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PubMed1982

Similar dose-related chromosome non-disjunction in young and old female mice after X-irradiation.

Radiation-induced chromosome non-disjunction has been investigated in young and old female mice. Chromosome numbers were screened in maternal and paternal pronuclei of 1-cell embryos. To avoid bias due to preparatory artefacts, only the numbers of hyperploid pronuclei were used as measures of chromosome non-disjunction. Spontaneous non-disjunction occurred more frequently in oocytes of old females (1.54%) compared to young females (0.19%). After X-irradiation, both young and old females displayed significant linear increases in non-disjunction with absorbed dose. The slopes of the regressions did not differ significantly. Maternal pronuclei of 1-cell embryos recovered from irradiated females occasionally contained chromosome structural aberrations. The numbers of aberrations showed significant linear relationships to absorbed dose in young and old females. No significant difference was present between the numbers of aberrations in young and old females. Analyses of numerical and structural chromosome anomalies have demonstrated, therefore, no increase in sensitivity to radiation to occur with maternal age.

Aging↗

PubMed1985

Dose-related chromosome non-disjunction in female mice after X-irradiation of dictyate oocytes.

The chromosome non-disjunction inducing effect of relatively large doses (100-600 cGy) of X-rays to various dictyate oocyte stages has been examined by chromosomal analysis of 1-cell embryos recovered from female mice 3.5-23.5 days after irradiation. Numerical chromosome anomalies, as a result of non-disjunction, occurred in significantly larger proportions of embryos from irradiated females compared to unirradiated controls. Moreover, non-disjunction was induced by X-irradiation in dose-related fashions which could be described by either quadratic or dose-squared curves. The different oocyte maturation stages sampled showed significantly different responses to X-irradiation. The most mature stage, sampled 3.5 days after treatment, was less responsive to the non-disjunction inducing effect of X-rays compared to other, younger maturation stages. Chromosome structural anomalies were also found significantly more frequently after X-irradiation of dictyate oocytes. Structural anomalies were induced in dose-related fashions in all oocyte maturation stages and could be described by either quadratic or dose-squared curves. A smaller proportion of embryos from females sampled at the shortest interval after irradiation contained structural anomalies compared to those from females sampled at the longer intervals. No evidence was obtained for a significant effect of X-irradiation on the frequency of triploid embryos.

Aneuploidy↗

PubMed1981

Induced gene mutation and mitotic non-disjunction in A. nidulans.

Toxicants of different classes were analysed for capacity to induce gene mutation and mitotic non-disjunction in Aspergillus nidulans, using selective and permissive tests, respectively. Ethanol, Amphotericin B and MIcanozole, all affecting membrane integrity, induced only non-disjunction, emphasizing the röle of the membrane in mitosis. Benomyl and isopropyl-3-chlorophenyl carbamate (CIPC), two pesticides which interfere with spindle system, induced only non-disjunction. Conversely, mitomycin C markedly increased mutation rate but not ono-disjunction and scarcely affected the viability. The comparative analysis of these two different genetic damages should prove useful in evaluating hazards of drugs.

Anti-Bacterial Agents↗

PubMed2006

Is this a dax which I see before me? Use of the logical argument disjunctive syllogism supports word-learning in children and adults.

Many authors have argued that word-learning constraints help guide a word-learner's hypotheses as to the meaning of a newly heard word. One such class of constraints derives from the observation that word-learners of all ages prefer to map novel labels to novel objects in situations of referential ambiguity. In this paper I use eye-tracking to document the mental computations that support this word-learning strategy. Adults and preschoolers saw images of known and novel objects, and were asked to find the referent of known and novel labels. Experiment 1 shows that adults systematically reject a known distractor (e.g. brush) before mapping a novel label (e.g. "dax") to a novel object. This is consistent with the proposal that participants worked through a Disjunctive Syllogism (i.e. Process-of-Elimination) to motivate the mapping of the novel label to the novel object. Experiment 2 shows that processing is similar for adults performing an implicit Disjunctive Syllogism (e.g. "the winner is the dax") and an explicit Disjunctive Syllogism (e.g. "the winner is not the iron"). Experiment 3 reveals that similar processes govern preschoolers' mapping of novel labels. Taken together, these results suggest that word-learners use Disjunctive Syllogism to motivate the mapping of novel labels to novel objects.

