SAT Subject Biology Practice Question 416: Answer and Explanation

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Question: 416

6. A self-pollinating plant with orange flowers and alternating leaf arrangement produces 47 plants with red flowers and alternating leaves, 103 plants with orange flowers and alternating leaves, and 51 plants with yellow flowers and alternating leaves.

The genotype of the original parent plant is

A. heterozygous for both flower color and leaf arrangement
B. homozygous for both flower color and leaf arrangement
C. homozygous for flower color and heterozygous for leaf arrangement
D. heterozygous for flower color and homozygous for leaf arrangement
E. heterozygous for flower color but unable to determine genotype for leaf arrangement

Correct Answer: D

Explanation:

D We know that the plant must be heterozygous for flower color, because that's the only way you can get orange flowers (the blended phenotype). Choices B and C can be eliminated. Furthermore, the plant must be homozygous for leaf arrangement because all progeny plants look like the parent plant. If the self-pollinated parent plant had been heterozygous for leaf arrangement, we would have expected to see different phenotypes in the offspring (choices A and E can be eliminated).

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