The effect of chirality phenotype and genotype on the fecundity and viability of Partula suturalis and Lymnaea stagnalis: Implications for the evolution of sinistral snails

Why are sinistral snails so rare? Two main hypotheses are that selection acts against the establishment of new coiling morphs, because dextral and sinistral snails have trouble mating, or else a developmental constraint prevents the establishment of sinistrals. We therefore used an isolate of the snail Lymnaea stagnalis, in which sinistrals are rare, and populations of Partula suturalis, in which sinistrals are common, as well as a mathematical model, to understand the circumstances by which new morphs evolve. The main finding is that the sinistral genotype is associated with reduced egg viability in L. stagnalis, but in P. suturalis individuals of sinistral and dextral genotype appear equally fecund, implying a lack of a constraint. As positive frequency-dependent selection against the rare chiral morph in P. suturalis also operates over a narrow range (< 3%), the results suggest a model for chiral evolution in snails in which weak positive frequency-dependent selection may be overcome by a negative frequency-dependent selection, such as reproductive character displacement. In snails, there is not always a developmental constraint. As the direction of cleavage, and thus the directional asymmetry of the entire body, does not generally vary in other Spiralia (annelids, echiurans, vestimentiferans, sipunculids and nemerteans), it remains an open question as to whether this is because of a constraint and/or because most taxa do not have a conspicuous external asymmetry (like a shell) upon which selection can act

Somatic genetic and chromosomal abnormalities in ovarian and breast carcinoma

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN019689 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Lattice Strain in Magnetic Ultrathin Films

A clear understanding of the mechanisms of interfacial magnetic anisotropy rests on the structural characterisation of magnetic multilayers which, typically, consist of two ferromagnetically coupled (F) layers separated by a non-magnetic spacer layer. Fe/Cu/Fe trilayers are of special interest since the coupling between the F layers of Fe changes from F to antiferromagnetic depending on the thickness of the Cu spacer layer. Here, a magnetic multilayer system, grown by molecular beam epitaxy (MBE), was modified by inserting Cr in the Cu : Ag(001)/8.7 Fe/3 Cu/6 Cr/3 Cu/5 Fe/10 Au where the integers refer to monolayers. Polarized K-edge XAFS spectra (E parallel to the substrate) were obtained from fluorescence measurements in the total reflection geometry. The multiple scattering paths were analysed for the Cr edge. The initial Cu grew pseudomorphically in a BCC structure on Fe/Ag(001). The Cr proved to be tetragonally distorted from its BCC structure. The overlayers of Fe on Cu are contracted by 1.27% within the plane and conserve the c lattice parameter of Fe, though the atomic volume is contracted by 2.8%. The Cu adopts a BCT, rather than keeping its bulk FCC, structure and the corresponding decrease in its atomic volume from the FCC is only 0.3%

Effective Coordination Numbers in Ultrathin Metallic Films

Nanostructures bave become a major field in material science. With molecular beam epitaxy it is possible to engineer multilayers with unusual anisotropic properties and metastable structures. For ultrathin films, or particles of small size, the coordination numbers are less than their bulk values. In fitting E X A F S data it is useful to be able to place limits on the coordination numbers or their ratios. W e have calculated the effective coordination numbers Ni , i= 1 to 5 for thin films with different crystal structures. The thickness o f the film is specified by the number o f layers Nz in the z-direction and the area in the x y plane by the number o f rows of atoms NXY along the side of a square domain. For fixed Nz, with the x-ray beam unpolarized or its electric vector parallel or perpendicular to the substrate (xy plane), the effective H approach hyperbolically the coordination number for a layer o f infinite area. Simple analytical expressions are fitted to the numerical results fix- bcc and fee crystals from which the H can be calculated for both NXY and Nz ≥ 2. Comparison is made with the effective coordination numbers obtained from polarized E X A F S measurements on epitaxial metallic films less than 10 monolayers thick

Characterisation of CYP3A gene subfamily expression in human gastrointestinal tissues.

The human CYP3A subfamily is of interest due to its multiplicity, activity toward known carcinogens, and extrahepatic expression. In situ hybridisation analysis of formalin fixed, routinely processed biopsy specimens was used to localise CYP3A mRNA in human gastrointestinal tissues from several individuals. CYP3A mRNA is abundant in human liver and in mucosal epithelial cells of all segments of the human small intestine. RNA blot analyses showed that the mRNA species observed in most livers and in human small intestine represent CYP3A3/3A4 transcripts. This was confirmed at the protein level by immunoblot comparison of small intestine microsomes to in vitro expressed CYP3A4 and CYP3A5 proteins. In liver and small intestine, CYP3A mRNA is not uniformly distributed, with grain density highest in cells within the respective non-proliferative compartments. CYP3A mRNA was also observed in human oesophagus and colon. RNA blot analysis of multiple colons showed heterogeneity in the CYP3A mRNAs present. Two CYP3A mRNAs (CYP3A3/3A4 and CYP3A5) were detected in colon samples from several individuals. In addition to those localisation studies, the capacity of expressed CYP3A4 and CYP3A5 to activate the dietary heterocyclic amine MeIQ in the presence of alpha-naphthoflavone was shown. These results show that there is considerable heterogeneity in the expression of the CYP3A subfamily in human gastrointestinal tissues

Effects of a metacognitive intervention on students' approaches to learning and self-efficacy in a first year medical course

Aim To determine the influence of metacognitive activities within the PBL tutorial environment on the development of deep learning approach, reduction in surface approach, and enhancement of individual learning self-efficacy. Method: Participants were first-year medical students (N = 213). A pre-test, post-test design was implemented with intervention and control cohorts, with intervention students experiencing a program of metacognitive activities within their PBL tutorials of at least 20 weeks duration. All students completed the Medical Course Learning Questionnaire at the commencement, and again at the completion of, the study. The metacognitive intervention itself consisted of reflection on the learning in PBL coupled with peer- and self-assessment. Results: Self-efficacy was significantly reduced for both control and intervention cohorts at the conclusion of the study. A significant reduction in the adoption of deep and strategic learning approach, matched by a corresponding increase in the use of surface learning, was demonstrated for both cohorts. There was a statistically significant association between high self-efficacy and deep learning approach, with older students over-represented in the group of efficacious deep learners. Conclusion: Over the course of first-year medical studies, students lose self-efficacy and move away from deep-strategic learning approaches towards more surface approaches. The program of metacognitive activities failed to reverse this trend. The substantial swing towards surface learning raises questions about the perceived capacity of PBL curricula to promote deep approaches to learning in dense curricula, and reinforces the importance of personal and contextual factors, such as study habits, workload and assessment, in determining individual approaches and idiosyncratic responses to learning situations