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 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 quantitative aspects of history

In a previous paper, in which a possible mathematical approach to history was outlined, it was shown that urbanization plays an important part in the propagation of new ideas. The rate of such propagation influences the rate of historical developments. The present paper deals in more detail with possible mechanisms of formation of earliest cities. Equations are derived which give the limiting size of such cities and their rate of growth. Of particular importance for the spread of new ideas is the spread of information. The latter largely depends on the fraction of individuals who travel between city and country. Expressions for this quantity are derived. An approach is outlined to the mathematical study of the earliest social classes, which may have been formed as a result of military, religious, or economic stratifications.     

Some aspects of cycadeoid evolution

First definite remains of the order Cycadeoidales appear at the beginning of the Mesozoic, and extinction occurred at the end of the Cretaceous. Reasoning on the assumption that the characters most frequently present in a group of related plants are primitive ones, an attempt is made to determine what the most primitive cycadeoids looked like and what the probable ancestors were. Most likely the most primitive cycadeoids had slender, elongated, branched stems, with numerous leaves. Pollen was borne in compound sporangia on leaf-like structures. The most likely ancestral form, on the basis of known Paleozoic fossil plants, are the pterido-sperms. Origin of cycadeoid cones is postulated as having occurred in one of at least three ways. One suggestion is that cones are portions of leaf systems, and that 'telescoping' of the stems' resulted in the displacement of the cone in Cycadeoidea to the axil of another leaf. Another suggestion is that cones are fertile axillary branches. A third idea is that eones represent branches arising from leaves.