Q.5 People with hemophilia are unable to produce a factor needed for blood clotting;
the cuts, bruises, and wounds of hemophiliacs continue to bleed and, if not stopped
by transfusion with clotting factor, can cause death.
Select the correct statement about hemophilia:
- (A) The principal type of hemophilia in humans is due to a recessive X-linked mutation.
- (B) These males have inherited the mutation from their heterozygous mothers.
- (C) Affected males never transmit the mutant allele to their sons.
- (D) Nearly all the individuals who have hemophilia are male.
Choose the correct answer from the options given below:
- (A), (B) and (D) only.
- (A), (B) and (C) only.
- (A), (B), (C) and (D).
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Hemophilia is an X-linked recessive disorder primarily affecting males due to clotting factor deficiencies. All four statements (A, B, C, D) are correct, making the answer (A), (B), (C) and (D).
Option Analysis
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(A) Correct: The main form (hemophilia A, factor VIII deficiency) is caused by a recessive mutation on the X chromosome.
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(B) Correct: Affected males inherit the mutant X from carrier (heterozygous) mothers, as fathers pass Y to sons.
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(C) Correct: Males pass their X only to daughters; sons get the Y chromosome, so the allele skips sons.
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(D) Correct: Males (XY) express the trait with one mutant X; females (XX) rarely do, needing two copies—about 1 in 10,000 males vs. 1 in 100 million females affected.(A), (B), (C) and (D).
Hemophilia X-linked inheritance explains why this blood clotting disorder predominantly strikes males. Caused by a recessive X-linked mutation, it prevents proper clotting factor production, leading to prolonged bleeding from cuts or bruises.
Why Hemophilia Affects Mostly Males
In hemophilia X-linked inheritance, the mutation on the X chromosome means males (XY) fully express it with one faulty copy, while females (XX) need two and are usually carriers. Nearly all cases occur in males, as females rarely inherit two mutant alleles.
How the Mutation Passes Down
Heterozygous carrier mothers transmit the recessive X-linked mutation to 50% of sons, who become affected. Affected males pass it to all daughters (carriers) but never to sons, since sons inherit the father’s Y chromosome.
Key Inheritance Patterns
| Scenario | Offspring Risk |
| Carrier mother + normal father | 50% sons affected; 50% daughters carriers |
| Affected father + normal mother | All daughters carriers; no sons affected |
| Both affected/carrier | Higher risks, up to 50% daughters affected |
This pattern underscores why hemophilia X-linked inheritance remains a classic genetics example for exams like GATE Life Sciences.
