2023/2/11LessonfourFoundationofgenetics遺傳學(xué)的基礎(chǔ)2023/2/12Earlytheoriesofinheritance

遺傳學(xué)的早期理論

EarlyideasofinheritanceincludedHippocrates’theoryofpangenesis[p?n'd?enisis]andAugustWeismann’s['vaismɑ:n]

germ[d??:m]

plasm['pl?z?m]

theory.遺傳學(xué)的早期理論包括希波克拉底（古希臘名醫(yī)）的泛生說和奧古斯特-魏斯曼(德國生物學(xué)家)的種質(zhì)理論。2023/2/13Basedonexperimentswithmice,Weismannproposedthathereditaryinformationingametes[ɡ?'m?t?z]

transmittedtraitstoprogeny['pr?d?ini]

.

基于小鼠實驗，魏斯曼提出配子中的遺傳信息可以將遺傳特性傳遞給后代。2023/2/14

Bothoftheseearlyviewsincorporated[in'k?:p?reitid]

theblending['blendi?]

theory:theyheldthatheritable['herit?bl]

traitsofthetwoparentsblend,sothatthedistinctcharacteristics[k?r?kt?'ristik]

ofeacharelostinoffspring.這兩個早期觀點組合起來形成混合理論：兩個親本的遺傳特征混合,那么每個親本的不同特征就在子代中喪失了.2023/2/15TheMendelTheory-themostpopularoneTheMendelTheoryis,byfar,thebestknownanduniversallyacceptedtheoryongeneticsandinheritance.Thetheorydealswithknownfactorsandwithasingletraitandthemannerinwhichthesequalitiesaretransmitted.Whatothertheoriesofinheritanceandgeneticsdoyouknow?2023/2/162.GregorMendelandtheBirthofGenetics

格里戈-孟德爾和遺傳學(xué)的誕生2023/2/17GregorMendel,anAugustinian[?:g?s'tini?n]

monk[m??k]

inthemonastery['m?n?st?ri]

atBrunn,Austria,isknownasthe“fatherofgenetics”.格里戈-孟德爾，是奧地利布魯恩的修道院的一名奧古斯丁修道士,是眾所周知的遺傳學(xué)之父。2023/2/18Havingbeenexposedtotheoriesoftheparticularnatureofmatterwhileauniversitystudentandhavingabackgroundinmathematics,Mendelcarriedoutaseriesofcarefullyplannedexperimentsthatdemonstratedtheparticulate[p?'tikjulit]

natureofheredity[h?'rediti]

.

孟德爾曾在讀大學(xué)時學(xué)習(xí)（接觸）了物質(zhì)的粒子屬性,并且，孟德爾有數(shù)學(xué)基礎(chǔ)，于是，他進(jìn)行了一系列周密安排的實驗來證實遺傳的顆粒屬性。2023/2/19HisrevolutionaryideaswereneitherunderstoodnoraccepteduntilmanyyearsafterMendeldied.直到他去世后若干年，他的創(chuàng)新性的理論才被理解和接受。2023/2/1103.Mendel’sClassicExperiments

孟德爾的經(jīng)典實驗2023/2/111Mendelstudiedgeneticsthroughplant-breedingexperimentswiththegardenpea,aplantthatisself-fertilizingandbreeds[bri:d]

true(eachoffspringisidenticaltotheparentinthetraitofinterest).孟德爾通過豌豆育種實驗來研究遺傳學(xué)，豌豆是自花授粉的,并且是真實遺傳的(每個子代和親本的遺傳特征是一樣的)。2023/2/112Totesttheblendingtheory,hefocusedhisresearchonsevendistinctcharacters.為驗證混合理論，他的研究主要集中在7個不同的特征上。2023/2/113Eachofthesecharacters,suchasseedcolorandplantheight,presentonlytwo,clear-cutpossibilities.每個特征如種子顏色，植株高度等，都只有兩個明確的可能性。Healsorecordedthetypeandnumberofallprogenyproducedfromeachpairofparentpeaplants,andfollowedtheresultsofeachcrossfortwogenerations.他也記錄了來自于每一對親本的所有子代的類型和數(shù)量，和兩個子代雜交的結(jié)果。2023/2/114Foreachofthecharactershestudied,Mendelfoundthatonetraitwasdominant

['d?min?nt]

whiletheotherwasrecessive[ri'sesiv]

.對于他研究的每個特征而言，孟德爾發(fā)現(xiàn)一個特征是顯性的,那么另一個就是隱性的。

Inthesecondfilial['filj?l]

(F2)generation,theratioofdominanttorecessivewas3:1.在子2代中,顯性與隱性比為3∶1。

2023/2/115Mendeldeducedthatthisresultswaspossibleonlyifeachindividualpossessesonlytwohereditaryunits,onefromeachparent.

