What is a Punnett square used for?

• A. A diagram that can be used to predict the genotype and phenotype combinations of a genetic cross.
• B. A chart showing the sequence of chromosomal mutations over generations.
• C. A method to measure gene expression levels in tissues.
• D. A tool for determining the exact DNA sequence of a gene.

Answer: (A)

A Punnett square is a diagram used to predict genotype and phenotype outcomes of a genetic cross. You lay out the possible gametes from each parent on the top and side, then fill in each cell with the resulting offspring genotype from that pairing. By counting how many cells show each genotype, you can estimate the probabilities of different genotypes, and, using dominance relationships, the corresponding phenotypes. This tool helps visualize Mendelian inheritance and quantify expected results when alleles segregate independently. It isn’t used to track chromosomal mutations over generations, measure gene expression levels, or determine the exact DNA sequence of a gene.