Nondisjunction

The left image at the blue arrow is nondisjunction taking place during meiosis II. The right image at the green arrow is nondisjunction taking place during meiosis I. Nondisjunction is when chromosomes fail to separate normally resulting in a gain or loss of chromosomes.

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division (mitosis/meiosis). There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis.[1][2][3] Nondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy).

Calvin Bridges and Thomas Hunt Morgan are credited with discovering nondisjunction in Drosophila melanogaster sex chromosomes in the spring of 1910, while working in the Zoological Laboratory of Columbia University.[4]

  1. ^ Simmons, D. Peter Snustad, Michael J. (2006). Principles of genetics (4th ed.). New York, NY [u.a.]: Wiley. ISBN 9780471699392.{{cite book}}: CS1 maint: multiple names: authors list (link)
  2. ^ Bacino, C.A.; Lee, B. (2011). "Chapter 76: Cytogenetics". In Kliegman, R.M.; Stanton, B.F.; St. Geme, J.W.; Schor, N.F.; Behrman, R.E. (eds.). Nelson Textbook of Pediatrics, 19th Edition (19th ed.). Philadelphia: Saunders. pp. 394–413. ISBN 9781437707557.
  3. ^ Strachan, Tom; Read, Andrew (2011). Human molecular genetics (4th ed.). New York: Garland Science. ISBN 9780815341499.
  4. ^ Thomas Hunt Morgan (August 31, 2012). Sex-Linked Inheritance in Drosophila. Ulan Press. pp. 10–11.