What is a Punnett square used for?

• A. To predict the probabilities of offspring genotypes for a simple genetic trait.
• B. To measure the rate of mutation.
• C. To determine blood type compatibility.
• D. To analyze genetic disorders.

Answer: (A)

A Punnett square shows the probabilities of the offspring’s genotypes for a simple genetic trait. By placing the possible gametes from each parent along the top and side, you fill in all potential zygotes and can read the chances of each genotype. For example, a cross between two heterozygous individuals (one gene with alleles A and a) yields a mix like AA, Aa, Aa, aa, illustrating genotype probabilities of 1/4, 1/2, and 1/4. When a dominant-recessive relationship is present, those genotypes often translate into phenotype probabilities too, though actual expression can depend on how the trait shows dominance. This tool isn’t used to measure mutation rates, determine blood type compatibility, or analyze more complex genetic disorders that involve multiple genes or non-Mendelian inheritance.