If a colour blind man marries a woman who is homozygous for normal colour vision,the probability 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 colorblind when a colorblind man marries a woman who is homozygous for normal color vision, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Genetics of Colorblindness**:
- Colorblindness is a sex-linked recessive trait located on the X chromosome. This means that males (XY) will express the trait if their single X chromosome carries the recessive allele. Females (XX) must have the recessive allele on both X chromosomes to express the trait.

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

3. **Determine Possible Gametes**:
- The man can pass on either his X^c chromosome or his Y chromosome.
- The woman can only pass on her normal X chromosome (since she is homozygous).

4. **Create a Punnett Square**:
- Set up a Punnett square to visualize the possible combinations of the gametes from both parents.
- The possible combinations are:
- From the father (X^c or Y)
- From the mother (X)
- The resulting combinations will be:
- X^c from father and X from mother → Daughter (X^cX) - Carrier
- Y from father and X from mother → Son (XY) - Normal vision

5. **Analyze the Offspring**:
- The son (XY) will inherit the Y chromosome from his father and the normal X chromosome from his mother. Therefore, he will have normal color vision.
- The daughter (X^cX) will be a carrier of the colorblind trait but will not express it since she has one normal X chromosome.

6. **Conclusion**:
- Since the son inherits a normal X chromosome from his mother, the probability of him being colorblind is 0.

### Final Answer:
The probability of their son being colorblind is **0**.

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