2. Consider a species of butterflies that has two isolated subpopulations of equ
ID: 81494 • Letter: 2
Question
2. Consider a species of butterflies that has two isolated subpopulations of equal sizes on two different islands. The allele frequencies for two loci are given below. Allele Frequency Island 1 Island 2 F(A) 0.5 0.9 Locus 1 F(a) 0.1 0.5 Locus 2 F(B) 0.2 0.8 F(b 0.8 0.2 The two loci are unlinked and mating is essentially random within each island, so you can assume that each of the subpopulations are in Hardy-Weinberg equilibrium and that the two loci are in linkage equilibrium (D 0) within each of the two subpopulations. i. Calculate the observed frequencies of the A and Balleles in the global population (i.e., both islands combined). [2 pts F(A) 0.7 F(B) 0.5 ii. Calculate the observed frequency of the AB haploid genotype in the global population (i.e., both islands combined). [4 pts] F(AB) (0.18 0.4Y2 0.29Explanation / Answer
i)
Since size of populations is equal, we can average the frequencies in both populations.
fA) = (0.9+0.5)/2 =1.4/2=0.7
f(B) = (0.2+0.8)/2 =1/2=0.5
ii)
In island 1, f(A) = 0.9. It means 90% of alleles in this locus are A alleles. The rest 10% are a alleles of course.
So, 90% of gametes (haploids) have A allele.
In the same island, f(B) = 0.2. It means 20% of alleles in this locus are B alleles. So, 20% of gametes (haploids) have A allele.
Now we want to know, how many gametes have AB alleles.
Of all the gametes, only 90% have A allele. Out of those, only 20% have B alleles.
What is 20% of 90?
(90/20) x 100 = 0.18 x 100 = 18%
So, 18% gametes have AB alleles.
So, frequency of AB haploids is 0.18
It can be directly calculated from allele frequencies also.
f(A) = 0.9
f(B)= 0.2
f(AB) haploids = 0.9 x 0.2 = 0.18
We have to do similar calculations for the second island.
f(A) = 0.5
f(B)= 0.8
f(AB) haploids = 0.5 x 0.8 = 0.4
To calculate frequency for global population, we need to average the frequencies of individual populations (Please note that size of population is same here. If it is different, we have to apply appropriate ratio)
(0.18 +0.4)/2 = 0.58/2 = 0.29
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