A normal women whose father had haemophilia married a normal man. What is the change of occurrence of disease in the progeny?

Options

A. `100%`
B. `50%`
C. `25%`
D. `75%`

Answer

To solve the problem of determining the chance of occurrence of hemophilia in the progeny of a normal woman whose father had hemophilia and a normal man, we can follow these steps:

### Step 1: Understand the Genetics of Hemophilia
Hemophilia is an X-linked recessive disorder. This means that the gene responsible for hemophilia is located on the X chromosome, and the disease manifests in males who have one affected X chromosome (X^hY) and in females who have two affected X chromosomes (X^hX^h). Females with one affected X chromosome (X^hX) are carriers but do not exhibit the disease.

### Step 2: Determine the Genotype of the Woman
Since the woman’s father had hemophilia, she must have inherited one affected X chromosome from him. Therefore, her genotype is X^hX (carrier). The other X chromosome comes from her mother, who is normal.

### Step 3: Determine the Genotype of the Man
The man is described as normal, which means he has a normal X chromosome and a Y chromosome. His genotype is XY.

### Step 4: Set Up a Punnett Square
To find the possible genotypes of the progeny, we can set up a Punnett square. The woman can contribute either X^h (the affected X chromosome) or X (the normal X chromosome), while the man can contribute either X (normal) or Y (male).

| | X (from father) | Y (from father) |
|----------|------------------|------------------|
| X^h (from mother) | X^hX (carrier female) | X^hY (hemophilic male) |
| X (from mother) | XX (normal female) | XY (normal male) |

### Step 5: Analyze the Results
From the Punnett square, we can see the following possible combinations for the progeny:
1. X^hX (carrier female)
2. XX (normal female)
3. X^hY (hemophilic male)
4. XY (normal male)

### Step 6: Calculate the Probability
Out of the four possible combinations:
- 1 combination is a hemophilic male (X^hY).
- 1 combination is a carrier female (X^hX).
- 2 combinations are normal (XX and XY).

Thus, the chance of having a hemophilic child is 1 out of 4, or 25%.

### Conclusion
The chance of occurrence of hemophilia in the progeny of this couple is **25%** (Option C).

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