蚜虫种群遗传多样性的影响因素及分子基础

蚜虫是一个复杂的类群 ,不同种群之间常常表现遗传多样性 ,特别是同种蚜虫的不同种群 ,这种多样性与环境因素 (寄主植物、地理气候条件等 )的影响密切相关 ,而且蚜虫种群多样性无论在细胞学水平 ,还是分子生物学水平均表现明显的遗传分化。该文在分析了蚜虫种群遗传多样性影响因素的基础上 ,从蚜虫核型变化、核DNA和线粒体DNA遗传分化和多样性方面总结了导致蚜虫种群遗传多样性的内在分子基础 ,并讨论了研究蚜虫种群遗传多样性的重要意义和前景     

QUANTITATIVE GENETICS IN PLANTS: THE EFFECT OF THE BREEDING SYSTEM ON GENETIC VARIABILITY

The expected effects of breeding system on quantitative genetic variation under various models for the maintenance of such variation are examined, with particular emphasis on the contrast between randomly mating and highly self-fertilizing populations. Estimates of quantitative genetic parameters from plant populations are reviewed. There is some evidence for reduced within-population genetic variance in highly inbreeding populations, compared with outbreeders, but more empirical work appears necessary. Although the estimate of the magnitude of the effect of breeding system is subject to considerable error, the reduction in genetic variance in inbreeding populations appears greater than expected if the variation were maintained by overdominance, or if it were due to neutral mutations. It is more consistent with models involving mutation-selection balance, although a rather larger reduction in genetic variance is estimated than is expected theoretically. We discuss some possible reasons for the lower level of genetic variance in selfers than is predicted by such models.     

The application of genetic approaches for investigations of mycorrhizal symbioses

Genetic analyses of mycorrhizal symbioses have been far less common to date than molecular biological investigations. This review aims to address the problem that genetic research approaches are some of the least familiar to non specialists by providing some detailed explanations of the requirements and processes involved, including concepts of genetic variation and genetic mapping. Each section includes examples of research progress which is restricted to studies of arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) symbioses. Most such research has focussed on AM hosts or EcM fungi. For AM hosts, some early work on natural genetic variation has not been exploited yet, but new research with barley and clover will enable genetic mapping of mycorrhizal associated QTLs for the first time. EcM fungal studies have shown a genetic basis for mycorrhizal capacity and quantitative genetic differences in mycorrhizal capacity. Some recent work with EcM hosts has begun genetic mapping of QTLs associated with mycorrhizal status. Most AM genetic research has focussed on analysis of nodulation-defective mutants for their AM host status. Map-based cloning and characterisation of the first genes shown by these analyses to be essential for establishment of both nodulation and mycorrhizal symbioses are anticipated shortly. Comparisons with molecular and genetic research on plant disease resistance genes and signalling pathways may prove useful as those studies are more advanced and underlying biochemical and evolutionary relationships are likely to exist.     

Construction of genetic code from evolutionary stability

The construction of the genetic code is investigated based on a stability principle. The concept and formulation of mutational deterioration (MD) of the genetic code is proposed. It is proved that the degeneracies of codon multiplets obey the rule to best resist MD. The MD for each ideal multiplet of codons is expressed by four parameters and it takes on a minimum value for real distributions of codons in the multiplet. Then the global mutational deterioration (GMD) of code table is calculated and the minimal code is deduced. The domain-like distribution of hydrophobic and hydrophilic amino acids on the genetic code is explained from the minimization of GMD. It is demonstrated that the standard code is approximately GMD-minimal. By introducing some constraints that are related to the initial condition of the system, we have deduced the standard genetic code from the minimization of GMD. The minimization shows the general trend of evolutionary process to some stable state while the constraints reflect a 'frozen accident.' Many deviant codon assignments are also explained through MD minimization assuming the changeable degrees of degeneracies for some multiplets. So, a possible answer to the question of "Why are synonymous codons and amino acids distributed in the code table just as they are?" is given.     

Breeding trees resistant to insects and diseases: putting theory into application

Tree species world-wide are under increasing threat from diseases and insects, many of which are non-native. The integrity of our natural, urban and plantation forest ecosystems, and the services they provide are seriously imperiled. Breeding programs that harness the natural genetic resistance within tree species can provide a durable solution to these threats. In many cases, genetic resistance offers the key to restoration of forests and may even prevent extinction of some tree species. The potential use of genetic resistance is often widely discussed, but the development of applied programs and use of resistant seed has only taken place in a relatively few species. The reflections here from some of the most advanced applied resistance programs, as well as some of the unknowns and limitations of implementing a resistance program will provide a guide to managers considering this approach. In any such program, there is a research component, a tree improvement component and a restoration and reforestation component. These three components, along with sustained management and public support, need to be linked for any genetic resistance program to be fully successful in facilitating the recovery of healthy forests. Other management activities and newly developing technologies may serve to complement genetic resistance or to expedite its development, but premature, over-emphasis on some of these may slow the operational program. An understanding of the level, frequency, durability and stability of resistance and its limitations are necessary to management planning.     

