A diseased man marries a normal women. They have three daughters and five sons. All the daughters were diseased and sons were normal . The gene of this disease is

Options

A. Sex - linked dominant
B. Sex- linked recessive
C. Autosomal recessive
D. Autosomal dominant

Answer

To solve the question regarding the inheritance pattern of a disease in a family, we will analyze the information provided step by step.

### Step 1: Understand the Family Structure
- A diseased man marries a normal woman.
- They have three daughters and five sons.
- All daughters are diseased, and all sons are normal.

### Step 2: Determine the Inheritance Pattern
- The man is diseased, meaning he carries the gene for the disease.
- The woman is normal, meaning she does not carry the gene for the disease.

### Step 3: Analyze the Offspring
- All daughters are diseased. This indicates that they must have inherited the disease-causing gene from their father.
- All sons are normal, indicating they did not inherit the disease-causing gene.

### Step 4: Consider the Possible Modes of Inheritance
1. **Autosomal Dominant**: If the disease were autosomal dominant, then at least some of the sons would also be affected, which contradicts the information given.
2. **Autosomal Recessive**: If the disease were autosomal recessive, the father would need to be homozygous recessive to express the disease, which is not possible since he is diseased. Thus, this option is ruled out.
3. **Sex-linked Dominant**: If the disease is sex-linked dominant, daughters inherit one X chromosome from their father (who has the disease) and one X chromosome from their mother (who is normal). Thus, all daughters would be affected.
4. **Sex-linked Recessive**: If the disease were sex-linked recessive, the father would not pass the disease to his daughters, which contradicts the information given.

### Step 5: Conclusion
Given that all daughters are diseased and all sons are normal, the only inheritance pattern that fits this scenario is **sex-linked dominant**. Therefore, the gene of this disease is:

**Answer: A. Sex-linked dominant**

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