In the rats identified in Problem 10, a third independently assorting gene involved in determination of coat color is the C gene. At this locus, the genotype C– permits expression of pigment from genes B and D. The cc genotype, however, prevents expression of coat color and results in albino rats. For each of the following crosses, determine the expected phenotype ratio of progeny.

bbDDCc×BBddCc

Key Concepts

Independent Assortment

Independent assortment is a fundamental principle of genetics that states genes for different traits are inherited independently of one another. This means that the alleles of one gene segregate into gametes without affecting the segregation of alleles for another gene. In the context of the question, the C gene's independent assortment with the B and D genes allows for a variety of phenotypic combinations in the progeny.

Genotype and Phenotype

The genotype refers to the genetic makeup of an organism, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype. In this case, the presence of the C gene (C– or cc) influences whether the coat color is expressed or if the rat is albino. Understanding the relationship between genotype and phenotype is crucial for predicting the outcomes of genetic crosses.

Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. By organizing the possible gametes from each parent, it allows for a visual representation of how alleles combine. In this question, constructing a Punnett square for the cross bbDDCc × BBddCc will help determine the expected phenotype ratios of the progeny based on the combinations of alleles inherited.