孟德尔式遗传分析及其扩展课件

Chapter3Mendel’sGeneticAnalysisandExtension

第三章孟德尔式遗传分析及其扩展3.1Mendel’slaws孟德尔遗传规律3.1.1Lawofsegregation分离律3.1.2Lawofindependentassortment自由组合律3.2多对相对性状杂交的遗传分析3.3二项式分布公式3.4Testsforgoodnessoffit:chi-squaretests

适合度检验-卡方检验3.5Interactionamonggenes基因互作3.5.1Interactionbetweenalleles等位基因间互作3.5.2Interactionbetweennon-alleles非等位基因间的相互作用3.6Genotype,phenotypeandenvironmental基因型、表型与环境Terms:

C1,C2InheritedtraitPhenotypeGenotypeDominantRecessivePure-breedingCrossTestcrossBackcrossSelf-crossReversecrossHybridHomozygousHeterozygousProgeny

3.1Mendel’slaws

Reasonsofchoosingpeaformaterial:stabletrue-breedingeasydistinguishablecharacteristicsselfandclosepollinationeasycountingLawofsegregation(分离规律)Lawofindependentassortment(自由组合规律）3.1.1LawofsegregationMendelstudiedinheritanceofsevenphenotypesinpea,weconcentrateononlyoneofthese-Petalcolor红花×白花F1红花F2929株(705红/224白，接近3∶1)白花×红花与正交结果完全一致why

705224F1和F2性状表现不受亲本组合方式影响ValidationandDetection(假设的验证和杂合体的检测)Onesimpleextensionofthe3:1phenotyperatioproducedwhenanF1individualiscrossedtothehomozygousrecessiveparent.F1canproducegameteswithdominantandrecessivealleles,andsotheprogenyofthecrosshavethedominantandrecessivephenotypeinequalnumbers,a1:1phenotyperatio.Thistypeofcrossistermedatestcross,andisusefulinanysituationwhereitisnecessarytodetermineifanindividualisheterozygous.Ccc

8581Essenceoflawofsegregation:

决定某一性状的等位基因在配子形成过程中彼此分离互不干扰，使得配子中仅含成对基因中的一个，产生数目相等的两种类型配子。Singleautosomaldominantgenedisorders:常染色体单基因显性遗传病的传递：

家族性多发性结肠息肉(polypus)、先天性白内障(cataract)、短肢症、Huntington’sdisease等1460多种性状。特点：双亲之一杂合态患者子女1/2得病，机率相等代代相传SymbolfordrawinghumanpedigreeMalemalesufferercoupletwinsfromseparatezygotesFemalefemalesufferercloserelativecoupletwinsfromsamezygotesIIInoprogeny12firstsuffererdecedentcarrierunknownsexsex-linkedrecessivecarrier3.1.2Lawofindependentassortment3:1isthebasicMendelianratio,everythingthatfollowsdependsonitDihybridcross(双因子杂交):

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

dihybridratio(双因子杂种比例)ThepredictedratiosofphenotypesandgenotypescanbedeterminedbyusingPunnettsquare(庞纳特方格).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.测交产生四种等比例配子，产生四种等比例表型及基因型后代。p77Table4-4Essenceoflawofindependentassortment:

位于非同源染色体上的等位基因，各自分离互不干扰，并且自由组合到不同的配子中去。事实上杂交后代遗传比例并非与理论值完全吻合,为什么呢?Observedandestimatedvaluearenotmatchedcompletely?

Probabilities(概率):

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

Thesumsrule(addition)isappliedtocombineprobabilitiesofeventswhicharemutuallyexclusive.Ageneticexamplewouldbeacrosswhereweexpectedtoget1/4red:2/4pink:1/4whiteflowers.Theprobabilityofanyparticularflowerbeingredorpinkis1/4+2/4=3/4用于互斥事件总的概率的计算。一个遗传学上的例子是：我们预测某次杂交后代的花色之比是1/4红:2/4粉红:1/4白，则某花为红或粉红的概率是1/4+2/4=3/4)Theproductsrule(乘法法则):Theproductsruleisappliedtoindependenteventsandeventshappeninginaspecificorder.用于独立的且以一定顺序发生的事件。Ageneticexampleisamarriagebetweentwopeopleheterozygousforarecessivegeneticdisease,sayphenylketonuria(PKU).Iftheyhavethreechildren,whatistheprobability(chance)ofallthreebeingaffected?Theprobabilityofachildbeinghomozygousfortherecessivealleleis¼,therefore:

P=¼×¼×¼=(1/4)3=1/64

3.3二项式分布公式：n为子代数r为某一基因型的子代p为一基因型的概率q为另一基因型的概率n-r为另一基因型的子代数目n!Prqn-rr!(n-r)!用以计算杂交后代某一特定基因型或表型出现的概率（适合小样本的一对质量性状）

