The recessive genes located on X-chromosome in humans are always

Options

A. lethal
B. sublethal
C. expressed in males
D. expressed in females

Explanation

**Step-by-Step Text Solution:**

1. **Understanding X-Linked Genes**: In humans, genes can be located on the X chromosome. These genes can be dominant or recessive. Recessive genes require two copies (one on each X chromosome) to be expressed in females, while males have only one X chromosome.

2. **Chromosomal Differences Between Genders**: Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). This difference is crucial in understanding how recessive genes are expressed.

3. **Expression in Females**: For a recessive gene located on the X chromosome to be expressed in females, it must be present on both X chromosomes. If a female has one normal allele and one recessive allele, the normal allele will mask the expression of the recessive gene.

4. **Expression in Males**: Since males have only one X chromosome, if a recessive gene is present on that X chromosome, it will be expressed. There is no second X chromosome to mask the effect of the recessive gene.

5. **Conclusion**: Therefore, recessive genes located on the X chromosome in humans are always expressed in males. In females, they are only expressed if both X chromosomes carry the recessive allele.

**Final Answer**: The recessive genes located on the X chromosome in humans are always expressed in males.

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