Practice question

Sweet pea Lathyrus odoratus flower color requires dominant alleles at two loci C and P encoding enzymes catalyzing anthocyanin biosynthesis. C- converts colorless precursor to intermediate, P- converts intermediate to purple pigment; absence of either dominant halts pathway yielding white flowers. Cross CcPp x CcPp selfed produces 9 C-P- purple and 7 white comprising 3 C-pp plus 3 ccP- plus 1 ccpp. Ratio 9:7 demonstrates complementary interaction where both dominants needed. Bateson, Punnett, and Saunders classic 1905 experiment discovering this founded concept of gene interaction and duplicate recessive epistasis.