Probability of male child of haemophilic father and normal mother becoming haemophilic is

Options

A. 0
B. 0.25
C. 0.5
D. 1

Answer

To determine the probability of a male child of a hemophilic father and a normal mother becoming hemophilic, we need to analyze the genetic inheritance pattern of hemophilia, which is an X-linked recessive disorder.

### Step-by-Step Solution:

1. **Understanding Hemophilia**:
- Hemophilia is caused by a recessive allele located on the X chromosome.
- Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

2. **Genotype of the Parents**:
- The father is hemophilic, so his genotype is X^hY (where X^h represents the X chromosome with the hemophilia allele).
- The mother is normal, meaning she has two normal alleles, so her genotype is XX (both X chromosomes are normal).

3. **Inheritance of X and Y Chromosomes**:
- A male child receives his Y chromosome from his father and one X chromosome from his mother.
- Since the father contributes the Y chromosome, he does not pass on his X chromosome (which carries the hemophilia allele) to his sons.

4. **Possible Genotypes of the Male Child**:
- The male child will inherit the Y chromosome from the father and one of the X chromosomes from the mother.
- Since the mother has two normal X chromosomes (XX), the male child will inherit a normal X chromosome from her.

5. **Conclusion**:
- Therefore, the genotype of the male child will be XY, where the X is normal from the mother and Y is from the father.
- As a result, the male child cannot be hemophilic because he does not inherit the hemophilia allele from either parent.

6. **Probability Calculation**:
- The probability of the male child being hemophilic is 0, as he cannot inherit the hemophilia allele from his father and his mother does not have the hemophilia allele to pass on.

### Final Answer:
The probability of a male child of a hemophilic father and a normal mother becoming hemophilic is **0**.