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?

Step-by-step solution

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+X X) and normal father has (44+X Y) Thus, progeny =50 % trisomics and 50 % normal child