Question

What is the typical F2 ratio in the case of dominant epistasis?

Answer 1

The F2 ratio in dominant epistasis varies, with an example being 9 agouti : 3 solid color : 4 albino in mice or 15 triangular : 1 ovoid in shepherd's purse plant, depending on the gene interaction.

Step-by-step explanation:

The typical F2 ratio in the case of dominant epistasis is typically not the classic 9:3:3:1 observed in Mendel's dihybrid crosses, but it varies depending on the specific interaction between the genes involved. In the example of coat color in mice, where one gene (C) masks the expression of another gene (A), the phenotypic ratio observed is 9 agouti : 3 solid color : 4 albino, assuming that a cross is made between heterozygotes for both genes (AaCc x AaCc). However, in another form of epistasis, such as in the shepherd's purse plant, a cross between heterozygotes for both genes (AaBb x AaBb) can yield offspring with a phenotypic ratio of 15 triangular : 1 ovoid. This indicates that epistasis can result in various phenotypic ratios that deviate from the simple 9:3:3:1 ratio when two genes interact.

Answer 2

12:3:1

Step-by-step explanation:

The typical F2 ratio in cases of dominant epistasis is 12:3:1.

The epistasis is a form of gene interaction in which an allele in one locus interacts with and modifies the effects of alleles in another locus. There are different types of epistasis depending on the type of alleles that are interacting. These include:

• Dominant/simple epistasis: Here, a dominant allele on one locus suppresses the expression of both alleles on another locus irrespective of whether they are dominant or recessive. Instead of the Mendelian dihybrid F2 ratio of 9:3:3:1, what is obtained is 12:3:1. Examples of this type of gene interaction are found in seed coat color in barley, skin color in mice, etc.
• Other types of epistasis include recessive epistasis (9:3:4), dominant inhibitory epistasis (13:3), duplicate recessive epistasis (9:7), duplicate dominant epistasis (15:1), and polymeric gene interaction (9:6:1).