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

If the phenotypic character expressed by one gene is influenced by another single or group of genes is known as “epistasis.”

Assume that the second pair of alleles are the epistatic and the recessive genotype of the hypostatic gene causes lack of the characteristic. The resulting phenotypes from the F2 generation will be as follows (dominant epistasis):

• 13 progeny recessive for the 1^st pair or dominant for the 2^nd pair (i.e. no manifestation of the characteristic)
• 3 progeny recessive for the 2^nd pair and dominant for the 1^st pair (i.e. manifestation of the characteristic present)

Thus, the resulting phenotypic proportion will be, 13:3.

In case of recessive epistasis,

• 9 progeny double dominant pair (i.e. manifestation of the characteristic present)
• 7 progeny dominant for the 2^nd pair and recessive for the 1^st pair pair (i.e. manifestation of the characteristic present)

Thus, the resulting phenotypic proportion will be, 9:7.