If a colour blind person marries a normal women whose father was colour blind, then what percentage of the male progeny will be affected ?

Options

A. `0%`
B. `25%`
C. `50%`
D. `75%`

Answer

To solve the problem, we need to analyze the genetics of color blindness, which is an X-linked recessive trait. Let's break down the steps:

### Step-by-Step Solution:

1. **Identify the Genotypes:**
- A color blind man has the genotype **X^cY** (where X^c represents the X chromosome with the color blindness allele).
- The normal woman has a father who is color blind, which means she must have inherited the color blindness allele from him. Therefore, her genotype is **X^cX** (she is a carrier).

2. **Determine the Gametes:**
- The color blind man can produce two types of gametes: **X^c** (carrying the color blindness allele) and **Y** (the male chromosome).
- The normal woman can produce two types of gametes: **X^c** (carrying the color blindness allele) and **X** (the normal allele).

3. **Create a Punnett Square:**
- Set up a Punnett square to visualize the possible offspring:

| | X^c (from mother) | X (from mother) |
|---------|--------------------|------------------|
| X^c (from father) | X^cX^c (carrier female) | X^cX (normal female) |
| Y (from father) | X^cY (color blind male) | XY (normal male) |

4. **Analyze the Offspring:**
- From the Punnett square, we can identify the possible genotypes of the offspring:
- **X^cX^c**: Carrier female (1)
- **X^cX**: Normal female (1)
- **X^cY**: Color blind male (1)
- **XY**: Normal male (1)

5. **Calculate the Percentage of Affected Male Progeny:**
- There are 4 possible offspring: 1 carrier female, 1 normal female, 1 color blind male, and 1 normal male.
- Out of these, only 1 male is affected (X^cY).
- Therefore, the percentage of affected male progeny is:
\[ \text{Percentage} = \left( \frac{\text{Number of affected males}}{\text{Total males}} \right) \times 100 = \left( \frac{1}{4} \right) \times 100 = 25\% \]

### Final Answer:
The percentage of affected male progeny will be **25%**.