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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?

Question

Quizplus · Accepted Answer

If 25% of the population has the recessive trait (aa), that means the remaining 75% must have at least one dominant allele. Because heterozygotes (Aa) are indistinguishable from homozygous dominants (AA), we know that 75% of the population must either be AA or Aa. Half of those individuals will be heterozygous (Aa), so the proportion of the population that is probably heterozygous is 0.50.

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