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NEET 2003 Biology question

BiologyPrinciples of Inheritance and VariationNEET 2003

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 :-

Answer: (3)

Solution

An affected mother has trisomy 21 (three copies of chromosome 21). During meiosis the three copies segregate so that half of her eggs carry one copy of chromosome 21 (n) and half carry two copies (n+1). The

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Question ID VK-089251