More men suffer from colour blindess than women because

Options

A. Women are more resistant to diseases
B. Male sex hormone trestosterone causes the disease
C. Colour blindness gen occurs on Y- chromosome
D. Men are hemizygous and one defective allele is neough to cause the disease

Answer

**Step-by-Step Solution:**

1. **Understanding Color Blindness**:
- Color blindness is a genetic condition that affects the ability to perceive colors correctly. It is primarily inherited in an X-linked recessive manner.

2. **Genetic Basis**:
- The gene responsible for color blindness is located on the X chromosome. Since it is a recessive trait, an individual needs to have two copies of the defective gene to express the condition if they are female (XX).

3. **Male Genotype**:
- Males have one X and one Y chromosome (XY). This means they are hemizygous for the X chromosome. The term "hemizygous" indicates that they have only one copy of the X chromosome.

4. **Impact of Hemizygosity**:
- Because males have only one X chromosome, if that X chromosome carries the gene for color blindness, they will express the condition. They do not have a second X chromosome that could potentially carry a normal allele to mask the effect of the defective allele.

5. **Female Genotype**:
- Females have two X chromosomes (XX). For a female to be color blind, she must inherit the defective allele on both of her X chromosomes. If she has one normal allele on one X chromosome, she will be a carrier but not express color blindness.

6. **Conclusion**:
- Therefore, more men suffer from color blindness than women because men are hemizygous for the X chromosome, and one defective allele is sufficient for them to exhibit the condition. In contrast, females require two defective alleles to express color blindness.

7. **Correct Answer**:
- The correct reason for the higher incidence of color blindness in men is: **Men are hemizygous, and one defective allele is enough to cause the disease (Option D).**

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