Adolescent↗

PubMed2005

Okadaic acid: chromosomal non-disjunction analysis in human lymphocytes and study of aneugenic pathway in CHO-K1 cells.

Okadaic acid (OA) is the main marine toxin implicated in the diarrhetic shellfish poisoning (DSP) in humans after consumption of contaminated bivalve molluscs. We have previously shown that OA was an in vitro aneugenic compound that induced chromosome loss via micronuclei formation in CHO-K1 cells. The aims of this study were to investigate the chromosomal non-disjunction (ND) potential of OA in human lymphocytes and the pathways involved for aneuploidy in CHO-K1 cells. Firstly, we analysed the formation of micronuclei and the non-disjunction for chromosomes 1 and 17 in binucleated human lymphocytes cells with the cytokinesis-blocked micronucleus (CBMN) assay coupled to a fluorescent in situ hybridization (FISH) technique with centromere-specific DNA probes. We showed that OA statistically increased the frequency of micronucleated lymphocytes in the dose range from 20 to 35 nM. However, FISH analysis did not reveal any increase in the non-disjunction for both chromosomes whatever the concentration between 2.5 and 35 nM. However, a significant increase in ND for the chromosome 17 was found at 1 nM. Secondly, in CHO-K1 cells, we investigated the dose and time dependent effects of OA: (i) on cell cycle progression, (ii) on mitotic-phase arrest and (ii) on mitotic spindle and centrosome abnormalities. The results showed that OA induced a progressive accumulation of mitotic CHO-K1 cells in prometaphase, an induction of multipolar mitotic spindle with centrosome amplification and the formation of multinucleated cells. We concluded that OA did not induce chromosome non-disjunction but should more likely induced chromosome loss in human lymphocytes. Moreover, our results obtained in CHO-K1 suggest that OA induced aneuploidy by preventing the chromosome attachment to the mitotic spindle and by amplifying the centrosome. The mode of action of the toxin in relation to its inhibition of protein phosphatases 1 (PP1) and 2A (PP2A) and the mitosis process is discussed.

Aneugens↗

PubMed2001

Genetic divergence of peripherally disjunct populations of the gastropod Batillariella estuarina in the Houtman Abrolhos Islands, Western Australia.

Geographically disjunct populations are unusual in marine species, but the Houtman Abrolhos Islands, Western Australia, provide opportunities to study highly disjunct peripheral isolates of several species. The intertidal snail Batillariella estuarina occurs in isolated tidal ponds in the Abrolhos Islands, where it is at its northern limit, disjunct from mainland populations by 600-900 km. The species is thus disjunct both geographically and among the peripherally isolated populations in the Abrolhos Islands. Comparisons of allozymes at 11 polymorphic loci were made among populations from 10 ponds in the Abrolhos Islands and six sites from relatively continuous tidal flats at Albany, 900 km away, the nearest major set of populations. Among all 16 populations, subdivision was high (FST = 0.455). Although there were subtle differences between the geographical regions, the large majority of divergence occurred among the isolated ponds in the Abrolhos (FST = 0.441), and divergence on the tidal flats at Albany was only moderate (FST = 0.085). Characteristic of peripheral isolates, the pond populations have less polymorphism and fewer alleles than the more connected populations at Albany. Combined with evidence of genetic divergence in the gastropods Bembicium vittatum and Austrocochlea constricta, which have very similar geographical distributions to that of B. estuarina, these results indicate the potential evolutionary significance of peripherally isolated marine populations in the unusual habitats of the Abrolhos Islands.

Alleles↗

PubMed1998

Elucidating the mechanisms of paternal non-disjunction of chromosome 21 in humans.

