The typical F2 ratios for recessive epistasis are 9:7, and for dominant epistasis 12:3:1 and 12:4.

Date: 2015-10-07; view: 634.

Epistasis

Epistasis is the term applied when one gene interferes with the expression of another (as in the baldness/widow's peak mentioned earlier). Bateson reported a different phenotypic ratio in sweet pea than could be explained by simple Mendelian inheritance. This ratio is 9:7 instead of the 9:3:3:1 one would expect of a dihybrid cross between heterozygotes. Of the two genes (C and P), when either is homozygous recessive (cc or pp) that gene is epistatic to (or hides) the other. To get purple flowers one must have both C and P alleles present.

There are two types of epistasis: recessive epistasis (when an epistatic gene is recessive) and dominant epistasis (when an epistatic gene is dominant).