Trisomy 21,or Down Syndrome,occurs When There Is a Normal Diploid

Multiple Choice

Trisomy 21,or Down syndrome,occurs when there is a normal diploid chromosomal complement but one extra) chromosome 21.Although fertility is reduced in both sexes,females have higher fertility rates than males.Van Dyke et al.1995; Down Syndrome Research and Practice 32 : 65-69 summarize data involving children born of Down syndrome individuals.Assume that children are born to a female with Down syndrome and a normal 46- chromosome male.What proportion of the offspring would be expected to have Down syndrome?

A) None of the offspring would be expected to have Down syndrome.
B) One- half of the offspring would be expected to have Down syndrome.
C) One- third of the offspring would be expected to have Down syndrome.
D) Two- thirds of the offspring would be expected to have Down syndrome.
E) All the children would be expected to have Down syndrome.