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Topic: Nondisjunction

Related Topics

Trisomy

Triple X syndrome

Trisomy 21

Karyotype

XYY

Meiosis

Incarceration

Issei Sagawa

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		Nondisjunction is a faulty cell division which results in an embryo with three number 21 chromosomes instead of two.
		Why nondisjunction occurs is currently unknown, although it does seem to be related to advancing maternal age.
		Unlike nondisjunction, maternal age is not linked to the risk of translocation.
	library.thinkquest.org /TQ0310111/down1.html (569 words)

	CHROMOSOMAL PATTERNS OF INHERITANCE
		Aneuploidy is due to nondisjunction, or failure of normal separation of a chromosome pair when the eggs or sperm are formed during meiosis.
		Nondisjunction leads to the formation of two chromosomally different eggs or sperm; one has a pair of chromosomes (disomic), and the other is missing a chromosome (nullisomic).
		Nondisjunction occurs when the normal separation of the chromosome pairs during meiosis is disrupted.
	www.usd.edu /med/som/genetics/curriculum/1DCHROM2.htm (1619 words)

	Some information about nondisjunction incurred by the r-x1 deletion
		This is due to the fact that the assumption of an aneuploid endosperm as the basis of seed size reduction may not be valid.
		Nondisjunction does not occur at the last division for the following reasons: If it occurs at the micropylar pole, 2/4 of embryos would be euploid, 1/4 of embryos hyperploid and 1/4 of embryos hypoploid.
		When nondisjunction takes place at the chalazal pole, all embryos produced are euploid, but half of the endosperms are euploid and the other half, aneuploid.
	www.agron.missouri.edu /mnl/59/70lin.html (718 words)

	Nondisjunction - Wikipedia, the free encyclopedia
		Nondisjunction is the failure of chromosome pairs to separate properly during meiosis or mitosis.
		When a chromosome is gained, it is called a Trisomy, in the case of a human gamete 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])
	en.wikipedia.org /wiki/Nondisjunction (265 words)

	Human Genetics - Chromosomal Inheritance 1
		Meiotic nondisjunction, the failure of the chromosomes to disjoin and pass to opposite poles, in either the first or second meiotic division is the major cause of chromosomal abnormalities.
		Increasing maternal age is associated with a higher incidence of chromosomal abnormalities attributed to nondisjunction.
		Nondisjunction, the failure of the chromosomes to disjoin and move to opposite poles may affect as many as 25% of all ova and 2% of all sperm.
	www.uic.edu /classes/bms/bms655/lesson9.html (2625 words)

	An Application of Molecular Genotyping in Mice
		This expands the opportunities for studying heritable conditions such as nondisjunction frequencies (15) and imprinting (as a consequence of uniparental inheritance of chromosomes or regions) on mouse development and viability, and places such studies on a solid statistical foundation.
		Nondisjunction rates and abnormal embryonic development in a mouse cross between heterozygotes carrying a (7,18) Robertsonian translocation chromosome.
		Molecular analysis of nondisjunction in mice heterozygous for a robertsonian translocation.
	www.biologicalprocedures.com /bpo/arts/1/53/m53.htm (3826 words)

	Developmental Biology Online: Human Meiosis (Site not responding. Last check: 2007-10-20)
		Nondisjunction means that a chromosome pair failed to separate during the meiotic division.
		In humans, for example, if nondisjunction of chromosome 13 occurs during first meiotic division, half the gametes will have an extra copy of chromosome 13 and thus contain 24 chromosomes instead of the normal haploid number of 23.
		XYY (due to a nondisjunction of the Y chromosome) individuals are often taller than their counterparts, and they may have learning disabilities as well.
	7e.devbio.com /article.php?ch=19&id=189 (1805 words)

	Results of the search
		Maternal meiosis II nondisjunction in trisomy 21 is associated with maternal low socioeconomic status.
		Nondisjunction of human acrocentric chromosomes: studies of 432 trisomic fetuses and liveborns.
		Secondary nondisjunction causing regular trisomy 21 in the offspring of a mosaic trisomy 21 mother.
	invention.swmed.edu /trite/abstracts/user-1015821170/results.shtml (3111 words)

	Chromosome Nondisjunction and Instabilities in Tapetal Cells Are Affected by B Chromosomes in Maize -- Chiavarino et ...
		Chromosome Nondisjunction and Instabilities in Tapetal Cells Are Affected by B Chromosomes in Maize -- Chiavarino et al.
		Chromosome Nondisjunction and Instabilities in Tapetal Cells Are Affected by B Chromosomes in Maize
		Nondisjunction of A chromosomes and micronuclei occur in tapetal
	www.genetics.org /cgi/content/full/155/2/889 (4073 words)

