Women rarely experience sex-linked defects because they must be:

Options

A. Homozygous
B. Carrier
C. Heterozygous
D. Develop immunity

Answer

**Step-by-Step Solution:**

1. **Understanding Sex-Linked Defects:**
- Sex-linked defects are typically associated with genes located on the sex chromosomes, particularly the X chromosome.

2. **Chromosomal Composition in Males and Females:**
- Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). This difference in chromosomal composition is crucial for understanding the inheritance of sex-linked traits.

3. **Expression of Sex-Linked Traits:**
- For a male, having a defective gene on his single X chromosome means he will express the trait or defect because there is no corresponding allele on the Y chromosome to mask it.
- In contrast, a female would need to have the defective gene on both of her X chromosomes to express the trait. If she has the defective gene on only one X chromosome, she is considered a carrier.

4. **Carrier Status in Females:**
- A female with one normal X chromosome and one defective X chromosome (heterozygous) will not express the defect but can pass the defective gene to her offspring. This is why women rarely experience sex-linked defects; they can be carriers without showing symptoms.

5. **Homozygous vs. Heterozygous:**
- If a female is homozygous for a defective gene (both X chromosomes have the defect), she will express the sex-linked defect. However, this is less common than being heterozygous (one normal and one defective X chromosome).

6. **Conclusion:**
- Therefore, the correct answer to the question is that women rarely experience sex-linked defects because they must be carriers (heterozygous) of the defective gene to show the condition.

**Final Answer:**
Women rarely experience sex-linked defects because they must be carriers of the defective gene.

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