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 of determining the probability that a child will be a colorblind boy, we can follow these steps:

### Step 1: Understand the Genetics of Colorblindness
Colorblindness is a sex-linked recessive trait, which means it is carried on the X chromosome. In this case:
- A normal vision female has the genotype XX (both X chromosomes are normal).
- A colorblind female has the genotype XcXc (both X chromosomes carry the colorblind allele).
- A normal vision male has the genotype XY (one normal X chromosome and one Y chromosome).
- A colorblind male has the genotype XcY (one colorblind X chromosome and one Y chromosome).

### Step 2: Determine the Genotype of the Woman
The woman has normal vision but her mother was colorblind. This means the woman must be a carrier for colorblindness. Therefore, her genotype is XcX (one normal X chromosome and one colorblind X chromosome).

### Step 3: Determine the Genotype of the Man
The man has normal vision, so his genotype is XY.

### Step 4: Set Up the Punnett Square
Now we can set up a Punnett square to determine the possible genotypes of their offspring. The woman (XcX) can produce gametes X and Xc, while the man (XY) can produce gametes X and Y.

| | X (from man) | Y (from man) |
|--------|---------------|---------------|
| X (from woman) | XX (normal female) | XY (normal male) |
| Xc (from woman) | XcX (carrier female) | XcY (colorblind male) |

### Step 5: Analyze the Results
From the Punnett square, we can see the possible genotypes of the children:
1. XX - Normal female
2. XY - Normal male
3. XcX - Carrier female
4. XcY - Colorblind male

### Step 6: Calculate the Probability of a Colorblind Boy
Out of the four possible outcomes:
- 1 is a colorblind boy (XcY).
- Therefore, the probability of having a colorblind boy is 1 out of 4.

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

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