	Consistent nondisjunction of B chromosomes in Black Mexican
		Therefore, it is possible that nondisjunction of all B chromosomes at the second pollen mitosis occurs 100% of the time and that plants containing an odd number of B chromosomes from 0B x B crosses actually represent subsequent instability of B chromosomes in somatic cell divisions.
		This indicates that the B chromosome nondisjunction rate is a maximum of 81%.
		For example, genes that shorten the duration of the division of the generative nucleus or lengthen the duration of replication of centromeric heterochromatin may have a strong positive influence on B chromosome nondisjunction.
	www.maizegdb.org /mnl/61/136staub.html (805 words)

	causes1 (Site not responding. Last check: 2007-10-20)
		Nondisjunction is a faulty cell division, which results in an embryo with three number 21 chromosomes instead of the normal two.
		The reason why nondisjunction occurs is currently unknown, though it does seem to be related to maternal age.
		Because the problem of cell division is often present in the egg prior to conception, it has theorized that environmental factors may be a cause of nondisjunction.
	www.msu.edu /~nowakchr/causes1.html (424 words)

	Human Genetics - Chromosomal Inheritance 2
		Just as simple meiotic nondisjunction is the leading cause of autosomal chromosome abnormalities, so is nondisjunction the leading cause of the X and Y abnormalities.
		In autosomal abnormalities an increase in nondisjunction was associated with increasing maternal age.
		The nondisjunction that results in a 45,X female can occur at either meiotic division in either spermatogenesis or oogenesis, but about 80% are the result of paternal nondisjunction.
	www.uic.edu /classes/bms/bms655/lesson10.html (2082 words)

	Molecular Analysis of Nondisjunction in Mice Heterozygous for a Robertsonian Translocation -- Underkoffler et al. 161 ...
		age effects on the incidence of nondisjunction to be assessed.
		of nondisjunction of chromosome 7 and 18 in females was not
		of maternal and paternal nondisjunction of chromosome 18 was
	www.genetics.org /cgi/content/full/161/3/1219 (2948 words)

	Signs of Nondisjunction - WrongDiagnosis.com
		The phrase "signs of Nondisjunction" should, strictly speaking, refer only to those signs and symptoms of Nondisjunction that are not readily apparent to the patient.
		The word "symptoms of Nondisjunction" is the more general meaning; see symptoms of Nondisjunction.
		This medical information about signs and symptoms for Nondisjunction has been gathered from various sources, may not be fully accurate, and may not be the full list of Nondisjunction signs or Nondisjunction symptoms.
	www.wrongdiagnosis.com /n/nondisjunction/signs.htm (401 words)

	Abstract: The origin of the extra chromsome 21
		Despite the clinical importance of trisomy 21, we have been ignorant of the causes of meiotic nondisjunction of chromosome 21.
		These observations have led to the idea that chromosome 21 nondisjunction requires 'two hits': first, the establishment in prophase I of a 'vulnerable' bivalent and second, abnormal processing of the bivalent at metaphase I or II.
		Studies also indicate that nondisjunction may require a second event, or "hit," involving the degredation of a meiotic process (a protein integral to the meiotic event).
	www.ds-health.com /abst/a0004.htm (488 words)

	Nucleolus organizer region heteromorphism in patients with Down syndrome and their parents
		ABSTRACT The study aimed to evaluate the role of nucleolus organizer region (NOR) heteromorphism as an etiological factor for parental nondisjunction in Down syndrome by comparing 25 patients affected by Down syndrome, and their parents with a control group of 80 non-affected Egyptians.
		The possible etiologies for nondisjunction include maternal and paternal age effect, genetic predisposition, seasonal variation, viral infection, parental irradiation and environmental chemicals [10].
		The frequency of maternal nondisjunction has been estimated to be 90%-95% (75% meiosis I, 25% meiosis II).
	www.emro.who.int /Publications/EMHJ/0502/11.htm (2267 words)

	Prevalence and Incidence of Nondisjunction - WrongDiagnosis.com
		Nondisjunction is listed as a "rare disease" by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH).
		The term 'prevalence' of Nondisjunction usually refers to the estimated population of people who are managing Nondisjunction at any given time.
		The term 'incidence' of Nondisjunction refers to the annual diagnosis rate, or the number of new cases of Nondisjunction diagnosed each year.
	www.wrongdiagnosis.com /n/nondisjunction/prevalence.htm (251 words)

