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.
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?
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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).