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At least 19 recordsLinked to original sources
PubMed1979

Factors predisposing to adjacent 2 and 3:1 disjunctions: study of 161 human reciprocal translocations.

Reciprocal translocations produce imbalances by three types of disjunction which are, in decreasing frequency, adjacent 1, 3:1, and adjacent 2. Adjacent 1 disjunction produces duplication deficiencies of inverse topography to those of adjacent 2. The imbalanced chromosome segments in one of these types are balanced in the other. The disjunction 3:1 produces pure trisomies and monosomies. The following situations predispose to adjacent 2 disjunction: translocations between the long arms of two acrocentric chromosomes or between one of these and that of a No 9 chromosome; centric segments, either short or carrying a heterochromatic zone (9qh); a balanced translocation in the mother. The factors predisposing to the disjunction adjacent 2 operate by selection, or directly on the meiotic configuration. Some of them (shortness of the interstitial segment, shortness of the short arms of translocation chromosomes) act in both these ways. Their influence is probably responsible for the repetitive and exclusive character of this disjunction. The conditions for the occurrence of the 3:1 disjunctions seem less strict than those for adjacent 2, although they should be of the same nature (involvement of acrocentrics or a chromosome 9 in the translocation, maternal origin).

Chromosome Banding↗
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↗
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↗
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↗
PubMed1977

Meiosis I non-disjunction as the main cause of trisomy 21.

The relative roles of Meiosis I and Meiosis II non-disjunctions in the causation of trisomy 21 have been assessed by analysing the distribution of polymorphic phenotypes of the chromosomes 21 in a group of individuals with Down's syndrome. The data suggest that the majority of cases of trisomy 21 are due to meiosis I non-disjunctions.

Chromosomes, Human, 21-22 and Y↗
PubMed1979

Relationships between satellite association and the occurrence of non-disjunction in man.

It has been reported that there is an increased incidence of Down's syndrome among the children of parents who have been exposed to ionizing radiations for radiodiagnostic or radiotherapeutic reasons. Work with Drosophila, mice and human lymphocytes has shown that irradiation with X- or gamma-rays induces aneuploidy, presumably by non-disjunction. It has been suggested that in man the frequency of satellite association (s.a.) of acrocentric chromosomes may be involved in the causation of chromosomal non-disjunction. In the present work the effects of radiation on s.a. have, therefore, been investigated. The frequency of s.a. between acrocentric chromosomes was determined after the exposure of human blood from normal and chromosomally abnormal individuals to various small doses of Co-60 gamma-rays. The criteria of Zang and Back were used for the evaluation of s.a. complexes. No effects of radiation on the frequency of s.a. were apparent within the dose range investigated. The same result was obtained when s.a. was evaluated using the silver-staining technique in which physical connections between the associating satellites may be observed and the association complexes evaluated directly. The effects of other radiation sources have also been investigated.

Aneuploidy↗
PubMed1977

Centromeric effect on the degree of nonrandom disjunction in the female Drosophila melanogaster.

From crosses of females possessing a heteromorphic X-chromosome bivalent, FR1/+, the shorter crossover products were recovered on the average more frequently than the longer reciprocals as predicted by Novitski's (1951) hypothesis of nonrandom disjunction (NRD). The present study stemmed from an unexpected result of these crosses. Evidence for a centromeric effect on NRD was obtained, suggested by a negative correlation between the degree of NRD, c, and the distance between the region of exchange and the centromere as inferred from SET's (single exchange tetrads). Studies on sex chromosome systems other than FR1 confirmed these results. An analogous centromeric effect on preferential segregation had been clearly demonstrated in maize (Kikudome 1958, 1959; Rhoades and Dempsey 1966). However, prior to the present investigation, no such effect of the centromere on NRD in Drosophila had been described, although reanalysis of part of the data of Novitski (1951) and Novitski and Sandler (1956) suggests some evidence of a seriation of increasing c values extending from the most distal region of the chromosome toward the centromere. A suggestion that the effect in Drosophila may be related in some way to the time required for chiasma terminalization, i.e., those terminalizing earlier (distally located crossovers) permitting more random disjunction of the chromatids from the asymmetric dyad and those terminalizing later, progressively less random, is considered and rejected since in general the expected pattern of c values for the various double exchange tetrads (DET's) is inconsistent with that prediction and provides evidence suggesting the possibility of reversals, in part, of c values obtained for SET's.

Animals↗
PubMed2026

A CCNA1 Missense Variant Associated With Chromatid Non-Disjunction in Abnormal-Headed Sperm and Male Infertility.

