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PubMed2003

Double fertilization in maize: the two male gametes from a pollen grain have the ability to fuse with egg cells.

In flowering plants, two male gametes from a single pollen grain fuse with two female gametes, the egg and central cells, to form the embryo and endosperm, respectively. The question then arises whether the two male gametes fuse randomly with the egg and central cells. We investigated this question using two nearly isogenic maize lines with supernumerary B chromosomes (TB10L18) or without (r-tester). B chromosomes regularly undergo non-disjunction at the second pollen mitosis, producing one sperm cell with zero B chromosomes and one with two. We first confirmed earlier studies showing an excess of transmission of the B chromosomes to the embryo rather than to the endosperm. We then tested the possibility of a directed fertilization. For TB10L18 pollen, we could demonstrate the existence of a size dimorphism between the two sperm cells, correlated to the content in B chromosomes, as detected by fluorescence in situ hybridization (FISH). However, no directed fusion of B chromosome containing sperm to egg cells could be detected when using in vitro fertilization. The absence of directed fusion in vitro could also be demonstrated for control lines. We conclude that both male gametes have the capacity to fuse with the egg cell in maize, although sexual reproduction results in a preferential transmission of supernumerary B chromosomes.

Chromosomes, Plant↗

PubMed2003

The relational narrative: implications for nurse practice and education.

Nurses frequently encounter situations in which they are compelled to make ethical decisions about what is good and right to do in their day-to-day practice. Often existing moral edicts prove to be inadequate in light of the patient's particular circumstances. To what, then, can the nurse turn? In response to this question, Gadow (1999) proposes a dialectical framework comprised of three ethical approaches: subjective immersion (ethical immediacy), objective detachment (ethical universalism), and intersubjective engagement (relational narrative). In this paper, the dialectic framework proposed by Gadow (1999) is examined with respect to some of its potential implications for nursing practice and education. This endeavour is undertaken in the spirit of extending the dialogue that Gadow has so eloquently initiated. Questions related to whether it is possible (or necessary) to reconcile the contradictory tenets of these ethical approaches or the potential disjunction between the knowledge embedded in the relational narrative and ensuing action on the part of the nurse are discussed. In addition, some of the potential implications of this dialectical framework for nurse education are explored, including the question of how nurses learn to enter into a relational narrative with another and the relevance of relational narratives to teacher-student relationships.

Decision Making↗

PubMed1997

Turner syndrome: a cytogenetic and molecular study.

Two hundred and eleven patients with a clinical diagnosis of Turner syndrome were studied. We report (i) the cytogenetic results, (ii) the frequency of cryptic mosaicism and (iii) the parental age and the parental origin of the abnormality. We scored 100 cells from blood cultures and found 97 patients to have a 45,X constitution, 15 to be 45,X/46,XX or 45,X/47,XXX mosaics, 86 to have a structurally abnormal X and 13 to have a structurally abnormal Y chromosome. Molecular methods were used to look for cryptic X and Y chromosome mosaicism in patients with a 45,X constitution. Two cryptic X but no cryptic Y mosaics were detected. In 74% of the 45,X patients the X was maternal in origin. The i(Xq)s were approximately equally likely to involve the paternal or maternal chromosome, while the majority of deletions and rings and virtually all the abnormal Y chromosomes were paternal in origin. We suggest that the preponderance of paternal errors in Turner syndrome may result from the absence of pairing along the greater part of the XY bivalent during paternal mei I, which may make the sex chromosomes particularly susceptible to both structural and non-disjunctional errors during male gametogenesis.

Adolescent↗

PubMed2003

Progamotaenia capricorniensis sp. nov. (Cestoda: Anoplocephalidae) from wallabies (Marsupialia: Macropodidae) from Queensland, Australia.

Progamotaenia capricorniensis sp. nov. (Cestoda: Anoplocephalidae) is described from the wallabies Macropus dorsalis (Gray, 1837) and Petrogale assimilis Ramsay, 1877 from Queensland, Australia. The new species is characterised by a fimbriated velum composed of 26-32 digitiform to triangular projections on each side of the proglottis, paired uteri and 140-190 testes distributed in a single band across the medulla. Minor variation occurs in the distribution of the testes. The above characters distinguish the new species from its most closely related congeners P. lagorchestis (Lewis, 1914), P. proterogyna (Fuhrmann, 1932), P. spearei Beveridge, 1980 and P. villosa (Lewis, 1914). P. capricorniensis appears to exhibit a highly disjunct distribution within its usual host, M. dorsalis.

Animals↗

PubMed2001

Learning in the field: curriculum issues in a diploma in public health nursing.

