A Punnett square is a simple diagram used in genetics to predict the possible genetic outcomes of a cross between two organisms. It helps visualize how alleles from each parent combine to form the genotypes of their offspring. Each square in the grid represents a possible genotype that the offspring could inherit. To create a Punnett square, you start by writing the alleles of one parent along the top and the alleles of the other parent along the side. By filling in the squares, you can see the probability of different traits appearing in the offspring, making it a valuable tool for understanding inheritance patterns.