Paternal non-disjunction of chromosome 21 accounts for 5-10% of Down syndrome cases, therefore, relative to the maternally derived cases, little is known about paternally derived trisomy 21. We present the first analysis of recombination and non-disjunction for a large paternally derived population of free trisomy 21 conceptuses ( n = 67). Unlike maternal cases where the ratio of meiosis I (MI) to meiosis II (MII) errors is 3:1, a near 1:1 ratio exists among paternal cases, with a slight excess of MII errors. We found no paternal age effect for the overall population nor when classifying cases according to stage of non-disjunction error. Among 22 MI cases, only five had an observable recombinant event. This differs significantly from the 11 expected events ( P < 0.02, Fisher's exact), suggesting reduced recombination along the non-disjoined chromosomes 21 involved in paternal MI non-disjunction. No difference in recombination was detected among 27 paternal MII cases as compared with controls. However, cases exhibited a slight increase in the frequency of proximal and medial exchange when compared with controls (0.37 versus 0.28, respectively). Lastly, this study confirmed previous reports of excess male probands among paternally derived trisomy 21 cases. However, we report evidence suggesting an MII stage-specific sex ratio disturbance where 2.5 male probands were found for each female proband. Classification of MII cases based on the position of the exchange event suggested that the proband sex ratio disturbance was restricted to non-telomeric exchange cases. Based on these findings, we propose new models to explain the association between paternally derived trisomy 21 and excessive male probands.

Chromosomes, Human, Pair 21↗

PubMed2026

Phylogenomics of Manticorini tiger beetles supports ancient Gondwanan vicariance and recent American amphitropical disjunction.

Disjunct distributions have long fascinated biologists, particularly those found in the Southern Hemisphere. Gondwanan vicariance has been invoked to explain these patterns, with relatively limited studies having phylogenetically tested this hypothesis. Another intriguing pattern of disjunction involving South America is the American amphitropical distribution, where Western Hemisphere taxa have close relatives either north or south of the tropics. While better known in plants, this pattern is rarely proposed for animals and only phylogenetically tested in a handful of studies on hymenopteran insects. The Manticorini is a tribe of large-bodied, flightless tiger beetles whose members possess a complex distribution pattern attributable to both Gondwanan vicariance and American amphitropical disjunction. Using genomic-scale data we perform phylogenetic analyses to produce a time-calibrated evolutionary history of the Manticorini. With the resultant time tree we perform ancestral range reconstruction in order to recover the historical biogeography of this group. Our results show deep divergence between most manticorine genera, contrasted with young crown ages indicative of recent diversification. Our analyses support Gondwanan vicariance and amphitropical disjunction resulting from recent dispersal as part of the historical biogeography of the tribe. These findings highlight the role of both vicariance and dispersal in shaping diversification and complex modern distributions.

Animals↗

PubMed2000

Restricted gene flow and incipient speciation in disjunct Pacific Ocean and Sea of Cortez populations of a reef fish species, Girella nigricans.

Population disjunctions have been proposed to play an important role in speciation processes. In this study, we have examined the possible role of the Pacific Ocean-Sea of Cortez disjunction as a contributing factor to cryptic speciation in a reef fish, the opaleye, Girella nigricans. Mitochondrial control region (D-loop) sequences (380 bp) of 117 individuals completely separated opaleye populations from the Pacific Ocean and the Sea of Cortez. Although opaleye exhibit pelagic larval stages that remain in the water column for several months, gene flow between the Pacific Ocean and the Sea of Cortez was found to be extremely limited (FST = 0.84, Nm = 0.10). Whereas limited gene flow and reciprocal monophyly suggest that the observed physical and genetic disjunction are potentially contributing to the incipient speciation of Pacific and Sea of Cortez opaleye, moderate levels of D-loop sequence divergence (3.3%) and the absence of fixed allozyme markers challenge this idea. Pacific Coast populations also exhibited restricted gene flow levels (FST = 0.25, Nm = 1.49) across Punta Eugenia, a recognized oceanographic boundary along the Baja California coast. Thus, opaleye individuals grouped into three clades: one clade in the Sea of Cortez, one Pacific clade south of Punta Eugenia, and one Pacific clade north of Punta Eugenia. Future work in this region will determine if our results can be generalized to other disjunct populations.

