What is the expected phenotypic ratio in a monohybrid cross?

In a monohybrid cross, which involves a single trait determined by one gene with two alleles, the expected phenotypic ratio is 3:1. This occurs when you cross two heterozygous individuals for that trait, typically represented as Aa x Aa, where A is the dominant allele and a is the recessive allele.

When you perform this cross, the possible gametes from each parent are A and a, leading to the following combinations in the offspring: AA, Aa, Aa, and aa. This results in three combinations (AA, Aa, Aa) that express the dominant phenotype and one combination (aa) that expresses the recessive phenotype. Therefore, the ratio of dominant phenotype to recessive phenotype among the offspring is 3:1.

This ratio arises due to the principles of segregation and independent assortment established by Mendel, where alleles separate during gamete formation. Understanding this foundational concept is crucial in genetics, as it lays the groundwork for predicting the inheritance of traits.