Variations in a Population


 
 
Concept Explanation
 

Variations in a Population

 Variation refers to the changes observed in phenotype, and genotype, the individuals in a population or between parents and their offspring. Suppose, twelve red beetles live in bushes with green leaves, their population grows by sexual reproduction and generates variations. In a population of beetles, variation may occur through the following means:

Case I

During reproduction, a colour variation may arise, which may lead to the production of a green beetle. It passes the green colour to its progeny. Crows cannot see green coloured beetles on green leaves, so they cannot eat them. Hence, the grey ones continues to be eaten and number of green beetles increases in the population. In this case, variation gives a survival advantage. The natural selection exerted by the crows will lead to the survival of green beetles.

                              

Case II

 In another situation, a colour variation arising during reproduction may result in a blue beetle instead of grey and all its progeny will be blue. Crows can see both blue and grey coloured beetles and therefore, can eat them. At the outset, there are a few blue beetles and more of grey beetles. Suddenly, an elephant stumps on the bushes and kills most of the beetles. By chance, the few beetles that survived were mostly blue, which gradually increase in number. This change in the frequency of some genes in a population which provides diversity without any survival disadvantage is called genetic drift.

                             

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Sample Questions
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Question : 1

In a forest ________________  cannot see green coloured beetles on green leaves, so they cannot eat them. 

Right Option : A
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Question : 2

 This change in the frequency of some genes in a population which provides diversity without any survival disadvantage is called _________________ .

Right Option : B
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Question : 3

Which of the following are correct ?

(a) Variation refers to the changes observed in phenotype, and genotype, of the individuals in a population or between parents and their offspring. 

(b) During reproduction variation of colour may arise, which may lead to the production of a green beetle. 

Right Option : C
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