Illuminative evaluation of a public health nursing curriculum shows that there was a gap between theory and practice, originating in the ways in which public health nursing was understood in the field, and therefore during students' placements, and in the university. The difference was chiefly in how the community staff and the lecturers understood primary health care. The former had a 'medical/professional' understanding of primary health care, implying that the professional knows best and that the client is an individual, a family or a group. The lecturers held a philosophy of primary health care with special emphasis on partnership with clients at all levels: individual, family, group and community; the partnership approach was intended to permeate the entire curriculum. Besides philosophical differences, there were other features of the theory practice gap demonstrated elsewhere. Fieldwork practice is integral to learning public health nursing so these contrasts created a serious disjunction within the curriculum. Actual and potential ways of improving curriculum integration are discussed.

Community Health Nursing↗

PubMed2001

Succession of events in desquamation of superficial urothelial cells as a response to stress induced by prolonged constant illumination.

The effect of moderate stress induced by prolonged illumination was analysed on urothelial cells of female mouse urinary bladders at ultrastructural and cytochemical levels. This study demonstrates that the urothelium responds to moderate stress with desquamation which involves two subsequent steps. The first step includes a local detachment of tight junctions and consequently the loss of the permeability barrier leading to expanded intercellular spaces among urothelial cells. During the second step, the disjunction of desmosomes accompanied by exocytosis of lysosomal enzymes (NADPase) in the intercellular space results in exfoliation of superficial cells. It is evident that moderate stress elicits an enhanced desquamation of only superficial cells by a subsequent dysfunction of first tight junctions and after that adherens-type junctions. A rapid restoration of the new tight junctions prevents a long-term malfunction of the blood-urine barrier.

Animals↗

PubMedDate not supplied

Geographic distribution and recombination of genomic fragments on the short arm of chromosome 2 of Arabidopsis thaliana.

Range expansion from Pleistocene refugia and anthropogenic influences contribute to the present distribution pattern of Arabidopsis thaliana. We scored a genome-wide set of CAPSs and found two markers with an east-west geographic distribution across the Eurasian range of the species. Regions around the two SNPs were sequenced in 98 accessions, including newly collected plants from Middle Asia and Western Siberia. These regions correspond to a gene ( approximately 1500 bp) and a non-coding region ( approximately 500 bp) 300 kbp apart on chromosome 2. Nucleotide diversities, pi, of the two sequenced fragments were 0.0032 and 0.0130. The haplotypes of both sequences belonged to one of two groups: a rather uniform "Asian" and a more variable "European" haplotype group, on the basis of non-disjunct clusters of SNPs. Recombination between "Asian" and "European" haplotypes occurs where they meet. Especially in the "European" haplotype, many rare SNP variants representing independent mutations are scattered among the shared haplotype-specific SNPs. This agrees with previous suggestions of two large haplotype groups in A. thaliana and the post-glacial colonization of central Europe from the east and the west. A clear correlation between climatic factors and the haplotype distribution may reflect the dispersal history rather than local climate adaptation. The pattern of SNP variation within the contiguous sequences explains why only a minority of SNPs selected across the genome show evidence of this geographic pattern.

Arabidopsis↗

PubMed2005

[Can data from quality assurance programs such as peri-/neonatal compilations be used for secondary epidemiological studies?].

BACKGROUND: The aim of this study was to explore whether population-based data from a regional quality control program can be utilized to compare the neonatal outcome of small for gestational age (SGA) and appropriate size for gestational age (AGA) new-borns. METHODS: The Center for Quality Management in Health Care maintains perinatal data for almost all births in Lower Saxony (Germany). Neonatal data are collected for all infants admitted to hospital within 10 postnatal days. We evaluated linked perinatal and neonatal datasets of 4126 very low birthweight infants (VLBW; < 1500 g), born in 1991 - 1996. After checking for completeness, representativeness, and validity, exclusion criteria were defined to minimize bias and to yield similar proportions of SGA- and AGA-neonates. Since inclusion of all multiple births would lead to an overestimation of maternal risk factors, one sibling was randomly selected from each set of multiples. Bias arising from not well defined study populations should be shown based on univariable mortality analyses (Kaplan-Meier survival curves). RESULTS: Application of exclusion criteria resulted in a final study population of 1623 independent (disjunctive) new-borns from 25 - 29 weeks gestation, 173 of whom were SGA, 1450 AGA. Kaplan-Meier curves from the initial study population and the well defined study base differed significantly. Trend analysis revealed a significant (p < 0.05) increase in proportions of both VLBW (from 0.95 % in 1991 to 1.11 % in 1996; + 17 %) and SGA infants (from 22.7 % to 27.4 %; + 21 %) within the observational period. A well defined data selection process is necessary if data collected for other purposes are to be used for epidemiological studies. Neglecting this labour-intensive work may be one reason for the varying results on the outcome of SGA and AGA infants.

Bias↗

PubMed1983

[Dual organization of sensorimotor activity].

