SAT Subject Biology Practice Question 199: Answer and Explanation

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Question: 199

9. Two parents with dimples have a child with no dimples. The allele Dfor dimples is dominant. What are the possible genotypes of the parents?

I. DDand Dd

II. Ddand Dd

III. DDand dd

A. I only
B. II only
C. I or II
D. II or III
E. I, II, or III

Correct Answer: B


Both parents have the dominant phenotype (dimples), but their child does not. The child must have the recessive genotype dd. The child must have inherited one recessive allele d from each parent. Therefore, both parents must be heterozygotes (Dd).

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