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PubMed1992

A selective method for studying primary sex chromosome non-disjunction in females and males and X-Y exchange in males of Drosophila melanogaster including a demonstration of euchromatic X-Y exchange.

A selective method was developed, based on negative complementation of the Abruptex alleles of the Notch locus, for studying primary sex chromosome non-disjunction in females and males of Drosophila melanogaster and X-Y exchange in males. The results show that the frequency of primary non-disjunction of structurally normal X chromosomes was lower than the frequency of X-derY non-disjunction in males. Double exchange between the X and the derY chromosome in the male occurs with a frequency of at least 0.091%. Single exchanges are naturally expected to occur with even higher frequency. Exchanges were interestingly at least partly of euchromatic nature. The origin of these exchanges is at least partly of gonial origin.

Animals↗

PubMed1982

Seasonality of pre-ovulatory non-disjunction and the aetiology of Down syndrome. A European collaborative study.

Six series of patients with Down syndrome (DS) from different European countries, altogether 287 cases, were divided into four categories according to parental origin of the additional chromosome 21 and meiotic division in which the nondisjunction had occurred. The monthly birth or conception frequencies per category were analysed by graph and compared with the total birth curve by Watson's adaptation of the Kolmogorov-Smirnov statistic for cyclic trends. Unexpectedly, the non-disjunctions during maternal meiosis I (63%), by far the largest category, occurred more frequently during the seasonal "restoration" and "inhibition" phase of the "ovulatory seasons" and less frequently when the ovulation rate is stabilized. The graph of the maternal meiosis II patients (17%) also seemed to conform to this phenomenon, though less obviously. In contrast to this, the paternal DS graph (20%) was very divergent, although a seasonal cluster of non-disjunctions may also occur here. From these findings a seasonal disturbance of preovulatory ripening of the ovum emerges as a possible cause of the first (and second) meiotic non-disjunction. Seasonal periodicity of the prolactin concentration in women and "transient hyperprolactinaemia", shown to be allied to delayed ovulation, may be related to these seasonal DS conception clusters.

Down Syndrome↗

PubMed1983

The genetic basis of non-disjunction: increased incidence of hyperploidy in oocytes from F1 hybrid mice.

Oocytes from parental mice strains NMRI/Han, C57/bl and Balb/c and from F1 hybrid lines were analysed for aneuploidy due to non-disjunction after gonadotropin-stimulated ovulation. No hyperploid oocytes were present in five of the strains studied. F1 hybrids from crosses of NMRI/HanxC57/bl did ovulate, however, a significantly increased number of hyperploid oocytes, although females from their parental strains show a rather low incidence of non-disjunction. The evidence for a genetic basis for non-disjunction is assessed and possible causative factors are discussed.

Animals↗

PubMed1986

A possible cause of non-disjunction of additional chromosome 21 in Down syndrome.

A possible cause of non-disjunction of chromosome 21 in Down Syndromes has been cytogenetically evaluated by examining the parents by Ag-staining technique. In all the cases studied so far, the contributing parents have active ribosomal cistrons on both chromosomes 21 i.e. both chromosomes are stained positively by silver staining. These results show that the active NORs might play an essential role in meiotic non-disjunction. Furthermore, the preliminary results demonstrate that the acrocentric associations of homologous and non-homologous nature involving chromosome 21 are the most frequent in the contributing parent which may further indicate the role of multiple cellular factors affecting the associations in promoting the nondisjunction in addition to active NORs. The possible mechanisms regarding the non-disjunction of chromosome 21 have been described.

Child↗

PubMed1976

[The disjunction zone in the slit-image-photograph of the human aging lens (author's transl)].

Standardised slit-image-photographs of 178 clear lenses were evaluated by microdensitometry. The mean distance of the disjunction zone from the anterior capsule and the density of the disjunction zone remain constant during life. Its thickness will be reduced and its extension into deeper layers increases with age. In contrast to these findings the thickness of the whole lens according to the increasing thickness of the cortex increases with age. Its density increases too in a not linear manner probably on behalf of the increasing number of reflecting zones (Alterskernstreifen). The density of the nucleus of the lens increases with age, whereas its densitometrically defined thickness remains constant during life. The disjunction zone behaves independently from age in contrast to other parts of the lens.

Adolescent↗

PubMed1976

[The disjunction zone in the slit-image-photograph of the human lens in eye diseases (author's transl)].

