A haemophilic man marries a normal homozygous woman. What is he probability that their son will be haemophilic ?

Options

A. 1
B. 0.75
C. 0.5
D. 0

Answer

To solve the problem of determining the probability that a son of a hemophilic man and a normal homozygous woman will be hemophilic, we can follow these steps:

### Step 1: Understand the Genetics of Hemophilia
Hemophilia is a sex-linked recessive disorder, which means that the gene responsible for hemophilia is located on the X chromosome. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

### Step 2: Determine the Genotypes of the Parents
- The hemophilic man has the genotype X^hY, where X^h represents the X chromosome carrying the hemophilia allele.
- The normal homozygous woman has the genotype XX, specifically X^NX^N, where X^N represents the normal allele.

### Step 3: Determine Possible Gametes
- The hemophilic man can produce two types of gametes: X^h (carrying the hemophilia allele) and Y (the male chromosome).
- The normal homozygous woman can only produce one type of gamete: X^N.

### Step 4: Create a Punnett Square
To find the probability of their son being hemophilic, we can set up a Punnett square:

| | X^N (from mother) | Y (from father) |
|--------|-------------------|------------------|
| X^h | X^hX^N (female) | X^hY (son) |
| Y | X^NY (daughter) | YY (son) |

### Step 5: Analyze the Results
From the Punnett square:
- The son (X^hY) will inherit the X chromosome from the mother (X^N) and the Y chromosome from the father.
- The son will have the genotype X^hY, which means he will be hemophilic.

### Conclusion
Since all sons will inherit the Y chromosome from the father and the normal X chromosome from the mother, none of the sons will inherit the hemophilia allele. Therefore, the probability that their son will be hemophilic is 0%.

### Final Answer
The probability that their son will be hemophilic is **0%** (Option D).

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