內(nèi)容遺傳學(xué)課件8linkage and mapping eukaryotes

Reviewforthelast tionsoftheprecisediploidcontentofchromosomesarecalledchromosomalaberrationsorchromosomalmutations.Deviationsinchromosomalnumber,ormutationsinReviewforthelast tionsoftheprecisediploidcontentofchromosomesarecalledchromosomalaberrationsorchromosomalmutations.Deviationsinchromosomalnumber,ormutationsinthestructureofthechromosomeoftenresultindeathorsubstantialchangesinthephenotype.Aneupoidymonosomy,trisomy,tetrasomy,andsoon.PolyploidyautopolyploidyorLargesegmentsofthechromosomecanbemodifiedbydeletionsorduplications.Deletionsandcri-du-chatsyndromeinInversionsandtranslocationsinitiallycauselittleornolossofgeneticinformationordeleterious有害的effects.FragileontheXchromosomeisassociatedwithinheritedmentalretardationinhuman.ChapterChapterLinkageHeredityandChromosomeMap連鎖遺傳作ConceptsofManygenesresideoneachchromosome.Unlesstheyareseparatedbycrossingover(交換allelesatthelocioneachhomologsegregateasaunitduringgameteformation.binantgametes(重組配子)resultingfromcrossingoverenhancegeneticvariabilitywithinaspeciesandserveasthebasisforconstructing(構(gòu)建)chromosomemaps.11LinkageLinkageisthetendencyforallelesofdifferentgenestobepassedtogetherfromonegenerationtothenext.Onlygenessituatedonthesamechromosomecanshowlinkage.Genesonnon-homologous（非同andalwaysshow50% Thedegreeoflinkagebetweentwogenesdependsonthefrequencyofcross-overs(交叉)thatoccurbetweenthemduringmeiosis.Theclosertheyaretogetherthelesslikelyacross-overwilloccurbetweenthem.Groupsofgenesthatarelinkedarecalledlinkagegroups(連鎖群 了 了 帶上Fig8.1aResultsFig8.1aResultsofwheretwogenesare(a)ontwodifferentpairsofFig8.1bResultswheretwosgenesareonthesamepairofbutwhereFigureFigureResultsofwheretwousgenesareonthesamepairwherean 2Cross-over2Cross-overpleteChiasma-typehypothesis交叉假 Janssens（1909）究兩棲類和直翅目昆蟲的減 假設(shè)）的地方（Figure8.7和8.8）（bination）Figure8.7），表示非姊妹染色單體FigureFigure8.8Crossingoveringrasshopper完全連 TheresultTheresultinFig8.10isduetothelinkagedistanceofthegenesFigure8.11Amapoftheyellow(y),white(w),and(m)genesontheXchromosomeofDrosophilamelanogaster.Eachnumberrepresentsthepercentageof binantoffspringproducedinoneofthreecrosses,eachinvolvingtwodifferent Figure8.13Figure8.13Theconsequencesofasingleexchangebetweentwononsisterchromatidsoccurringinthetetradstage.Twononcrossover(parental)andtwocrossover( gametesareproduced. SeveralSeveralchiasmatafoundthefirstmeioticFigure8.14Consequencesofadoubleexchangetwononsisterchromatids.Becausetheexchangesinvolvetwochromatids,twononcrossover(非交換型parental)andtwodouble-crossovergametesareFigure Figure 與Figure與Figure8.19子一代雜合體為雌蠶時，測交后代只兩種表型，比數(shù)為1:1，沒有重組類型出 FigureFigure8.20子一代雜合體雄蠶與雙隱性雌蠶交配時，出LinkageThreepointtest。oranadrevat發(fā)現(xiàn)，把這三個包括在同一次交配中，即用三雜合體ac/或a+/++與隱性ac/ac測交，即可完成3次兩點試驗。這種試驗叫做三點測交。其優(yōu)點如下：例：果蠅ec（echinus棘眼例：果蠅ec（echinus棘眼），sc（scute缺少某些胸部剛毛），cv（crossveinless翅上橫脈缺失），這三個都是X連鎖的。 ec－ec－ct的重組值是三個重組值中最大的，是18.4%，但剛好等于另外兩個重組值ec—ct間距離時，必須加上兩倍的雙交換，即18.4%+×0.1%=10.28.4%20.1%18.4% Example:（Example:（ecct+/++cv）×（ecctcv/Y）,表型+++和ecctcv cv位于中間，而這三個的順序是（eccvct），因此交（ec+ct/+cv+）×（eccvct/Figure8.22只有當(dāng)cv位于中間時，同時發(fā)生兩個單交 +++和cccvct 注意這2這這個順序正返返棘Apartialgeneticmapof棘ApartialgeneticmapofthefourofDrosophilaThefourpairschromosomesof 表8-1幾種生物的連鎖群數(shù)目等于單倍數(shù)連鎖群數(shù)接近n，或等于n，但不會超過nThegeneticmapsofchromosomesarebasedontheaverageThegeneticmapsofchromosomesarebasedontheaveragenumberofcrossoversthatoccurduringmeiosis.Mapdistancesareestimatedbycalculatingthefrequencyof betweengenesinexperimentalcrossesorbycountingchiasmata(交叉)incytologicalpreparations.Onechiasma(交叉)isequivalenttoadistanceof50cM. binationfrequencieslessthan20to25percentestimatemapdistancedirectly.However,frequenciesgreaterthan20to25percentusuallyunderestimatemapdistancebecausesomeofthemultiplecrossoversthatoccurdonotcontributetothe frequency.