# What is the Mendelian ratio?

For a monohybrid cross, the phenotypic ratio is $3 : 1$. This occurs because when $\text{Aa}$ $\times$ $\text{Aa}$, the result is $1$ $\text{AA}$, $2$ $\text{Aa}$, and $1$ $\text{aa}$.
The $\text{AA}$ and $2$ $\text{Aa}$ represent the dominant phenotype since they contain the dominant allele $\text{A}$.
There is only $1$ cross that results in a recessive phenotype: $\text{aa}$.
Since there are three dominant phenotypes to one recessive, the common ratio is $3 : 1$.
There is also a common ratio for a dihybrid cross: $9 : 3 : 3 : 1$.