Although the Most Frequent Forms of Down Syndrome Are Caused

Multiple Choice

Although the most frequent forms of Down syndrome are caused by a random error,nondisjunction of chromosome 21,Down syndrome occasionally runs in families.The cause of this form of familial Down syndrome is ____.

A) a maternal age effect
B) a chromosomal aberration involving chromosome 1
C) an inversion involving chromosome 21
D) a translocation between chromosome 21 and a member of the D chromosome group
E) too many X chromosomes