What is the primary purpose of a Punnett square in a monohybrid cross?

• A. To determine the phenotype of the parents
• B. To predict genotype frequencies in offspring
• C. To measure the dominance relationship
• D. To calculate mutation rate

Answer: (B)

A Punnett square lets you visualize how alleles from each parent may combine in offspring, showing all possible genotypes and how likely each is to occur. In a monohybrid cross, you’re tracking one gene with two alleles, so by laying out the parental gametes and filling in the grid, you directly see the resulting zygotes and their probabilities. This is why the primary purpose is to predict genotype frequencies in the offspring; from those you can infer phenotype ratios if the trait shows dominance. The tool doesn’t determine parental phenotypes, it doesn’t measure how dominance works beyond what the genotype implies, and it doesn’t address mutation rates.