Practice question

Mouse coat color system involving C locus for tyrosinase pigment production and B locus for black versus brown exemplifies recessive epistasis. Genotype cc lacks tyrosinase, preventing melanin synthesis entirely, producing albino phenotype regardless of B- or bb genotype, thereby masking agouti brown variation. Meanwhile C-B- yields agouti, C-bb brown producing remaining visible classes. Combined albino class includes 3 ccB- plus 1 ccbb totaling 4, yielding 9:3:4 ratio. Sweet pea demonstrates 9:7 complementary, rice awn duplicate dominant, squash dominant epistasis, mouse illustrating supplementary recessive masking.