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

Question

Quizplus · Accepted Answer

Familial Down syndrome is often caused by a Robertsonian translocation, where chromosome 21 is attached to another chromosome, typically a member of the D chromosome group (chromosomes 13, 14, or 15).

Although the Most Frequent Forms of Down Syndrome Are Caused