What is the expected genotypic ratio from a monohybrid cross?

In a monohybrid cross, where two heterozygous individuals for a single trait are crossed (often represented as Aa x Aa), the expected genotypic ratio arises from the combination of alleles during gamete formation and fertilization.

The possible gametes produced by each parent are A and a, leading to the following combinations in the offspring:

1. AA

2. Aa

3. aA (which is functionally the same as Aa)

4. aa

When counted, this results in a genotypic ratio of 1 AA (homozygous dominant), 2 Aa (heterozygous), and 1 aa (homozygous recessive). Therefore, the full ratio can be represented as 1:2:1. This means that for every four offspring, one is expected to be homozygous dominant, two are heterozygous, and one is homozygous recessive.

This 1:2:1 ratio reflects the underlying principles of Mendelian genetics, where alleles segregate independently during gamete formation, following Mendel's laws. Understanding this ratio is crucial for predicting the inheritance patterns of traits and is a foundational concept in genetics.