If a colour -blind man marries a woman who is homzygous for normal colour vision , the probailty of their son being colour -blind is

Options

A. 0
B. 0.5
C. 0.75
D. 1

Answer

To solve the problem of determining the probability of a son being color-blind when a color-blind man marries a woman who is homozygous for normal color vision, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Genetic Basis of Color Blindness**:
- Color blindness is an X-linked recessive disorder. This means that the gene responsible for color blindness is located on the X chromosome, and a male (XY) only needs one copy of the mutated gene on his single X chromosome to express the trait.

2. **Determine the Genotypes of the Parents**:
- The color-blind man has the genotype X^cY, where X^c represents the X chromosome with the color-blind allele.
- The woman who is homozygous for normal color vision has the genotype XX, specifically XX (both X chromosomes are normal).

3. **Identify Possible Gametes**:
- The man can produce two types of gametes: X^c (color-blind X chromosome) and Y (Y chromosome).
- The woman can produce only one type of gamete: X (normal X chromosome).

4. **Set Up a Punnett Square**:
- Create a Punnett square to visualize the possible combinations of gametes from the parents.
- The rows represent the father's gametes (X^c and Y), and the columns represent the mother's gametes (X).

| | X | X |
|-------|-------|-------|
| X^c | X^cX | X^cX |
| Y | XY | XY |

5. **Analyze the Offspring Genotypes**:
- The possible genotypes for the offspring are:
- X^cX (female, carrier of color blindness but not color blind)
- XY (male, normal color vision)
- There are no offspring with the genotype X^cY (male color-blind) because the son inherits the Y chromosome from the father and the normal X chromosome from the mother.

6. **Calculate the Probability**:
- Since the only male offspring genotype is XY (normal vision), the probability of their son being color-blind is 0%.

### Final Answer:
The probability of their son being color-blind is **0%**.