In the rats identified in Problem 10, a third independently assorting gene involved in the 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

검증된 단계별 안내

Identify the three genes involved in the problem: B, D, and C. The B and D genes determine coat color, while the C gene determines whether pigment is expressed at all. The genotype C– (C_ or CC) allows pigment expression, while cc results in albino rats regardless of the B and D genotypes.

Determine the genotypes of the parents: BbDDCc × BbDdCc. For each gene, note the possible alleles contributed by each parent. For example, for the B gene, both parents are Bb, so they can contribute either B or b alleles.

Set up a Punnett square for each gene independently. For the B gene, cross Bb × Bb. For the D gene, cross DD × Dd. For the C gene, cross Cc × Cc. This will give the probabilities of each genotype for each gene in the progeny.

Combine the probabilities from the individual Punnett squares to determine the overall genotype probabilities for the progeny. Since the genes assort independently, multiply the probabilities of each genotype from the B, D, and C genes to get the combined probabilities.

Determine the phenotypes based on the combined genotypes. Remember that cc results in albino rats, regardless of the B and D genotypes. For progeny with at least one C allele (C–), use the B and D genotypes to determine coat color. Finally, calculate the expected phenotype ratio by summing the probabilities for each phenotype.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

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

Genotype refers to the genetic constitution of an organism, specifically the alleles present at a given locus. Phenotype, on the other hand, is the observable physical or biochemical characteristics of an organism, which result from the interaction of its genotype with the environment. In this question, the genotypes BbDDCc and BbDdCc will produce different phenotypes based on the expression of the C gene and its interaction with the B and D genes.

Punnett Square and Phenotypic Ratios

A Punnett square is a diagram used to predict the outcome of a genetic cross by displaying the possible combinations of alleles from the parents. By filling out the Punnett square for the given genotypes, one can determine the expected phenotypic ratios of the offspring. In this case, the ratios will reflect the influence of the C gene on coat color, leading to a specific distribution of phenotypes among the progeny.