模拟自然选择条件下黑腹果蝇基因频率变化的实验

条件致死突变是指在某些条件下存活,而在另一些条件下致死的突变。利用黑腹果蝇的条件致死突变,模拟自然选择的环境,将自然选择在一个较短的时间内还原出来,探究了在自然选择条件下黑腹果蝇的基因频率的变化情况。本实验为人教版高中《生物遗传与进化（必修2）》中,探究实验“自然选择对基因频率变化的影响”人为创设的情境提供了实验的支持,也为自然选择的机制等相关内容的教学提供了实践背景。     

用数学方法探究基因频率变化的活动设计

利用不同颜色的纸片模拟不同的"自然环境"和"猎物",让学生充当"捕食者"参与活动,以小组合作的方式来探究基因频率变化。实验结果表明,以小组合作的方式让学生进行数据统计、计算分析、绘制图表、交流讨论,能使其很好地理解种群、种群基因库和基因频率3个基本概念,使其深刻体验自然选择下种群基因频率的变化,并学会基因频率的计算方法。     

遗传平衡定律的推广及应用

生物进化的实质是种群基因频率的改变.介绍了遗传平衡定律的适用范围、表达式、推广及应用,概述了突变、基因重组、自然选择、迁移、遗传漂变等因素对遗传平衡及基因频率的影响.     

探究细菌群体快速自然选择和适应的实验

介绍一个简单、快速、低成本的实验,以大肠杆菌为实验材料来探究细菌群体在盐含量梯度下的生长情况,并定量表示其在盐含量选择压力下的适应性变化.通过进一步从分子水平上阐明盐含量选择压力对细菌群体遗传变异的作用机理,帮助学生进一步理解自然选择使种群的基因频率定向改变并决定生物进化的方向.     

利用肝脏转录组数据分析地山雀的适应性进化

肝脏是生物新陈代谢的重要器官。为了探究青藏高原特有鸟类地山雀(Parus humilis)如何适应低温、低氧等恶劣环境,我们对其肝脏转录组数据进行分析,并结合斑胸草雀基因组数据进行了比较研究。结果显示,地山雀肝脏转录组中的大部分高表达基因都直接参与机体的新陈代谢活动;通过与斑胸草雀基因组数据进行比较,对筛选出的214个快速进化基因进行代谢通路的功能富集,发现多数基因富集到与能量代谢、免疫反应和消化相关的通路上。本研究表明,高表达基因的功能一方面验证了肝脏是机体新陈代谢的主要场所,参与胆汁分泌、脂肪酸的转化及解毒等多项生理活动;另一方面也说明这些高表达基因对于维持肝脏的正常功能是必要的。快速进化基因的功能富集分析揭示了地山雀中与能量代谢、免疫反应和食性等相关的基因受到自然选择压力的影响而发生了适应性的快速进化。     

模拟自然选择条件下细菌抗药性的探究实验

基于细菌在抗生素培养基中抗药性逐渐增强的原理,通过模拟自然选择条件,将自然选择在较短的时间内还原出来,进而探究在自然选择条件下大肠杆菌和金黄色葡萄球菌的抗药性,以及培养条件改变时,细菌由抗药型转变为野生型的情况。本实验为沪科版高中《生命科学》必修3中"生物进化"人为创设选择情境提供了可操作的实验支持,也丰富了自然选择等相关内容的教学。     

假基因的组成、分布及其分子进化

假基因(pseudogene)是指基因组中与正常基因序列相似, 但是缺乏功能的DNA 序列。通过序列同源性搜索, 可以收集基因组中假基因的群体特性、染色体分布和同源家族等特性。假基因很好地保留了数百万年前基因组中祖先基因的分子记录, 被视为“基因化石”, 因此假基因在进化和比较基因组学中是重要的资源。应用假基因和基因比较体系, 可以探究生物基因的进化史和基因组稳定性。如: 用Ka/Ks比值确定假基因的自然选择压、物种亲缘关系和进化距离, 分析假基因自身的进化趋势, 探讨DNA 突变的成因等。     

适合度的相对性与路径依赖的自然选择

自然选择理论认为生物个体或者种群在进化的过程中, 其基因或者性状、行为策略的选择一定是能够提高其适合度或者达到某个可期的“目标”。然而, 随着某个突变基因或者性状特征、行为策略在种群中扩散, 其期望收益将随着其在种群中分布的密度变化或环境改变而发生改变, 这就是适合度景观的悖论, 即静态的、固定可期望的收益可能因此而不存在。基于动态而非静态适合度景观的概念, 我们提出路径依赖的自然选择概念。路径依赖的自然选择过程中, 一个突变的基因或表型在某种环境下随机产生, 但是该基因或表型在某些特定环境下会产生正反馈。尤其是在正反馈与随机漂变的共同作用下, 多条路径的演化就可能发生, 并且其路径的形成将同时受到其种群进化历史过程和空间特征分布等因素的强烈影响。而在不同路径下, 由于观测维度、角度和尺度的不同, 适合度意义将因此而存在不同。在此意义下, 自然选择更可能选择路径频率而不是适合度大小。基于上述概念, 我们借鉴现代物理学中复函数的方法, 来描述多重动力对物种形成或者生物特征、种群进化等路径依赖的演化过程, 以期为同域物种、隐存种形成以及生物多样性演化提供解释机制。     

