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MCAT Biology Question — Stable Expression of Traits

Stable expression of harmful recessive traits across generations most likely occurs in populations with a high level of:


A. emigration

B. natural selection

C. inbreeding

D. random mating

Click for Explanation

Stable expression of traits, even harmful recessive traits, most likely occurs in populations which satisfy the Hardy-Weinberg equilibrium conditions: 1) large population, 2) mutational equilibrium, 3) no immigration or emigration, 4) random mating, and 5) no selection for the fittest organism. The only answer choice satisfying one of these conditions is answer choice d) random mating.

A. emigration, incorrect, Emigration from a population will artificially alter the gene pool frequencies.

B. natural selection, incorrect, Selection for fittest organisms introduces bias towards certain genes in the pool, again taking away the random criterion for the statistical gene stability defined by Hardy-Weinberg.

C. inbreeding, incorrect, Inbreeding tends to increase the frequency of harmful recessive traits because it artificially creates a smaller subpopulation within the larger gene pool. These smaller populations also frequently share deleterious genes between relatives, thereby amplifying recessive gene expression. Inbreeding contradicts the large population and the random mating criteria of Hardy-Weinberg.

D. random mating, correct.

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