Question

In a population of jaguars, a gene with two alleles encodes the fur color. Allele B causes melanism (dark fur) and is dominant over allele b, which results in light colored fur. Suppose that there is a migration event, producing a population with 60% BB, 20% Bb and 20% bb individuals. If we assume Hardy-Weinberg equilibrium for future generations, what would the genotypes frequencies be after 5 generations?

So the answer is 49% BB, 42% Bb, 9% bb.
But I'm confused. So BB which is p^2 = .6. Square rooting .6 is rougly .775 so P = .775. this means that Q = .225

but the answer has P = .7 and Q = .3

I know that you get the answer by finding P + 1/2pq for allele frequency of P, but how come it isn't the same as the other method of finding the answer?

Answer 1

The number of generations shouldn't affect the the genotype frequencies. the first thing to do is calculate allele frequencies, which is 0.7 for B and .3 for b.

B+b=1=allele frequencies

Since in the parental generation there are 49 individuals with the genotype BB, 42 individuals with the genotype Bb, and 9 individuals with the genotype bb, the frequency of B alleles will be the number of B alleles/total number of alleles, which is equal to [2(49)+42]/200=0.7. Solving for b using the equation above (b=1-B), we get b=0.3.

B=0.7
b=0.3

The genotype frequency is equal to the following:

(B+b)^2=B^2 +2Bb+b^2= 0.49 +0.42 + 0.09


Multiplying you values for B^2, 2Bb, and b^2 by 100

BB=49%
Bb=42%
bb=9%