3.4Testsforgoodnessoffit:chi-squaretests(适合度检验：X2卡方检验)Goodnessoffittestcalculatetheprobabilityofobserveddatabeingobtainedbychanceifthatdataissampledfromahypothesizedpopulationordistribution.Theusualtestistocalculatechi-square.适合度检验可计算从一假设的分布群体或区域中随机观察到某数据的概率。常用检测方法-卡平方X2检验法：以指数值表示实得数与理论数的差异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.从X2表中可查到随机得到某一结果的概率。X2表中不同的横行代表不同的自由度，找到正确的自由度，再找到大于和小于计算值的数值，最后从表顶行读出对应的概率

Levelofsignificance(显著水平)

Thelevelofsignificanceistheprobabilitybelowwhichweassumethedataobserveddoesnotfitexpectations.Thisisconventionally0.05.Whenthereisaprobabilityoflessthan0.05,thentorejectthenullhypothesisasprobablybeingfalseandsaythedatadoesnotfit.显著水平就是一个概率，当低于此概率时，我们便认为观察值不符合预期值。显著性水平在习惯上取0.05。如果某数据的概率低于0.05则我们认为数据与预期值不符而放弃（即差异显著）。

P>0.05,试验值与理论值相符,差异不显著;0.01<=P<=0.05,试验值与理论值不符,差异显著;P<=0.01,试验值与理论值极不相符,差异极显著.查表得概率(P)介于0.5~0.10之间,说明这种偏差50%以上由机会造成.试验值与理论值相符,差异不显著.

3.5Interactionamonggenes基因互作3.5.1

Interactionbetweenalleles

等位基因间互作：

1.Incompletedominance(不完全显性)：thephenotypeofF1isbetweentwoparents.杂交后代表型介于双亲中间的类型。e.g.红花紫茉莉(CC)×白花紫茉莉(cc)C对c不完全显性

Cc粉红紫茉莉自交

1CC:2Cc:1cc

基因型比=表现型比=1：2：12.Co-dominance(共显性):Theheterozygotedisplaysbothalleles.一对等位基因在杂合体中都表现出性状的现象e.g.InhumanstheMNbloodgroupiscontrolledbyasinglegene.onlytwoallelesexist,LMandLN.人类中MN血型由单基因控制，只有LMandLN两个等位基因存在。LMLM--M型LMLN--MN型LNLN--N型LM、LN基因分别控制红细胞表面M抗原、N抗原的产生，在杂合体中红细胞表面既有M抗原又有N抗原，属共显性现象。瓢虫鞘翅色泽AAxEE前缘黑后缘黑AE前后缘均黑1AA2AE1EE前缘黑前后缘均黑后缘黑3.Mosaicdominance(镶嵌显性)：双亲性状在后代个体的某一部位上都得到了表现，形成镶嵌图式，这种显性遗传现象为镶嵌显性

4.Lethalalleles(致死等位基因):

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

(p93)

黄鼠X黄鼠AaAa1黑鼠:2黄鼠:1胚胎死亡AAAaaa5.

Multiplealleles(复等位基因):

在群体中，同源染色体同一基因座上存在两个以上的决定同一性状的基因。AwellknownexampleofmultipleallelesisthehumanABObloodgroupsystem.IA,

IB,i复等位基因决定红细胞表面抗原的特异性

O----iiPhenotypeA----IAIAIAiB----IBIBIBi可用于亲子间的鉴定

AB---IAIB

3.5.2Interactionbetweennon-alleles非等位基因间的相互作用:Complementaryeffect(互补型)：e.g.用白花品种的豌豆(CCpp)与另一白花品种的豌豆(ccPP)杂交白花(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花青素前体P花青素紫色

1-3叠加效应；4-6上位效应·

两显性基因同时存在，共同决定某一新性状·缺少其中任何一种显性基因，不表现新性状·

F2表型比9:（3：3：1）=9：72.Additiveeffect(累加型):e.g.用两个不同品种的圆形南瓜进行杂交

圆形(AAbb)×圆形(aaBB)

扁形(AaBb)自交

扁形(A_B_)圆形(A_bb+aaB_)长形(aabb)9/163/16+3/161/16·两显性基因单独存在，表现相似性状·两显性基因共同存在，作用累加表现另一性状·无显性基因时表现另一性状·F2表型比9：（3：3）：1=9:6:13.Duplicateeffect(重叠型):

e.g.三角形蒴果的荠菜与卵形蒴果的荠菜杂交三角形(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+3/161/16·两种或两种以上显性基因互作，产生相同表型，其中任何一种显性基因存在，则性状表现一致·无显性基因则表现另一性状·F2表型比（9：3：3）：1=15:14.Dominantepistasis(显性上位)·显性白皮基因(W)对显性黄皮基因(Y)具上位性作用·W上位基因存在，阻碍Y基因作用，表型白色·缺少W基因，Y基因表现黄色·W、Y均都不存在，yy绿色表型显现·F2表型（9：3）：3：1=12:3:15.Recessiveepistasis

(隐性上位):黑·

隐性纯合cc阻止色素形成表现白化·无cc则R、r基因控制的黑色、淡黄色性状分别表现·F2表型比9：3：（3：1）=9:3:4.Epistasis(上位效应):

Epistasisreferstosituationswheretheexpectedratioofphenotypeisnotobservedduetosomeformofphysiologicalinteractionbetweenthegenesinvolved.Thisisusuallyseenasadistortionofthe9:3:3:1ratio