title: Origin of extra chromosome in trisomy 21.
mesh_terms: D002904:Chromosomes, Human, 21-22 and Y; D004314:Down Syndrome / Q000209:etiology / Q000235:genetics*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008423:Maternal Age; D008540:Meiosis; D014314:Trisomy