What does a Punnett Square help you do?

• A. Determine the ratio of phenotypes, determine the ratio of genotypes, and predict possible traits the offspring will have
• B. Determine the age of the offspring
• C. List the parental genotypes
• D. Determine the mating compatibility

Answer: (A)

The Punnett Square is a tool for predicting inheritance by organizing the possible allele combinations from each parent and showing how often each genotype and phenotype can occur. You lay out one parent’s gametes across the top and the other parent’s across the side, then fill in each box with the resulting offspring genotype. From there you can read the genotype ratios and, if a dominant allele is involved, the phenotype ratios as well.

For example, crossing two heterozygotes (Aa x Aa) yields AA, Aa, Aa, and aa, a 1:2:1 genotype ratio, and, if A is dominant, a 3:1 phenotype ratio for the dominant trait. This is why the best choice describes that it determines the ratios of phenotypes and genotypes and predicts possible traits the offspring will have. It doesn’t tell you anything about age or mating compatibility, which aren’t about genetic inheritance.