In breeding, the F2 phenotypic ratio of a monohybrid cross is three to one for each trait that is individually tested. This means that the dominant phenotype can arise in three different ways, with the recessive phenotype only having one chance of arising.
The three to one phenotypic ratio of a monohybrid cross was initially discovered by Gregor Mendel in his experiments in breeding pea plants. Mendel's testing was based on the assumption that each sperm has an equal chance of fertilizing an egg. In genetics, this concept is visualized using a Punnett square, which shows that each new plant has a three in four chance of having at least one dominant allele.