AaBb × AaBb → 9:3:3:1 phenotype ratio
A dihybrid cross examines the inheritance of two independent traits simultaneously. Mendel's law of independent assortment states that alleles of different genes sort independently during gamete formation (when on different chromosomes). A cross of AaBb × AaBb produces a 4×4 Punnett square with 16 possible offspring combinations. The expected phenotype ratio is 9:3:3:1 — 9/16 show both dominant traits, 3/16 show first dominant + second recessive, 3/16 show first recessive + second dominant, 1/16 shows both recessive. Deviations from 9:3:3:1 indicate linked genes, epistasis, or other non-Mendelian inheritance patterns.