Nondisjunction
Encyclopedia : N : NO : NON : Nondisjunction
Overview
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 [haploid cell]) (2n means 2 copies of each chromosome)[diploid 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
- Down's syndrome
- Edward's syndrome
- Klinefelter's syndrome
- Meiosis
- Mitosis
- Pallister-Killian syndrome
- Patau syndrome
- Turner syndrome
- XYY syndrome
- XXX syndrome
External links
(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)
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