以重組頻率作為遺傳圖距，也可利用細(xì)胞學(xué)制片計數(shù)交叉?zhèn)€二線雙交實際相關(guān)3.2Interferenceandcoefficientof3.2Interferenceandcoefficientof–如果相鄰兩交換間互不影響，即交換獨立發(fā)生，那么根據(jù)乘法定理，雙交換發(fā)生的理論頻率理論雙交換值例：wx-sh-c三點測驗中，wx-sh交換值sh-c為0.035，則wx- 間理論雙交換值應(yīng)為0.184×0.035=0.64%干擾–為了度量兩次交換間相互影響的程度，提出了符合系符合系數(shù)也稱為并發(fā)系數(shù)：用以衡量兩次交換間相互影的性質(zhì)和程度例如剛符合系數(shù)符合系*某些微生物中往往大于1，稱為負(fù)干3.3Somaticcellandhumangene人鼠細(xì)胞融合培雜種細(xì)胞篩各種雜種細(xì)胞生化分析和細(xì)胞學(xué)觀察比較、分析、圖有有 。同理可分析 在3 上 不明確 在1 上通過許多這樣的實驗就可知 的連鎖關(guān)系Figure8.30Representativeregionalgeneassignmentshumanchromosome1and hybridizationtechniques.theXchromosome.Many 4Haploidorganismsinlinkageand Neurosporacrassa4Haploidorganismsinlinkageand Neurosporacrassa粗造鏈孢霉Prototroph野生型原養(yǎng)型子囊孢子黑色Auxotroph營養(yǎng)缺陷型Lysinelysine 賴氨酸缺陷 子囊孢子灰Hypha菌絲hyphaeAscusAscosporeHypha 可以簡單明了地看出分離比和計算重可以以著絲粒作為一個座位（ls），計算某一與著絲粒的重組率。子囊中子囊孢子的對稱性，證明減數(shù)是一個交互程（reciprocal4可以檢驗染色單體的交換有否現(xiàn)象，而且還可用它來進(jìn)行轉(zhuǎn)變的研究。(5)四線分析（-adis）證明，每一交換只包括線中的兩線，但多重交換可以包括一個雙價體的兩線、三線或四線。一個一個發(fā)生交換的子囊內(nèi)只有半數(shù)字囊孢子是交換的5SisterChromatidHomologouschromosomesdo5SisterChromatidHomologouschromosomesdonotusuallypairuporsynapseinsomaticcells(Drosophilaisanexception),eachindividualchromosomeinprophaseandmetaphaseofmitosisconsistsoftwoidenticalsisterchromatids,joinedatacommoncentromere.Knowingthatcrossingoveroccursbetweensynapsedhomologsinmeiosis,wemightaskwhethersuchaphysicalexchangeoccursbetweenhomologsduringmitosis.LightmicrographofsisterLightmicrographofsisterinmitoticchromosomes.Sometimescalledharlequin丑角chromosomesbecause斑紋,斑點）appearance.Thesechromosomeswerestainedwith33258-Hoechstreagentandacridine（吖啶,氮蒽）orangeandthenviewedunderfluorescence binationandbinationisanessentialfeaturein reproduction.Duringmeiosis,whenchromosomescometogetherandcrossover,thereisanopportunitytocreatenewcombinationsofalleles.Someofthesemaybenefittheorganismbyenhancingsurvivalorreproductiveability.Overtime（隨著Overtime（隨著時間的推移）,suchbeneficialcombinationswouldbeexpectedtospreadthroughapopulationand estandardfeaturesofthegeneticmakeup(組成，結(jié)構(gòu)，天性)ofthespecies. binationisthereforeawayofshuffling（混合，攪亂）geneticvariationtopotentiate（加強）evolutionarychange.7摩爾根對遺傳學(xué)的證發(fā)在上的分離定律和自由組合定的連鎖和交換，因而僅是位于不上 才可以自由組合 自由組合定律成為特例發(fā) 是以直線方式排列率的大小測定 間的相對距離，繪出了表 上證發(fā)三體、多倍體、發(fā)發(fā) 是以直線方式排列率的大小測定 間的相對距離，繪出了表 上證發(fā)三體、多倍體、發(fā)是結(jié)構(gòu)變異（不分開等）1933年，摩爾根以遺傳學(xué)成就 生理和醫(yī)獎ChapterChapterGeneslocatedonthesamechromosomearesaid）,thereforecanbetransmittedtogetherduringgameteformationHowever,crossingoverbetweenhomologsduringmeiosisresultsinthereshuffling（改組）ofallelesandtherebycontributesto（貢獻(xiàn)）geneticvariabilitywithinLinkageex inswhytheparentalgenecombinationsstayTherearetwotypesofmeiotic bination（間重組）isachievedbyMendelianindependentassortmentandresultsinabinantfrequencyof bination（ 內(nèi)重組）occurswhenthephysicallinkageoftheparentalgenecombinationspreventsfullassortmentofthegenepairs,andthe frequencyislessthan50%.Sturtevant,astudentofMorgan‘Sturtevant,astudentofMorgan‘s,developedamethodofdetermining（測定）thedistancebetweengenepairsonageneticmapbasedonthepercentageof Geneticistsrealizedthatcrossingoverprovidesanexperimentalbasisformapthelocationoflinkedgenesrelativetooneanotheralongthechromosome.Somaticcell（體細(xì)胞）hybridizationtechniqueshavemadepossiblelinkageandmapysisofhuman studiesmay