SAT Subject Biology Practice Question 120: Answer and Explanation

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Question: 120

10. A test cross with an organism with a homozygous recessive genotype results in 50% of the offspring exhibiting the recessive trait. What is the genotype of the test-cross parent?

I. Homozygous recessive

II. Homozygous dominant

III. Heterozygous

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

Correct Answer: C

Explanation:

A test cross is when an individual reproduces with another whose genotype is known to be homozygous recessive. If the parent with unknown genotype is heterozygous, 50% of offspring will exhibit the dominant trait.

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