Question

A small portion of a population migrates to an isolated island. Its genotypic frequencies are 0.8 AA, 0.1 Aa and 0.1 aa. These individuals start a new population on this island.  

1. What phenomenon is being described here?
2. Calculate the allele frequencies for this new island population.
3. Assume that this population is not undergoing evolution and undergoes random mating. What genotypic frequencies will you see in this population after one generation of random mating?
4. What will the allele and genotype frequencies be after 5 generations?

Answer 1

Q.1 What phenomenon is being described here?

Ans: Founder effect which is the special case of genetic drift

Q.2 Calculate the allele frequencies for this new island population.

Ans: AA= 0.8, Aa=0.1 and aa=0.1 then

Allelic frequency of (A) = freq (AA) + 1/2 freq (Aa)

= 0.8 + 1/2 (0.1)

= 0.8+0.1/2

= (1.6 + 0.1)/2

= 1.7/2

P=0.85 i.e frequency of allele (A)

we know, p + q =1

0.85 + q =1

q = 1- 0.85

q = 0.15 i.e frequency of allele (a)

Q. 3 genotypic frequencies will you see in this population after one generation of random mating?

Ans: As we know p2 + 2pq + q2 =1

Freq (AA) = p2

  = (0.85)2

   (AA)  = 0.723

Freq (Aa) = 2pq

= 2 (0.85 × 0.15)

(Aa) = 0.22

Freq (aa) = q2

= (0.15)2

   (aa) = 0.023

Q.4 What will the allele and genotype frequencies be after 5 generations?

Ans: Frequencies of allele and genotype will not change after five generations. As we know that in Hardy-Weinberg equilibrium key points that when a population is in Hardy-Weinberg equilibrium for a gene is not evolving then the allele and genotype frequencies will remain constant.