specific trait, abnormality or disease. Some of the important standard symbols used in the pedigree analysis have been shown in Figure 5.13.

As you have studied in this chapter, each and every feature in any organism is controlled by one or the other gene located on the DNA present in the chromosome. DNA is the carrier of genetic information. It is hence transmitted from one generation to the other without any change or alteration. However, changes or alteration do take place occasionally. Such an alteration or change in the genetic material is referred to as mutation. A number of disorders in human beings have been found to be associated with the inheritance of changed or altered genes or chromosomes.

Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sicklecell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. It is important to mention here that such Mendelian disorders may be dominant or recessive. By pedigree analysis one can easily understand whether the trait in question is dominant or recessive. Similarly, the trait may also be linked to the sex chromosome as in case of haemophilia. It is evident that this X-linked recessive trait shows transmission from carrier female to male progeny. A representative pedigree is shown in Figure 5.14 for dominant and recessive traits. Discuss with your teacher and design pedigrees for characters linked to both autosomes and sex chromosome.


In addition to the above, mutation also arise due to change in a single base pair of DNA. This is known as point mutation. A classical example of such a mutation is sickle cell anemia. Deletions and insertions of base pairs of DNA, causes frame-shift mutations.

The mechanism of mutation is beyond the scope of this discussion, at this level. However, there are many chemical and physical factors that induce mutations. These are referred to as mutagens. UV radiations can cause mutations in organisms – it is a mutagen.

The idea that disorders are inherited has been prevailing in the human society since long. This was based on the heritability of certain characteristic features in families. After the rediscovery of Mendel’s work the practice of analysing inheritance pattern of traits in human beings began. Since it is evident that control crosses that can be performed in pea plant or some other organisms, are not possible in case of human beings, study of the family history about inheritance of a particular trait provides an alternative. Such an analysis of traits in a several of generations of a family is called the pedigree analysis. In the pedigree analysis the inheritance of a particular trait is represented in the family tree over generations. In human genetics, pedigree study provides a strong tool, which is utilised to trace the inheritance of a specific trait, abnormality or disease. Some of the important standard symbols used in the pedigree analysis have been shown in Figure 5.13.

As you have studied in this chapter, each and every feature in any organism is controlled by one or the other gene located on the DNA present in the chromosome. DNA is the carrier of genetic information. It is hence transmitted from one generation to the other without any change or alteration. However, changes or alteration do take place occasionally. Such an alteration or change in the genetic material is referred to as mutation. A number of disorders in human beings have been found to be associated with the inheritance of changed or altered genes or chromosomes.

Broadly, genetic disorders may be grouped into two categories – Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sicklecell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc. It is important to mention here that such Mendelian disorders may be dominant or recessive. By pedigree analysis one can easily understand whether the trait in question is dominant or recessive. Similarly, the trait may also be linked to the sex chromosome as in case of haemophilia. It is evident that this X-linked recessive trait shows transmission from carrier female to male progeny. A representative pedigree is shown in Figure 5.14 for dominant and recessive traits. Discuss with your teacher and design pedigrees for characters linked to both autosomes and sex chromosome.

Colour Blidness : It is a sex-linked recessive disorder due to defect in either red or green cone of eye resulting in failure to discriminate between red and green colour. This defect is due to mutation in certain genes present in the X chromosome. It occurs in about 8 per cent of males and only about 0.4 per cent of females. This is because the genes that lead to red-green colour blindness are on the X chromosome. Males have only one X chromosome and females have two. The son of a woman who carries the gene has a 50 per cent chance of being colour blind. The mother is not herself colour blind because the gene is recessive. That means that its effect is suppressed by her matching dominant normal gene. A daughter will not normally be colour blind, unless her mother is a carrier and her father is colour blind.

Haemophilia : This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia may transmit the disease to sons. The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life). The family pedigree of Queen Victoria shows a number of haemophilic descendents as she was a carrier of the disease.

Sickle-cell anaemia : This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous). The disease is controlled by a singlepair of allele, HbA and HbS. Out of the three possible genotypes only homozygous individuals for HbS (HbSHbS) show the diseased phenotype. Heterozygous (HbAHbS) individuals appear apparently unaffected but they are carrier of the disease as there is 50 per cent probability of transmission of the mutant gene to the progeny, thus exhibiting sickle-cell trait (Figure 5.15). The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG. The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle like structure (Figure 5.15).

Phenylketonuria : This inborn error of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme that converts the amino acid phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives. Accumulation of these in brain results in mental retardation. These are also excreted through urine because of its poor absorption by kidney.