Duplicate dominant epistasis produces a phenotypic ratio of
Duplicate dominant epistasis arises when dominant allele at either of two loci sufficient to produce same phenotype, so only double recessive expresses alternative phenotype. Pathway redundancy underlies mechanism where two genes encode duplicate enzymes or parallel routes leading to same end product, providing genetic robustness. In dihybrid cross AaBb x AaBb, phenotypic classes A-B- 9, A-bb 3, aaB- 3 all share dominant phenotype carrying at least one dominant, totaling 15, versus 1 aabb alternate, resulting in 15:1 ratio. Deviation from 9:3:3:1 signals functional redundancy and modifies Mend
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 6: Duplicate Dominant Epistasis 15:1