Final answer:
In a Punnett square, the alleles produced by each parent are shown along the sides of the grid, which represents the genetic combinations possible from the fertilization of their gametes.
Step-by-step explanation:
The alleles produced by each parent are shown along the sides of a Punnett square. A Punnett square is a visual tool used in genetics to predict the probability of offspring inheriting certain genotypes from their parents during sexual reproduction. When looking at a monohybrid cross, such as in the case of pea plants with different seed colors, one parent's alleles for a certain gene are listed across the top, and the other parent's alleles are listed down the side of the grid. These represent the gametes, which are haploid, containing only one allele of each gene. The fertilization of these gametes produces a zygote, which is diploid, having two alleles for each gene. In the Punnett square, each box where the gametes' alleles meet represents the possible genotype of an offspring resulting from the combination of those two gametes.