Practice question

Dominant epistasis emerges when dominant allele at one locus inhibits expression of second locus irrespective of its genotype, acting as dominant suppressor or inhibitor. In summer squash white fruit gene W masks yellow gene Y, producing twelve white fruits carrying W, three yellow with ww Y_, and one green with ww yy, giving 12:3:1 distribution. This three-class pattern distinguishes dominant epistasis from duplicates giving two classes or recessive epistasis giving 9:3:4. Recognising twelve as largest class signals dominant inhibitor acting upstream in pigment biosynthetic pathway blocking downstream colour manifestation.