Standardised slit-image-photographs of the clear human lens in 78 eyes with wide angle glaucoma, 29 eyes with uveitis and 35 eyes after an operation of a retinal detachment were evaluated by microdensitometry and compared with clear lenses of 178 eyes without eye diseases. Most significant alterations were observed in the anterior disjunction zone. Its thickness was increased in all these diseases with the exception of the glaucoma eyes treated with derivates of phenylephrine and/or cholinesteraseinhibitors. Under these conditions the disjunction zone disappeared. The alterations of the lens cortex and of the nucleus of the lens with respect to the thickness and its density were mostly accelerations of the normal aging process and only glaucoma eyes were partly in contrast to this process. Thickening of the anterior disjunction zone may be combined with a thickening of the whole lens and vice versa.

Adolescent↗

PubMed1997

Alphoid variant-specific FISH probes can distinguish autosomal meiosis I from meiosis II non-disjunction in human sperm.

Over the past few years, several groups have used fluorescence in situ hybridization (FISH) to study aneuploidy in human sperm. Several important observations have derived from these studies, including the demonstration of chromosome-specific variation in non-disjunction frequencies, and the possible association of aneuploidy with environmental agents and with increasing paternal age. However, an important technical limitation of these studies has been the inability to distinguish between autosomal non-disjunction occurring at meiosis I and meiosis II. In the present report, we describe a simple FISH-based approach designed to overcome this limitation. Using oligonucleotide probes capable of distinguishing subtle differences in the alpha satellite sequences of chromosome 17, we demonstrate that (in appropriate heterozygotes) it is possible to simultaneously identify disomic sperm and to determine the meiotic stage of origin of the additional chromosome. This novel approach has important implications for future FISH sperm studies, since the ability to distinguish between meiosis I and meiosis II non-disjunction will make it possible to determine whether putative etiological agents affect chromosome segregation at both, or only one, of the two meiotic stages.

Base Sequence↗

PubMedDate not supplied

Uncertainty and the difficulty of thinking through disjunctions.

This paper considers the relationship between decision under uncertainty and thinking through disjunctions. Decision situations that lead to violations of Savage's sure-thing principle are examined, and a variety of simple reasoning problems that often generate confusion and error are reviewed. The common difficulty is attributed to people's reluctance to think through disjunctions. Instead of hypothetically traveling through the branches of a decision tree, it is suggested, people suspend judgement and remain at the node. This interpretation is applied to instances of decision making, information search, deductive and inductive reasoning, probabilistic judgement, games, puzzles and paradoxes. Some implications of the reluctance to think through disjunctions, as well as potential corrective procedures, are discussed.

Decision Making↗

PubMed1979

Aspergillus nidulans as a test organism for assessing radio-induced chromosomal non-disjunction.

A genetically marked heterozygous diploid of Aspergillus nidulans was synthesized and the feasibility of using this system for the simultaneous estimation of radio-induced mitotic crossing-over and non-disjunction has been investigated. In the case of the latter, serious experimental problems have been encountered. Nevertheless, induction curves for non-disjunction with 15-MeV electrons, 50-kVp X-rays, beta-particles and alpha-particles are presented showing an increase in non-disjunction with increasing LET.

Aspergillus nidulans↗

PubMed1991

Chromosome damage and non-disjunction measured at the first cleavage division in normal and chromosomally mutant female mice irradiated at the diakinesis stage of female meiosis.

We have irradiated primary murine oocytes at the diakinesis stage of the first meiotic division with 0.6 Gy X-rays. Fertilized oocytes were cultured overnight to arrest the first cleavage division and display pronuclear chromosomes. All preparations were preferentially stained for centric constitutive heterochromatin and analyzed for structural and numerical radiation effects. Females of 3 different karyotypes were irradiated (all on a Swiss random-bred genetic background): +/+ (221 female pronuclei analyzed), Rb(11.13)4Bnr T(1;13)70H/Rb(1.13)4Bnr T(1;13)70H with 11.13(1) and 1(13) large and small marker bivalents (RbT/RbT, 242 zygotes analyzed) and the same karyotype but with a 1(13)H;1(13) Wa heteromorphic bivalent (RbT/RbT*, 126 zygotes analyzed). Hyperploid chromosome counts were encountered with frequencies of 11.8% (+/+), 11.9% (RbT/RbT) and 16.6% (RbT/RbT*). In this order of karyotypes, the frequencies of dicentrics per zygote were 0.07, 0.16 and 0.11 and the frequencies of fragments 0.13, 0.18 and 0.31. In about half of the supernumerary chromosome spreads, a dicentric chromosome was included. The long marker bivalent 11.13(1) had a non-disjunction frequency of 2.5 times its control value, partially because it was involved in dicentric formation as well. For the RbT/RbT karyotype, the spontaneous maternal non-disjunction level was 5.4%. For the RbT/RbT* karyotype, it can be assumed to be the same or slightly higher because of the 1(13)H;1(13) Wa heteromorphic bivalent. This increased intrinsic sensitivity for non-disjunction was not expressed as an increased sensitivity for aneuploidy after irradiation. This fact and the numerical association between hyperploidy and dicentric formation, both for normal bivalents and for the 11.13(1) marker bivalent, lead us to suppose that in the female mouse, irradiation-caused aneuploidy is effectuated via chromatid exchange. The data presented do not rule out the existence of another mechanism.

