Final answer:
To determine each parent's genotype for flower color, understanding that white is recessive, and knowing the offspring’s genotypes are crucial. A purple-flowered parent mating with a white-flowered parent can be heterozygous (Bb) if the offspring include white-flowered plants. A Punnett square helps illustrate the probable genotypic ratios, like a 3:1 ratio for Bb parents.
Step-by-step explanation:
Understanding Punnett Squares and Genotypes
To determine the genotype of each parent in a genetic cross, information about the offspring’s phenotypes and genotypes is often needed. In the case of a purple-flowered and a white-flowered parent where the white flower phenotype is recessive (bb), and two of the offspring are white-flowered, we can deduce that both parents contributed a recessive allele (b). Thus, the purple-flowered parent must have been heterozygous (Bb), with B being the dominant allele for purple flowers. This means that each parent supplied one allele to the offspring, and the combination of these alleles determines the offspring's genotype.
Using a Punnett square, we can predict the statistical probabilities of the genotypes of offspring from a genetic cross. For example, if both parents are heterozygous for flower color (Bb), the Punnett square would display a 3:1 ratio of purple-flowered to white-flowered offspring. This illustrates that in a large number of offspring, approximately 75% would display the dominant purple trait.
While the actual ratio of offspring genotypes can vary with small sample sizes, larger numbers of crosses will demonstrate ratios that are very close to those predicted by the Punnett square. This is analogous to large numbers of coin tosses approximating the expected 50/50 distribution of heads to tails.