What is the purpose of a Punnett square in genetics?

The purpose of a Punnett square in genetics is to visualize the genotype ratios that result from genetic crosses. It is a simple grid that allows geneticists to predict the probability of offspring inheriting particular combinations of alleles from their parents. By mapping out the alleles contributed by each parent, the Punnett square demonstrates how these combinations can produce different genotypes in the offspring. This tool is especially useful for understanding Mendelian inheritance patterns, such as those seen with dominant and recessive traits, and helps clarify the likelihood of various genetic outcomes based on parental genotypes.

In contrast, the other options do not accurately describe the function of a Punnett square. Calculating the number of chromosomes pertains more to karyotyping rather than genetic crosses. Computing total genetic variation involves population genetics and is not a direct function of a Punnett square. Likewise, determining environmental influences on traits falls under the field of epigenetics and ecology, rather than the statistical determination of genotypes based on Mendelian inheritance.