Aneuploidy↗

PubMed1995

Initiation of disjunctive smooth pursuit in monkeys: evidence that Hering's law of equal innervation is not obeyed by the smooth pursuit system.

Monkeys generated disjunctive smooth pursuit eye movements when they tracked visual targets that moved toward or away from them. Eye acceleration was computed during the initial 100 msec of pursuit (the open-loop interval) for various target trajectories. The initial acceleration of either eye was a function of the target's motion with respect to that eye, regardless of whether or not the pursuit was conjugate or disjunctive, or performed with one eye occluded. Eye movements produced by fusional vergence could be separated temporally from eye movements produced by smooth pursuit using step-ramp paradigms. The separation of the two responses demonstrates that the fusional vergence system operates in parallel with the smooth pursuit system, presumably to minimize disparity, but not to generate disjunctive components of smooth pursuit eye movements.

Animals↗

PubMed2001

Spindle poisons induce allelic loss in mouse lymphoma cells through mitotic non-disjunction.

Aneuploidy is an important contributor to reproductive failure and tumor development. It arises spontaneously or as a result of exposure to aneugenic agents through non-disjunction. Two spindle poisons, colchicine (COL) and vinblastine (VBL) are mutagenic in the mouse lymphoma assay (MLA), a gene mutation assay that targets the heterozygous thymidine kinase (tk) gene on chromosome 11 in mouse lymphoma L5178Y tk+/- 3.7.2c cells. To investigate the mechanisms of spindle poison mutagenesis, we analyzed the COL- and VBL-induced TK mutants at the molecular and cytogenetic level. Loss of heterozygosity (LOH) analysis employing a microsatellite region within the tk locus revealed that almost all mutants had lost the functional tk allele. To determine the extent of the LOH, we further examined LOH mutants for heterozygosity at nine microsatellite loci spanning the entire chromosome 11. Interestingly, every microsatellite marker showed LOH in all COL- and VBL-induced LOH mutants, suggesting that these mutants were generated by loss of the whole chromosome 11 through mitotic non-disjunction. Chromosome painting analysis supported this hypothesis; there were no mutants showing structural changes such as deletions or translocations involving chromosome 11. In contrast, spontaneous TK mutants followed from point mutations, deletions and recombinational events as well as whole chromosome loss. Our present study indicates that spindle poisons induce mutations through mitotic non-disjunction without structural DNA changes and supports a possible mechanism in which a recessive mutation mediated by aneuploidy may develop tumors.

Alleles↗

PubMed1989

The influence of the Robertsonian translocation Rb(X.2)2Ad on anaphase I non-disjunction in male laboratory mice.

A Robertsonian translocation in the mouse between the X chromosome and chromosome 2 is described. The male and female carriers of the Rb(X.2)2Ad were fertile. A homozygous/hemizygous line was maintained. The influence of the X-autosomal Robertsonian translocation on anaphase I non-disjunction in male mice was studied by chromosome counts in cells at metaphase II of meiosis and by assessment of aneuploid progeny. The results conclusively show that the inclusion of Rb2Ad in the male genome induces non-disjunction at the first meoitic division. In second metaphase cells the frequency of sex-chromosomal aneuploidy was 10.8%, and secondary spermatocytes containing two or no sex chromosome were equally frequent. The Rb2Ad males sired 3.9% sex-chromosome aneuploid progeny. The difference in aneuploidy frequencies in the germ cells and among the progeny suggests that the viability of XO and XXY individuals is reduced. The pairing configurations of chromosomes 2, Rb2Ad and Y were studied during meiotic prophase by light and electron microscopy. Trivalent pairing was seen in all well spread nuclei. Complete pairing of the acrocentric autosome 2 with the corresponding segment of the Rb2Ad chromosome was only seen in 3.2% of the cells analysed in the electron microscope. The pairing between the X and Y chromosome in the Rb2Ad males corresponded to that in males with normal karyotype. Reasons for sex-chromosomal non-disjunction despite the normal pairing pattern between the sex chromosomes may be seen in the terminal chiasma location coupled with the asynchronous separation of the sex chromosomes and the autosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaphase↗

PubMed1997

Disjunct habitats as islands: genetic variability in the Caucasian rock lizard Lacerta portschinskii.