假基因的组成、分布及其分子进化

假基因（pseudogene）是指基因组中与正常基因序列相似,但是缺乏功能的DNA序列.通过序列同源性搜索,可以收集基因组中假基因的群体特性、染色体分布和同源家族等特性.假基因很好地保留了数百万年前基因组中祖先基因的分子记录,被视为＂基因化石＂,因此假基因在进化和比较基因组学中是重要的资源.应用假基因和基因比较体系,可以探究生物基因的进化史和基因组稳定性.如：用Ka/Ks比值确定假基因的自然选择压、物种亲缘关系和进化距离,分析假基因自身的进化趋势,探讨DNA突变的成因等.     

果蝇自然群体同工酶遗传多态的研究

用凝胶电泳技术我们检测了果蝇(D.virilis)4个地方群体6个编码酶的基因位点的遗传变异。发现50％的检测位点是多态的。每个个体杂合位点所占的比例为27.13％。遗传变异量在不同位点上相差是很大的,Est-α,Est-β,Amy位点是高度多态的,Mdh,αGpdh,Acph则几乎是单态的。Mdh在53℃的热稳定性没有差异。对一个给定的位点来说等位基因频率在各地方群体之间是很相似的。测定4个地方群体间的遗传分化,发现地理距离与遗传距离间没有线性相关性。结果表明自然选择和随机过程都可以造成遗传变异,而我们所研究的6个基因位点的变异究竟是自然选择造成的,还是随机过程决定的则有待于进一步的研究。     

On an extremum principle in the genetical theory of natural selection

Natural selection causes gene frequency changes in a large population leading to genetic evolution over evolutionary time scales. Such gene frequency changes, however, involve an optimizing principle. According to Kimura, such changes, over a short interval of time, occur in a manner such that the increase in population fitness is maximum for a given distance between parent and daughter generation gene frequencies. But according to Ewens, of all gene frequency changes, including those that lead to the same partial increase in mean fitness as the natural selection gene frequency changes, the natural selection values minimize the generalized distance measure between parent and daughter generation gene frequency values. These two optimality principles happen to be mirror images of each other. However, the optimality principles are restricted to the case where the increase in mean fitness is to thefirst order in natural selection gene frequency changes. I show in this paper that, instead of linear approximation to the increase in mean fitness, the treatment can be fairly general, and the exact increase in mean fitness can be considered so as to include the dominance effects of the genes.     

An optimizing principle of natural selection in evolutionary population genetics

This paper brings together two themes in evolutionary population genetics theory. The first concerns Fisher's Fundamental Theorem of Natural Selection: a recent interpretation of this theorem claims that it is an exact result, relating to the so-called "partial" increase in mean fitness. The second theme concerns the desire to find an optimality principle in genetic evolution. Such a principle is found here: of all gene frequency changes which lead to the same partial increase in mean fitness as the natural selection gene frequency changes, the natural selection values minimize a generalized distance measure between parent and daughter generation gene frequency values.     

Interpretation of Data Obtained with Recombination-Defective Meiotic Mutants

Gene frequency distributions observed in large-scale surveys of species of Drosophila are shown to be incompatible with a genetic model involving neutral mutations and genetic drift alone. The data are, however, qualitatively similar to predictions based on an alternative model of natural selection for an optimal level of enzyme activity in addition to drift and mutation. The intensity of selection detected reduces the mean rate of gene substitution to less than one-quarter that expected on the neutral-allele hypothesis.     

Selection in natural and experimental populations of Drosophila pseudoobscura

The inverted gene arrangements of Drosophila pseudoobscura were used by Th. Dobzhansky in pioneering analyses of natural selection. Recent experiments have shed light on the mechanisms of selection contributing to the balanced polymorphism for the gene arrangements. In experimental populations, both major components of fitness, viability and fertility, are frequency dependent, and rare genotypes often have a selective advantage. Viabilities are also density dependent. The frequency dependence and density dependence of the fitness components are not universal. Some karyotypes are strongly influenced by frequency or density, some are slightly influenced, and some do not appear to be influenced at all. The role of heterozygote advantage in the selection on the gene arrangements is not clear. It is probably one important element in the overall selection, but viability and fertility do not always show a heterozygote advantage. Viability and fertility components of selection seem to be about equally important in changing inversion frequencies. Male mating success is an important component of selection in natural populations, and in one population rare male karyotypes have been found to have a pronounced mating advantage.     

