Practice question

Duplicate dominant epistasis occurs when dominant alleles at either of two loci independently encode functionally redundant enzymes producing identical phenotype. Only double homozygous recessive aabb lacks any functional copy and displays alternate trait, while all genotypes carrying at least one dominant allele A or B show common phenotype because either enzyme suffices. This redundancy causes fifteen individuals in F2 to share dominant outcome and one to show recessive, generating exactly two phenotypic classes 15:1. Shepherd's purse capsule or rice awn examples demonstrate interchangeable loci where either gene alone completes same developmental step effectively.