BACKGROUND: Macrozoospermia is a rare form of teratozoospermia characterized by tetraploids, large-headed spermatozoa with multiple flagella, usually caused by bi-allelic AURKC mutations. The etiology of atypical phenotypes with a lower proportion of large headed spermatozoa and single flagella however often remains unresolved. OBJECTIVE: To investigate the genetic cause of severe sperm-head abnormalities with moderate macrozoospermia without multiflagellated spermatozoa in a patient with repeated ICSI failure. An infertile male with three failed ICSI attempts underwent semen analysis, revealing complete teratozoospermia, including 25% macrocephalic spermatozoa. METHODS: Multi-probe FISH targeting chromosomes 13, 18, 21, X, Y assessed chromosomal segregation. Whole-exome sequencing (WES) was performed to identify a candidate variant associated with meiotic abnormalities. RESULTS: FISH analysis revealed a high proportion of spermatozoa with n (23) chromosomes and 2c DNA content, consistent with sister chromatid non-disjunction during meiosis II. WES identified a homozygous missense variation in CCNA1, coding for a protein described to be essential for meiotic progression and chromatin remodeling in male germ cells. DISCUSSION: The variant affects a highly conserved residue within a functional domain and is predicted to be deleterious. This study establishes the first clinical association between CCNA1 mutations and chromatid non-disjunction in human spermatogenesis. It highlights the limitations of current morphology-based diagnostic thresholds and supports cytogenetic and genomic assessment for severe teratozoospermia (especially head abnormalities) and ART failure. CONCLUSION: Expanding genetic screening panels to include CCNA1 may improve diagnostic precision and clinical management in atypical macrozoospermia cases.

ART failure↗
PubMed1979

Stress analysis of disjunct removable partial dentures.

The (1) tooth-supported, (2) ridge-supported, and (3) tooth- and ridge-supported variations of the disjunct removable partial denture were studied. When testing loads were applied to three sites, bilaterally and unilaterally, it was found that the stresses were highest when the removable partial framework was tooth-support. No significant difference was recorded between the ridge-supported partial denture and the tooth- and ridge-supported partial framework. Further refinement of the pinsleeve mechanism may be necessary to effect better control over the distributions of the stresses.

Alveolar Process↗
PubMed1979

A first exploration of a Robertsonian translocation heterozygote in the mouse for its usefulness in cytological evaluation of radiation-induced meiotic autosomal non-disjunction.

In this report some data concerning the male meiotic system of mice heterozygous for Rb(11.13)4Bnr are presented and compared with those of a chromosomally normal Swiss random-bred stock. Change of the genetic background from a C3H/Swiss hybrid situation to the fourth backcross generation (to the Swiss random-bred stock), did not alter the average frequency of aneuploid secondary spermatocytes. This was confirmed by studies on post-implantation loss. Spermatogenic characteristics of Rb4/+ mice, such as testis weight, sperm production and the number of diplotene-metaphase-I figures found in stage XII of the seminiferous epithelium, suggest delay and cell death during this period. These data support our working hypothesis that such an aberrant chromosome system may be more prone to radiation effects and therefore is promising in our cytological studies into the causes of spontaneous and in our cytological studies into the causes of spontaneous and induced autosomal non-disjunction during meiosis in the mouse.

Animals↗
PubMed1979

Additional pedigree supporting the frequent origin of XXYY from consecutive meiotic non-disjunction in paternal gametogenesis.

A 48,XXYY Sardinian patient, born to a 46,XX mother heterozygous for the Gd Mediterranean mutant, and to a 46,XY father hemizygous for the same mutant, was found to have a mosaic distribution of G6PD(+) and G6PD(-) peripheral red blood cells. The most likely interpretation of this finding is that the propositus is an additional example of an XXYY zygote derived from a consecutive meiotic non-disjunction during paternal gametogenesis.

Adult↗
PubMed1978

Non-random centromere division: a mechanism of non-disjunction causing aneuploidy?

Early centromere separation was investigated in 12 normal children, 14 patients with Down's syndrome and in 12 patients of children with autosomal trisomies. A significantly non-random centromere division of chromosomes was found in each of the cases. A higher frequency of early separated G chromosomes was observed in Down's syndrome. In 2 mothers of trisomy-18 patients, the early division of chromosomes 18, generally seen in normal individuals, could not be demonstrated. The possible assoication between altered sequence of centromere disision and non-disjunction needs further confirmation.

Aneuploidy↗
PubMed1978

Lack of effect on the chromosomal non-disjunction in aged female mice after low dose X-irradiation.

Karyotypes were determined in 1064 embryos of aged C57/BL mothers. The virgin female mice were irradiated with 0, 4, 8 or 16 R of X-rays, respectively, and placed with young untreated males 5 days after irradiation. 10.5-days old embryos were recovered from the uterus. Aneuploid embryos classified as alive (heart beats observed at the dissection) were 1 monosomic in the control group (496 embryos) and 2 trisomics in the irradiated group (568 embryos). The number of aneuploid embryos classified as dead was 4 trisomic cases in the control group and 3 trisomics in the irradiated group. The data indicate that trisomic embryos are not uncommon in the mouse but are eliminated in post-implantation death. In contrast to the results of Yamamoto et al. the present data do not demonstrate an increased frequency of chromosome abnormalities in embryos of aged mice X-irradiated before mating as compared to non-irradiated ones.

Aging↗