MCAT Biology Question 169: Answer and Explanation
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Question: 169
4. If a test cross on a species of plants reveals the appearance of a recessive phenotype in the offspring, what must be true of the phenotypically dominant parent?
- A. It must be genotypically heterozygous.
- B. It must be genotypically homozygous.
- C. It could be either genotypically heterozygous or homozygous.
- D. It must have the same genotype as the test cross control parent.
Correct Answer: A
Explanation:
The control parent in a test cross is always recessive. Therefore, if the test parent is phenotypically dominant, yet can provide a recessive allele (as evidenced by the presence of recessive children), then the parent must have both a dominant and recessive allele. Therefore, this test parent must by heterozygous.