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?NEET 2003

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Down syndrome is an autosomal disorder and is caused by an extra copy of chromosome number 21 . According to the question, affected mother carries 47 chromosomes $(45 + XX)$ and normal father has $(44 + X Y)$
Thus, progeny $= 50%$ trisomics and $50%$ normal child

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