1. An organism with the genotype AABBCCDD is crossed with an organism with the genotype aabbccdd. For now, we'll only think about the A and the B genes. In the F2 generation, what proportion of the offspring would you expect to show the dominant phenotypes for both A and B?
2. In the F2 generation, what proportion of the offspring would you expect to be aaBbCCDd?
3. In the F2 generation, what proportion of the offspring would you expect to show the dominant trait for exactly 3 of the 4 genes?
Answer.
3).
A_B_C_ dd = 3/4 * 3/4 * 3/4 * 1/4 = 27/256
A_B_ cc D_ = 3/4 * 3/4 * 1/4 * 3/4 = 27/256
A_bb C_D_ = 3/4 * 1/4 * 3/4 * 3/4 = 27/256
aa_B_C_D_ = 1/4 * 3/4 * 3/4 * 3/4 = 27/256
Dominant phenotype for three genes out of four genes = 27/256 + 27/256 + 27/256 + 27/256 = 108/256 = 0.421
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