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Punnett Squares

Punnett Squares are a well known genetics tool that was created by an English geneticist, Reginald Punnett, which can visually demonstrate all the possible genotypes that an offspring can receive, given the genotypes of their parents. Each parent carries two alleles, which can be shown on the top and the side of the chart, and each contribute one of them towards reproduction at a time. Each of the squares in the middle demonstrates the number of times each pairing of parental alleles could combine to make potential offspring. Using probabilities, one can then determine which genotypes the parents can create, and at what frequencies they can be created.

For example, if two parents both have a heterozygous genotype, then there would be a 50% chance for their offspring to have the same genotype, and a 50% chance they would have a homozygous genotype. Since they could possibly contribute two identical alleles, the 50% would be halved to 25% to account for each type of homozygote, whether this was a homozygous dominant genotype, or a homozygous recessive genotype.