MCAT Biology Question 170: Answer and Explanation
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Question: 170
5. Which of the following definitions is FALSE?
- A. Penetrance—the percentage of individuals in the population carrying the allele who actually express the phenotype associated with it
- B. Expressivity—the percentage of individuals in the population carrying the allele who do not express the phenotype associated with it
- C. Incomplete dominance—occurs when the phenotype of the heterozygote is an intermediate of the phenotypes of the homozygotes
- D. Codominance—occurs when multiple alleles exist for a given gene and more than one of them is dominant
Correct Answer: B
Explanation:
The definition given here for expressivity is a much better match for defining penetrance (or, really, one minus the penetrance). Expressivity refers to the variable manifestations of a given genotype as different phenotypes; the degree to which various phenotypes are expressed. All of the other definitions given are accurate.