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.While there is reduced fertility in both sexes,females have higher fertility than males.Van Dyke et al.1995; Down Syndrome Research and Practice 32 : 65- 69 summarize data involving children born of Down syndrome individuals.Given the fact that conceptuses with 48 chromosomes four #21 chromosomes are not likely to survive early development,what percentage of surviving offspring would be expected to have Down syndrome if both parents have Down syndrome?

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