O遗传的变异培训课件

O1遗传的变异要点基因和等位基因基因是带有可产生特定蛋白的遗传密码的DNA片段。一个基因可有许多等位基因，而个体可有纯合或杂合的基因型。表达的表现型取决于等位基因是显性的、隐性的还是共显性的。种群中存在的所有基因组和等位基因叫做基因库。GenesarepiecesofDNAwhichcontainthegeneticcodenecessarytoproduceaspecificprotein.Agenecanhavemanyallelesandindividualscanhaveahomozygousorheterozygousgenotype.Thephenotypeexpresseddependsonwhetherallelesaredominant,recessiveorcodominant.Thetotalsetofgenesandallelespresentinapopulationisknownasthegenepool.KeyNotesGenesandallelesO1

GENETICVARIATION测定遗传变异种群和物种内的遗传变异可直接由DNA或蛋白（别构酶）变异来估计。蛋白或DNA片段可通过凝胶电泳分离，呈现可刻划的带来决定个体的基因型。对个体DNA的详细调查产生了一种独特的遗传指纹，对建立父子关系很有用。多型多型指的是种群中等位基因的存在。一个种群或物种可能颜色是多型的，如蜗牛，或者一些生化特性是多型的，如植物的毒性。一些多型可能是由自然选择保持下来的，但其他是由于许多基因控制多型性状的结果。polymorphismThetermpolymorphismreferstothepresenceofallelesinapopulation.Apopulationorspeciesmaybepolymorphicforcolor,asinsnails,orforsomebiochemicalfunction,asinplanttoxicity.Somepolymorphismsaremaintainedbynaturalselection,butothersappeartoresultfromtheeffectofmanygenescontrollingthepolymorphiccharacter.GeneticvariationwithinpopulationsandspeciescanbeestimateddirectlyfromtheDNAorfromprotein(allozyme)variation.ProteinsorDNAfragmentsareseparatedbygelelectrophoresistogivebandsthatcanbescoredtodeterminethegenotypeofindividuals.DetailedinvestigationoftheDNAofindividualsyieldsauniquegeneticfingerprint,usefulforestablishingpaternity.MeasuringgeneticvariationGeneticdriftGeneticdriftisarandomchangeingenefrequencyarisingthroughchancealone.Ittendstobemoreapparentinsmallpopulationsallelefrequenciesdriftawayfromtheirstartingvalues,increasing,decreasingorfluctuatingupanddown.Itoccursbecausethereisanelementofchanceinwhichindividualsandwhichgameteswillproduceoffspringandwhichindividualswilldiebeforereproducing.Randomchangesinallelefrequencycanleadtofixationandtheprogressivelossofgeneticvariationfromthepopulation.GeneticbottleneckWhenapopulationundergoesanabruptcontractioninnumbers,thisisaccompaniedbyachangeingenefrequenciesandadeclineinthetotalgeneticvariation.Geneticdriftinthesmallpopulationduringthebottleneckresultsinthelossofgeneticvariation.Althoughpopulationnumbersmayrecover,geneticvariationwillremainlowformanygenerations.建立者效应建立者效应描述由一个或几个个体建立新种群，导致低水平的遗传变异和在亲本种群中稀少的等位基因的经常不成比例的数量。人类中特定遗传病的高发病率可归因于建立者效应。相关主题适应（B1）稀有物种、生境损失和灭绝（V1）RelatedtopicsAdaptation(B1)Rarespecies,habitatlossandextinction(V1)FoundereffectThistermdescribestheestablishmentofanewpopulationbyoneorafewindividual(s),resultinginlowlevelsofgeneticvariationandoftenadisproportionatenumberofallelesthatarerateintheparentpopulation.Inhumanpopulationsthehighincidenceofcertaingeneticdiseasescanbetracedtofoundereffects.O2物种形成要点繁殖种的概念繁殖种的概念，集中在如下思想：物种延续并保持其遗传的完整性和独特性是因为不进行异种杂交。生物种概念和识别种概念都根据相互杂交定义种。本观点与实际的物种定义不同的是后者以明显的形态学性状为基础。基因流基因流描述的是基因在种群内通过相互杂交、扩散和迁移进行的运动。高基因流使种群遗传上彼此相似。受到限制的基因流使种群间发生分化。Thereproductivespeciesconceptfocusesontheideathatspeciesexistandmaintaintheirgeneticintegrityanddistinctnessbecausetheydonotinterbreed.Thebiologicalspeciesconceptandtherecognitionspeciesconceptbothdefinespeciesintermsofinterbreeding.Hisviewcontrastswiththepracticaldefinitionofspeciesonthebasisofdistinguishingmorphologicalcharacters.KeyNotesReproductivespeciesconceptO2

SPECIATIONGeneflowdescribeshemovementofgenesamongpopulationsthroughinterbreeding,dispersalandmigration.Highgeneflowcausespopulationstobecomegeneticallysimilartooneanother.Restrictedgeneflowallowsdifferentiationtooccuramongpopulations.Geneflow生物种的概念生物种概念认为种是一组可以相互杂交的自然种群，它们与其他种群间具有繁殖隔离。该概念将没有明显形态学差别的种群分成分离的姊妹种，因为它们不能彼此交换基因。生物种由繁殖隔离机制来保持。识别种的概念识别种的概念定义种是一组具有共同的交配识别系统（SMRS）的个体。交配识别系统包括交配的所有方面，如繁殖器官和配子的兼容性、求偶鸣叫、行为和仪式。该种定义强调将种保持在一起的因素。Thisconceptviewsspeciesasagroupofinterbreedingnaturalpopulationsthatarereproductivelyisolatedfromothersuchgroups.Itallowspopulationsthatareindistinguishablemorphologicallytobeclassifiedasseparate,siblingspeciesbecausetheydonotinterchangegenes.Biologicalspeciesaremaintainedbyreproductiveisolatingmechanisms.BiologicalspeciesconceptTherecognitionconceptviewsaspeciesasagroupofindividualswithacommonSpecificMateRecognitionSystem(SMRS).TheSMRSconsistsofallaspectsofmatingsuchascompatibilityofreproductiveorgansandgametes,courtshipsongandbehaviorandpheromones.Thisspeciesdefinitionemphasizesthefactorsthatkeepspeciestogether.Recognitionspeciesconcept异域性物种形成与原来种由于地理隔离而进化形成新种，为异域性物种形成。异域性物种形成最易发生在边缘隔离、处在种分布区的极端边缘的小种群。小的非典型种群与极端环境条件的混合作用可产生迅速而广泛的遗传重组（遗传革命），从而导致物种形成。邻域性物种形成邻域性物种形成发生在分布区相邻，但分布区内不同地点环境（如气候）条件不同的种群。如在环形种中那样，可发现中间杂种，但包括的很大的距离使两种类型不能完全混合。Allopatricspeciationoccurswhenthenewspeciesevolvesingeographicisolationfromtheparentspecies.Itmaytakeplacemostreadilyinperipheralisolates,smallpopulationsattheextremeedgeofaspeciesrange.Thecombinedeffectofasmallatypicalpopulationandextremeenvironmnentalconditionscancauserapidandextensivegeneticreorganization(ageneticrevolution)leadingtospeciation.AllopatricspeciationThisformofspeciationoccurswherethespeciatingpopulationsarecontiguousbutsubjecttodifferentenvironmental(e.g.climatic)conditionsindifferentpartsoftherange,Intermediatehybridsarefound,asinringspecies,butthelargedistancesinvolvedpreventthetwotypesfrommergingcompletely.Parapatric