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. white females x sepia males

Key Concepts

X-linked Inheritance

X-linked inheritance refers to genes located on the X chromosome. In Drosophila, males have one X and one Y chromosome, while females have two X chromosomes. This means that X-linked recessive traits, like the white eye mutation, will manifest in males if they inherit the affected X chromosome, 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 is affected by another gene. In this case, the white eye mutation is epistatic to the sepia mutation, meaning that the presence of the white allele will mask the expression of the sepia allele, regardless of its genotype. This concept is crucial for predicting phenotypic outcomes in genetic crosses.

Punnett Square

A Punnett square is a diagram used to predict the genotypic and phenotypic ratios of offspring from a genetic cross. By organizing the alleles of the parents, it allows for a visual representation of possible combinations in the F₁ and F₂ generations. This tool is essential for understanding inheritance patterns, especially in complex crosses involving multiple alleles and epistatic interactions.