孟德爾推論:只有在每個個體僅擁有兩個遺傳單元，并每個單元來自一個親本時，實驗結(jié)果才成立。2023/2/116TheunitsMendelhypothesized[hai'p?θisaiz]

aretodayknownasalleles

[?'li:l]

,alternativeformsofgenes.孟德爾假設(shè)的遺傳單元就是今天共識的等位基因,基因的兩種形式。Genesarethebasicunitsofheredity.基因是遺傳的基本單元.2023/2/117Anorganismthatinheritsidenticalallelesforatraitfromeachparentissaidtobehomozygous[h?m?'zaig?s]

forthattrait;ifdifferentallelesforatraitareinherited,theorganismisheterozygous[het?r?u'zaig?s]

forthattrait.

從親本遺傳而來的是一個特征的兩個相同的等位基因的個體被認(rèn)為是純合的。反之,遺傳而來的是兩個不同的等位基因的個體，就是雜合的。2023/2/118

Whenanorganismisheterozygousforatrait,theresultingphenotypeforthattraitexpressesonlythedominantallele.

對某一個特征而言,當(dāng)個體是雜合時，它的表型僅由顯性基因決定。Thus,theorganism’sphenotype['fi:n?taip]

—itsphysicalappearanceandproperties—differsfromitsgenotype['d?en?taip]

,whichmayincludebothadominantandarecessiveallele.因此，生物的表型與基因型是不同的,表型是個體的物理特征和品質(zhì),而基因型包括一個顯性基因和一個隱性基因。

2023/2/119ApictorialrepresentationofallpossiblecombinationofageneticcrossisknownasaPunnettsquare.遺傳雜交的所有可能的組合圖表被稱為旁納特方格。Punnettsquare：amethodusedtodeterminetheprobabilitiesofcombinationinazygote['zaig?ut]

.2023/2/120TheresultsofMendel’sexperimentsondominantandrecessiveinheritanceledtoMendel’sfirstlaw:thelawofsegregation.基于顯性和隱性遺傳的實驗結(jié)果,孟德爾提出了分離定律。2023/2/121Thislawstatesthatforagiventraitanorganisminheritsoneallelefromeachparent.該定律認(rèn)為:對一個給定的特征而言,個體從每個親本獲得一個等位基因。

Togethertheseallelesformtheallelepair.這些等位基因一起形成等位基因?qū)Α?023/2/122Whengametes[g?'mi:t]

areformedduringmeiosis,thetwoallelesbecomeseparated(halvingofchromosomenumber).減數(shù)分裂期形成配子時兩個等位基因分離(染色體數(shù)目的減半)。2023/2/123Testcross：acrossbetweenaheterozygoteofunknowngenotypeandanindividualhomozygousfortherecessivegenesinquestion.TogainevidenceforhistheoryMendelperformedtestcrosses,matingplantsofunknowngenotypetoplantsthatwerehomozygous[h?m?'zaig?us]

recessive[ri'sesiv]

forthetraitofinterest.

為驗證此理論，他做了測交實驗，即基因型未知的植物個體與純合隱性的個體雜交。2023/2/124Theratioofdominantphenotypes(ifany)intheprogenymakesclearwhethertheunknowngenotypeisheterozygous[het?r?u'zaig?s]

,homozygousdominant,orhomozygousrecessive.子代顯性表型的比例可以明確測得該未知基因型是雜合的,純合顯性的,還是純合隱性的。

2023/2/1254.Mendel’sideasandthelawof

independentassortment2023/2/126Mendelalsoperformeddihybrid[dai'haibrid]

crosses,whichenabledhimtoconsiderhowtwotraitsareinheritedrelativetooneanother.孟德爾也進(jìn)行了雙因子雜交試驗，該實驗說明了兩個特征相互間是如何遺傳的。

