In a cross in Drosophila involving the X-linked recessive eye mutation white and the autosomally linked recessive eye mutation sepia (resulting in a dark eye), predict the F₁ and F₂ results of crossing true-breeding parents of the following phenotypes: Note that white is epistatic to the expression of sepia. sepia females x white males

Key Concepts

X-linked Inheritance

X-linked inheritance refers to genes located on the X chromosome, where males (XY) have only one X chromosome, while females (XX) have two. This means that recessive mutations on the X chromosome, such as the white eye mutation in Drosophila, will manifest in males regardless of the presence of a dominant allele, while females require two copies of the recessive allele to express the trait.

Epistasis

Epistasis is a genetic interaction where the expression of one gene (the epistatic gene) masks or modifies the expression of another gene. In this case, the white eye mutation is epistatic to the sepia mutation, meaning that if an individual has the white mutation, it will prevent the sepia phenotype from being expressed, regardless of the sepia genotype.

Punnett Square Analysis

A Punnett square is a diagram used to predict the genotypic and phenotypic outcomes of a genetic cross. By organizing the alleles of the parents, it allows for a visual representation of the possible combinations in the offspring. In this scenario, constructing a Punnett square for the sepia females and white males will help determine the expected ratios of the F₁ and F₂ generations based on the inheritance patterns of the X-linked and autosomal traits.