Animals↗

PubMed2003

Vicariance and dispersal across Baja California in disjunct marine fish populations.

Population disjunctions, as a first step toward complete allopatry, present an interesting situation to study incipient speciation. The geological formation of the Baja California Peninsula currently divides 19 species of fish into disjunct populations that are found on its Pacific Coast and in the northern part of the Gulf of California (also called the Sea of Cortez), but are absent from the Cape (Cabo San Lucas) region. We studied the genetic makeup of disjunct populations for 12 of these 19 fish species. Phylogeographic patterns for the 12 species can be separated into two major classes: a first group (eight species) showed reciprocal monophyly and high genetic divergence between disjunct populations. A second group (four species) displayed what appeared to be panmictic populations. Population structure between Pacific Coast populations, across the Punta Eugenia biogeographic boundary, was also evaluated. While dispersal potential (inferred by pelagic larval duration) was a poor predictor of population structure between Gulf of California and Pacific populations, we found that population genetic subdivision along the Pacific Coast at Punta Eugenia was always positively correlated with differentiation between Pacific and Gulf of California populations. Vicariant events, ongoing gene flow, and ecological characteristics played essential roles in shaping the population structures observed in this study.

Animals↗

PubMed2005

Tempo and mode of speciation in the Baja California disjunct fish species Anisotremus davidsonii.

The Baja California region provides a natural setting for studying the early mechanisms of allopatric speciation in marine systems. Disjunct fish populations from several species that occur in the northern Gulf of California and northern Pacific coast of Baja California, but are absent from its southern shores, were previously shown to be genetically isolated, making them excellent candidates for studying allopatry. In addition, one of these species, the sargo Anisotremus davidsonii, has two pairs of congeneric Panamic trans-isthmian geminate species that allow for internal molecular clock calibration. Phylogeographic and demographic approaches based on mitochondrial (cytochrome b) and nuclear (S7 ribosomal protein) sequences showed that A. davidsonii entered the gulf from the south, and later colonized the Pacific coast, approximately 0.6-0.16 million years ago. Pacific coast colonization may have used a route either around the southern cape of Baja California or across the peninsula through a natural seaway. However, while several seaways have been described from different geological times, none matches the dates of population disjunction, yet much geological work remains to be done in that area. At the present time, there is no evidence for dispersal around the southern tip of the Baja California Peninsula. Signatures of incipient allopatric speciation were observed, such as the reciprocal monophyly of disjunct populations for the mitochondrial marker. However, other characteristics were lacking, such as a strong difference in divergence and coalescence times. Taken together, these results suggest that disjunct populations of A. davidsonii may be consistent with the earliest stages of allopatric speciation.

Animals↗

PubMed2006

Disjunct distributions during glacial and interglacial periods in mountain butterflies: Erebia epiphron as an example.

Over several decades, the distribution patterns and evolution of alpine disjunct species has become an increasingly discussed subject. Large scale genetic analysis has allowed the resolution of the past range changes and intraspecific evolution of many species, in Europe especially of Mediterranean origin. However, the phylogeographic structures of species with arctic-alpine disjunct distribution patterns are relatively poorly studied. The existing phylogeographic analysis (mostly of alpine plant species) supports disjunct distributions during glacial as well as post-glacial periods for a number of species. However, several questions still remain unresolved and we therefore analysed the Mountain Ringlet Erebia epiphron as a model for such alpine disjunct species. We found strong differentiation into five different lineages supporting five differentiation centres: (i) the eastern Pyrenees, (ii) the mountain ranges between the central Pyrenees and south-western Alps, (iii, iv) two areas along the southern Alps margin and (v) the northern Alps margin. We propose that these patterns evolved due to the humidity requirements of this species, which did not allow survival in the dry glacial steppes, but along the margins of the wetter glaciated high mountain ranges.

Animals↗

PubMed1975

Premature centromere division: a mechanism of non-disjunction causing X chromosome aneuploidy in somatic cells of man.

