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) The mother had a chromosomal duplication.
C) One member of the couple underwent nondisjunction in somatic cell production.
D) One of the gametes in the mother most likely underwent nondisjunction during meiosis.

Question

Quizplus · Accepted Answer

The most common cause of Down syndrome is nondisjunction during meiosis in one of the gametes, typically in the mother. The risk of nondisjunction increases with maternal age, which in this case is 39 years old. Therefore, option D is the most likely cause of the child's condition. The other options are less likely to be the cause of Down syndrome in this case.

A Couple Has a Child with Down Syndrome