An anatomical symmetry of the bilateral organism and the functional assignment of brain hemispheres each to one side of the body are preconditions for sensorimotor brain localization. The invariant system elements necessary for this consist of "modules". These are associations of about 2 500 cortical cells in each case. When we refer to duality, we do not mean dualistically separated, but mutually assigned or mutually coordinated half-systems. The mainly decussated sensory and nervous systems of the vertebrates probably give rise to their rhythmic gait coordinated in relation to the axis of the body. Compared to such vital movements, human motor activity varies between voluntary action and involuntary expression. Cortical projection duplicates in the form of secondary or supplementary sensorimotor areas are ascribed hypothetically to an identifiable somatosensory sensation. A development leading to man is likely to have commenced as the brain halves of a pithecanthropus gained asymmetric degrees of freedom in relation to their somatotopic binding to the body. This phylogenetic differentiation led to a dual disjunction of the cerebral hemispheres which enabled a side-different "either/or" in human actions. Speech and thought as transitive order forms are also based on functional asymmetries of the human cerebrum.

Cerebral Cortex↗

PubMed1986

[Long-term follow up of the lenses of diabetic patients using Scheimpflug photography linear densitometry].

This article reports on changes in lenses of diabetics, detected by means of Scheimpflug photos. Diabetics aged between 20 and 70 have been undergoing regular ophthalmogical check-ups for 26 months. Linear densitometry of negatives revealed an increase in light scatter at the anterior adjacent clear zone of disjunction (areas 1,2) and the anterior cortex (areas 3,4) in clinically clear lenses over the 26-month period. This change in light scatter is not related to the age of the patients; it is correlated to the duration of diabetes and fasting blood sugar.

Adult↗

PubMed2006

A generalization of the charge equilibration method for nonmetallic materials.

Assigning effective atomic charges that properly reproduce the electrostatic fields of molecules is a crucial step in the construction of accurate interatomic potentials. We propose a new approach to calculate these charges, which as previous approaches are, is based on the idea of charge equilibration. However, we only allow charge to flow between covalently bonded neighbors by using the concept of so-called split charges. The semiempirical fit parameters in our approach do not only reflect atomic properties (electronegativity and atomic hardness) but also bond-dependent properties. The new method contains two popular but hitherto disjunct approaches as limiting cases. We apply our methodology to a set of molecules containing the elements silicon, carbon, oxygen, and hydrogen. Effective charges derived from electrostatic potential surfaces can be predicted more than twice as accurately as with previous works, at the expense of one additional fit parameter per bond type controlling the polarizability between two bonded atoms. Additional bond-type parameters can be introduced, but barely improve the results. An increase in accuracy of only 30% over existing techniques is achieved when predicting Mulliken charges. However, this could be improved with additional bond-type parameters.

Journal Article↗

PubMed2000

On the origin of metacentric, attached-X (A-X) chromosomes in Drosophila melanogaster males.

We describe here the isolation and cytogenetic characterization of a mutation inseparabile which generates in males a high frequency of A-X females. The mutation, segregating in low frequency in a laboratory stock, maps to cytological location 82F7-11 in the third chromosome. The mutation acts premeiotically in the male germ line. Disrupting the X chromosome centromeric heterochromatin suppresses the formation of A-X chromosome, implying that the mutation is involved in chromatid cohesion. The inseparabile mutation also affects disjunction of the chromosome 4 in males. We suspect that the mutation was responsible for the original A-X female found by L. V. Morgan in 1921.

Animals↗

PubMed1976

Birds on islands in the sky: Origin of the montane avifauna of Northern Melanesia.

Biogeographers have long been fascinated by the disjunct distributions of species stranded on mountaintops. This paper analyzes, for the montane bird populations of Northern Melanesian islands, how many such populations there are, why they are restricted to mountains, and how they dispersed to mountains. The number of populations increases with island elevation and with montane area, and decreases with lowland area, exemplifying the problem of continental species diversity. Most species with montane populations on some island(s) have sea-level populations on some other island(s). These altitudinal niche shifts can be variously related to interisland differences either in altitudinal distribution of area or else in competitive pressure in the lowlands or mountains. Restriction of Northern Melanesian bird populations to mountains is more often due to lowland competitors than to inability to survive under the physical conditions of the lowlands. Of four possible mechanisms for the origin of a montane population (referred to as jumping, land-bridge crossing, trickling, and push-pull shifts), only the first and last have been significant for Northern Melanesian birds.

Journal Article↗

PubMed1985

Caenorhabditis elegans DNA that directs segregation in yeast cells.

