Nondisjunction
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Nondisjunction
In biology, nondisjunction is the failure of a chromosome to split correctly during meiosis.
meiotic nondisjunction
the failure of two members of a chromosome pair to separate properly during meiosis, so that both members go to one daughter cell, and the other daughter cell receives neither ...
nondisjunction The failure of chromosomes to separate properly during cell division. The unequal segregation of chromosomes during meiosis.
nondisjunction
[L. non, not + disjungere, to separate]
An accident of meiosis or mitosis, in which both members of a pair of homologous chromosomes or both sister chromatids fail to move apart properly.
nonpolar covalent bond ...
Nondisjunction The failure of a chromosome pair to separate at the first meiotic division, or for two chromatids of a replicated chromosome to separate at mitosis (or at the second meiotic division), so that both pass to the same daughter cell.
Nondisjunction
Nondisjunction occurs when chromosomes fail to "disjoin" during meiosis or mitosis.
Meiosis ...
Nondisjunction
Chromosome pairs do not 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 (trisomy).
Related Terms:
Chromosome ...
Nondisjunction- homologues don't separate in meiosis 1
Results in aneuploidy
Usually embryo lethal
Trisomy 21, exception leading to Downs syndrome
Sex chromosomes
Turner syndrome: monosomy X
Klinefelter syndrome: XXY ...
nondisjunction. Failure of a pair of homologous chromosomes to separate during meiosis, leading to one gamete with n + 1 chromosomes (see trisomy) and another gamete with n _ 1 chromosomes.
In humans, nondisjunction is most often associated with the 21st chromosome, producing a disease known as Down's syndrome (also referred to as trisomy 21).
Advanced maternal age -- women over age 34 (age 35 at delivery) at increased risk for nondisjunction trisomy in fetus. Alcoholism -- a chronic and progressive condition characterized by the inability to control the consumption of alcohol.
Examples of major genetic principles established by Drosophila researchers in the early 1900s are nondisjunction and its consequences, the genetic behavior of chromosome aberrations, the mutagenicity of ionizing radiation, ...
On rare occasions, nondisjunction occurs during meiosis with the loss of one X chromosome. Animals with a single X are males and are able to fertilize the eggs of the hermaphrodites (with more success than they have themselves).
C.
Trisomy
The term proposed by Blakeslee (1922) to describe an otherwise diploid individual which has one of the chromosomes represented three times instead of twice. Caused by nondisjunction during cell division.
Disjunction: Separation of homologous chromosomes during anaphase of mitotic or meiotic divisions (see also nondisjunction).
 See also: Disjunction, Chromosome, Chromosomes, Cell, Cells
  
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