Heredity PDF

CHAPTER 8 Heredity W e have seen that reproductive processes give rise to new individuals that are similar, but subtly different. We have discussed how some...

CHAPTER 8 Heredity W e have seen that reproductive processes give rise to new individuals that are similar, but subtly different. We have discussed how some amount of variation is produced even during asexual reproduction. And the number of successful variations are maximised by the process of sexual reproduction. If we observe a field of sugarcane we find very little variations among the individual plants. But in a number of animals including human beings, which reproduce sexually, quite distinct variations are visible among different individuals. In this chapter, we shall be studying the mechanism by which variations are created and inherited. 8. 1 A CCUMUL ATION OF V ARIA VARIA TION ARIATION DURING REPRODUCTION Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation. Now think about what would happen when this new generation, in its turn, reproduces. The second generation will have differences that they inherit from the first generation, as well as newly created differences (Fig. 8.1). Figure 8.1 would represent the situation if a single individual reproduces, as happens in asexual reproduction. If one bacterium divides, and then the Figure 8.1 resultant two bacteria divide again, the four Creation of diversity over succeeding individual bacteria generated would be very similar. generations. The original organism at the top There would be only very minor differences between will give rise to, say, two individuals, similar them, generated due to small inaccuracies in DNA in body design, but with subtle differences. copying. However, if sexual reproduction is involved, Each of them, in turn, will give rise to two even greater diversity will be generated, as we will individuals in the next generation. Each of see when we discuss the rules of inheritance. the four individuals in the bottom row will be different from each other. While some of Do all these variations in a species have equal these differences will be unique, others will chances of surviving in the environment in which they be inherited from their respective parents, find themselves? Obviously not. Depending on the who were different from each other. nature of variations, different individuals would have 128 Science 2024-25