Trisomy-21 results from a mutation to the chromosomes in

a) body cells
b) somatic cells
c) gametes
d) skin cells

The right answer is C) gametes.

In its most common form, trisomy 21 is characterized by the presence of three chromosomes 21. In general, the origin of this trisomy is a fertilization between a gamete possessing a chromosome 21 and a gamete possessing two chromosomes 21. In the very In the vast majority of cases, the anomaly is borne by the oocyte. Indeed, the aging of the oocytes is at the origin of meiotic anomalies favoring the occurrence of trisomy. This pathophysiological aspect explains that the risk of T21 is directly related to maternal age.