2023/2/127Thisworkledtothelawofindependentassortment,whichstatesthattheallelesofgenesgoverningdifferentcharactersareinheritedindependently.試驗結(jié)果產(chǎn)生了自由組合定律，即控制不同性狀的等位基因是獨立遺傳的。2023/2/128AnapparentexceptiontoMendel’slawisincompletedominance,aphenomenoninwhichoffspringofacrossexhibitaphenotypethatisintermediatebetweenthoseoftheparents.孟德爾定律的一個特例是，不完全顯性，即雜交后子代的表型是父母親本的中間類型。

2023/2/129However,incompletedominancereflectsthefactthatbothallelesforthetraitinquestionexertaneffectonthephenotype.但是，不完全顯性說明了兩個等位基因可能對表型有影響。Theallelesthemselvesremainseparate.等位基因本身仍然是分離的。2023/2/130Mendelpresentedhisideasin1866inascientificpaperpublishedbytheBrunnSocietyforNaturalHistory.1866年，孟德爾將其想法發(fā)表在由布魯恩自然歷史學(xué)會出版的科學(xué)論文上。

Unfortunately,themeaningofhisresearchwasnotunderstoodbyotherscientistsoftheday.不幸運的是，他的研究沒被當(dāng)時科學(xué)家所接受。Hisworkwasrediscoveredin1900byCarlCorrensandHugodeVries.在1900年，他的著作再次被CarlCorrensandHugodeVries（科倫斯和德弗里斯）發(fā)現(xiàn)。

2023/2/1315.ChromosomesandMendelianGenetics2023/2/132SoonafterMendel’sworkwasrediscovered,WalterSuttonandTheodorBoveriindependentlyproposedthatthehereditaryunitsmightbelocatedonchromosomes.孟德爾著作再次被發(fā)現(xiàn)不久，WalterSutton和TheodorBoveri（薩頓和鮑維里）提出，遺傳單位可能定位在染色體上。

ExperimentstoprovethishypothesiswerecarriedoutbyThomasHuntMorganandhisstudentsatColumbiaUniversity,inresearchonthesexchromosomesoffruitflies.哥倫比亞大學(xué)的ThomasHuntMorgan（摩爾根）和他的學(xué)生進(jìn)行的果蠅伴性遺傳的研究證明了這一觀點。2023/2/133Morgon’sstudieswerealsothefirstexplorationofsex-linkedtraits.同時，Morgan也是研究伴性性狀的第一位科學(xué)家。

Italsoledtothediscoveryin1916byCalvinBridgesofthephenomenonofnondisjunction[n?ndis'd??nk??n]

,inwhichachromosomepairfailstosegregateduringmeiosis.1916年，伴性遺傳也導(dǎo)致了CalvinBridges（C.布里奇斯）的不分離現(xiàn)象的發(fā)現(xiàn)，即在減數(shù)分裂中，染色體對不分離。2023/2/134Theend!pangenesis[p?n'd?enisis]泛生說gametes[ɡ?'m?t?z]characteristics[k?r?kt?'ristik]progeny['pr?d?ini]dominant

['d?min?nt]recessive[ri'sesiv]

.filial['filj?l]exert[英][?g?z?:t]alleles

[?'li:l]homozygous[h?m?'zaig?s]heterozygous[het?r?u'zaig?s]phenotype['fi:n?taip]genotype['d?en?taip]gametes[g?'mi:t]dihybrid[dai'haibrid]2023/2/137ChemicalAbstractService2023/2/138化學(xué)文摘服務(wù)社CAS（ChemicalAbstractService）美國化學(xué)學(xué)會（ACS）旗下所出版的《ChemicalAbstract》化學(xué)文摘的在線版數(shù)據(jù)庫.“化學(xué)文摘”是化學(xué)和生命科學(xué)研究領(lǐng)域中不可或缺的參考和研究工具，也是資料量最大，最具權(quán)威的出版物。AboutCAS2023/2/1392023/2/140TheCASSourceIndex(CASSI)SearchToolisanotherfreeonlineresourceintendedtosupportresearchersandlibrarianswhoneedaccuratebibliographicinformation.Usethisfreetooltoquicklyidentifyor