Population genetics of tunas

Population genetic studies on tunas are reviewed. These studies have focused on phylogenetic reconstructions, species identifications and stock delineation, and have used tools ranging from blood group and allozyme analysis to PCR-aided examination of mitochondrial DNA variation. Both allozyme and mtDNA approaches show tunas in the genus Thunnus to be very closely related to one another, but also indicate that the two presently recognized subspecies of northern bluefin tuna, Thunnus thynnus thynnus and T. t. orientalis , in fact may be worthy of species status. These techniques also permit the unequivocal recognition of specimens, which is not always possible on morphological grounds. However, it is arguable that, until recently, tunas have not received their due attention from geneticists given their commercial significance and the need for information on stock structure to ensure sustainable management. This may be because tunas are known to be highly vagile and therefore levels of population differentiation are expected to be low. None the less, population subdivision has been recorded in several species (skipjack, yellowfin, albacore), although this tends to be on a broad (intra- or inter-oceanic) rather than on a more local scale. New molecular tools, including the PCR-based analyses of nuclear genes and microsatellite loci, are yielding new, highly polymorphic markers, and will enable more powerful analyses of stock structure than have hitherto been possible.     

Population genetics of freshwater snails

Freshwater snails have attracted the attention of biologists for a long time, because they are intermediate hosts of schistosomes, agents of bilharziases. However, population-genetic studies of freshwater snails have been undertaken only during the past decade, covering topics such as the relative roles of genetic drift and gene flow in subdivided populations and the roles of extinction and recolonization events in determining population structure. Other studies in freshwater snails have investigated the maintenance of sex and the evolution of selling, widening a debate restricted mainly to plant populations. The possible role of parasites in freshwater-snail population genetics has also been investigated.     

植物病原物的群体遗传学

品种单一化、生产密集型和一年多茬的现代农业特点导致病原物呈现出进化速度加快、致病力增强及流行风险增大趋势。深入研究病原物群体遗传学对认识病害的流行、有效选育和使用抗性品种乃至控制病害具有重要意义。文章阐述了植物病原物群体遗传学的研究目标和内容、突变、基因迁移、基因重组、随机遗传漂变和自然选择5大遗传机制在植物病原物进化过程中的作用, 以及目前植物病原物群体遗传学研究的现状。     

植物病原物的群体遗传学

品种单一化、生产密集型和一年多茬的现代农业特点导致病原物呈现出进化速度加快、致病力增强及流行风险增大趋势。深入研究病原物群体遗传学对认识病害的流行、有效选育和使用抗性品种乃至控制病害具有重要意义。文章阐述了植物病原物群体遗传学的研究目标和内容、突变、基因迁移、基因重组、随机遗传漂变和自然选择5大遗传机制在植物病原物进化过程中的作用,以及目前植物病原物群体遗传学研究的现状。     

Population genetics of translational robustness

Recent work has shown that expression level is the main predictor of a gene's evolutionary rate and that more highly expressed genes evolve slower. A possible explanation for this observation is selection for proteins that fold properly despite mistranslation, in short selection for translational robustness. Translational robustness leads to the somewhat paradoxical prediction that highly expressed genes are extremely tolerant to missense substitutions but nevertheless evolve very slowly. Here, we study a simple theoretical model of translational robustness that allows us to gain analytic insight into how this paradoxical behavior arises.     

Population aspects of forensic genetics

The paper presents the methodology of forensic genetics as a synthesis of population genetics and forensic medicine. Main population genetic problems, appearing in calculation of probability statistics and interpretation of the results of forensic genetic investigations, are discussed in detail.     

Population genetics of transgene containment

Several strategies have been proposed for creating transgenic cultivars from which transgene escape to wild relatives would seem unlikely; for example, to impede escape through pollen, a transgene could be inserted into chloroplast DNA (cpDNA), which in many crops is rarely transmitted through pollen. None of these strategies would be failsafe; for example, the rate of cpDNA transmission through pollen may be low but non‐zero in many crops. Here, we study how the probability distribution of escape time depends on the rates of pollen and seed flow from the crop to wild populations, the number and sizes of the wild populations, the selection coefficient for the transgene, and a leakage parameter characteristic of the strategy, for example, the rate of cpDNA transmission through pollen. We find that even with a leakage parameter as small as 10^?3, the probability of escape within as few as 10 generations could be appreciable.     

Population genetics meets behavioral ecology

Populations are often composed of more than just randomly mating subpopulations - many organisms from social groups with distinct patterns of mating and dispersal. Such patterns have recieved much attention in behavioral ecology, yet theories of population genetics rarely take social structures into account. Consequently, population geneticists often report high levels of apparent in breeding and concomitantly low efective sizes, even for species that avoid mating between close kin. Recently, a view of gene dynamics has been introduced that takes dispersal and social structure into account. Accounting for social structure in population genetics leads to a different perspective on how genetic variation is partitoned and the rate at which genic diversity is lost in natural populations - a view that is more consistent with observed behaviors for the minimization of inbreeding.     

Population genetics of haplodiploid insects

Genic variation of seven species of Hymenoptera is described, using electrophoretic techniques. The heterozygosities range from 0.033 to 0.084. An average heterozygosity is calculated for 23 species of haplodiploid insects, and this value is significantly different from the same value for 18 Drosophila species or for 24 diploid insect species (including Drosophila). The niche width-genetic variation hypothesis is rejected as an explanation. A comparison of selection models and neutral models shows that both hypotheses are capable of explaining the data.     

Population genetics without intraspecific data

A central goal of computational biology is the prediction of phenotype from DNA and protein sequence data. Recent models of sequence change use in silico prediction systems to incorporate the effects of phenotype on evolutionary rates. These models have been designed for analyzing sequence data from different species and have been accompanied by statistical techniques for estimating model parameters when the incorporation of phenotype induces dependent change among sequence positions. A difficulty with these efforts to link phenotype and interspecific evolution is that evolution occurs within populations, and parameters of interspecific models should have population genetic interpretations. We show, with two examples, how population genetic interpretations can be assigned to evolutionary models. The first example considers the impact of RNA secondary structure on sequence change, and the second reflects the tendency for protein tertiary structure to influence nonsynonymous substitution rates. We argue that statistical fit to data should not be the sole criterion for assessing models of sequence change. A good interspecific model should also yield a clear and biologically plausible population genetic interpretation.