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Definition of Meiotic nondisjunction
Medically reviewed by Dr. Otari Nergadze, Neurosurgeon | Updated: January 2026
Meiotic nondisjunction: Failure of two members of a chromosome pair to separate from one another during meiosis, causing both chromosomes to go to a single daughter cell. Meiotic nondisjunction is responsible for the extra chromosome 21 in trisomy 21 (Down syndrome) and for extra and missing chromosomes that cause other birth defects and many miscarriages.