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 (A2A2), the same percent 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 proportion of the population is most likely heterozygous (A1A2) for this trait?
A) 0.05
B) 0.25
C) 0.50
D) 0.75

Question

Quizplus · Accepted Answer

Given that 25% of the population displays the recessive trait (A2A2), we can deduce that the frequency of the recessive allele (a2) is 0.5 (since the square root of 0.25 is 0.5). This means that the frequency of the dominant allele (A1) is also 0.5 to make up the total allele frequency of 1. Using the Hardy-Weinberg principle, the proportion of heterozygotes (2pq) in the population can be calculated as 2(0.5)(0.5) = 0.50, indicating that 50% of the population is most likely heterozygous (A1A2).

A Large Population of Laboratory Animals Has Been Allowed to Breed