Nondisjunction ("not coming apart") is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2. This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes. Such a cell is said to be aneuploid. Loss of a single chromosome (2n-1), in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs, is referred to as a monosomy. Gaining a single chromosome, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs is referred to as a trisomy. The following diagram shows the two possible types of nondisjunction in meiosis:
2n / \ n+1 n-1 / \ / \ n+1 n+1 n-1 n-1
2n / \ n n / \ / \ n n n+1 n-1
Schematic of nondisjunction in meiosis I. Duplicated chromosomes in diploid cell (2n).
All gametes are affected by nondisjunction in meiosis I. Two gametes have a single extra chromosome; two gametes are missing a single chromosome.
Schematic of nondisjunction in meiosis II. Duplicated chromosomes in diploid cell (2n).
Half of the gametes are affected by nondisjunction in meiosis II. One gamete has a single extra chromosome; one gamete is missing a single chromosome.
"n" denotes a cell with a single copy of each chromosome (haploid cell); 2n denotes a cell with two copies of each chromosome (diploid cell)
Pathology: chromosome abnormalities (Q90–Q99 · 758) Autosomal1q21.1 deletion syndrome/1q21.1 duplication syndrome/TAR syndrome (1) · Wolf-Hirschhorn syndrome (4) · Cri du chat/Chromosome 5q deletion syndrome (5) · Williams syndrome (7) · Jacobsen syndrome (11) · Miller–Dieker syndrome/Smith–Magenis syndrome (17) · DiGeorge syndrome (22) · 22q13 deletion syndrome (22)
genomic imprinting (Angelman syndrome/Prader–Willi syndrome (15))Distal 18q-/Proximal 18q-
X/Y linked TranslocationsLymphoidMyeloidOther Other
Snustad, D.P., Simmons, M.J.(2006). Principles of Genetics (4th ed.). Hoboken: John Wiley & Sons, Inc.
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Nondisjunction — Nondisjunction, Ausbleiben der Trennung von Schwesterchromatiden eines Chromosoms in der Mitose (mitotische Disjunction) oder von homologen Chromatiden in der Meiose (meiotische Disjunction); führt zu ⇒ Aneuploidie … Deutsch wörterbuch der biologie
nondisjunction — [nän΄dis juŋk′shən] n. Biol. the failure of paired chromosomes to pass to separate cells in meiosis … English World dictionary
Nondisjunction — Failure of paired chromosomes to disjoin (separate) during cell division so that both chromosomes go to one daughter cell and none to the other. Nondisjunction causes errors in chromosome number such as trisomy 21 (Down s syndrome) and monosomy X … Medical dictionary
nondisjunction — noun Etymology: International Scientific Vocabulary Date: 1913 failure of homologous chromosomes or sister chromatids to separate subsequent to metaphase in meiosis or mitosis so that one daughter cell has both and the other neither of the… … New Collegiate Dictionary
nondisjunction — n. [L. non, not; disjunctus, unyolked] The failure to separate of paired chromosomes during meiosis … Dictionary of invertebrate zoology
nondisjunction — /non dis jungk sheuhn/, n. Biol. the failure of chromosomes to separate and segregate into daughter cells at division. [1910 15; NON + DISJUNCTION] * * * … Universalium
nondisjunction — noun The failure of chromosome pairs to separate properly during meiosis See Also: disjunction, nondisjunct, nondisjunctive … Wiktionary
Nondisjunction — Non|dis|junc|tion, auch Non Dis|junc|tion [nɔndis dʒʌŋkʃən] die; <zu engl. non »nicht « u. disjunction »Trennung«> unregelmäßiger Teilungsprozess von ↑Chromosomen bei der Reifeteilung (Biol.) … Das große Fremdwörterbuch
nondisjunction — n. nonseparation of paired chromosomes during cell division (Biology) … English contemporary dictionary
nondisjunction — non·disjunction … English syllables