MIGRATION-SELECTION BALANCE AND LOCAL ADAPTATION OF MITOCHONDRIAL HAPLOTYPES IN RUFOUS-COLLARED SPARROWS (ZONOTRICHIA CAPENSIS) ALONG AN ELEVATIONAL GRADIENT

Variable selection pressures across heterogeneous landscapes can lead to local adaptation of populations. The extent of local adaptation depends on the interplay between natural selection and gene flow, but the nature of this relationship is complex. Gene flow can constrain local adaptation by eroding differentiation driven by natural selection, or local adaptation can itself constrain gene flow through selection against maladapted immigrants. Here we test for evidence that natural selection constrains gene flow among populations of a widespread passerine bird ( Zonotrichia capensis ) that are distributed along an elevational gradient in the Peruvian Andes. Using multilocus sequences and microsatellites screened in 142 individuals collected along a series of replicate transects, we found that mitochondrial gene flow was significantly reduced along elevational transects relative to latitudinal control transects. Nuclear gene flow, however, was not similarly reduced. Clines in mitochondrial haplotype frequency were strongly associated with transitions in environmental variables along the elevational transects, but this association was not observed for the nuclear markers. These results suggest that natural selection constrains mitochondrial gene flow along elevational gradients and that the mitonuclear discrepancy may be due to local adaptation of mitochondrial haplotypes.     

Simulating natural selection in landscape genetics

Linking landscape effects to key evolutionary processes through individual organism movement and natural selection is essential to provide a foundation for evolutionary landscape genetics. Of particular importance is determining how spatially-explicit, individual-based models differ from classic population genetics and evolutionary ecology models based on ideal panmictic populations in an allopatric setting in their predictions of population structure and frequency of fixation of adaptive alleles. We explore initial applications of a spatially-explicit, individual-based evolutionary landscape genetics program that incorporates all factors--mutation, gene flow, genetic drift and selection--that affect the frequency of an allele in a population. We incorporate natural selection by imposing differential survival rates defined by local relative fitness values on a landscape. Selection coefficients thus can vary not only for genotypes, but also in space as functions of local environmental variability. This simulator enables coupling of gene flow (governed by resistance surfaces), with natural selection (governed by selection surfaces). We validate the individual-based simulations under Wright-Fisher assumptions. We show that under isolation-by-distance processes, there are deviations in the rate of change and equilibrium values of allele frequency. The program provides a valuable tool (cdpop v1.0; http://cel.dbs.umt.edu/software/CDPOP/) for the study of evolutionary landscape genetics that allows explicit evaluation of the interactions between gene flow and selection in complex landscapes.     

A Simulation Study of Truncation Selection for a Quantitative Trait Opposed by Natural Selection

A quantitative character controlled at one locus with two alleles was submitted to artificial (mass) selection and to three modes of opposing natural selection (directional selection, overdominance and underdominance) in a large random-mating population. The selection response and the limits of the selective process were studied by deterministic simulation. The lifetime of the process was generally between 20 and 100 generations and did not appear to depend on the mode of natural selection. However, depending on the values of the parameters (initial gene frequency, selection intensity, ratio of the effect of the gene to the environmental standard deviation, fitness values) the following outcomes of selection were observed: fixation of the allele favored by artificial selection, stable nontrivial equilibrium, unstable equilibrium and loss of the allele favored by artificial selection. Finally, the results of the simulation were compared to the results of selection experiments.     

植物诱变技术的研究进展

植物诱变技术是指利用外界因素加快物种遗传变异,在短期内获得有利用价值的突变体,为培育新种质、新品种及基因功能的研究等创造条件。相对于自然的选择,诱变技术具有高频率、广突变、周期短等特性。主要论述了常用的化学诱变、物理诱变、空间诱变和生物诱变等诱变手段,并详细介绍了上述诱变技术的诱变机理、生物学效应、常用的诱变方式及其在植物应用中的研究现状。针对现行各种诱变技术的不足提出了今后努力的方向。     

Allozyme genotype-environment relationships in natural populations of Drosophila buzzatii

Allozyme frequency data from natural populations of Drosophila buzzatii were analyzed for genotype-environment relationships. Allele frequency and heterozygosity at six loci polymorphic throughout eastern Australia and a number of environmental factors (both means and variabilities) were examined by a variety of multivariate techniques. Significant genotype-environment associations were found for five of the six loci, and after correcting for geographic location significant associations remained for Est-2 and Adh-1 gene frequencies and heterozygosities and for Pgm gene frequencies. The results are discussed in relation to selection and gene flow and provide the basis for laboratory studies to disentangle confounded effects of (1) environmental means and environmental variabilities and (2) allele frequency and heterozygosity, and thus to further test for and determine the nature of any natural selection at particular allozyme loci.This work was supported by a grant from the Australian Research Grants Committee to J. S. F. B.     

Time required for gene frequency change in a deterministic model of gene-culture coevolution, with special reference to the lactose absorption problem

The time required for gene frequency change under natural selection in a deterministic model of gene-culture coevolution is investigated. A discrete generations model is formulated, and its continuous time approximation is derived. In passing to the continuous time limit, it is assumed that the frequency of the culturally transmitted trait does not change under oblique (between generations) transmission. The system of ordinary differential equations thus obtained are solved, and the dependence on the parameters of horizontal (within generations) transmission and natural selection is examined. The time required is found to be substantially longer when the determination of a phenotypic difference subject to natural selection is partly cultural rather than completely genetic. The predictions are relevant to the possibility of the coevolution of lactose absorbers and milk drinkers in some human populations. Alternative hypotheses are briefly discussed in the light of the theoretical results.