Practice question

Color inheritance in summer squash Cucurbita involves loci W for white dominance and Y for yellow versus green. Dominant W inhibits carotenoid biosynthesis, producing white fruit regardless of Y genotype, while ww allows color expression yellow Y- versus green yy. Cross WwYy x WwYy produces 12 white comprising 9 W-Y- plus 3 W-yy, 3 yellow wwY-, 1 green wwyy, giving 12:3:1 diagnostic of dominant epistasis. One dominant allele masks another gene effect. This contrasts with mouse coat recessive epistasis where cc masks, and poultry comb interaction where both dominants needed for novel walnut phenotype.