Haemophilia does not occur in women

Options

A. It is autosomal recessive
B. women have to be homozygous which is fatal
C. They have only one X- chromosome
D. Theyare more resistant to this disorder

Answer

**Step-by-Step Solution:**

1. **Understanding Hemophilia**: Hemophilia is a genetic disorder that affects the blood's ability to clot. It is primarily inherited in a sex-linked manner, specifically linked to the X chromosome.

2. **Inheritance Pattern**: Hemophilia is caused by a recessive allele located on the X chromosome. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

3. **Expression in Males**: Since males have only one X chromosome, if they inherit the recessive allele for hemophilia from their mother (who could be a carrier or affected), they will express the disorder. This is because there is no second X chromosome to mask the effect of the recessive allele.

4. **Expression in Females**: For females to express hemophilia, they must inherit the recessive allele from both parents. This means they must be homozygous for the hemophilia allele (XhXh), where 'h' represents the hemophilia allele.

5. **Homozygous Condition in Females**: Being homozygous for the hemophilia allele is rare and can be fatal. This is because the inability to clot blood can lead to severe complications, including excessive bleeding from minor injuries.

6. **Conclusion**: Therefore, hemophilia does not commonly occur in women because it requires them to be homozygous for the recessive allele, which is a life-threatening condition. Most women are either carriers (heterozygous, XhX) or unaffected (homozygous dominant, XX).

**Final Answer**: Hemophilia does not occur in women because they need to be homozygous for the recessive allele, which is fatal.

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