Genetics,geography, and culture: The population of S. Pietro Island (Sardinia,Italy)

An interesting aspect of the island of Sardinia (Italy) is the wide range of genetic variability within the island itself. The variability is widened by the presence of some populations of different ethnic origin who speak a language other than Sardinian. This work deals with the study of the genetic structure of the Carloforte population which inhabits the tiny island of S. Pietro 4 km off the southwest coast of Sardinia. S. Pietro was first populated in 1738 by emigrants coming from the island of Tabarka (Tunisia) who spoke an archaic form of the Ligurian dialect. Data on genetic polymorphisms in the Carloforte population are presented and discussed in relation to some Sardinian and Italian populations. Data on demographic and matrimonial structure are also presented. The genetic analyses show the Carloforte population as being clearly separated from both Sardinians and continental Italians. The isolation of Carloforte, highlighted by language diversity, endogamy, and consanguinity levels and marriage area, supports the idea of genetic diversity linked to cultural peculiarity. © 1996 Wiley-Liss, Inc.     

The effect of drying on the content of nucleic acids and mutational changes in microorganisms

The literary and own experimental data on the genetic apparatus changes in microorganisms after drying are reviewed. In the survived drying cells the total content of nucleic acids decreases, some amount of mainly high-molecule ribonucleic acid decomposes. The RNA isolation into the suspended medium is also observed in connection with the destructive processes in the cytoplasmic membrane and the decomposition of some intracellular structures. The dehydration of microbial cells violates the normal processes of DNA replication, and sometimes it leads to the conformational changes in molecule structure. In some cases the damage in the genetic apparatus causes the mutation changes of microorganisms. This should be taken into account in experiments where lyophilized cultures are used.     

Genetic engineering, welfare, and accountability

Comments on the implications of genetic engineering for animal welfare. Welfare problems associated with techniques used to achieve genetic changes; Detrimental effects of genetic modifications to welfare; Modification of farm animals for biomedical products. Implications of genetic engineering for animal welfare are changing rapidly and need to be reviewed regularly. They include the welfare problems associated with techniques used to achieve genetic changes, which are similar to problems of other experimental approaches; these should be considered carefully, especially where techniques are used on a routine basis. When it comes to the genetic modifications themselves, some are detrimental to welfare, some are neutral, and some are beneficial; these results include direct effects of the intended change, side effects, and indirect effects. Currently, the two main applications are modification of farm animals for biomedical products--which appears to be largely neutral for welfare--and modification of mice as models for human disease, which results in suffering, often severe suffering. Beneficial applications are rare and still experimental or theoretical. The situation is similar with regard to the use of recombinant hormones and viruses; use of recombinant vaccines has potential for improving welfare, but may raise other ethical problems. Although few, if any, of these concerns are specific to genetic engineering, various factors combine to suggest that particular safeguards are needed in this field. These include the facts that changes can be produced rapidly and repeatedly, and that one of the driving forces behind genetic engineering is commercial exploitation of technology. In general, ethical evaluation still is done on a case-by-case basis, using the limited criteria seen as directly relevant to each case, rather than on a broader framework. There also is little public accountability, whereby the public can have confidence that such evaluation is being carried out properly. Calls for advisory “watchdog ”committees to consider ethical questions on the use of animals are endorsed by this article. Furthermore, it is essential for public confidence in the safeguarding of animal welfare that the procedures of such committees should be well-publicized.     

Functional significance of genetic polymorphisms

Natural genetic polymorphisms are gifts from nature and sources of variations at all levels. The postgenomic era permits new perspectives on interpreting genetic polymorphisms and also poses challenges for scientists to answer system questions. Rather than a comprehensive coverage of genetic polymorphisms up-to-date, this review attempts to present some of the results in a somewhat coherent manner to highlight the needs and potentials of pertinent studies.     

