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GATE 2026 BT – Question 64

Genetics, Cellular and Molecular Biology · Genetics: Mendelian inheritance, gene interaction, complementation, linkage, recombination, chromosome mapping, extrachromosomal inheritance · 2 marks · Numerical answer

A disease-associated allele shows X-linked recessive inheritance. If the mother is a carrier of the disease, the father is genetically normal and the child born is a son, then the probability that he is born with the disease is _______. (rounded off to one decimal place)

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Correct answer: 0.49 to 0.51

Explanation

A son gets his X chromosome from his mother. A carrier mother passes the disease allele to half of her sons, and the normal father gives him only a Y chromosome. So the probability is 0.5.