Nondisjunction.
D000818:Animals; D002869:Chromosome Aberrations; D004314:Down Syndrome / Q000235:genetics*; D005260:Female; D006801:Humans; D008297:Male; D008540:Meiosis; D008938:Mitosis; D009030:Mosaicism; D011247:Pregnancy; D011832:Radiation Injuries / Q000235:genetics; D012729:Sex Chromosome Aberrations / Q000235:genetics; D014314:Trisomy; D014960:X Chromosome; D014998:Y Chromosome