Practice question

When both parents carry heterozygous genotype Aa, each produces gametes A and a in equal 50% frequency due to Mendelian segregation at meiosis. Random union generates Punnett square proportions AA 25%, Aa 50%, aa 25%. Because A is completely dominant over a, both AA and Aa exhibit dominant phenotype, together comprising 75% or three quarters, while aa exhibits recessive phenotype one quarter. This yields characteristic 3:1 dominant to recessive F2 ratio. Ratio appears only when both parents are heterozygous; any homozygous parent distorts segregation toward uniformity or 1:1 test cross pattern.