What is the result of a genetic cross that produces a 3:1 phenotype ratio?

The observation of a 3:1 phenotype ratio in a genetic cross typically indicates complete dominance of one allele over another. This ratio commonly arises in a monohybrid cross, where two heterozygous individuals (both carrying one dominant and one recessive allele) are crossed. In this scenario, the dominant allele completely masks the expression of the recessive allele in the phenotype of the heterozygous individuals.

As a result, when the offspring are analyzed, approximately three-quarters will display the dominant trait, while one-quarter will show the recessive trait, leading to the characteristic 3:1 ratio. This clear differentiation between dominant and recessive traits illustrates how dominant alleles can overshadow the effects of recessive alleles in a phenotype when they are present.