Final answer:
A Punnett square predicts offspring genotypes by combining known parental alleles in a grid, demonstrating possible outcomes of their mating.
Step-by-step explanation:
A Punnett square can predict the genotype of offspring if the alleles of both parents are known. It is a chart used to determine the expected percentages of different genotypes and their associated phenotypes.
The true-breeding parental genotypes (YY for yellow seeds and yy for green seeds in the case of pea plants) are placed along the top and side of the grid.
Inside the grid, possible combinations of parental alleles that could result from their mating are filled out. Since the dominant trait for seed color is yellow, the cross of a YY parent with a yy parent results in all Yy offspring, meaning the offspring seeds will be yellow. A self-cross of a heterozygous (Yy) organism would yield a genotypic ratio of 1:2:1 for YY:Yy:yy, and a phenotypic ratio of 3 yellow:1 green if the dominant-recessive pattern is followed.
It can show genotypic and phenotypic ratios, illustrated in the cross of pea plants where the dominant yellow allele in Yy offspring results in yellow seeds.