Apparent acentric fragments which replaced a C-group chromosome in cultured blood lymphocytes from a woman patient were shown by autoradiography, G-banding and C-banding to be complete X chromosomes in which the centromere had divided prematurely in relation to the centromeres of other chromosomes in the same metaphase. Metaphases with multiple 'fragments' suggested that non-disjunction of the 'fragments' had occurred. This anomaly of the X chromosome was associated with increased aneuploidy of a C-group chromosome, presumed to be X. Premature centromere division of the X chromosome (PCD, X) appeared to be a mechanism of non-disjunction which caused significant monosomy and trisomy of the X chromosome in blood cells and skin fibroblasts. The frequency of cells with multiple fragments and the extent of the aneuploidy in 48 hr. blood cultures indicated that this mechanism of non-disjunction operated during mitosis both in vivo and in vitro. Premature centromere division occurred at a lower frequency in normal women donors, and was age-related, being four times more frequent in women 60 years and older than in women under 40. Associated with the higher frequency of PCD, the older women also showed evidence of increased X chromosome aneuploidy. Premature centromere division of the X chromosome is considered to be the mechanism of non-disjunction, causing the well-documented increased number of 45, -C metaphases in ageing women. Premature centromere division was rare in men, but an age effect was again suggested.

Adult↗

PubMed1999

[Disjunction patterns: the morphological and ultrastructural bases of bladder instability in the male].

OBJECTIVE: To apply the new protocols and recent contributions on detrusor ultrastructural morphology in order to standardize criteria and evaluate our findings relative to the ultrastructural morphology, the presence of a dysfunction pattern, changes in nerve supply and formation of a chained cellular syncytium in hyperactive detrusor bladder instability in the male. METHODS: We studied 480 ultrastructural preparations of detrusor muscle from 32 male patients with bladder outlet obstruction with and without urodynamically demonstrated bladder hyperactivity. Bladder biopsies were obtained from the anterior aspect of the bladder and prepared according to the standard procedures for ultrastructural study. Semiquantitative nerve supply ultrastructural patterns, syncytial composition, and complete and incomplete disjunction were analyzed. RESULTS: Lower urinary tract obstruction was demonstrated in all patients; 6 of these patients had involuntary phasic detrusor contractions during filling. No significant decrease in nerve supply was found in isolated obstruction or in bladder hyperactivity. No axonal degeneration was observed in any of the patients and the myelin sheath structure was normal. Nerve effector endings were also normal. Four patients with hyperactive detrusor showed complete and two incomplete disjunction pattern. Incomplete disjunction pattern was also demonstrated in two patients with isolated obstruction. CONCLUSIONS: The change in the properties of the detrusor muscle in the unstable bladder is due to a complete reduction in excitatory nerve relation to smooth muscle. Having established the concept of common final myogenic pathway that explains involuntary detrusor contraction, complete dysfunction ultrastructural patterns have been defined with univocal relation to hyperactive detrusor. These patterns indicate the existence of a syncytium of chained muscle cells with changes in the excitation threshold that are absent in the normal stable detrusor. Two ultrastructural components sustain this hypothesis: 1) the major loss observed in intermediate cellular unions that are thought to mediate in the mechanical coupling of cellular contraction and 2) the presence in all the microscopic fields of abutments in the narrow cellular unions like gap-junctions, which mediate the electrical coupling. In the present study we have found this pattern in 4 out of 6 patients with hyperactive detrusor, and congruent with other studies, the incomplete disjunction pattern could be the prelude of bladder hyperactivity.

Aged↗

PubMed2026

Evaluating three alternative scenarios for the origin of a disjunct Arctium tomentosum population in the Pyrenees.

