MCAT Biology Question 171: Answer and Explanation

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Question: 171

6. In a species of plant, a homozygous red flower (RR) is crossed with a homozygous yellow flower (rr). If the F₁2

A. Codominance
B. Incomplete dominance
C. Penetrance
D. Expressivity

Correct Answer: B

Explanation:

Some progeny in the second generation are apparently blends of the parental phenotypes. The orange color is the result of the combined effects of the red and yellow alleles. An allele is incompletely dominant if the phenotype of the heterozygotes is an intermediate of the phenotypes of the homozygotes.

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