What is the source of the extra chromosome 21 in an individual with Down syndrome?

Question

Quizplus · Accepted Answer

Down syndrome is caused by an extra copy of chromosome 21, which can result from nondisjunction during meiosis in either the mother or the father. Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis, leading to an abnormal number of chromosomes in the resulting gametes. Therefore, the best choice is D, nondisjunction in either parent.

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