This question refers to eye colour in the fruit fly. In this sex-linked trait, the allele for red eye is dominant to that for white eye. If a heterozygous red-eyed female is crossed with a white-eyed male, what percentage of the female offsprings will be white-eyed?

Options

A. `0%`
B. `25%`
C. `50%`
D. `100%`

Answer

To solve the problem regarding the inheritance of eye color in fruit flies, we need to follow these steps:

### Step 1: Understand the Genetic Notation
- Let’s denote the allele for red eyes as **X^R** (dominant) and the allele for white eyes as **X^r** (recessive).
- The heterozygous red-eyed female will have the genotype **X^R X^r**.
- The white-eyed male will have the genotype **X^r Y** (since males have one X and one Y chromosome).

### Step 2: Set Up the Punnett Square
- We will set up a Punnett square to determine the possible genotypes of the offspring from the cross between the heterozygous red-eyed female (X^R X^r) and the white-eyed male (X^r Y).

### Step 3: Fill in the Punnett Square
- The female gametes (from X^R X^r) are X^R and X^r.
- The male gametes (from X^r Y) are X^r and Y.

The Punnett square will look like this:

| | X^r (from male) | Y (from male) |
|-------|------------------|----------------|
| X^R | X^R X^r (red) | X^R Y (red) |
| X^r | X^r X^r (white) | X^r Y (white) |

### Step 4: Analyze the Offspring Genotypes
- From the Punnett square, we can see the possible genotypes of the offspring:
- X^R X^r (red-eyed female)
- X^R Y (red-eyed male)
- X^r X^r (white-eyed female)
- X^r Y (white-eyed male)

### Step 5: Determine the Percentage of White-Eyed Females
- The offspring genotypes show that there is one X^r X^r (white-eyed female) out of four total offspring.
- Therefore, the percentage of female offspring that will be white-eyed is:
\[ \text{Percentage of white-eyed females} = \left( \frac{1}{4} \right) \times 100 = 25\% \]

### Final Answer
- **25% of the female offspring will be white-eyed.**

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