Dihybrid cross: independent assortment, gene linkage and crossing over

BiologyGeneticsAges 17–18

A two-gene Punnett square shows each parent's gametes and their frequencies, cells colour-coded by phenotype, and genotype–phenotype ratios computed automatically (9:3:3:1 under independent assortment). Switch to gene linkage with a recombination frequency f: parental gametes each (1−f)/2, recombinant gametes each f/2, and the offspring ratio shifts with f and with the cis/trans arrangement. Students can change the parental genotypes, drag f, and cross 100 random individuals to compare experimental results with theory.