Question

In the hybridization of 2 genes (4 different alleles, 2 of each pair), how does epistasis affect the proportion of phenotypic forms in the F2 generation?

Answer 1

In dihybridism without epistasis, double heterozygous parents cross-breed and 4 phenotypical forms appear in F2. The proportion is 9 individuals double dominant, 3 individuals dominant for the first pair and recessive for the second pair, 3 individuals recessive for the first pair and dominant for the second pair, and 1 individual double recessive (9:3:3:1).

Considering that the epistatic gene is the second pair and that the recessive genotype of the hypostatic gene implies the lack of the characteristic, in the F2 generation of dominant epistasis, the following phenotypic forms would emerge: 13 individuals dominant for the second pair or recessive for the first pair, meaning that the characteristic is not manifest; 3 individuals dominant for the first pair and recessive for the second pair, meaning that the character is manifest.

The phenotypical proportion would be 13:3. In recessive epistasis, the phenotypical forms that would emerge in F2 are 9 individuals double dominant (the characteristic is manifest) and 7 individuals recessive for the first pair or recessive for the second pair, meaning that the character is not manifest. Therefore, the phenotypical proportion would be 9:7.