What phenotypic ratio is expected when two heterozygous organisms for a single trait mate?

When two heterozygous organisms for a single trait mate, the expected phenotypic ratio is 3:1. This outcome is derived from Mendel's principles of inheritance, specifically the segregation of alleles.

To understand this, consider two heterozygous individuals, each possessing one dominant allele and one recessive allele (genotype Aa). When these organisms are crossed, the potential gametes formed would be A and a from each parent. When forming a Punnett square for this cross, the combinations of alleles among the offspring can be represented as follows:

• AA (homozygous dominant)

• Aa (heterozygous dominant)

• Aa (heterozygous dominant)

• aa (homozygous recessive)

This results in the following ratio:

• 1 AA (dominant phenotype)

• 2 Aa (dominant phenotype)

• 1 aa (recessive phenotype)

This can be simplified to 3 offspring exhibiting the dominant phenotype (AA and Aa) and 1 offspring exhibiting the recessive phenotype (aa), leading to the 3:1 phenotypic ratio.

This 3:1 ratio is a hallmark of Mendelian inheritance for traits that follow simple dominance, where