A man with a certain disease marries a normal woman. They have eight children (3 daughters and 5 sons). All the daughters suffer from their father's disease but none of the sons are affected. Which of the following mode of inheritance do you suggest for this disease?

Options

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

Answer

To solve the question regarding the mode of inheritance for the disease in the family described, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Parents' Genotypes**:
- The man has a disease, which suggests he carries the affected allele. Since he is male, he has one X and one Y chromosome. We can denote his X chromosome with the disease as X^D (disease allele) and his Y chromosome as Y.
- The woman is normal, meaning she has two normal X chromosomes, which we can denote as X^N X^N.

2. **Determine the Possible Genotypes of the Children**:
- The children of this couple will inherit one chromosome from each parent.
- Daughters inherit one X chromosome from their father and one from their mother. Therefore, all daughters will inherit X^D from the father and X^N from the mother, resulting in the genotype X^D X^N. This means all daughters are affected by the disease.
- Sons inherit the Y chromosome from their father and one X chromosome from their mother. Therefore, all sons will inherit Y from the father and X^N from the mother, resulting in the genotype X^N Y. This means none of the sons are affected.

3. **Analyze the Inheritance Pattern**:
- Since all daughters are affected and none of the sons are affected, this indicates that the disease is linked to the X chromosome and is dominant. This is characteristic of a sex-linked dominant inheritance pattern.

4. **Conclusion**:
- Based on the analysis, we conclude that the mode of inheritance for this disease is **sex-linked dominant**.

### Final Answer:
The mode of inheritance suggested for this disease is **sex-linked dominant**.

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