We have isolated seven DNA fragments from Caenorhabditis elegans that enhance the mitotic segregation of autonomously replicating plasmids in the yeast Saccharomyces cerevisiae. These segregators, designated SEG1-SEG7, behave like isolated yeast chromosomes: they increase the stability and simultaneously lower the copy number of circular plasmids during mitotic growth in yeast. During meiosis, plasmids containing the C. elegans segregators show higher levels of precocious or aberrant disjunction than do plasmids bearing isolated yeast centromeres. Yet one of the segregators improved the meiotic segregation of the parental plasmid. We estimate that there may be as many as 30 segregator sequences in the C. elegans genome, a value that is consistent with the polycentric nature of C. elegans chromosomes. Five of the seven segregators are linked to sequences that are repeated in the worm genome, and four of these five segregators cross-hybridize. Other members of this family of repetitive DNA do not contain segregator function. Segregator sequences may prove useful for probing the structure of centromeres of both C. elegans and S. cerevisiae chromosomes.

Animals↗

PubMed1988

RED1: a yeast gene required for the segregation of chromosomes during the reductional division of meiosis.

A mutation at the RED1 locus was identified in a search for sporulation-proficient, meiotic-lethal yeast mutants. The few viable spores produced in the red1-1 mutant are highly aneuploid, suggesting that the spore lethality results from a high frequency of chromosome nondisjunction. Disomic spores produced by the red1-1 mutant contain nonsister chromatids and the red1-1 spore inviability phenotype is alleviated in red1-1 spo13 double mutants; these results indicate that nondisjunction occurs at the first meiotic division. The red1-1 mutant is recombination-proficient. The RED1 gene was cloned by complementation of the meiotic lethal phenotype; strains carrying a disruption of the gene are mitotically viable. We propose that the RED1 gene product is involved in meiosis I chromosome disjunction, perhaps by maintaining the connections between homologous chromosomes through metaphase I.

Aneuploidy↗

PubMed1990

Multiple origins of polyploids in the Glycine tabacina complex inferred from chloroplast DNA polymorphism.

The Glycine tabacina polyploid complex has been shown to include a minimum of two morphological and crossing groups, which also differ in chloroplast DNA (cpDNA) restriction map and nuclear ribosomal gene repeat phenotype. These AAB2B2 and BBB2B2 G. tabacina polyploids contain plastomes referable to the A and B diploid plastome groups of subgenus Glycine, respectively. Eight different cpDNA variants were observed among the 65 B-type polyploids studied, six of which were identical for numerous restriction site characters to plastome types found among the highly polymorphic B genome diploid species. It is hypothesized that there have been numerous independent origins of polyploid G. tabacina: at least one AA x B2B2 event and a minimum of five BB x B2B2 events involving different BB types as female progenitor. Low amounts of cpDNA divergence between diploid and polyploid plastomes and among the plastomes of geographically disjunct polyploids suggest that the origin and dispersal of polyploids are relatively recent events. All hypothesized diploid progenitors are native to Australia, while both A- and B-type G. tabacina polyploids occur on islands of the Pacific outside the range of diploids. The presence of several different plastome types of polyploid G. tabacina in the Pacific islands suggests that several colonization events have occurred.

Journal Article↗

PubMed1990

Localization of androgen receptors and estrogen receptors in the same cells of the songbird brain.

Estrogens and androgens each have unique effects but act together for the neural differentiation and control of sexual behaviors in male vertebrates, such as the canary. The neuronal basis for these synergistic effects is elusive because the spatial relation between estrogen target cells and androgen target cells is unknown. This study localized estrogen receptor (ER)-containing cells by using immunocytochemistry and androgen receptor (AR)-containing cells by using autoradiography in the same sections of the male canary brain. Three cell types, those containing only ER, those containing only AR, and those containing both ER and AR, were found in tissue-specific frequencies. The midbrain nucleus intercollicularis exhibited the highest number of cells expressing both ER and AR, whereas ER and AR are expressed only in disjunctive cell populations in the forebrain nucleus hyperstriatalis ventrale, pars caudale. Synergistic effects of androgens and estrogens for the neural behavorial control could result from cells containing both ER and AR (intracellular) and from neural circuits containing ER and AR in different cells (intercellular).

Animals↗

PubMed1991

Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalian cells but do not prevent exit from mitosis.

DNA topoisomerase II (EC 5.99.1.3) is necessary for chromosome condensation and disjunction in yeast but not for other functions. In mammalian cells, it has been reported to be necessary for progression toward mitosis but not for transit through mitosis. We have found, on the contrary, that specific inhibition of topoisomerase II (but not of topoisomerase I) interferes with mammalian mitotic progression. Metaphase is prolonged, and anaphase separation of chromatids is completely inhibited, in cells given high concentrations of topoisomerase II inhibitors; nevertheless these cells attempt cleavage, sometimes generating nucleate and anucleate daughters. Lower concentrations of inhibitors interfere with anaphase and produce abnormalities of segregation. DNA topoisomerase II activity is therefore necessary for mammalian chromatid separation, but it is not tightly coupled to the control of other mitotic events.

Anaphase↗