One of the genes present exclusive on the X- chromosome in humans is concerned with :

Options

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

Explanation

To solve the question regarding which gene is present exclusively on the X chromosome in humans, we will analyze each option provided:

1. **Baldness**:
- Baldness is often associated with genetic factors and is considered a sex-influenced trait. This means that while it can manifest in both males and females, the expression of the trait is influenced by sex hormones. However, it is not exclusively linked to the X chromosome; rather, it is influenced by autosomal genes.
- **Conclusion**: Baldness is not the correct answer.

2. **Red-green color blindness**:
- Red-green color blindness is a well-known genetic condition that is classified as an X-linked recessive trait. This means that the gene responsible for this condition is located on the X chromosome. Males (who have one X chromosome) are more likely to express this trait if they inherit the affected X chromosome, while females (who have two X chromosomes) would need to inherit the affected gene from both parents to express the trait.
- **Conclusion**: Red-green color blindness is the correct answer.

3. **Facial hair in males**:
- The development of facial hair is a trait influenced by male hormones (androgens) and is considered a sex-limited trait. This means that while the genetic basis for facial hair may be present in both sexes, it is only expressed in males due to the influence of male hormones. This trait is not linked to the X chromosome.
- **Conclusion**: Facial hair in males is not the correct answer.

4. **Night blindness**:
- Night blindness is typically associated with a deficiency in vitamin A or other conditions and is classified as an autosomal recessive disorder. It is not linked to the X chromosome.
- **Conclusion**: Night blindness is not the correct answer.

**Final Answer**: The gene present exclusively on the X chromosome in humans is concerned with **red-green color blindness**.