Practice question

Dominant and recessive epistasis combines dominant masking at one locus with recessive masking effect from interaction across loci, generating unusual 13:3 ratio. Genotypes containing dominant suppressor A- show suppressed phenotype regardless of B locus, while among aa genotypes, B- shows active phenotype and bb shares suppressed phenotype with A- class, causing grouping 9+3+1 =13 suppressed versus 3 active. Mechanistically dominant inhibitor in one pathway plus recessive loss blocks pigment, as seen in white feather color chicken and grain color. Pattern distinct from simple 12:3:1 dominant or 9:3:4 recessive epistasis.