Use this information to answer the following questions.
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 proportion of the population is probably heterozygous (Aa)for this trait?
A) 0.05
B) 0.25
C) 0.50
D) 0.75

Question

Quizplus · Accepted Answer

If 25% of the population displays the recessive trait (aa), and we assume that these individuals are homozgyous recessive (aa), then the remaining 75% of the population must be either heterozygous (Aa) or homozygous dominant (AA). Since heterozygotes and homozygous dominants are indistinguishable in appearance, we can assume that the proportion of heterozygotes is equal to the proportion of homozygous dominants. Therefore, the proportion of heterozygotes is 0.75/2 = 0.375 or 37.5%, which is closest to option C (0.50).

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