The genotypes of parents of a baby girl who is born with haemophilia would be:
Correct answer: C. Mother is carrier, father is hemophiliac
- A. Mother is carrier, father is normal
- B. Mother is hemophiliac, father is normal
- C. Mother is carrier, father is hemophiliac
- D. Mother is normal, father is hemophiliac
Explanation
C is the correct option.For a female to have haemophilia, she must inherit an affected X chromosome from each parent. This can occur if the mother is a carrier (XHXh) and the father is hemophiliac (XhY). Any other combination would either make the daughter a carrier or normal, but not affected. In option A, the daughter would be a carrier. In option B, the daughter would also be a carrier because she inherits one normal X from her father. In option D, the daughter would again be a carrier, inheriting one affected X from her father and a normal X from her mother.
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About X-linked Recessive Inheritance
X-linked recessive inheritance involves genes on the X chromosome, so males express a recessive allele with no corresponding allele on their single X chromosome, while females may be carriers. Pedigrees cover haemophilia and red-green colour blindness, including carrier mothers, affected sons and the absence of father-to-son transmission.
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