The phenotypic ratio in Mendel’s monohybrid F2 generation was 3:1.
This result appears when two F1 hybrids, each carrying one dominant and one recessive allele, are crossed. Their expected genotypes are 1 homozygous dominant, 2 heterozygous, and 1 homozygous recessive. Because both the homozygous dominant and heterozygous plants show the dominant appearance, the visible phenotypes occur in a 3:1 ratio.
For Mendel’s pea experiments, three-quarters of the F2 plants typically displayed the dominant trait and one-quarter displayed the recessive trait. The ratio is a theoretical expectation; actual counts can vary because biological experiments involve chance and finite sample sizes.
The commonly confused ratio 9:3:3:1 belongs to a dihybrid cross, in which two traits are followed at once. The corresponding monohybrid genotypic ratio is 1:2:1, not 3:1.