孟德爾式遺傳分析及其擴(kuò)展課件

Chapter3Mendel’sGeneticAnalysisandExtension

第三章孟德爾式遺傳分析及其擴(kuò)展3.1Mendel’slaws孟德爾遺傳規(guī)律3.1.1Lawofsegregation分離律3.1.2Lawofindependentassortment自由組合律3.2多對(duì)相對(duì)性狀雜交的遺傳分析3.3二項(xiàng)式分布公式3.4Testsforgoodnessoffit:chi-squaretests

適合度檢驗(yàn)-卡方檢驗(yàn)3.5Interactionamonggenes基因互作3.5.1Interactionbetweenalleles等位基因間互作3.5.2Interactionbetweennon-alleles非等位基因間的相互作用3.6Genotype,phenotypeandenvironmental基因型、表型與環(huán)境Terms:

C1,C2InheritedtraitPhenotypeGenotypeDominantRecessivePure-breedingCrossTestcrossBackcrossSelf-crossReversecrossHybridHomozygousHeterozygousProgeny

3.1Mendel’slaws

Reasonsofchoosingpeaformaterial:stabletrue-breedingeasydistinguishablecharacteristicsselfandclosepollinationeasycountingLawofsegregation(分離規(guī)律)Lawofindependentassortment(自由組合規(guī)律）3.1.1LawofsegregationMendelstudiedinheritanceofsevenphenotypesinpea,weconcentrateononlyoneofthese-Petalcolor紅花×白花F1紅花F2929株(705紅/224白，接近3∶1)白花×紅花與正交結(jié)果完全一致why

705224F1和F2性狀表現(xiàn)不受親本組合方式影響ValidationandDetection(假設(shè)的驗(yàn)證和雜合體的檢測(cè))Onesimpleextensionofthe3:1phenotyperatioproducedwhenanF1individualiscrossedtothehomozygousrecessiveparent.F1canproducegameteswithdominantandrecessivealleles,andsotheprogenyofthecrosshavethedominantandrecessivephenotypeinequalnumbers,a1:1phenotyperatio.Thistypeofcrossistermedatestcross,andisusefulinanysituationwhereitisnecessarytodetermineifanindividualisheterozygous.Ccc

8581Essenceoflawofsegregation:

決定某一性狀的等位基因在配子形成過程中彼此分離互不干擾，使得配子中僅含成對(duì)基因中的一個(gè)，產(chǎn)生數(shù)目相等的兩種類型配子。Singleautosomaldominantgenedisorders:常染色體單基因顯性遺傳病的傳遞：

家族性多發(fā)性結(jié)腸息肉(polypus)、先天性白內(nèi)障(cataract)、短肢癥、Huntington’sdisease等1460多種性狀。特點(diǎn)：雙親之一雜合態(tài)患者子女1/2得病，機(jī)率相等代代相傳SymbolfordrawinghumanpedigreeMalemalesufferercoupletwinsfromseparatezygotesFemalefemalesufferercloserelativecoupletwinsfromsamezygotesIIInoprogeny12firstsuffererdecedentcarrierunknownsexsex-linkedrecessivecarrier3.1.2Lawofindependentassortment3:1isthebasicMendelianratio,everythingthatfollowsdependsonitDihybridcross(雙因子雜交):

Acrossbetweenthetwopure-breedingparentallinesyieldedanF1generationwhichconsistedonlyofroundyellow.Of556seeds,found315roundyellow,108roundgreen,101wrinkledyellow,32wrinkledgreen.Thisisclosetoaratioof9:3:3:1,whichisreferredtoasthe

dihybridratio(雙因子雜種比例)ThepredictedratiosofphenotypesandgenotypescanbedeterminedbyusingPunnettsquare(龐納特方格).The9:3:3:1ratioissimplytwo3:1ratioscombined,andshowsthattheallelesofthetwogenesbehaveindependentlyofeachother.Taketheseedsshapegenefirst:intheF2ratioof3roundto1wrinkled.Thenthecolor:3yellowto1green.Iftheratiosforthetwophenotypesaremultipliedacrossthe9:3:3:1ratioisobtained.Soanynumberofgenescanbecalculatedbytheexpression(3:1)n,nisthenumberofallelesinvolved.(108+32):(101+315)=1:3Fourkindsofgametewithequalamountproducedaftertestcross,andthereforefourtypesofprogenywithequalratioofphenotypesandgenotypesproduced.測(cè)交產(chǎn)生四種等比例配子，產(chǎn)生四種等比例表型及基因型后代。p77Table4-4Essenceoflawofindependentassortment:

位于非同源染色體上的等位基因，各自分離互不干擾，并且自由組合到不同的配子中去。事實(shí)上雜交后代遺傳比例并非與理論值完全吻合,為什么呢?Observedandestimatedvaluearenotmatchedcompletely?