Genetic diversity at 37 allozyme loci was surveyed in Lacerta portschinskii from contiguous populations and from a disjunct population. Indices of genetic diversity (heterozygosity, number of alleles per locus, and percentage of loci polymorphic) were greater in contiguous populations than in the smaller disjunct population. In this regard, disjunct populations appear to be similar to island populations. Indices of genetic diversity in Caucasian Lacerta are less than those reported from vagile lizard taxa and more similar to those of sit-and-wait predators.

Journal Article↗

PubMed2004

Reduced recombination in maternal meiosis coupled with non-disjunction at meiosis II leading to recurrent 47,XXX.

We determined the meiotic origin and the stage of non-disjunction of the extra X chromosomes in two sisters with 47,XXX chromosomal complements. Segregation of the X chromosomes in all family members was analyzed using X-linked short tandem repeat polymorphic (STRP) markers. Densitometric analysis of two STRP markers confirmed that both sisters had three copies of the X chromosome and the extra X chromosomes were maternally derived. Both sisters did not share the same maternal homologue suggesting that the recurrent trisomy is non-homologous X chromosome-specific. Haplotype analysis demonstrated a reduction to homozygosity for markers examined, covering most of the length of the X chromosomes in both sisters. These findings suggested that the extra X chromosomes have derived from meiotic II non-disjunction following a nullitransitional meiosis I (MI). A lack of recombination in the X chromosomes of both sisters suggests a possible maternal genetic defect leading to an erratic recombination at MI. This information may contribute to further understanding of mechanisms leading to X chromosome non-disjunction and may assist in counseling of families with this chromosomal rearrangement.

Adolescent↗

PubMed2003

Homologue disjunction in mouse oocytes requires proteolysis of securin and cyclin B1.

Disjunction of pairs of homologous chromosomes during the first meiotic division (MI) requires anaphase-promoting complex (APC)-mediated activation of separase in budding yeast and Caenorhabditis elegans, but not Xenopus laevis. It is not clear which model best fits the mammalian system. Here we show that homologue disjunction in mouse oocytes is dependent on proteolysis of the separase inhibitor securin and the Cdk1 regulatory sub-unit cyclin B1. Proteolysis of both proteins was entirely dependent on their conserved destruction box (D-box) motifs, through which they are targeted to the APC. These data indicate that the mechanisms regulating homologue disjunction in mammalian oocytes are similar to those of budding yeast and C.elegans.

Animals↗

PubMed2003

The genetic structure of a columnar cactus with a disjunct distribution: Stenocereus gummosus in the Sonoran desert.

Stenocereus gummosus is a columnar cactus endemic to the Sonoran desert that exhibits a disjunct distribution: it is widely distributed in Baja California and restricted to a small coastal area in mainland Sonora. In this paper, we examine the genetic structure and the mating system of this species in order to explore the origin of the disjunction and describe aspects of the pollination biology. Flowers are nocturnal, pollinated mainly by sphingids and self-incompatible. Polymorphism for allozymes (11 loci) was relatively high (P=75%) but moderate levels of heterozygosity were detected (H(o)=0.103 and H(e)=0.261). Sonoran populations exhibited higher levels of genetic variation than peninsular populations. H(e) declined with latitude when just peninsular and two island populations are included. Substantial levels of inbreeding within populations (f=0.60), moderate differentiation among populations (theta=0.10), and no evidence of isolation by distance were detected. The neighbor-joining phenogram showed Sonoran and island populations nested within peninsular populations. Mainland populations showed greater genetic similarity to island populations, supporting a dispersal hypothesis for the origin of the disjunction. Future studies using DNA markers are suggested in order to better understand the forces that have shaped the genetic structure of this species.

Cactaceae↗

PubMed2001

Posterior transpalatal distraction with pterygoid disjunction: a short-term model study.

The transpalatal distractor (TPD) allows for maxillary expansion according to the concepts of distraction osteogenesis. Unlike tooth-borne, surgically assisted rapid palatal expansion devices, the bone-borne TPD is designed to avoid periodontal ligament compression, buccal root resorption, fenestration, tooth tipping, and orthodontic relapse during and after the expansion. When the distractor is placed on the palate at the level of the second premolar and pterygomaxillary disjunction is not performed, more expansion occurs in the anterior part of the maxilla than it does in the posterior. The aim of this investigation was to test the hypothesis that pterygomaxillary disjunction and placement of the TPD on the palate at the level of the first molars result in more parallel expansion of the maxillary segments. Twenty consecutive patients were included in a prospective way, and their predistraction and postdistraction models were electronically analyzed. The change in resistance and force application resulted, on average, in parallel segment expansion. The results showed that pterygomaxillary disjunction and posterior placement of the TPD are indicated for patients having transverse maxillary deficiency with lateroposterior crossbite.

Adolescent↗