Genetic studies of an animal show that eye color is controlled by an autosomal gene with the dominant allele (R) for red
eye color and the recessive allele (r) for yellow eye color. A second autosomal gene has the dominant allele (T) for paws
with thumbs and the recessive allele (t) for paws without thumbs. The genetic cross RRTT x rrtt creates offspring with
genotype RrTt. One of those dihybrids is mated in a testcross (RrTt x rrtt). Based on the principle of independent
assortment, the testcross should produce offspring with the phenotype ratio ____.
a. 3 red-eyed with thumbs : 1 yellow-eyed without thumbs
b. 1 red-eyed with thumbs : 1 yellow-eyed with thumbs: 1 red-eyed without thumbs: 1 yellow-eyed without
thumbs
c. 1 red-eyed with thumbs : 1 yellow-eyed without thumbs
d. 9 red-eyed with thumbs : 3 yellow-eyed with thumbs: 3 red-eyed without thumbs: 1 yellow-eyed without
thumbs
e. 3 yellow-eyed with thumbs : 1 red-eyed without thumbs
ANSWER: b
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