Probabilities(概率):

Whenwetossacoinwecannotsaywhichwayupitwilllandbecauseeachlandingisarandomorstochasticevent.Inscience,ourhypothesispredictstheprobabilitiesofparticularresults,andallowsustotestthathypothesis.Thesumsrule(加法法則):

Thesumsrule(addition)isappliedtocombineprobabilitiesofeventswhicharemutuallyexclusive.Ageneticexamplewouldbeacrosswhereweexpectedtoget1/4red:2/4pink:1/4whiteflowers.Theprobabilityofanyparticularflowerbeingredorpinkis1/4+2/4=3/4用于互斥事件總的概率的計(jì)算。一個(gè)遺傳學(xué)上的例子是：我們預(yù)測(cè)某次雜交后代的花色之比是1/4紅:2/4粉紅:1/4白，則某花為紅或粉紅的概率是1/4+2/4=3/4)Theproductsrule(乘法法則):Theproductsruleisappliedtoindependenteventsandeventshappeninginaspecificorder.用于獨(dú)立的且以一定順序發(fā)生的事件。Ageneticexampleisamarriagebetweentwopeopleheterozygousforarecessivegeneticdisease,sayphenylketonuria(PKU).Iftheyhavethreechildren,whatistheprobability(chance)ofallthreebeingaffected?Theprobabilityofachildbeinghomozygousfortherecessivealleleis?,therefore:

P=?×?×?=(1/4)3=1/64

3.3二項(xiàng)式分布公式：n為子代數(shù)r為某一基因型的子代p為一基因型的概率q為另一基因型的概率n-r為另一基因型的子代數(shù)目n!Prqn-rr!(n-r)!用以計(jì)算雜交后代某一特定基因型或表型出現(xiàn)的概率（適合小樣本的一對(duì)質(zhì)量性狀）

3.4Testsforgoodnessoffit:chi-squaretests(適合度檢驗(yàn)：X2卡方檢驗(yàn))Goodnessoffittestcalculatetheprobabilityofobserveddatabeingobtainedbychanceifthatdataissampledfromahypothesizedpopulationordistribution.Theusualtestistocalculatechi-square.適合度檢驗(yàn)可計(jì)算從一假設(shè)的分布群體或區(qū)域中隨機(jī)觀察到某數(shù)據(jù)的概率。常用檢測(cè)方法-卡平方X2檢驗(yàn)法：以指數(shù)值表示實(shí)得數(shù)與理論數(shù)的差異nP0.990.950.500.100.050.020.0112345100.000160.02010.1150.2970.5542.5580.00390.130.3520.7111.1453.9400.151.392.373.364.359.342.174.616.257.789.2415.993.845.997.829.4911.0718.315.417.829.8411.6713.3921.166.649.2111.3513.2815.0923.21X2表Usingchi-squareprobabilitytables:TheprobabilityofgettingaresultbychanceislookedupintablesofX2.Lookingalongtherowfortheappropriatedegreesoffreedom,findthevaluesgreaterandsmallerthanthatcalculated,andreadtheprobabilityatthetop.從X2表中可查到隨機(jī)得到某一結(jié)果的概率。X2表中不同的橫行代表不同的自由度，找到正確的自由度，再找到大于和小于計(jì)算值的數(shù)值，最后從表頂行讀出對(duì)應(yīng)的概率

Levelofsignificance(顯著水平)

Thelevelofsignificanceistheprobabilitybelowwhichweassumethedataobserveddoesnotfitexpectations.Thisisconventionally0.05.Whenthereisaprobabilityoflessthan0.05,thentorejectthenullhypothesisasprobablybeingfalseandsaythedatadoesnotfit.顯著水平就是一個(gè)概率，當(dāng)?shù)陀诖烁怕蕰r(shí)，我們便認(rèn)為觀察值不符合預(yù)期值。顯著性水平在習(xí)慣上取0.05。如果某數(shù)據(jù)的概率低于0.05則我們認(rèn)為數(shù)據(jù)與預(yù)期值不符而放棄（即差異顯著）。

P>0.05,試驗(yàn)值與理論值相符,差異不顯著;0.01<=P<=0.05,試驗(yàn)值與理論值不符,差異顯著;P<=0.01,試驗(yàn)值與理論值極不相符,差異極顯著.查表得概率(P)介于0.5~0.10之間,說明這種偏差50%以上由機(jī)會(huì)造成.試驗(yàn)值與理論值相符,差異不顯著.

