What is the source of the extra chromosome 21 in an individual with Down syndrome?
A) nondisjunction in the mother only
B) nondisjunction in the father only
C) duplication of the chromosome
D) nondisjunction or translocation in either parent
E) It is impossible to detect with current technology.

Question

Quizplus · Accepted Answer

Down syndrome is caused by either the failure of chromosome 21 to separate during meiosis (nondisjunction) or a translocation where a part of chromosome 21 is attached to another chromosome. These events can occur in either the mother or the father. Therefore, the extra chromosome 21 can be inherited from either parent, or it can occur spontaneously during the formation of the egg or sperm.

What Is the Source of the Extra Chromosome 21 in an Individual