Mendel’s pea-plant experiments produced a typical F2 phenotypic ratio of 3:1 for a single-trait cross.
Gregor Mendel crossed pea plants differing in one contrasting characteristic, such as seed color or seed shape. The first-generation offspring, or F1 generation, generally displayed the dominant phenotype. When F1 plants self-fertilized, the recessive phenotype reappeared in the second generation.
For a simple dominant–recessive trait, about three F2 plants showed the dominant appearance for every one showing the recessive appearance. At the allele level, the expected genotype ratio was 1:2:1, which is different from the visible phenotype ratio.
The 3:1 result applies to a standard monohybrid cross under Mendelian assumptions. Real traits can be affected by incomplete dominance, multiple genes, environmental conditions, or viability differences, so not every biological trait follows this exact pattern.