nondisjunction


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nondisjunction

 [non″dis-jungk´shun]
failure either of two homologous chromosomes to pass to separate cells during the first meiotic division, or of the two chromatids of a chromosome to pass to separate cells during mitosis or during the second meiotic division. As a result, one daughter cell has two chromosomes or two chromatids, and the other has none. If this happens during meiosis, an aneuploid individual (for example, a child with Down syndrome) may develop following fertilization.
Nondisjunction. Normal meiosis (A) is contrasted with failure of homologous chromosomes to separate in meiosis I (B) or of sister chromatids to separate in meiosis II (C). From Dorland's, 2000.

non·dis·junc·tion

(non'dis-jŭnk'shŭn), [MIM*257300]
Failure of one or more pairs of chromosomes to separate at the meiotic stage of karyokinesis, with the result that both chromosomes are carried to one daughter cell and none to the other.

nondisjunction

(nŏn′dĭs-jŭngk′shən)
n.
The failure of paired chromosomes or sister chromatids to separate and go to different cells during meiosis.

non′dis·junc′tion·al adj.

non·dis·junc·tion

(non'dis-jŭngk'shŭn)
Failure of one or more pairs of chromosomes to separate at the meiotic stage of karyokinesis, with the result that both chromosomes are carried to one daughter cell and none to the other.
Enlarge picture
NONDISJUNCTION

nondisjunction

(nŏn″dĭs-jŭnk′shŭn)
The failure of a pair of chromosomes to separate during meiosis, allowing one daughter cell to have two chromosomes and the other to have none.
See: illustration
Nondisjunctionclick for a larger image
Fig. 230 Nondisjunction . (a) Normal disjunction (b) Nondisjunction.

nondisjunction

the failure of chromosomes (in eukaryotes) to go to opposite poles during nuclear division, leading to unequal numbers of chromosomes in the daughter cells (see ANEUPLOIDY). See Fig. 230 . Nondisjunction produces abnormal numbers of both AUTOSOMES (e.g. DOWN'S SYNDROME) and SEX CHROMOSOMES (e.g. TURNERS SYNDROME).

Nondisjunction

A genetic term referring to an event which takes place during cell division, in which a genetic accident causes an egg or sperm cell to have 24 chromosomes, rather than the normal 23.
Mentioned in: Down Syndrome
References in periodicals archive ?
Chromosome nondisjunction and instabilities in tapetal cells are affected by B chromosomes in maize.
Edwards syndrome occurs because of meiotic nondisjunction. Careful pathological examination of foetus can confirm the clinical diagnosis and help in identifying unexpected anomalies.
For younger mothers, the mechanism behind the nondisjunction is not well understood.
Druschel et al., "Maternal age and risk for trisomy 21 assessed by the origin of chromosome nondisjunction: a report from the Atlanta and National Down Syndrome Projects," Human Genetics, vol.
SMC1[beta]-deficient female mice provide evidence that cohesins are a missing link in age-related nondisjunction. Nature Genetics, 37, 1351-1355.
In summary, this work permitted confirmig and broadening the genomic and molecular knowledge of nondisjunction in DS via open-access bioinformatic tools.
Almost 95% of cases are caused by nondisjunction, meaning the chromosome 21 pair fails to separate during cellular division (Nehring, 2010).
Sperm chromosome complements in infertile men with normal 46,XY karyotype have been studied to determine whether meiosis in these men is prone to errors of nondisjunction, leading to aneuploidy.
This model explains the extreme size difference between XR and neo-Y, the distal association between both elements, the existence of a neocentromere in XL and the very irregular male meiotic behavior of the sex bivalent (asynapsis, lagging, nondisjunction), as well as some peculiarities of the neoX/neo-X bivalent in female meiosis.
Chromosome nondisjunction yields tetraploid rather than aneuploid cells in human cell lines.
The B chromosomes show instability during meiosis, but present preferential segregation for the nuclei which form gametes, and normal behaviour during the mitotic process, except in the second division of the microspores in the endosperm and tapetal cell, where they show high nondisjunction rates (RANDOLPH, 1941; RHOADES et al., 1967; CARLSON, 1986; GONZALEZ-SANCHEZ et al., 2004).
Pericentric inversion of chromosome 9: prevalence in 300 Down syndrome families and molecular studies of nondisjunction. Am J Med Genet.