O遺傳的變異培訓(xùn)課件

O1遺傳的變異要點基因和等位基因基因是帶有可產(chǎn)生特定蛋白的遺傳密碼的DNA片段。一個基因可有許多等位基因，而個體可有純合或雜合的基因型。表達(dá)的表現(xiàn)型取決于等位基因是顯性的、隱性的還是共顯性的。種群中存在的所有基因組和等位基因叫做基因庫。GenesarepiecesofDNAwhichcontainthegeneticcodenecessarytoproduceaspecificprotein.Agenecanhavemanyallelesandindividualscanhaveahomozygousorheterozygousgenotype.Thephenotypeexpresseddependsonwhetherallelesaredominant,recessiveorcodominant.Thetotalsetofgenesandallelespresentinapopulationisknownasthegenepool.KeyNotesGenesandallelesO1

GENETICVARIATION測定遺傳變異種群和物種內(nèi)的遺傳變異可直接由DNA或蛋白（別構(gòu)酶）變異來估計。蛋白或DNA片段可通過凝膠電泳分離，呈現(xiàn)可刻劃的帶來決定個體的基因型。對個體DNA的詳細(xì)調(diào)查產(chǎn)生了一種獨特的遺傳指紋，對建立父子關(guān)系很有用。多型多型指的是種群中等位基因的存在。一個種群或物種可能顏色是多型的，如蝸牛，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選擇保持下來的，但其他是由于許多基因控制多型性狀的結(jié)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.建立者效應(yīng)建立者效應(yīng)描述由一個或幾個個體建立新種群，導(dǎo)致低水平的遺傳變異和在親本種群中稀少的等位基因的經(jīng)常不成比例的數(shù)量。人類中特定遺傳病的高發(fā)病率可歸因于建立者效應(yīng)。相關(guān)主題適應(yīng)（B1）稀有物種、生境損失和滅絕（V1）RelatedtopicsAdaptation(B1)Rarespecies,habitatlossandextinction(V1)FoundereffectThistermdescribestheestablishmentofanewpopulationbyoneorafewindividual(s),resultinginlowlevelsofgeneticvariationandoftenadisproportionatenumberofallelesthatarerateintheparentpopulation.Inhumanpopulationsthehighincidenceofcertaingeneticdiseasescanbetracedtofoundereffects.O2物種形成要點繁殖種的概念繁殖種的概念，集中在如下思想：物種延續(xù)并保持其遺傳的完整性和獨特性是因為不進行異種雜交。生物種概念和識別種概念都根據(jù)相互雜交定義種。本觀點與實際的物種定義不同的是后者以明顯的形態(tài)學(xué)性狀為基礎(chǔ)?；蛄骰蛄髅枋龅氖腔蛟诜N群內(nèi)通過相互雜交、擴散和遷移進行的運動。高基因流使種群遺傳上彼此相似。受到限制的基因流使種群間發(fā)生分化。Thereproductivespeciesconceptfocusesontheideathatspeciesexistandmaintaintheirgeneticintegrityanddistinctnessbecausetheydonotinterbreed.Thebiologicalspeciesconceptandtherecognitionspeciesconceptbothdefinespeciesintermsofinterbreeding.Hisviewcontrastswiththepracticaldefinitionofspeciesonthebasisofdistinguishingmorphologicalcharacters.KeyNotesReproductivespeciesconceptO2

SPECIATIONGeneflowdescribeshemovementofgenesamongpopulationsthroughinterbreeding,dispersalandmigration.Highgeneflowcausespopulationstobecomegeneticallysimilartooneanother.Restrictedgeneflowallowsdifferentiationtooccuramongpopulations.Geneflow生物種的概念生物種概念認(rèn)為種是一組可以相互雜交的自然種群，它們與其他種群間具有繁殖隔離。該概念將沒有明顯形態(tài)學(xué)差別的種群分成分離的姊妹種，因為它們不能彼此交換基因。生物種由繁殖隔離機制來保持。識別種的概念識別種的概念定義種是一組具有共同的交配識別系統(tǒng)（SMRS）的個體。交配識別系統(tǒng)包括交配的所有方面，如繁殖器官和配子的兼容性、求偶鳴叫、行為和儀式。該種定義強調(diào)將種保持在一起的因素。Thisconceptviewsspeciesasagroupofinterbreedingnaturalpopulationsthatarereproductivelyisolatedfromothersuchgroups.Itallowspopulationsthatareindistinguishablemorphologicallytobeclassifiedasseparate,siblingspeciesbecausetheydonotinterchangegenes.Biologicalspeciesaremaintainedbyreproductiveisolatingmechanisms.BiologicalspeciesconceptTherecognitionconceptviewsaspeciesasagroupofindividualswithacommonSpecificMateRecognitionSystem(SMRS).TheSMRSconsistsofallaspectsofmatingsuchascompatibilityofreproductiveorgansandgametes,courtshipsongandbehaviorandpheromones.Thisspeciesdefinitionemphasizesthefactorsthatkeepspeciestogether.Recognitionspeciesconcept異域性物種形成與原來種由于地理隔離而進化形成新種，為異域性物種形成。異域性物種形成最易發(fā)生在邊緣隔離、處在種分布區(qū)的極端邊緣的小種群。小的非典型種群與極端環(huán)境條件的混合作用可產(chǎn)生迅速而廣泛的遺傳重組（遺傳革命），從而導(dǎo)致物種形成。鄰域性物種形成鄰域性物種形成發(fā)生在分布區(qū)相鄰，但分布區(qū)內(nèi)不同地點環(huán)境（如氣候）條件不同的種群。如在環(huán)形種中那樣，可發(fā)現(xiàn)中間雜種，但包括的很大的距離使兩種類型不能完全混合。Allopatricspeciationoccurswhenthenewspeciesevolvesingeographicisolationfromtheparentspecies.Itmaytakeplacemostreadilyinperipheralisolates,smallpopulationsattheextremeedgeofaspeciesrange.Thecombinedeffectofasmallatypicalpopulationandextremeenvironmnentalconditionscancauserapidandextensivegeneticreorganization(ageneticrevolution)leadingtospeciation.AllopatricspeciationThisformofspeciationoccurswherethespeciatingpopulationsarecontiguousbutsubjecttodifferentenvironmental(e.g.climatic)conditionsindifferentpartsoftherange,Intermediatehybridsarefound,asinringspecies,butthelargedistancesinvolvedpreventthetwotypesfrommergingcompletely.Parapatric