Practice question

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 Mendelian expectation profoundly.