What phenotypic ratio results from a heterozygous cross of two alleles?

• A. 1:1:1
• B. 1:2:1
• C. 3:1
• D. 1:2:1:1

Answer: (B)

The phenotypic ratio resulting from a heterozygous cross of two alleles is 1:2:1. This scenario typically refers to a cross between two heterozygous individuals (for example, Aa × Aa) where "A" represents one allele and "a" represents another.

When you perform this cross, you can set up a Punnett square which includes the following combinations of alleles in the offspring: AA, Aa, Aa, and aa. This results in one homozygous dominant genotype (AA), two heterozygous genotypes (Aa), and one homozygous recessive genotype (aa). When looking at the phenotypes, if "A" is dominant over "a," then the phenotypes will show one individual exhibiting the dominant trait (AA) and two individuals exhibiting the same dominant trait (Aa), along with one individual exhibiting the recessive trait (aa). This phenotype ratio thus emerges as 3 showing the dominant trait to 1 showing the recessive trait.

However, the ratio 1:2:1 specifically pertains to the genotype ratio (1 AA : 2 Aa : 1 aa) obtained from the cross, indicating the various types of genotypes produced. This