In X linked recessive inheritance, the criss cross pattern means that a trait typically passes from
Correct answer: D. an affected man to his grandsons through his carrier daughters
- A. father to son directly
- B. mother to daughter only
- C. father to every one of his sons
- D. an affected man to his grandsons through his carrier daughters
Explanation
An affected father gives his X, and therefore the allele, to all of his daughters, who become carriers, and half of their sons then inherit it, so the trait reappears in the grandsons. A father can never pass an X linked allele to a son, because a son receives his Y from the father and his X from the mother. That impossibility is the quickest way to rule out X linkage in a pedigree.
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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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