Functional significance of genetic polymorphisms

Natural genetic polymorphisms are gifts from nature and sources of variations at all levels. The postgenomic era permits new perspectives on interpreting genetic polymorphisms and also poses challenges for scientists to answer system questions. Rather than a comprehensive coverage of genetic polymorphisms upto-date, this review attempts to present some of the results in a somewhat coherent manner to highlight the needs and potentials of pertinent studies.     

草坪草-高羊茅遗传育种研究进展

随着我国草坪业的快速发展 ,草坪草遗传育种工作越来越受到人们的关注。简要介绍了高羊茅的育种历史和现状 ,并对高羊茅植株再生体系的建立及遗传转化方面的研究进展进行了综述。此外 ,还提出了我国高羊茅育种的几点建议。     

OPTIMIZATION MODELS,QUANTITATIVE GENETICS,AND MUTATION

The process of selection on a multivariate set of characters subject to functional constraints is considered from the points of view of both evolutionary optimization theory and quantitative genetics. Special attention is given to life-history characteristics. It is shown that, under suitable conditions (including weak selection), useful approximate formulas for the relations between the functional constraints and the additive genetic variance-covariance matrix can be derived. These can be used to show that the conditions for equilibrium under selection according to the two different approaches are approximately equivalent. Although large negative genetic correlations are to be expected between some pairs of life-history traits in populations at equilibrium under selection, in general some small negative genetic correlations and some positive genetic correlations will also be present. Thus, the observation of a positive genetic correlation between a pair of life-history traits does not necessarily refute the possibility of trade-offs among a multivariate set of traits that contains the pair in question. The relation between the pattern of functional constraints and the genetic correlations is often complex, and little insight into the former can be derived from the latter. The effects of mutations that lower the overall efficiency of resource utilization, thereby creating a positive component to the genetic covariances among life-history traits, are also considered for a specific model. Although such mutations can have a substantial effect on the form of the life history, extreme conditions seem to be needed for them to produce a large effect on the pattern of genetic correlations in a random-mating population. They can, however, cause the appearance of positive correlations following inbreeding, due to the exposure of deleterious recessive or partially recessive mutations. The analysis also suggests that the population means of individual components of a constrained multivariate system may often equilibrate at values that are far from the optima that would be attained if they were selected in isolation from the other members of the system.     

HLA gene and haplotype frequencies in galicia (NW Spain)

The genetic structure of six populations of Iran (Turks, Kurds, Lurs, Zabolis, Baluchis and Zoroastrians) was examined using data on blood groups, serum proteins and cell enzymes. Our results show conclusively that there are genetic differences among the six populations and the analysis of superimposed R and S matrices defined by Harpending & Jenkins (1973) show that the dispersion of some of the alleles correspond to the dispersion of the populations. The F_ST estimates are not large enough to favour selection on any of the loci studied. The F_IT and F_IS estimates are positive and moderately high suggesting that the genetic differentiation to some extent is influenced by inbreeding.     

Population genetics of the people of Iran II. Genetic differentiation and population structure

The genetic structure of six populations of Iran (Turks, Kurds, Lurs, Zabolis, Baluchis and Zoroastrians) was examined using data on blood groups, serum proteins and cell enzymes. Our results show conclusively that there are genetic differences among the six populations and the analysis of superimposed R and S matrices defined Harpending & Jenkins (1973) show by that the dispersion of some of the alleles correspond to the dispersion of the populations. The F_ST estimates are not large enough to favour selection on any of the loci studied. The F_IT and F_IS estimates are positive and moderately high suggesting that the genetic differentiation to some extent is influenced by inbreeding.     

How similar are amino acid mutations in human genetic diseases and evolution

Accumulating evidence indicates that some deleterious mutations responsible for genetic diseases may offer benefits for human to prevent other diseases. Therefore, human genetic diseases and evolution were tentatively regarded as the two sides of the same coin, which stimulated our interest to explore how similar are amino acid mutations in human genetic diseases and evolution. Through a large-scale analysis on amino acid mutation patterns of genetic diseases and evolution of Hominidae (Homo sapiens and Pan troglodytes), it was found that there exist significant correlations between two mutation patterns. Besides, there also exist some evident differences between both mutations, especially those associated with four amino acids C, G, R, and L. These findings are of significance to understanding the subtle connections between human genetic diseases and evolution.     

