What is a Punnett square used for?

• A. Predicting genotype and phenotype frequencies in offspring from parental alleles
• B. Determining the sequence of parental genes
• C. Measuring mutation rates in a population
• D. Tracing evolutionary relationships among species

Answer: (A)

A Punnett square is a simple probability tool used to predict genotype and phenotype frequencies in offspring from the parental alleles. By laying out the possible gametes from each parent along the top and side, it shows every potential combination of alleles the offspring could inherit and thus how often different genotypes and corresponding traits are expected to appear under Mendelian inheritance.

For example, crossing two heterozygotes (one dominant allele and one recessive allele for the trait in question) yields four equally likely outcomes: two carry the dominant and recessive combination, one is homozygous dominant, and one is homozygous recessive. This translates into a 1:2:1 genotype ratio and a corresponding phenotype ratio depending on whether the dominant trait manifests in the heterozygote as well.

This tool helps you visualize inheritance probabilities, not how genes are sequenced, how mutation rates are measured, or how evolutionary relationships among species are inferred.