A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?
A) The woman inherited this tendency from her parents.
B) One member of the couple carried a translocation.
C) One member of the couple underwent nondisjunction in somatic cell production.
D) One member of the couple underwent nondisjunction in gamete production.
E) The mother had a chromosomal duplication.

Question

Quizplus · Accepted Answer

The most common cause of Down syndrome is nondisjunction during gamete production. In this case, one of the parents likely produced a gamete with an extra copy of chromosome 21, which resulted in the trisomy 21 condition in the child. The age of the mother (39 years old) is a known risk factor for chromosomal abnormalities during gamete production. The other answer choices are less likely or not relevant to the situation described.

A Couple Has a Child with Down Syndrome