Question

question 8 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. 2:1:0:1
b. 1:2:1:0
c. 2:0:1:1
d. 0:2:1:1

Explanation:

Step1: Determine the genotypes

Let \(X^R\) represent the allele for red eyes and \(X^r\) represent the allele for white eyes. 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

Gametes of female (\(X^R X^r\))	Gametes of male (\(X^R Y\))
\(X^r\)	\(X^R X^r\) (red - eyed female)	\(X^r Y\) (white - eyed male)

Step3: Analyze the phenotypes

• Red - eyed females: \(X^R X^R\) and \(X^R X^r\) (2 individuals)
• White - eyed females: \(0\) (females need two \(X^r\) alleles, and the male only donates \(X^R\) or \(Y\))
• Red - eyed males: \(X^R Y\) (1 individual)
• White - eyed males: \(X^r Y\) (1 individual)

Answer:

C. \(2:0:1:1\)