Practice question

Complementary gene interaction involves two independently assorting non-allelic loci controlling one trait through sequential biosynthetic pathway where each dominant allele encodes distinct enzyme. Neither allele alone can produce final end product because intermediate from first reaction must be processed by second enzyme. Classic sweet pea flower colour illustrates mechanism: genes C and P convert colourless precursor to purple anthocyanin stepwise requiring both dominant alleles together; any homozygous recessive genotype remains white. This functional cooperation yields characteristic 9:7 ratio in F2 progeny, demonstrating pathway dependence.