When crossing two heterozygous individuals, what is the expected phenotypic ratio in the offspring?

When crossing two heterozygous individuals for a trait governed by simple Mendelian inheritance, the expected phenotypic ratio in their offspring can be derived from a Punnett square analysis.

In this scenario, each parent has one dominant allele and one recessive allele (let’s denote them as "A" for the dominant trait and "a" for the recessive trait), resulting in the genotypes of the parents being Aa x Aa. When these are crossed, the potential offspring genotypes are obtained from the combinations of alleles:

• AA (homozygous dominant)

• Aa (heterozygous dominant)

• Aa (heterozygous dominant)

• aa (homozygous recessive)

This results in the following distribution:

• 1 AA (phenotypically dominant)

• 2 Aa (phenotypically dominant)

• 1 aa (phenotypically recessive)

In terms of phenotype, both AA and Aa exhibit the dominant trait, making the total for the dominant phenotype 3 (1 AA + 2 Aa) and the recessive phenotype total as 1 (1 aa).

Hence, the expected phenotypic ratio of the offspring from two heterozygous parents is 3 dominant to