BACKGROUND: Disjunctions in species distributions offer natural experiments for investigating the mechanisms underlying distributional breaks, such as range contraction, long-distance pollen transport, or long-distance seed dispersal. Here, we document and characterise a floristic novelty in the Pyrenean and Iberian regions, and use it as a case study to investigate the processes underlying disjunct species distributions. Our analysis focuses on Arctium L. (burdocks), a genus native to Eurasia comprising several cosmopolitan weedy species. It is characterised by hooked capitula that facilitate epizoochorous dispersal. METHODS: To clarify the taxonomic identity of a previously undocumented Pyrenean population resembling A. tomentosum, we adopted an integrative approach, combining distribution information, morphology, genome size, repetitive DNA analysis and chloroplast data across the four known European species. Additionally, we conducted a comparative study of functional capitulum traits, predispersal fruit predation, and associated entomofauna for the newly discovered population and nearby A. minus populations. RESULTS: The discovered population constitutes a floristic novelty for the region and is identified as A. tomentosum, exhibiting signatures of past introgression from A. minus, as indicated by cytonuclear discordance. We evaluated three alternative scenarios to explain its origin: (i) persistence as a relict from a previously wider distribution, (ii) long-distance pollination by migrating insects, and (iii) long-distance seed dispersal from an A. tomentosum population with a history of past introgression. Of these, only the third is consistent with the available evidence. These results highlight the complexity of interpreting disjunct species distributions and underscore the value of integrative approaches for resolving population identity, origin, dispersal, and persistence across environments.

Arctium↗

PubMed2004

Constitutional trisomy 8 mosaicism due to meiosis II non-disjunction in a phenotypically normal woman with hematologic abnormalities.

Constitutional trisomy 8 mosaicism (CT8M) in liveborns is typically caused by mitotic non-disjunction and exhibits wide phenotypic variability. By contrast, CT8M due to meiotic errors usually results in miscarriage. We describe a case of CT8M due to a paternal meiosis II non-disjunction error. The patient, a 32-year-old woman, was phenotypically normal except for a history of recurrent aphthous ulcers since childhood and a 4-year history of macrocytosis. The ulcers were refractory to steroids, but responded well to thalidomide. To the best of our knowledge, this is the first report of CT8M due to meiotic non-disjunction in a phenotypically normal individual.

Adult↗

PubMed2006

Bayesian analysis for the meiosis I non-disjunction fraction in numerical chromosomal anomalies.

The main causes of numerical chromosomal anomalies, including trisomies, arise from an error in the chromosomal segregation during the meiotic process, named a non-disjunction. One of the most used techniques to analyze chromosomal anomalies nowadays is the polymerase chain reaction (PCR), which counts the number of peaks or alleles in a polymorphic microsatellite locus. It was shown in previous works that the number of peaks has a multinomial distribution whose probabilities depend on the non-disjunction fraction F. In this work, we propose a Bayesian approach for estimating the meiosis I non-disjunction fraction F. in the absence of the parental information. Since samples of trisomic patients are, in general, small, the Bayesian approach can be a good alternative for solving this problem. We consider the sampling/importance resampling technique and the Simpson rule to extract information from the posterior distribution of F. Bayes and maximum likelihood estimators are compared through a Monte Carlo simulation, focusing on the influence of different sample sizes and prior specifications in the estimates. We apply the proposed method to estimate F. for patients with trisomy of chromosome 21 providing a sensitivity analysis for the method. The results obtained show that Bayes estimators are better in almost all situations.

Algorithms↗

PubMed2000

Molecular phylogeny of Coriaria, with special emphasis on the disjunct distribution.

Coriaria, which has the most conspicuously disjunct distribution of the flowering plants, is distributed in four separate areas of the world. The phylogenetic relationships of 12 Coriaria species collected from the representative disjunct areas were inferred by comparing 2416 bp of the combined data set of rbcL (a large subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase) and matK (maturase K) genes. The phylogenetic tree shows that the Chile-Papua New Guinea-New Zealand-Pacific islands species and the Central America-northern South America species form a sister group, and the Eurasian clade is more basal to them. The divergence time between the Eurasian group and the other species was estimated as 63 or 59 million years ago using rbcL and matK molecular clocks, respectively. These results do not support previously proposed hypotheses which explain the disjunct distribution on the basis of continental drift but suggest that the distribution pattern was formed by several geographical migrations and separations in the Cenozoic.

Cucurbitaceae↗