Question

which of the following is an accurate phenotypic ratio of a cross between 2 heterozygous individuals of any trait?
○ 1:0
○ 1:2:1
○ 1:1
○ 3:1

Explanation:

Step1: Recall Mendelian genetics

When two heterozygous individuals (e.g., Aa × Aa) for a single trait are crossed, using a Punnett square: the possible genotypes are AA, Aa, Aa, aa.

Step2: Determine phenotypic ratios

• AA and Aa show the dominant phenotype, aa shows the recessive. So dominant (AA + Aa + Aa) : recessive (aa) = 3:1.
• 1:0 would be if all offspring have one phenotype (e.g., homozygous dominant × anything dominant), not heterozygous cross.
• 1:2:1 is the genotypic ratio (AA:Aa:aa) for this cross, not phenotypic.
• 1:1 is the phenotypic ratio for a test cross (Aa × aa), not heterozygous × heterozygous.

Answer:

D. 3:1 (assuming the options are labeled as such, with the last option being 3:1)