What is the most common source of the extra chromosome 21 in an individual with Down syndrome?
A) nondisjunction in the mother
B) nondisjunction in the father
C) duplication of chromosome 21
D) deletion in either parent

Question

Quizplus · Accepted Answer

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division, resulting in an abnormal number of chromosomes in the daughter cells. Nondisjunction in meiosis I in the mother is the most common source of the extra chromosome 21, which leads to Down syndrome.

What Is the Most Common Source of the Extra Chromosome