In a genetic cross having recessive epistasis, F2 phenotypic ratio would be 9:3:4. The recessive epistasis is illustrated by coat colour in mouse, the coat colour is determined by A\/a pair, recessive allele b is epistatic over A∕a. Thus, in the presence of bb both A and a give the same phenotype (albino). The F2 ratio is generally 9: 3: 4