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At least 199 records · Page 11Linked to original sources
PubMed1995

Endoscopic nasofrontal disjunction.

Disjunction of the nasofrontal junction was performed under endoscopic control in three patients who underwent a monoblock nasal framework osteotomy and two patients who underwent a modified Le Fort type II osteotomy through a small midscalp incision, a stub wound at the root of the nose, and an intercartilaginous incision. A bilateral intercartilaginous incision and nasal root stub wound were used in one case. An osteotomy of the nasal root was performed using a specially designed detachable osteotomy consisting of a thin staff and large handle. The end of the staff was inserted through the access incision and pulled through a stub wound created in the nasal root. The staff was then attached to the handle, and the osteotomy was performed under endoscopic control. This approach minimizes the surgical scar, the area of the subperiosteal dissection, and postoperative swelling of the face, in comparison with the coronal approach.

Adolescent↗
PubMed1997

Phylogeny and disjunct distribution: evolution of Saintpaulia (Gesneriaceae).

The molecular phylogeny of African violets (Saintpaulia H. Wendl.), based on ribosomal DNA internal transcribed spacer (ITS) sequences, follows the disjunct biogeography of the genus. Sequence analysis by parsimony of 19 accessions, representing 17 currently recognized Saintpaulia species, resulted in four trees of 182 steps. The first major division is between S. goetzeana, from the Uluguru Mts, Tanzania, and the rest of the genus. The basal position of S. goetzeana, and its putative primitive characters, may indicate an Uluguru origin for Saintpaulia and subsequent colonization of the more northerly mountains. Of the remainder, S. teitensis, from the Teita Hills of Kenya, is sister taxon to the other species (which occur mainly in the Usambara Mts of north-east Tanzania). A group of nine Usambaran species that we call the 'ionantha complex' show minimal ITS genetic differentiation and are also taxonomically critical. Species diversity in the Usambara Mts appears to be the result of rapid, recent (possibly Pleistocene) radiation. This study reveals the limitations of ITS sequences for elucidating the radiation of poorly differentiated species (the ionantha complex). However, the molecular data strongly suggest that conservation of the Uluguru and Teita populations is essential for the protection of the full range of diversity within the genus.

DNA, Plant↗
PubMed2002

Inferring the phylogeny of disjunct populations of the azure-winged magpie Cyanopica cyanus from mitochondrial control region sequences.

The azure-winged magpie (AWM), Cyanopica cyanus, is found in Asia and Iberia. This remarkable disjunct distribution has been variously explained by either the sixteenth-century introduction of birds into Iberia from the Far East, or by the loss of individuals from the central part of their range as a result of Pleistocene glaciations. We have used the mitochondrial control region to undertake a molecular phylogenetic analysis of the AWM, with sequences examined from individuals collected from across the current distribution range and incorporating representatives of all currently defined subspecies. The Western birds are genetically distinct from their Asian congeners and their divergence is basal in the phylogenetic tree. This indicates that the AWM is native to Iberia and not the result of a recent introduction from Asia. In Asia, two major mitochondrial DNA lineages were identified. These correspond to an Inland Asia group and a Pacific Seaboard group, and are separated topographically by the Da Hingan Ling mountains and the Yellow Sea. Molecular clock estimates suggest that these divergences are associated with Pleistocene glaciations. Furthermore, our data do not support the current classification of the AWM into 10 subspecies, as defined based on morphology and geographical distribution.

Animals↗
PubMed2001

A Caenorhabditis elegans cohesion protein with functions in meiotic chromosome pairing and disjunction.

We have studied four Caenorhabditis elegans homologs of the Rad21/Scc1/Rec8 sister-chromatid cohesion protein family. Based on the RNAi phenotype and protein localization, it is concluded that one of them, W02A2.6p, is the likely worm ortholog of yeast Rec8p. The depletion of C. elegans W02A2.6p (called REC-8) by RNAi, induced univalent formation and splitting of chromosomes into sister chromatids at diakinesis. Chromosome synapsis at pachytene was defective, but primary homology recognition seemed unaffected, as a closer-than-random association of homologous fluorescence in situ hybridization (FISH) signals at leptotene/zygotene was observed. Depletion of REC-8 also induced chromosome fragmentation at diakinesis. We interpret these fragments as products of unrepaired meiotic double-stranded DNA breaks (DSBs), because fragmentation was suppressed in a spo-11 background. Thus, REC-8 seems to be required for successful repair of DSBs. The occurrence of DSBs in REC-8-depleted meiocytes suggests that DSB formation does not depend on homologous synapsis. Anti-REC-8 immunostaining decorated synaptonemal complexes (SCs) at pachytene and chromosomal axes in bivalents and univalents at diakinesis. Between metaphase I and metaphase II, REC-8 is partially lost from the chromosomes. The partial loss of REC-8 from chromosomes between metaphase I and metaphase II suggests that worm REC-8 might function similarly to yeast Rec8p. The loss of yeast Rec8p from chromosome arms at meiosis I and centromeres at meiosis II coordinates the disjunction of homologs and sister chromatids at the two meiotic divisions.

