Question

question 9 of 10
eye color in fruit flies is a sex - linked trait. red eye color is dominant over white eye color. a heterozygous, red - eyed female is crossed with a red - eyed male.
in their offspring, what is the expected phenotypic ratio of red - eyed females to white - eyed females to red - eyed males to white - eyed males?
a. 2:0:1:1
b. 2:1:0:1
c. 1:2:1:0
d. 0:2:1:1

Explanation:

Step1: Determine the genotypes

Let \(X^R\) represent the red - eye allele and \(X^r\) represent the white - eye allele. The heterozygous red - eyed female has the genotype \(X^R X^r\), and the red - eyed male has the genotype \(X^R Y\).

Step2: Set up the Punnett square

The possible gametes from the female are \(X^R\) and \(X^r\), and from the male are \(X^R\) and \(Y\).

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

Step3: Analyze the phenotypes

• Females: \(X^R X^R\) and \(X^R X^r\) (both red - eyed, so 2 red - eyed females, 0 white - eyed females).
• Males: \(X^R Y\) (red - eyed) and \(X^r Y\) (white - eyed, so 1 red - eyed male, 1 white - eyed male).

So the ratio is 2 (red - eyed females):0 (white - eyed females):1 (red - eyed males):1 (white - eyed males).

Answer:

A. 2:0:1:1