In rats, the following genotypes of two independently assorting autosomal genes determine coat color: A— B— (gray) A — bb. (yellow) aaB— (black) aabb (cream) A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses: AaBbCc×AaBbcc

Verified step by step guidance

1. Identify the genotypes of the parents: AaBbCc and AaBbcc.
2. Determine the possible gametes each parent can produce. For AaBbCc, the gametes are ABC, ABc, AbC, Abc, aBC, aBc, abC, abc. For AaBbcc, the gametes are ABc, Abc, aBc, abc.
3. Set up a Punnett square to determine the genotypes of the F₁ offspring by combining the gametes from each parent.
4. Identify the phenotypes based on the genotypes. Remember that cc results in albino, overriding other color expressions.
5. Count the number of offspring for each phenotype to determine the phenotypic ratio.

Key Concepts

Independent Assortment

Independent assortment is a fundamental principle of genetics stating that alleles for different genes segregate independently of one another during gamete formation. This means that the inheritance of one trait will not affect the inheritance of another, allowing for a variety of combinations in offspring. In the context of the question, this principle is crucial for predicting the phenotypic ratios resulting from the crosses of the given genotypes.

Phenotypic Ratio

The phenotypic ratio is the relative frequency of different phenotypes in the offspring resulting from a genetic cross. It is determined by the combination of alleles inherited from the parents. In this case, calculating the phenotypic ratio involves considering the effects of both the A and B genes on coat color, as well as the influence of the C gene on whether color is expressed or not.

Epistasis

Epistasis occurs when the expression of one gene is affected by one or more other genes. In this scenario, the C gene is epistatic to the A and B genes, meaning that the presence of the cc genotype will mask the expression of the coat color determined by the A and B alleles. Understanding this interaction is essential for accurately determining the phenotypic outcomes of the genetic crosses presented in the question.