Question

in fruit flies eye color is a sex-linked trait where red eyes are dominant to the white eye phenotype. cross a male with red eyes with a female who carries the white eye gene. use
\ for red and
\ for white.

Explanation:

Step1: Define parental genotypes

For sex-linked traits (X-chromosome in fruit flies):

• Red-eyed male: $X^R Y$ (males have one X and one Y; dominant red eye allele on X)
• Female carrier: $X^R X^r$ (carries recessive white eye allele, has red eyes)

Step2: Identify parental gametes

Male gametes: $X^R$, $Y$
Female gametes: $X^R$, $X^r$

Step3: Set up Punnett square

$$\begin{array}{c|cc} & X^R & X^r \\ \hline X^R & X^R X^R & X^R X^r \\ Y & X^R Y & X^r Y \\ \end{array}$$

Step4: Assign phenotypes to genotypes

• $X^R X^R$: Red-eyed female
• $X^R X^r$: Red-eyed female (carrier)
• $X^R Y$: Red-eyed male
• $X^r Y$: White-eyed male

Answer:

Fill the Punnett square (and dropdowns) with the following:

1. Top-left cell: Genotype $X^R X^R$, Phenotype Red-eyed female
2. Top-right cell: Genotype $X^R X^r$, Phenotype Red-eyed female (carrier)
3. Bottom-left cell: Genotype $X^R Y$, Phenotype Red-eyed male
4. Bottom-right cell: Genotype $X^r Y$, Phenotype White-eyed male