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

Question

Quizplus · Accepted Answer

The extra chromosome 21 in an individual with Down syndrome is usually caused by nondisjunction or translocation of chromosome 21 in either parent. Nondisjunction is more common and occurs when a pair of chromosomes fails to separate properly during meiosis, resulting in one gamete (sperm or egg) with an extra chromosome 21. Translocation occurs when part of chromosome 21 breaks off and attaches to another chromosome, which can also result in an extra chromosome 21 in the offspring. It is important to note that the mother's age is a risk factor for nondisjunction, but it can occur in fathers as well.

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