Definition of "nondisjunction" [nondisjunction]

• The failure of paired chromosomes or sister chromatids to separate and go to different cells during meiosis. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Embryos that are trisomic contain, instead of matched pairs of chromosomes, one too many of a given chromosome, most commonly chromosome 13, 18, 21 (which is responsible for Down syndrome), X, or Y. Trisomies are the result of a glitch known as nondisjunction, which occurs principally during the creation of egg cells (although sperm cells may also exhibit such errors)."
• "When nondisjunction occurs, the resulting eggs may carry too few or too many chromosomes, a state called aneuploidy."
• "This makes sense, since these cancers often fail to inactivate the X chromosome, and X chromosome nondisjunction leads to more male worms."