In a monohybrid cross, the genotypes of the parental generation (P) typically consist of one homozygous dominant (AA) and one homozygous recessive (aa) individual. The F1 generation will all be heterozygous (Aa). When two F1 individuals are crossed (Aa x Aa), the F2 generation's genotypic ratio is:
- 1 AA (homozygous dominant)
- 2 Aa (heterozygous)
- 1 aa (homozygous recessive)
The frequency of the heterozygous genotype (Aa) in the F2 generation is therefore \( \frac{2}{4} = 50% \).
So the answer is 50%.