10QuantitativeGenetics

1、xunchao xiang southwest university of science and technology xunchao xiang southwest university of science and technology 質(zhì)量性狀質(zhì)量性狀數(shù)量性狀數(shù)量性狀xunchao xiang southwest university of science and technology n質(zhì)量性狀質(zhì)量性狀(qualitative character)：表現(xiàn)不連續(xù)(discontinuous)變異的性狀。n如：豌豆花色、子葉顏色、籽粒飽滿程度等等n數(shù)量性狀數(shù)量性狀(quantitativ

2、e character) ：表現(xiàn)連續(xù)(continuous)變異的性狀。n人的身高、植株生育期、果實(shí)大小、種子產(chǎn)量等n數(shù)量性狀在自然群體或雜種后代群體內(nèi)，很難對(duì)不同個(gè)體的性狀進(jìn)行明確的分組，求出不同級(jí)之間的比例，所以不能采用質(zhì)量性狀的分析方法，通過(guò)對(duì)表現(xiàn)型變異的分析推斷群體的遺傳變異。借助于數(shù)理統(tǒng)計(jì)分析方法數(shù)理統(tǒng)計(jì)分析方法，可以有效地分析數(shù)量性狀的遺傳規(guī)律。 xunchao xiang southwest university of science and technology the height exhibited a continuous gradation of phenotypes.

3、thus, quantitative traits are difficulty to study by mendel mode.xunchao xiang southwest university of science and technology in each case, a bell-shaped distribution was observed, with most individuals similar in length to the selected f2 parents, but with considerable variation around this value.t

4、he experiments demonstrated that although the variation in corolla length seemed continuous, experimental crosses resulted in the segregation of distinct phenotypic classes as observed in the three independent f3 categories.xunchao xiang southwest university of science and technology 數(shù)量性狀的特征性狀表現(xiàn)為連續(xù)變

5、異；性狀表現(xiàn)為連續(xù)變異；易受環(huán)境條件的影響，并表現(xiàn)較復(fù)雜的互作易受環(huán)境條件的影響，并表現(xiàn)較復(fù)雜的互作關(guān)系。關(guān)系。伊斯特(east, e. m. 1910)對(duì)玉米穗長(zhǎng)遺傳的研究xunchao xiang southwest university of science and technology 多基因假說(shuō)(multiple factor hypothesis)普通小麥籽粒色遺傳尼爾遜埃爾(nilson-ehle, h. 1909)小麥種皮顏色：紅色(r)、白色(r)一對(duì)基因差異在一對(duì)基因f2的紅粒中：1/3與紅粒親本一致、2/3與f1一致，表現(xiàn)為不完全顯性xunchao xiang south

6、west university of science and technology 兩對(duì)基因差異紅色基因表現(xiàn)為重疊作用，但是r基因同時(shí)表現(xiàn)累加效應(yīng)f2紅粒中表現(xiàn)為一系列顏色梯度，每增加一個(gè)r基因籽粒顏色更深一些xunchao xiang southwest university of science and technology 三對(duì)基因差異xunchao xiang southwest university of science and technology 4 additive allelesnonadditive allele2 additive allelesredwhite=151x

7、unchao xiang southwest university of science and technology when 2 gene pairs are involved, only 5 f2 phenotypic categories, in a 14641 ratio, are expected.as greater numbers of gene pairs become involved, the number of classes increases and results in more complex ratios.xunchao xiang southwest uni

8、versity of science and technology (r/2+r/2)2當(dāng)性狀由n對(duì)獨(dú)立基因決定時(shí)，則f2的表現(xiàn)型頻率為： (r/2+r/2)2n當(dāng)n = 2時(shí) (r/2+r/2)22 =1/16+4/16+6/16+4/16+1/16 4r 3r 2r 1r 0r當(dāng)n = 3時(shí) (r/2+r/2)23 =1/64+6/64+15/64+20/64+15/64+6/64+1/64 6r 5r 4r 3r 2r 1r 0r 由于f1能夠產(chǎn)生具有等數(shù)r和r的雌配子和雄配子，所以當(dāng)某性狀由一對(duì)基因決定時(shí)f1可以產(chǎn)生同等數(shù)目的雄配子( r+ r)和雌配子( r+ r)，雌雄配子受精后，

9、得f2的表現(xiàn)型頻率為：xunchao xiang southwest university of science and technology 多基因假說(shuō)多基因假說(shuō)n數(shù)量性狀受許多彼此獨(dú)立的基因共同控制，每個(gè)數(shù)量性狀受許多彼此獨(dú)立的基因共同控制，每個(gè)基因?qū)π誀畋憩F(xiàn)的效果較微，但各對(duì)基因遺傳方基因?qū)π誀畋憩F(xiàn)的效果較微，但各對(duì)基因遺傳方式仍然服從孟德?tīng)栠z傳規(guī)律。式仍然服從孟德?tīng)栠z傳規(guī)律。xunchao xiang southwest university of science and technology xunchao xiang southwest university of science

