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Small populations are prone to change in...

Small populations are prone to change in allelic frequencies which decrease genetic variability, this is explained by:

A

Sewall-Wright effect

B

Genetic load

C

Genetic flow

D

Mutation

Text Solution

Verified by Experts

The correct Answer is:
A
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observe the below diagram showing variation in beetle population and its impact. Let us consider a group of eweleve beetles. They live in bushes on green leaves. Their population will grow by sexual reproduction. So they were able to generate variations in population. Let us assume crows eat these red beetles. If the crows eat more Red beeles, their population is slowly reduced. let us disuss the above 3 different situations in detail. A. Situation-1 : in this situation a colour variation arises during reproduction. So that there appears one beetle that is green n colour instead of red moreover this green coloured beetle passes it's colur to it's offspring (Progeny ). So that all its progeny are green. 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 gren 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 word it was naturaly selected. 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 more 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 envirnment better. Let us think of another situation. Situation-2: In this situation a colour variation occurs again in its progeny during reproducation 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 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, butmost 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 change in the frequency of genes in small populations. this is known as genetic drift, which provides diversity in the population. Situation-3: In this case beetles population is increasing, but suddently bushes were affected by a lant disease in which leaf material were destroyed or in which leaves are affected by this beetles got les food material. So beetles are poorly nourished. So the weight of beetles decrease but no changes take place in their genetic material (DNA). After a few years the plant diseases are eliminated. Bushes are healthy with plenty of leaves. (Q) What do you think will be conditin of the beetles?

In a population, which is in Hardy-Weinberg equilibrium, the recessive allelic frequency is 0.8, in a population of 1300. Find out the number of dominant individuals in that population, if the gene in reference has only two alleles.

Knowledge Check

  • Random change in gene/allelic frequency occurring by chance but not under the control of natural selection is called

    A
    Genetic drift
    B
    Natural selection
    C
    Isolation
    D
    Adaptive radiation

  • (A) : Photoelectric effect can only be explained by the particle nature of light. (R): For every metal there exists a limiting frequency of the incident light called, threshold frequency, below which electron einission is not possible.

    A
    A and R are true and R is the correct explanation of A.
    B
    A and R are true and R is not the correct explanation of A.
    C
    A is true, R is false.
    D
    A is false, R is true.

  • Which of the following are reasons for population explosion? i) Increased health facilities ii) Rapid increase in MMR iii) Rapid increase in IMR iv) Rapid decrease in IMR v) Decrease in number of people reaching reproducable age

    A
    i& iv
    B
    iii & v
    C
    ii & iv
    D
    i & v

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