A woman with normal vision whose mother was colourblind married a man with normal vision. The woman is pregnant with her first child. What is the probability that the cild will be a colour blind boy?

Options

A. `1//4`
B. `1//2`
C. `3//4`
D. 0

Answer

To solve the problem, we need to analyze the genetic background of the individuals involved and use a Punnett square to determine the probability of having a colorblind boy.

### Step-by-Step Solution:

1. **Identify the Genetic Makeup of the Woman**:
- The woman has normal vision but her mother is colorblind. Since colorblindness is an X-linked recessive trait, this means that the woman must carry one normal vision allele (X^N) and one colorblind allele (X^c). Therefore, her genotype is X^N X^c.

2. **Identify the Genetic Makeup of the Man**:
- The man has normal vision. Since colorblindness is X-linked and he has normal vision, his genotype is X^N Y.

3. **Set Up the Punnett Square**:
- We will set up a Punnett square to find the possible genotypes of their children. The woman can contribute either X^N or X^c, and the man can contribute either X^N or Y.

| | X^N (from father) | Y (from father) |
|---------|-------------------|------------------|
| X^N (from mother) | X^N X^N (Normal girl) | X^N Y (Normal boy) |
| X^c (from mother) | X^c X^N (Carrier girl) | X^c Y (Colorblind boy) |

4. **Determine the Possible Outcomes**:
- From the Punnett square, we have the following possible genotypes for the children:
- X^N X^N: Normal girl
- X^N Y: Normal boy
- X^c X^N: Carrier girl (normal vision)
- X^c Y: Colorblind boy

5. **Count the Outcomes**:
- There are 4 possible outcomes:
- 1 Normal girl (X^N X^N)
- 1 Normal boy (X^N Y)
- 1 Carrier girl (X^c X^N)
- 1 Colorblind boy (X^c Y)

6. **Calculate the Probability of a Colorblind Boy**:
- Out of the 4 possible outcomes, only 1 outcome is a colorblind boy (X^c Y).
- Therefore, the probability of having a colorblind boy is 1 out of 4, or 1/4.

### Final Answer:
The probability that the child will be a colorblind boy is **1/4**.