Heredity and Evolution

Quickly browse through questions and notes on related topics. You can also download and read this topic offline.

• Questions
• Summary

The change in inherited traits in a biological population over subsequent generations is called evolution.

Acquired Traits

1. These are the traits which are developed in an individual due to special conditions.
2. They cannot be transferred to the progeny.
3. They cannot direct evolution.E.g., the Low weight of starving beetles.

Inherited Traits

1. These are the traits which are passed from one generation to the next.
2. They get transferred to the progeny.
3. They are helpful in evolution.E.g., Colour of eyes and hair.

Scientists have proven that life evolved in the form of simple unicellular organisms on this earth; and all the organisms which are present today have evolved from a common ancestor. The idea of evolution is based on the premise of a common ancestry.

A group of twelve beetles. They live in bushes on green leaves. Their population will grow by sexual reproduction. So they were able to generate variations in the population.

Situation -1: Let us consider a case of red and green beetles:

A colour variation arises during reproduction. So that there appears one beetle that is green in colour instead of red.

Crows cannot see the green coloured beetles on green leaves of the bushes and therefore crows cannot eat them. But crows can see the red beetles and eat them. As a result, there are more and more green beetles than red ones which decrease in their number. The variation of colour in beetle ‘green’ gave a survival advantage to ‘green beetles’ than red beetles. In other words, it was naturally selected.

Conclusion:

We can see that the ‘natural selection’ was exerted by the crows. The more crows there are, the more red beetles would be eaten and the number of green beetles in the population would be. Thus the natural selection is directing evolution in the beetle population. It results in adaptation in the beetle population to fit in their environment better.

Situation-2: Let us consider a case of red and blue beetles:

In this situation, a colour variation occurs again in its progeny during reproduction, but now it results in ‘Blue’ colour beetles instead of ‘red’ colour beetle. This blue colour beetle can pass its colour to its progeny. So that all its progeny are blue.

Crows can see blue coloured beetles on the green leaves of the bushes and the red ones as well. And therefore crows can eat both red and blue coloured beetles. In this case, there is no survival
the advantage for blue coloured beetles as we have seen in case of green coloured beetles.

What happens initially in the population, there are a few blue beetles, but most are red. Imagine at this point an elephant comes by and stamps on the bushes where the beetles live. This kills most of the beetles. By chance, the few beetles survived are mostly blue. Again the beetle population slowly increases. But in the beetle population, most of them are in blue colour.

Thus sometimes accidents may also result in changes in certain characters of the population. Characters, as we know, are governed by genes.

Thus there is the change in the frequency of genes in small populations. This is known as “Genetic drift’, which provides diversity in the population.