Practice question

Incomplete dominance occurs when single dose of functional product from dominant allele insufficient to reach threshold for full dominant phenotype, while recessive allele produces nonfunctional or low activity product. Heterozygote Aa therefore synthesizes intermediate amount of pigment, receptor, or enzyme, leading to phenotype distinct from both homozygotes, such as pink flowers from red RR x white rr. This contrasts with complete dominance where heterozygote resembles dominant homozygote, and with codominance where both allele products fully expressed simultaneously and detectable side by side, such as AB blood group antigens.