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

/non·dis·junc·tion/ (-dis-junk´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.
Enlarge picture
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).

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.

nondisjunction

[-disjungk′chən]
Etymology: L, non + disjungere, to disjoint
failure of homologous pairs of chromosomes to separate during the first meiotic division or of the two chromatids of a chromosome to split during anaphase of mitosis or the second meiotic division. The result is an abnormal number of chromosomes in the daughter cells. Compare disjunction. See also monosomy, trisomy.

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

nondisjunction

failure (1) of two homologous chromosomes to pass to separate cells during the first division of meiosis, or (2) 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. Death of the fetus or chromosomal anomalies may result.
References in periodicals archive ?
Chromosome nondisjunction and instabilities in tapetal cells are affected by B chromosomes in maize.
sup][19] However, the effect of consanguinity on nondisjunction of chromosome 21 has not been clearly defined.
The B chromosome of maize has a complex genetic organization with at least four different regions that influence the nondisjunction process, which happens on the male side only.
The risk for abnormalities due mainly to nondisjunction of chromosomes during meiosis increases with increasing age.
Investigators found a higher incidence of aneuploidy in semen samples from men with a deficient sperm count, indicating that "men with abnormal semen parameters may have decreased recombination and pairing leading to both meiotic arrest (oligozoospermia) and nondisjunction of the sex chromosomes," they reported (Fertil.
In trisomy 21 cells, the distribution of chromosome 21 homologs in rosettes was such that two of the three homologs were closely juxtaposed, a pattern consistent with our current understanding of the mechanism of chromosomal nondisjunction.
Chromosome problems causing miscarriage or other pregnancy losses may be due to a previously known or unknown chromosome problem in one or both parents (thereby increasing the risk of a subsequent pregnancy loss) or may be due to an error in cell division during egg or sperm cell production ("packaging error") known as nondisjunction, or in fertilization.
1995), such centromeric incompatibilities may be produced by mechanical pairing deficiencies leading to chromosomal nondisjunction (Redi and Capanna 1988).
The meiotic stage of nondisjunction in trisomy 21: determination by using DNA polymorphisms.
Increased chromosome X, Y, and 18 nondisjunction in sperm from infertile patients that were identified as normal by strict morphology: implication for intracytoplasmic sperm injection.
Evidence for genetic control of nondisjunction in man.
It is postulated that PMD occurs when 1 ovum is fertilized by 2 spermatozoa or involves a single ovum and spermatozoa with a maternal nondisjunction error during the first meiotic division.