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?

Question

Quizplus · Accepted Answer

Down syndrome is caused by an extra chromosome 21, also known as trisomy 21. The most common cause of this condition is nondisjunction during gamete production, which results in an egg or sperm with an extra chromosome 21. The risk of nondisjunction increases as the mother's age increases, which is why the mother being 39 years old is a significant factor. The other choices are not likely causes of Down syndrome.

A Couple Has a Child with Down Syndrome