Dissection of the genetic architecture of body weight in chicken reveals the impact of epistasis on domestication traits

In this contribution, we study the genetic mechanisms leading to differences in the observed growth patterns of domesticated White Leghorn chickens and their wild ancestor the red jungle fowl. An epistatic QTL analysis for several body-weight measures from hatch to adulthood confirms earlier findings that polymorphisms at >15 loci contribute to body-weight determination in an F(2) intercross between these populations and that many loci are involved in complex genetic interactions. Here, we use a new genetic model to decompose the genetic effects of this multilocus epistatic genetic network. The results show how the functional modeling of genetic effects provides new insights into how genetic interactions in a large set of loci jointly contribute to phenotypic expression. By exploring the functional effects of QTL alleles, we show that some alleles can display temporal shifts in the expression of genetic effects due to their dependencies on the genetic background. Our results demonstrate that the effects of many genes are dependent on genetic interactions with other loci and how their involvement in the domestication process relies on these interactions.     

论克隆植物的遗传多样性

概述了克隆植物的类型与特点 ,对克隆植物的遗传多样性及其遗传结构的一些特点进行了综述 ,并讨论了克隆植物遗传变异的来源。总体而言 ,克隆植物拥有比早期推测大得多的遗传变异 ,虽然克隆种与其近缘有性繁殖种相比 ,遗传多样性较低 ,但广泛的遗传单态性却很罕见。克隆植物种群的遗传结构有所改变 ,广布基因型很少 ,大多数基因型仅分布于某一种群之内 ,种群间基因型多态性存在广泛的变异。不同克隆植物之间遗传多样性相差很大 ,遗传结构也有巨大差异。说明除生殖模式外 ,其他的一些因素 ,如地理分布范围、生境特点 ,散布方式和种群历史等都对克隆植物遗传多样性有重要影响。     

Genetic algorithm with local optimization

A hybrid of genetic algorithm and local optimization was tested on a massively multimodal spin-lattice problem involving a huge configuration space. The results are good, and global optima will probably be achieved in a sizeable proportion of cases, especially if a selection scheme is applied that maintains genetic diversity by introducing a spatial separation between the members of the population. If we use single-point cross-over, the performance of the algorithm depends strongly on the order of the units corresponding to individual spins in the bit strings that the genetic part of the algorithm processes. Due to some interplay between the genetic algorithm and local optimization, the best performance is achieved with a peculiar ordering, while the results with the most obvious ordering are much worse. I introduce an ordering-invariant crossover operation that gives excellent performance: it almost always yields states of the lowest energy. I expect this or some similar crossover operation to work well in the hybrid scheme for many other problems as well.     

Alu insertions in the Iberian Peninsula and north west Africa--genetic boundaries or melting pot?

The Western Mediterranean Basin joins a set of ethnically different populations as Iberians and Basques in the North shore and Berbers and Arab-speakers in the South one. In spite of this differentiation, they have maintained historical contacts since ancient times. The existence of a possible common genetic background (specially for Berbers and Iberians) together with the genetic impact of the Islamic occupation of the Iberian Peninsula during 7 centuries are some of the intriguing anthropological questions that have been studied in this area using several classical and DNA markers. The aim of this work is to present the results on a survey of polymorphic Alu elements in 10 human populations of the Western Mediterranean. Recent Alu subfamilies include a significant number of polymorphic Alu insertions in humans. The polymorphic Alu elements are neutral genetic markers of identical descent with known ancestral states. This fact turns Alu insertions into useful markers for the study of human population genetics. A total number of 14 Alu insertions were analyzed in 5 Iberian populations, 3 Berber groups from North-Western Africa, an Arab-speaker population from Morocco and a sub-Saharan ethnic group from Ivory Coast. The results of this study allow the genetic characterization of Berber populations, which show a certain degree of differentiation from Arab-speaking groups of the same geographic area. Furthermore, a closer genetic distance between South Spain and Moroccan Berbers as compared with other Spanish samples supports a major genetic influx consistent with some (but not all) previous genetic studies on populations from the two shores of the Gibraltar Straits.     

Canalization: A molecular genetic perspective

The phenomenon of ‘canalization’ - the genetic capacity to buffer developmental pathways against mutational or environmental perturbations - was first characterized in the late 1930s and early 1940s. Despite enormous subsequent progress in understanding the nature of the genetic material and the molecular basis of gene expression, there have been few attempts to interpret the classical work on canalization in molecular genetic terms. Some recent findings, however, bear on one form of canalization, ‘genetic canalization’, the stabilization of development against mutational effects. These data indicate that co-expressed paralogous genes can function as mutual ‘back-up’ elements in developmental processes. Paralogues, however, are far from the only basis of canalization: other genetic sources can be readily envisaged and some of these are described here. The evolutionary questions about genetic canalization and the mechanistic questions about developmental instability that still need to be addressed are also briefly discussed.