What is the expected phenotypic ratio in a monohybrid cross?

In a monohybrid cross, which examines the inheritance of a single trait, the typical expected phenotypic ratio is 3:1. This ratio arises from crossing two heterozygous parents for a particular trait. For example, if we consider a trait governed by a dominant allele (represented as "A") and a recessive allele (represented as "a"), the parental genotypes would be both "Aa".

When the gametes are formed, the combinations can result in these genotypes in the offspring:

1. AA (homozygous dominant)

2. Aa (heterozygous)

3. aa (homozygous recessive)

When analyzed, three out of four possible genotype combinations exhibit the dominant phenotype (AA and Aa), while only one exhibits the recessive phenotype (aa). This yields a phenotypic ratio of 3 exhibiting the dominant trait to 1 exhibiting the recessive trait, hence the ratio of 3:1.

In monohybrid crosses, this is a fundamental concept reflecting how traits segregate and assort during reproduction and provides a straightforward insight into Mendelian inheritance.