Question:easy
Haemophilia is a genetic disorder of coagulation seen only in males. It is transmitted as
Haemophilia is a genetic disorder of coagulation seen only in males. It is transmitted as
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Work out what a male needs on his single X chromosome to be affected, compared to a female.
Updated On: Jul 7, 2026
- X-linked dominant
- Y-linked dominant
- X-linked recessive
- Autosomal recessive
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept.
Look at how X and Y chromosomes are handed down and what happens when only one copy of a gene is faulty.
Step 2: Key Formula or Approach.
If a single faulty copy on the X chromosome is enough to cause disease in a male, but a female needs the fault on both her X chromosomes, the gene follows X-linked recessive inheritance.
Step 3: Detailed Explanation.
Picture a mother who carries one faulty X and one normal X. She is healthy, since her normal X makes enough clotting factor. Each son gets one X from her and a Y from his father. If he happens to get her faulty X, he has no backup copy, so he bleeds easily and is diagnosed with haemophilia.
A daughter in the same family gets one X from her mother and one X from her father. Even if she gets the faulty X from her mother, her father usually gives her a normal X, so she becomes a carrier rather than a patient. This explains the classic family pattern seen in haemophilia, sons affected, daughters silent carriers, skipping generations through the maternal line.
If the gene acted as dominant, carrier mothers would also show bleeding, which is not seen. If it sat on the Y chromosome, disease would move only from father to son, with mothers playing no part, which again does not match. If it were autosomal recessive, sons and daughters would be affected in similar numbers, but haemophilia strongly favours males.
Step 4: Final Answer.
The inheritance fits an X-linked recessive pattern, so the answer is X-linked recessive.
Look at how X and Y chromosomes are handed down and what happens when only one copy of a gene is faulty.
Step 2: Key Formula or Approach.
If a single faulty copy on the X chromosome is enough to cause disease in a male, but a female needs the fault on both her X chromosomes, the gene follows X-linked recessive inheritance.
Step 3: Detailed Explanation.
Picture a mother who carries one faulty X and one normal X. She is healthy, since her normal X makes enough clotting factor. Each son gets one X from her and a Y from his father. If he happens to get her faulty X, he has no backup copy, so he bleeds easily and is diagnosed with haemophilia.
A daughter in the same family gets one X from her mother and one X from her father. Even if she gets the faulty X from her mother, her father usually gives her a normal X, so she becomes a carrier rather than a patient. This explains the classic family pattern seen in haemophilia, sons affected, daughters silent carriers, skipping generations through the maternal line.
If the gene acted as dominant, carrier mothers would also show bleeding, which is not seen. If it sat on the Y chromosome, disease would move only from father to son, with mothers playing no part, which again does not match. If it were autosomal recessive, sons and daughters would be affected in similar numbers, but haemophilia strongly favours males.
Step 4: Final Answer.
The inheritance fits an X-linked recessive pattern, so the answer is X-linked recessive.
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