The F2 phenotypic ratio of a dihybrid cross between two heterozygotes is
- A. 9:3:3:1
- B. 3:1
- C. 1:1:1:1
- D. 12:3:1
Explanation
Each gene independently gives a three to one ratio, so combining two of them multiplies out to nine both dominant, three of each single dominant and one both recessive. The ratio holds only if the two genes assort independently, which requires them to be on different chromosomes. 1:1:1:1 is what a dihybrid test cross gives, and 12:3:1 arises when one gene masks another.
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