3.5Interactionamonggenes基因互作3.5.1

Interactionbetweenalleles

等位基因間互作：

1.Incompletedominance(不完全顯性)：thephenotypeofF1isbetweentwoparents.雜交后代表型介于雙親中間的類型。e.g.紅花紫茉莉(CC)×白花紫茉莉(cc)C對(duì)c不完全顯性

Cc粉紅紫茉莉自交

1CC:2Cc:1cc

基因型比=表現(xiàn)型比=1：2：12.Co-dominance(共顯性):Theheterozygotedisplaysbothalleles.一對(duì)等位基因在雜合體中都表現(xiàn)出性狀的現(xiàn)象e.g.InhumanstheMNbloodgroupiscontrolledbyasinglegene.onlytwoallelesexist,LMandLN.人類中MN血型由單基因控制，只有LMandLN兩個(gè)等位基因存在。LMLM--M型LMLN--MN型LNLN--N型LM、LN基因分別控制紅細(xì)胞表面M抗原、N抗原的產(chǎn)生，在雜合體中紅細(xì)胞表面既有M抗原又有N抗原，屬共顯性現(xiàn)象。瓢蟲鞘翅色澤AAxEE前緣黑后緣黑AE前后緣均黑1AA2AE1EE前緣黑前后緣均黑后緣黑3.Mosaicdominance(鑲嵌顯性)：雙親性狀在后代個(gè)體的某一部位上都得到了表現(xiàn)，形成鑲嵌圖式，這種顯性遺傳現(xiàn)象為鑲嵌顯性

4.Lethalalleles(致死等位基因):

Someallelesaffecttheviabilityofindividualsthatcarrythem.Therearelethaldominantandrecessivegenes.Inmostcases,thehomozygousrecessivedoesnotsurvivebuttheheterozygotesmayhavenormallife-spanfortherecessivegenecarrier.Individualswithlethaldominantgenediebeforegrown-upwithoutanyprogeny.

(p93)

黃鼠X黃鼠AaAa1黑鼠:2黃鼠:1胚胎死亡AAAaaa5.

Multiplealleles(復(fù)等位基因):

在群體中，同源染色體同一基因座上存在兩個(gè)以上的決定同一性狀的基因。AwellknownexampleofmultipleallelesisthehumanABObloodgroupsystem.IA,

IB,i復(fù)等位基因決定紅細(xì)胞表面抗原的特異性

O----iiPhenotypeA----IAIAIAiB----IBIBIBi可用于親子間的鑒定

AB---IAIB

3.5.2Interactionbetweennon-alleles非等位基因間的相互作用:Complementaryeffect(互補(bǔ)型)：e.g.用白花品種的豌豆(CCpp)與另一白花品種的豌豆(ccPP)雜交白花(CCpp)×白花(ccPP)紫花(PpCc)自交紫花(C_P_)白花(C_pp)白花(ccP_)白花(ccpp)9/163/16+3/16+1/16C花青素前體P花青素紫色

1-3疊加效應(yīng)；4-6上位效應(yīng)·

兩顯性基因同時(shí)存在，共同決定某一新性狀·缺少其中任何一種顯性基因，不表現(xiàn)新性狀·

F2表型比9:（3：3：1）=9：72.Additiveeffect(累加型):e.g.用兩個(gè)不同品種的圓形南瓜進(jìn)行雜交

圓形(AAbb)×圓形(aaBB)

扁形(AaBb)自交

扁形(A_B_)圓形(A_bb+aaB_)長(zhǎng)形(aabb)9/163/16+3/161/16·兩顯性基因單獨(dú)存在，表現(xiàn)相似性狀·兩顯性基因共同存在，作用累加表現(xiàn)另一性狀·無顯性基因時(shí)表現(xiàn)另一性狀·F2表型比9：（3：3）：1=9:6:13.Duplicateeffect(重疊型):

e.g.三角形蒴果的薺菜與卵形蒴果的薺菜雜交三角形(T1T1T2T2)×卵形(t1t1t2t2)三角形(T1t1T2t2)自交三角形(T1_T2_)三角形(T1_t2t2)三角形(t1t1T2_)卵形(t1t1t2t2)9/16+3/16+3/161/16·兩種或兩種以上顯性基因互作，產(chǎn)生相同表型，其中任何一種顯性基因存在，則性狀表現(xiàn)一致·無顯性基因則表現(xiàn)另一性狀·F2表型比（9：3：3）：1=15:14.Dominantepistasis(顯性上位)·顯性白皮基因(W)對(duì)顯性黃皮基因(Y)具上位性作用·W上位基因存在，阻礙Y基因作用，表型白色·缺少W基因，Y基因表現(xiàn)黃色·W、Y均都不存在，yy綠色表型顯現(xiàn)·F2表型（9：3）：3：1=12:3:15.Recessiveepistasis

(隱性上位):黑·

隱性純合cc阻止色素形成表現(xiàn)白化·無cc則R、r基因控制的黑色、淡黃色性狀分別表現(xiàn)·F2表型比9：3：（3：1）=9:3:4.Epistasis(上位效應(yīng)):

Epistasisreferstosituationswheretheexpectedratioofphenotypeisnotobservedduetosomeformofphysiologicalinteractionbetweenthegenesinvolved.Thisisusuallyseenasadistortionofthe9:3:3:1ratio