Please use the following information to answer the questions below.
A large population of laboratory animals has been allowed to breed randomly for a number of generations.After several generations,25% of the animals display a recessive trait (aa),the same percentage as at the beginning of the breeding program.The rest of the animals show the dominant phenotype,with heterozygotes indistinguishable from the homozygous dominants.
-What is the estimated frequency of allele A in the gene pool?
A)0.25
B)0.50
C)0.75
D)0.125

Question

Quizplus · Accepted Answer

Since 25% of the population exhibits the recessive trait, we can assume that they are all homozygous recessive (aa). Therefore, the frequency of aa genotype is 0.25. 
Let’s assume that p and q are the frequencies of alleles A and a respectively. Then, 
p + q = 1 
We know that aa frequency is q2 = 0.25 
So, 
q2 = 0.25 
q = 0.5 (square root both sides) 
p = 1 - q = 1 - 0.5 = 0.5 
Therefore, the frequency of allele A is 0.5.

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