Animals↗
PubMed2001

Correlation ratchets: four current reversals and disjunct "windows".

Multinoise correlation ratchets with a simple sawtooth potential are considered. It is proved that in the case of symmetric nonequilibrium three-level Markovian noise the direction and value of the induced current can be controlled by thermal noise. Moreover, it is established that four current reversals (CRs) occur and that for the CRs there exist characteristic disjunct "windows" in temperature and switching rate as control parameters. The necessary and sufficient conditions for the existence of the above effects are given and can be used in particle separation techniques.

Journal Article↗
PubMed2006

Generalized disjunction decomposition for evolvable hardware.

Evolvable hardware (EHW) refers to self-reconfiguration hardware design, where the configuration is under the control of an evolutionary algorithm (EA). One of the main difficulties in using EHW to solve real-world problems is scalability, which limits the size of the circuit that may be evolved. This paper outlines a new type of decomposition strategy for EHW, the "generalized disjunction decomposition" (GDD), which allows the evolution of large circuits. The proposed method has been extensively tested, not only with multipliers and parity bit problems traditionally used in the EHW community, but also with logic circuits taken from the Microelectronics Center of North Carolina (MCNC) benchmark library and randomly generated circuits. In order to achieve statistically relevant results, each analyzed logic circuit has been evolved 100 times, and the average of these results is presented and compared with other EHW techniques. This approach is necessary because of the probabilistic nature of EA; the same logic circuit may not be solved in the same way if tested several times. The proposed method has been examined in an extrinsic EHW system using the (1 + lambda) evolution strategy. The results obtained demonstrate that GDD significantly improves the evolution of logic circuits in terms of the number of generations, reduces computational time as it is able to reduce the required time for a single iteration of the EA, and enables the evolution of larger circuits never before evolved. In addition to the proposed method, a short overview of EHW systems together with the most recent applications in electrical circuit design is provided.

Algorithms↗
PubMed2006

Comparative phylogeography of coastal limpets across a marine disjunction in New Zealand.

Cook Strait, which separates the North and South Island of New Zealand, has been a transient, but re-occurring feature of the New Zealand land mass throughout the Pleistocene, maintaining its current width and depth for the past 5000 years. Historic land fragmentation coupled with the complex hydrography of the Greater Cook Strait region has created both biogeographic and phylogeographic disjunctions between the North and South Island in several marine species. Here we use mitochondrial cytochrome b DNA sequences of three endemic intertidal limpets, Cellana ornata, Cellana radians and Cellana flava to assess intraspecific phylogeographic patterns across Cook Strait and to look for interspecific concordance of ecological and evolutionary processes among closely related taxa. We sequenced 328-359 bp in 85-321 individuals from 8-31 populations spanning the biogeographic range of the three species. Intraspecific phylogeographic analyses show moderate to strong genetic discontinuity among North and South Island populations due to allopatric fragmentation. This pattern was broadly concordant across the three species and the observed divergence among this group of intertidal limpets (0.3-2.0%) is similar to that of previously studied subtidal organisms. For each species, divergence time calculations suggest contemporary North and South Island lineages diverged from their respective most recent common ancestor approximately 200 000 to 300 000 years before present (bp), significantly earlier than previous estimates in other coastal marine taxa that arose from a miscalculation of divergence time.

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↗
PubMed1985

Increased frequency of lymphocytic mitotic non-disjunction in recurrent spontaneous aborters.

Hypermodal chromosomal spreads occurred significantly more frequently in lymphocytes from couples with recurrent spontaneous abortion than from comparison populations. Previously, we reported a similarly increased frequency in couples with aneuploid offspring. Considering the frequency of aneuploidy among first trimester spontaneous abortions, we suggest that there may be a sub-population of persons predisposed to non-disjunction among couples with reproductive wastage.

Abortion, Habitual↗
PubMed1990

Triploidy arising from a first meiotic non-disjunction in a mother carrying a reciprocal translocation.

We report on a 22 year old mother, a carrier of a 6;14 balanced reciprocal translocation, who aborted a triploid conceptus carrying a similar translocation. We showed the maternal origin of this triploidy, after non-disjunction at meiosis I. The phenotypic expression as a non-molar pregnancy, the contribution of the maternal translocation, and possible aetiological factors of triploidy are discussed.

