Final answer:
Punnett squares effectively predict the offspring genotypes and phenotypes from parental crosses, with the results closely matching the predicted ratios in large offspring sample sizes.
Step-by-step explanation:
A Punnett square is a graphical representation used in biology to predict the possible genotypes of offspring from a cross between two parental genotypes. When both parents are heterozygous for a particular trait, such as flower color in pea plants (Bb), the Punnett square shows that the expected genotypic ratio among the offspring would be 25% BB, 25% bb, and 50% Bb. This would lead to a phenotypic ratio of purple to white flowers if purple is dominant. Actual percentages may vary in smaller sample sizes but should closely align with predicted percentages in larger numbers of offspring.
For a cross between two true-breeding pea plants, one with yellow seeds and one with green seeds (YY and yy, respectively), the Punnett square predicts all F₁ offspring to be heterozygous (Yy) with a yellow phenotype, assuming yellow is dominant over green. Here, the Punnett square demonstrates the utility of predicting consistent phenotypic results from specific parental combinations.