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2023Q2(i)(b)Genetics – Some Basic Fundamentals
Biological termModerate1 mark
2(i)

Name the following:

A genetic disorder in which the blood does not clot.

Topic: Haemophilia

Previous-year question practice database

Answer

Exam answer

HAEMOPHILIA.

Explanation

Haemophilia is a SEX-LINKED RECESSIVE disorder carried on the X chromosome. The sufferer lacks a clotting factor, so even a minor cut or internal bruise bleeds for a dangerously long time.

WHY IT AFFECTS MAINLY MALES: a male is XY, so a single defective X from his mother is enough — the Y carries no corresponding allele to mask it. A female would need a defective X from BOTH parents, which is very rare. Women are usually CARRIERS, like the mother in the 2026 colour-blindness question.

It is called the ROYAL DISEASE because it ran through the descendants of Queen Victoria into several European royal families.

The other common sex-linked disorder is COLOUR BLINDNESS, and the two are almost always asked together.

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