Adult↗
PubMed1975

Meiotic disjunction in t(14;15)6ca heterozygotes and fate of chromosomally unbalanced gametes in embryonic development.

In heterozygous carriers of the mouse reciprocal translocation T(14;15)6Ca, the frequency of nondisjunction involving the minute marker chromosome was 4.4% in the male and 22.2% in the female. The fate of gametes with unbalanced genomes derived from normal as well as abnormal meiotic disjunction in T6 heterozygotes was investigated on the basis of chromosome counts at metaphase II and karyotype analyses in early postimplantation embryos produced by backcrossing with chromosomally normal animals. Results obtained indicate that meiotic, gametic, and zygotic selection attributable to specific types of chromosomal imbalances is minimal, if any, by the late blastocyst stage. All zygotes with unbalanced genomes, except those with 20 normal pairs plus the minute marker, however, die off in the latter half of pregnancy. Therefore, the increased incidence of translocation trisomics among progeny of female as compared with male heterozygotes reflects the higher incidence of nondisjunction in primary oocytes than in spermatocytes.

Animals↗
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↗
PubMed1999

Recombination and disjunction in female germ cells of Drosophila depend on the germline activity of the gene sex-lethal.

Gametogenesis in males and females differs in many ways. An important difference in Drosophila is that recombination between homologous chromosomes occurs only in female meiosis. Here, we report that this process relies on the correct functioning of Sex-lethal (Sxl) which is primarily known as the master gene in somatic sex determination. Certain alleles of this gene (Sxl(fs)) disrupt the germline, but not the somatic function of Sxl and cause an arrest of germ cell development during cystocyte proliferation. Using dominant suppressor mutations that relieve this early block in Sxl(fs) mutant females, we discovered additional requirements of Sxl for normal meiotic differentiation of the oocyte. Females mutant for Sxl(fs) and carrying a suppressor become fertile, but pairing of homologous chromosomes and formation of chiasmata is severely perturbed, resulting in an almost complete lack of recombinants and a high incidence of non-disjunction events. Similar results were obtained when germline expression of wild-type Sxl was compromised by mutations in virilizer (vir), a positive regulator of Sxl. Ectopic expression of a Sxl transgene in premeiotic stages of male germline development, on the other hand, is not sufficient to allow recombination to take place, which suggests that Sxl does not have a discriminatory role in this female-specific process. We propose that Sxl performs at least two tasks in oogenesis: an 'early' function in formation of the egg chamber, and a 'late' function in progression of the meiotic cell cycle, suggesting that both events are coordinated by a common mechanism.

Animals↗
PubMed2004

Sister-chromatid cohesion mediated by the alternative RF-CCtf18/Dcc1/Ctf8, the helicase Chl1 and the polymerase-alpha-associated protein Ctf4 is essential for chromatid disjunction during meiosis II.

Cohesion between sister chromatids mediated by a multisubunit complex called cohesin is established during DNA replication and is essential for the orderly segregation of chromatids during anaphase. In budding yeast, a specialized replication factor C called RF-C(Ctf18/Dcc1/Ctf8) and the DNA-polymerase-alpha-associated protein Ctf4 are required to maintain sister-chromatid cohesion in cells arrested for long periods in mitosis. We show here that CTF8, CTF4 and a helicase encoded by CHL1 are required for efficient sister chromatid cohesion in unperturbed mitotic cells, and provide evidence that Chl1 functions during S-phase. We also show that, in contrast to mitosis, RF-C(Ctf18/Dcc1/Cft8), Ctf4 and Chl1 are essential for chromosome segregation during meiosis and for the viability of meiotic products. Our finding that cells deleted for CTF8, CTF4 or CHL1 undergo massive meiosis II non-disjunction suggests that the second meiotic division is particularly sensitive to cohesion defects. Using a functional as well as a cytological assay, we demonstrate that CTF8, CHL1 and CTF4 are essential for cohesion between sister centromeres during meiosis but dispensable for cohesin's association with centromeric DNA. Our finding that mutants in fission yeast ctf18 and dcc1 have similar defects suggests that the involvement of the alternative RF-C(Ctf18/Dcc1/Ctf8) complex in sister chromatid cohesion might be highly conserved.

Chromatids↗
PubMed1992

Mutants of the microtubule motor protein, nonclaret disjunctional, affect spindle structure and chromosome movement in meiosis and mitosis.

