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Subject Test Biology

Question 20 of 24

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SAT Subject Test

The multiple choice questions have five answer choices — one (and only one) is correct in each case.

In a breeding experiment using gray and white mice of unknown genotypes, the following results were obtained.

Results of Breeding Experiment
  Parents Offspring
Cross Female   Male Gray White
I Gray X White 82 78
II Gray X Gray 118 39
III White X White 0 50
IV Gray X White 74 0

If two gray progeny of cross IV mate with each other, what is the probability that any one individual offspring will be gray?

Select an Answer

100 percent

Correct Answer: 

75 percent

Correct Answer: 

50 percent

Correct Answer: 

25 percent

Correct Answer: 

0 percent

Correct Answer: 

In cross IV, since the gray female parent must be homozygous dominant and the male parent is homozygous recessive, all of the offspring are heterozygous. The expected results from a cross of two heterozygous individuals is a phenotypic ratio of 3:1, resulting in a 0.75 (or 75%) probability that the offspring will show the dominant phenotype (gray) and a 0.25 (or 25%) probability that the offspring will show the recessive phenotype (white).

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