Overview

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Nondisjunction is the failure of chromosome pairs to separate properly during meiosis or mitosis. The result of this error is a cell with an imbalance of chromosomes. When a chromosome is lost, it is called a Monosomy, in which the gamete with the defect will have one or more chromosomes missing from one of its pairs. When a chromosome is gained, it is called a Trisomy, in the case of a human cell it will have a set of 24 chromosomes instead of the usual 23.

A diagram of 2 possible occurrences of nondisjunction in meiosis: (n means 1 copy of each chromosome cell) (2n means 2 copies of each chromosome)cell)

4n (duplicated chromosomes in diploid cell) / \ (non-disjunction occurs here) 3n 1n / \ / \ n+1 n+1 n-1 n-1 (Two gametes have one extra chromosome and the other 2 are missing a chromosome)

4n (duplicated chromosomes in diploid cell) / \ 2n 2n / \ / \ (non-disjunction occurs here) n n n+1 n-1 (2 Gametes are normal, but on the right side, one gamete has an extra chromosome, and the other is missing one)

See also

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• Down's syndrome
• Edward's syndrome
• Klinefelter's syndrome
• Meiosis
• Mitosis
• Pallister-Killian syndrome
• Patau syndrome
• Turner syndrome
• XYY syndrome
• XXX syndrome

External links

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(Great place for in-depth insight on this subject)

• Human Genetics 1 (http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20101/Bio%20101%20Laboratory/Human%20Genetics%201/Nondisjunction.htm)
• Genetics Home Reference (http://ghr.nlm.nih.gov/ghr/glossary/nondisjunction)
• Other Syndromes (http://www.thedoctorslounge.net/studlounge/downdirty/syndromes.htm)