Some aspects of autotetraploid population dynamics

Summary Self-compatible autotetraploids are likely to set much of their seed by selfing. Formulae are presented for the frequencies in any generation of states of loci, from homozygous to quadri-allelic, considering the frequencies of selfing and of double reduction but not allowing for the effects of inbreeding depression on population structure. The changing structure of populations over generations is also explored by computer simulation, incorporating selection against inbreds but ignoring double reduction. The findings are discussed in relation to mass-selection programmes.     

Some fundamental aspects of building protein structures from fragment libraries

We have investigated some of the basic principles that influence generation of protein structures using a fragment-based, random insertion method. We tested buildup methods and fragment library quality for accuracy in constructing a set of known structures. The parameters most influential in the construction procedure are bond and torsion angles with minor inaccuracies in bond angles alone causing >6 A CalphaRMSD for a 150-residue protein. Idealization to a standard set of values corrects this problem, but changes the torsion angles and does not work for every structure. Alternatively, we found using Cartesian coordinates instead of torsion angles did not reduce performance and can potentially increase speed and accuracy. Under conditions simulating ab initio structure prediction, fragment library quality can be suboptimal and still produce near-native structures. Using various clustering criteria, we created a number of libraries and used them to predict a set of native structures based on nonnative fragments. Local CalphaRMSD fit of fragments, library size, and takeoff/landing angle criteria weakly influence the accuracy of the models. Based on a fragment's minimal perturbation upon insertion into a known structure, a seminative fragment library was created that produced more accurate structures with fragments that were less similar to native fragments than the other sets. These results suggest that fragments need only contain native-like subsections, which when correctly overlapped, can recreate a native-like model. For fragment-based, random insertion methods used in protein structure prediction and design, our findings help to define the parameters this method needs to generate near-native structures.     

Some fundamental aspects of epidemiology: a guide for laboratory scientists.

Epidemiologic methods used to study human diseases are often unfamiliar to the laboratory scientist. This paper outlines the standard method by which epidemiologic studies are classified, explains the methodologic strengths and weaknesses of different kinds of studies, and notes the kinds of inferences that can be drawn from each. Surveys on populations are treated first, followed by sample surveys. Prospective (follow-up) studies, in which groups of subjects are followed in time, are a basic epidemiologic method. Alternatives to these studies that do not require similar time commitments but may allow similar inferences are record studies. Retrospective, or case-control studies, are often the only feasible method for studying rare diseases. However, diseases with long latency periods and problems in control selection can make these studies difficult to analyze and interpret.     

Some aspects of ion sheath dynamics under the action of pulsed voltage

The time evolution of an unsteady cathode ion sheath in plasma has been studied numerically. The calculations demonstrate the presence of spikes in the ion current density and electric field strength at the cathode. The amplitudes of these spikes significantly exceeds the steady-state level, which agrees with data from other studies. Approximate formulas are derived that describe the spike amplitudes as functions of the rise time and amplitude of the applied voltage pulse, the mass and charge of ions, and the density and temperature of plasma electrons.     

Motor activity of infusoria: fundamental and applied aspects

The article considers morpho-functional organization of the cilia, locomotor organelle of the infusoria, and demonstrates the complicity of locomotor behavior of these protista. The problem of control of locomotion of infusoria is whole organism in discussed; and conclusion is drawn that system of control of movements could be multilevel and include receptor, afferent, central, efferent and effector units. In this context the macronucleus, could act as a central integrator and coordinator of the locomotor behavior being closely connected with periphery by dynamic elements of cytoskeleton. The eradication of infusoria parasitizing in humans and animals by interrupting of locomotion of the protista is also discussed.     

Legal aspects of genetic information

The federally funded Human Genome Initiative will lead to the development of new capabilities to learn about an individual''s genetic status. Legal issues are raised concerning patients'' and other parties'' access to that information. This article discusses the effect of existing statutes and case law on three pivotal questions: To what sort of information are people entitled? What control should people have over their genetic information? Do people have a right to refuse genetic information? The article emphasizes that the law protects a patient''s right to obtain or refuse genetic information about oneself, as well as the right to control the dissemination of that information to others.     

Oncoimmunology: Some fundamental problems of cancer immunotherapy

The review briefly discusses several central problems of modern oncoimmunology. The controversies surrounding the concept of immunological surveillance, as well as the problem of immunological tolerance to tumors, are considered. The discovery of tumor antigens is a great advance towards the identification of possible therapeutic targets. However, antigen-specific vaccinations against cancer have, so far, a very limited use, mainly for prevention of virus-associated cancers, which is essentially based on the antiviral immune response. On the other hand, antibodies to cancer antigens are widely used in cancer diagnosis, and there are remarkable examples of their therapeutic applications. The future opportunities in both theoretical and applied oncoimmunology will directly depend on further advances in basic science.     

Some metabolic aspects of ecology

Summary

Due to the similarity of the major metabolic pathways in all living organisms it might be thought unlikely that the study of metabolic variation would add to an understanding of ecological differences. However, a quantitative study of the regulation of metabolism and its end-products indicates a link between cell biochemistry and the capability of certain species to succeed in particular environments. A study of anaerobic metabolism in animals and plants shows a number of similarities in those species able to survive in oxygen-poor environments. These include the production of nontoxic end-products and the avoidance of a large oxygen debt. As a large variety of organisms is examined, these comparisons suggest that the metabolic solutions to a given environmental stress, whether in plants or animals, can be strikingly similar. Therefore, although the main metabolic pathways in most living organism are the same, the regulation of metabolism varies with the ecology of the species. Examples are discussed in which a knowledge of metabolism in relation to ecology could have practical applications in forestry and agriculture.