The Drosophila microtubule motor protein, nonclaret disjunctional (ncd), is required for proper chromosome distribution in meiosis and mitosis. We have examined the meiotic and mitotic divisions in wild-type Drosophila oocytes and early embryos, and the effects of three ncd mutants (cand, ncd and ncdD) on spindle structure and chromosome movement. The ncd mutants cause abnormalities in spindle structure early in meiosis I, and abnormal chromosome configurations throughout meiosis I and II. Defective divisions continue in early embryos of the motor null mutant, cand, with abnormal early mitotic spindles. The effects of mutants on spindle structure suggest that ncd is required for proper meiotic spindle assembly, and may play a role in forming or maintaining spindle poles in meiosis. The disruption of normal meiotic and mitotic chromosome distribution by ncd mutants can be attributed to its role as a spindle motor, although a role for ncd as a chromosome-associated motor protein is not excluded. The ncd motor protein functions not only in meiosis, but also performs an active role in the early mitotic divisions of the embryo.

Animals↗
PubMed1994

Synaptonemal complex proteins: occurrence, epitope mapping and chromosome disjunction.

We have used polyclonal antibodies against fusion proteins produced from cDNA fragments of a meiotic chromosome core protein, Cor1, and a protein present only in the synapsed portions of the cores, Syn1, to detect the occurrence and the locations of these proteins in rodent meiotic prophase chromosomes. The 234 amino acid Cor1 protein is present in early unpaired cores, in the lateral domains of the synaptonemal complex and in the chromosome cores when they separate at diplotene. A novel observation showed the presence of Cor1 axial to the metaphase I chromosomes and substantial amounts of Cor1 in association with pairs of sister centromeres. The centromere-associated Cor1 protein becomes dissociated from the centromeres at anaphase II and it is not found in mitotic metaphase centromeres. The extended presence of Cor1 suggests that it may have a role in chromosome disjunction by fastening chiasmata at metaphase I and by joining sister kinetochores, which ensures co-segregation at anaphase I. Two-colour immunofluorescence of Cor1 and Syn1 demonstrates that synapsis between homologous cores is initiated at few sites but advances rapidly relative to the establishment of new initiation sites. If the rapid advance of synapsis deters additional initiation sites between pairs of homologues, it may provide a mechanism for positive recombination interference. Immunogold epitope mapping of antibodies to four Syn1 fusion proteins places the amino terminus of Syn1 towards the centre of the synaptonemal complex while the carboxyl terminus extends well into the lateral domain of the synaptonemal complex. The Syn1 fusion proteins have a non-specific DNA binding capacity. Immunogold labelling of Cor1 antigens indicates that the lateral domain of the synaptonemal complex is about twice as wide as the apparent width of lateral elements when stained with electron-dense metal ions. Electron microscopy of shadow-cast surface-spread SCs confirms the greater width of the lateral domain. The implication of these dimensions is that the proteins that comprise the synaptic domain overlap with the protein constituents of the lateral domains of the synaptonemal complex more than was apparent from earlier observations. This arrangement suggests that direct interactions might be expected between some of the synaptonemal complex proteins.

Amino Acid Sequence↗
PubMed1983

Meiosis and early cleavage in Drosophila melanogaster eggs: effects of the claret-non-disjunctional mutation.

The claret-non-disjunctional (cand) mutation is a female-specific mutation in Drosophila melanogaster, which causes a high frequency of mortality (89--90%) in eggs laid by the homozygous females. Among the progeny that survive to the adult stage, greater than 50% are aneuploid and/or mosaic for the X and number 4 chromosomes. The genetic studies of cand indicate that it is homologous to the claret mutation (ca-simulans) in Drosophila simulans. The cytological effect of the cand mutation on meiosis I and the early cleavage divisions has been observed at the light microscope level in stage 14 ovarian and fertilized uterine eggs, respectively. Four classes of metaphase I figures were observed. These include those with: (1) two or more spindles; (2) spindles that were abnormally wide and the bivalents widely separated; (3) unipolar spindles; and (4) apparently normal bipolar spindles. The three abnormal classes of metaphase I figures included 80% of the eggs examined at this stage. Among the cleavage stage eggs examined 69% showed highly abnormal mitotic figures, including multipolar spindles, and the nuclei in these eggs were found in clusters, rather than dispersed throughout the ooplasm. In addition to the cytological abnormalities observed, 17--23% of the eggs produced by the cand females showed morphological abnormalities. These abnormalities included eggs having three of four dorsal filaments, eggs that had a truncated shape, and abnormally small eggs. These abnormalities may not be an aspect of the cand syndrome, but they are due to recessive genes located on the third chromosome. Although the cand and ca-simulans mutations both affect the formation of the spindle apparatus during meiosis and the early cleavage divisions, the effects of these two mutations differ considerably in detail. The effect of the ca-simulans mutation appears to be more severe than the effect of cand. A model to explain the relationship between the effect of the cand mutation on meiosis I and the early cleavage divisions is presented, and evidence to support the model is discussed.

Animals↗