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 \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) results of crossing true-breeding parents of the following phenotypes: (a) white females \(\times\) sepia males (b) sepia females \(\times\) white males Note that white is epistatic to the expression of sepia.

Step 1: Determine the genotypes of the parents White female = XwXw (homozygous recessive white) Sepia male = XsY, ss (hemizygous sepia, homozygous recessive sepia) Step 2: Perform the cross and find F1 results Each offspring will inherit one X-linked gene from the mother and one autosomal gene from both parents. Offspring's genotypes: XwXs, sS Phenotypes for F1: All females will have white eyes, as white mutation is epistatic.

Step 1: Determine the genotype of the parents Sepia female = XX, ss (homozygous recessive sepia) White male = XwY (hemizygous recessive white) Step 2: Perform the cross and find F1 results Each offspring will inherit one X-linked gene from both parents and one autosomal gene from the mother. Offspring's genotypes: - Female: XsXw, sS (sepia and white double heterozygous) - Male: XsY, sS (hemizygous sepia) Phenotypes for F1: - All females will have white eyes, as white mutation is epistatic. - All males will have sepia eyes.

For (a), all offspring in the F1 generation are XwXs, sS. Since no males are available for mating, it's not possible to predict the F2 generation for cross (a). For (b), the F1 generation consists of XsXw, sS females and XsY, sS males. By crossing F1 females with F1 males, we can analyze their combinations of genes: Offspring's genotypes: - Female: XsXs, sS (sepia heterozygous) - Female: XsXw, sS (white heterozygous) - Male: XsY, sS (sepia hemizygous) - Male: XwY, sS (white hemizygous) Phenotypes for F2: - Females: 50% white eyes (as white mutation is epistatic), 50% sepia eyes - Males: 50% white eyes (as white mutation is epistatic), 50% sepia eyes In conclusion, for cross (a), the F1 generation will have all white-eyed females but no F2 results can be predicted. For cross (b), the F1 generation consists of white-eyed females and sepia-eyed males, and the F2 generation will have 50% white-eyed and 50% sepia-eyed offspring for both males and females.