Genes of which one of the following is present exclusively on the X - chromosomes in humans ?

Options

A. Baldness
B. Red - green colour blindness
C. Night blindness
D. Facial hair in males

Answer

To solve the question regarding which gene is present exclusively on the X chromosome in humans, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: We need to identify which gene from the given options is located solely on the X chromosome in humans.

2. **Analyze the Options**:
- **Option A: Baldness** - This trait can be influenced by genes on both X and Y chromosomes, so it is not exclusive to the X chromosome.
- **Option B: Red-Green Color Blindness** - This is known to be an X-linked recessive disorder, meaning the gene responsible for this condition is located on the X chromosome.
- **Option C: Night Blindness** - This condition is not exclusively linked to the X chromosome; it can be caused by various factors and genes on different chromosomes.
- **Option D: Facial Hair in Males** - This trait is influenced by genes on the Y chromosome and other autosomes, not exclusively on the X chromosome.

3. **Identify the Correct Answer**: Based on the analysis, the gene for **Red-Green Color Blindness** (Option B) is the only one that is present exclusively on the X chromosome in humans.

4. **Conclusion**: Therefore, the answer to the question is **Option B: Red-Green Color Blindness**.