NEET Biology question

Biology Principles of Inheritance and Variation NEET

Down's syndrome is caused by an extra copy of chromosome number 21. What percentage of offspring produced by an affected mother and a normal father would be affected by this disorder?

(A)100%
(B)75%
(C)50%Correct
(D)25%

Answer: (C)

Solution

An affected mother carries a trivalent (three copies) of chromosome 21 during meiosis; on average, non-disjunction-prone segregation of this trivalent results in roughly half of her eggs carrying the extra chromosome 21 and the other half

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Question ID VK-120225