Hi, I typed the question in the format given from a to e. Thank you in advance.

Question

Hi, I typed the question in the format given from a to e. Thank you in advance.

5. Imagine a diploid animal species with a single gene that controls the production of a particular digestive enzyme. Currently, there are 3 alleles for this gene present in the population you are studying, and the population is in Hardy-Weinbern equilibrium.

a. Assume we are using typical notation to designate allele frequencies. Describe in words what adding up these values tells you about the population. Be as specific as possible, but use the information given in the problem.

2pq + 2pr + 2qr

b. Which of these eight situations could cause there to be one individual in this population that carries one copy of a new, different form of this gene? (circle all correct answers)

Non-random mating mutation genetic drift

directional selection          speciation gene flow

sexual reproduction predation

c. Suppose that this population has 1billion individuals. Based on part a, and assuming that part b occurs, define “s” and explain why someone might say that p + q + r +s = 1 and why someone else might reasonably argue that p + q + r = 1.

d. Make up and describe a specific situation where the introduction of this fourth allele for the digestive enzyme gene makes no difference at all in the microevolution of this population. Be complete, specific and concise in your explanation.

e. Make up and describe a specific situation where the introduction of this fourth digestive enzyme allele does make a difference in the population’s evolution and genetic drift is involved. Be complete, specific and concise in your explanation.

f. Make up and describe a specific situation where the introduction of this fourth digestive enzyme allele does make a difference in the population’s evolution and sexual selection is involved. Be complete, specific and concise in your explanation.

Explanation / Answer

a. The question deals with 3 alleles occupying the locus. The hardy Weinberg equation concerning 3 alleles is :
(p + q + r)2 = p2 + 2pq + q2 + 2qr + r2 + 2pr = 1
The values 2pq + 2pr + 2qr = heterozygosity of the 3 alleles.

b. The evolution of one copy of a new form of a gene means new type of allele. The new allele can form only when it enters from outside the population (gene flow) or when a mutation occurs in the existing population and new form arises (mutation). The speciation can also give rise to new alleles in the population. Rest all condition given in the question, only reshuffle the gene pool to create new combination but do not add anything new.

c. The new allele 's' is the new entrant. It also adds up to the hardy Weinberg equilibrium and add upto 1. So this might show that p+q+r+s = 1. Since, population is 1 billion, it might play a significant role.
However, this formula works only when there is random mating in the population. So it may still not count with other alleles and formula would remain as p+q+r = 1.

d. The new allele is for digestive enzyme. In the microevolution, this new entrant must have a significant advantage. Assuming that this allele 's' is only a minor missese mutation and does not change the structure and function of the digestive enzyme. This one allele will not make a difference. The new form can alter the gene of the enzyme , but structure of the enzyme would remain the same , and so is the function.

e. Let us say this new allele arose due to mutation at one of the coding region of the digestive gene. This mutation is a non sense mutation and it produced a truncated protein. This new enzyme cannot function properly and as a result digestion will be affected. In such a situation, this new allele will make a difference on the population. In case of genetic drift, randomly some forms may get selected and other may get eliminated. Since genetic drift is non selective in nature, the new allele would not have any impact on the chance of drift.

f. Assuming similar situation where the truncated enzyme produced by the mutation has created a gene pool of individuals with low digestive capacity. Now these individuals will be weak and cannot compete with the other members during sexual selection. Thus the mutated allele bearers will be eliminated without chance to reproduce. As a result the frequency of the new allele would decrease and there might only be carriers for the alleles and not the homozygous individuals.

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