Dihybrid Cross

Problem 2: When does a phenotype ratio of 9:3:3:1 occur?

Correct!

A phenotype ratio of 9:3:3:1 in the offspring of a mating of two organisms heterozygous for two traits is expected when:

A. the genes reside on the same chromosome
B. each gene contains two mutations
C. the gene pairs assort independently during meiosis
The parental organisms have the same phenotype, but their offspring have 4 different phenotypes. The 9: 3: 3: 1 ratio can only occur if the two traits assort independently during meiosis.

D. only recessive traits are scored
E. none of the above.

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Revised: October 30, 2003
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