	NONDISJUNCTION
		When nondisjunction results in an embryo that is ______________ one or more chromosomes, the embryo usually develops deformities that are so severe that the embryo dies.
		When nondisjunction results in an embryo that inherits one or more __________ chromosomes, the embryo usually develops deformities that are so severe that the embryo dies.
		o Results from nondisjunction during _________________________ of ___________________________ in the father’s spermatocyte (a normal egg is fertilized by an abnormal YY-bearing sperm).
	www.soc.hawaii.edu /ws350/spr04/nondisjunction.htm (1313 words)

	Indian Pediatrics - Editorial
		Antonarakis(10) has shown that 95% of T21 cases are maternal in origin due to meiotic nondisjunction and most errors in maternal meiosis occur in meiosis I and the mean maternal age in this population is 32 years.
		Subsequently, a population based analysis using DNA markers have shown that maternal nondisjunction accounts for 86 per cent of all cases of T21, with 75 percent of cases occurring at meiosis-I (M-I) and 25 percent at meiosis-II (M-II)(11).
		Because of the importance of methionine synthase reaction in maintaining normal folate metabolism and DNA methylation, the authors have hypothesized that this poly-morphism could be a second maternal genetic risk factor for Down syndrome.
	www.indianpediatrics.net /feb2003/feb-115-123.htm (3363 words)

	MEDICAL BIOLOGY: ON CHROMOSOME NONDISJUNCTION (Site not responding. Last check: 2007-10-20)
		However, it is clear that almost all cases involve errors in meiosis, the complex process in which one round of DNA replication is followed by two cellular divisions to generate haploid gametes.
		Nondisjunction can occur at either of these stages and can generally be distinguished with the use of polymorphic genetic markers at or near the centromere of the nondisjoined chromosomes.
		Characterization of susceptible chiasma configurations that increase the risk for maternal nondisjunction of chromosome 21.
	scienceweek.com /2005/sb050218-6.htm (1963 words)

	Nondisjunction - definition from Biology-Online.org (Site not responding. Last check: 2007-10-20)
		It results in aneuploid cells, where the daughter cell has two chromosomes or two chromatids and the other has none.
		Nondisjunction of the x chromosome in drosophila confirmed the theory of chromosomal inheritance.
		Meiosis in which there is a failure of paired homologous chromosomes to separate; results in an abnormal number of chromosomes in the daughter cells.
	www.biology-online.org /dictionary/Nondisjunction (157 words)

	Down Syndrome
		This trisomy is due to nondisjunction occurring randomly during meiosis (gamete formation).
		Nondisjunction is the failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II) to separate and migrate to opposite poles.
		Although maternal nondisjunction is the main cause of Down syndrome, nondisjunction can also occur after fertilization.
	www.altonweb.com /cs/downsyndrome/riscoe.html (2151 words)

	Chapter 12: Patterns of Inheritance (Part 2) (Site not responding. Last check: 2007-10-20)
		Nondisjunction during meiosis causes an abnormal chromosome number in gametes produced.
		Nondisjunction is a failure of one or more chromosomes to separate.
		Nondisjunction can occur when homologous chromosomes fail to separate during meiosis I or
	www.sirinet.net /~jgjohnso/apbio12B.html (1985 words)

	Molecular Analysis of Nondisjunction in Down Syndrome Patients With and Without Atrioventricular Septal Defects -- ... (Site not responding. Last check: 2007-10-20)
		c, Meiosis II nondisjunction with no prior recombination: A daughter cell is produced containing two identical copies of one of the parental chromosomes (disomic homozygosity or reduced).
		d, Meiosis II nondisjunction with a prior single recombination event: This produces a daughter cell that is disomic homozygous at alleles centromeric to the recombination and disomic heterozygous at alleles telomeric to the recombination.
		The nondisjunction was maternal in origin (marker f) and consistent with a meiosis II error (marker a).
	circ.ahajournals.org /cgi/content/full/92/10/2803 (4169 words)

	Chromosome nondisjunction yields tetraploid rather than aneuploid cells in human cell lines : Nature
		Here we show that chromosome nondisjunction is tightly coupled to regulation of cytokinesis in human cell lines, such that nondisjunction results in the formation of tetraploid rather than aneuploid cells.
		Nondisjunction occurred with high frequency in cells that became binucleated by furrow regression, but not in cells that completed cytokinesis to form two mononucleated cells.
		Our findings indicate that nondisjunction does not directly yield aneuploid cells, but rather tetraploid cells that may subsequently become aneuploid through further division.
	www.nature.com /nature/journal/v437/n7061/abs/nature03958.html (344 words)

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