Question

scientists have observed that populations of salmon are migrating 2 weeks earlier on average than they did 40 years ago. based on this change in phenotype frequency, what must be true about the genes in the population? choose 1 answer: a the genes underlying the trait for earlier migration have become more common in the population. b the genes underlying the trait for later migration have become more common in the population. c the genes of the salmon have not been not affected, because this is a behavioral change.

Explanation:

• Option A: If salmon are migrating earlier, the genes for earlier migration trait likely increased in frequency (since phenotype frequency change reflects genotypic changes related to the trait).
• Option B: If later migration genes were more common, migration would be later, not earlier—so B is wrong.
• Option C: Behavioral traits like migration can be genetic; a phenotypic change (earlier migration) implies genetic changes, so C is wrong.

Answer:

A. The genes underlying the trait for earlier migration have become more common in the population.