Which of the following is a sex linked recessive disease?

Options

A. Hemophilia
B. Colour blindness
C. Both (a) and (b)
D. Down's syndrome

Answer

To determine which of the following is a sex-linked recessive disease, we need to understand the concept of sex-linked inheritance, particularly X-linked recessive inheritance.

### Step-by-Step Solution:

1. **Understand Sex-Linked Recessive Diseases**:
- These diseases are caused by mutations on the X chromosome.
- Males (XY) have one X and one Y chromosome, while females (XX) have two X chromosomes.

2. **Carrier Status in Females**:
- If a female has one normal X chromosome and one mutated X chromosome, she is a carrier but does not express the disease.
- A female will only express the disease if both of her X chromosomes are mutated.

3. **Expression in Males**:
- Males will express the disease if their single X chromosome carries the mutation since they do not have a second X chromosome to mask the effect.

4. **Examples of Sex-Linked Recessive Diseases**:
- Common examples include hemophilia and color blindness. Both of these conditions are inherited through the X chromosome and are expressed in males when the X chromosome is affected.

5. **Evaluate the Options**:
- If the options provided include hemophilia and color blindness, these would be considered sex-linked recessive diseases.
- Other options like Down syndrome are not sex-linked; they are chromosomal disorders caused by an extra chromosome (trisomy 21).

6. **Conclusion**:
- Based on the understanding of sex-linked recessive inheritance, the correct answer would be options that include hemophilia and color blindness.

### Final Answer:
The sex-linked recessive diseases from the options provided are hemophilia and color blindness.