10、and technology xunchao xiang southwest university of science and technology xunchao xiang southwest university of science and technology 微效多基因與主效基因微效多基因(polygenes)或微效基因(minor gene)：控制數(shù)量性狀遺傳的一系列效應(yīng)微小的基因；由于效應(yīng)微小，難以根據(jù)表型將微效基因間區(qū)別開(kāi)來(lái)；主效基因/主基因(major gene)：控制質(zhì)量性狀遺傳的一對(duì)或少數(shù)幾對(duì)效應(yīng)明顯的基因；可以根據(jù)表型區(qū)分類(lèi)別，并進(jìn)行基因型推斷xunchao xia

11、ng southwest university of science and technology 近年來(lái)，借助于分子標(biāo)記和數(shù)量性狀基因位點(diǎn)(quantitative trait loci，簡(jiǎn)稱(chēng)qtl)作圖技術(shù)，已經(jīng)可以在分子標(biāo)記連鎖圖上標(biāo)出單個(gè)基因位點(diǎn)的位置、并確定其基因效應(yīng)。數(shù)量性狀可以由少數(shù)效應(yīng)較大的主效基因控制，也可由數(shù)目較多、效應(yīng)較小的微效多基因或微效基因(minor gene)所控制。各個(gè)微效基因的遺傳效應(yīng)值不盡相等，效應(yīng)的類(lèi)型包括等位基因的加性效應(yīng)、顯性效應(yīng)，以及非等位基因間的上位性效應(yīng)，還包括這些基因主效應(yīng)與環(huán)境的互作效應(yīng)。也有一些性狀雖然主要由少數(shù)主效基因控制，但另外還存在一

12、些效應(yīng)微小的修飾基因(modifying gene)，這些基因的作用是增強(qiáng)或削弱其它主基因?qū)Ρ憩F(xiàn)型的作用。 多基因假說(shuō)的發(fā)展xunchao xiang southwest university of science and technology 14nratio of f2 individuals expressing either extreme phenotype=1/16, n=2xunchao xiang southwest university of science and technology 超親遺傳(transgressive inheritance)超親遺傳現(xiàn)象：植物雜交時(shí)，

13、雜種后代的性狀表現(xiàn)可能超出雙親表型的范圍。例如：小麥籽粒顏色遺傳；又如：水稻熟期遺傳及其解釋。xunchao xiang southwest university of science and technology xunchao xiang southwest university of science and technology xunchao xiang southwest university of science and technology xunchao xiang southwest university of science and technology x=xinsum

14、of individual valuesnumber of individual valuesd frequencyd traitxxunchao xiang southwest university of science and technology although the mean provides a descriptive summary of the sample, it is of itself of limited value.two normal frequency distribution with the same mean but different amounts o

15、f variation.xunchao xiang southwest university of science and technology s2=(xi-x)2n-1=x2-nx2n-1xunchao xiang southwest university of science and technology xd frequencyd trait68.3%-1+1xunchao xiang southwest university of science and technology sx=sns standard deviationn sample sizexunchao xiang so

16、uthwest university of science and technology xunchao xiang southwest university of science and technology genetic factorsenvironmental influenceheritability is a measure of how much quantitative genes influence phenotype.xunchao xiang southwest university of science and technology vpxunchao xiang so

17、uthwest university of science and technology =vavpxunchao xiang southwest university of science and technology n根據(jù)各世代性狀觀察值可以直接估計(jì)各世代性狀表型方差(總方差)vp，但是不能直接估計(jì)遺傳方差vg；n在不分離世代(p1, p2和f1)中，由于個(gè)體間基因型一致，因而遺傳方差為0，即：nvg = 0 vp = ve vp1 = vp2 = vf1 = ven在分離世代(如f2)中，個(gè)體間基因型不同：nvp = vg + ve vf2 = vg + vexunchao xiang

18、 southwest university of science and technology n綜上所述：n可以用三個(gè)不分離世代的表型方差(vp1, vp2 , vf1)來(lái)估計(jì)ven ve = (vp1 + vp2) / 2n ve = vf1n ve = (vp1 + vp2 + vf1) / 3n ve = (vp1 +2 vf1 + vp2) / 4n此時(shí)遺傳方差 vg =vp - ven用分離世代方差(vf2 )來(lái)估計(jì)性狀的總方差。xunchao xiang southwest university of science and technology n三個(gè)不同環(huán)境方差估計(jì)方法的應(yīng)用

19、場(chǎng)合：n對(duì)于動(dòng)物和異花授粉植物，由于可能存在嚴(yán)重的自交衰退現(xiàn)象，嚴(yán)重影響兩純合親本(p1, p2)的性狀表現(xiàn)，所以通常只用f1的表型方差估計(jì)環(huán)境方差；n而對(duì)于自花授粉植物，也可以用純合親本、純合親本與雜種f1的表型共同估計(jì)環(huán)境方差。n這也體現(xiàn)了生物交配方式對(duì)數(shù)量性狀遺傳的影響。xunchao xiang southwest university of science and technology 基因效應(yīng)加性-顯性遺傳模型在一對(duì)基因(c, c)差異的兩個(gè)親本p1, p2的雜交組合中，f2有三種基因型個(gè)體：cc/cc/cc；設(shè)：+a表示中親值正向的基因型加性假定的理論值，即表示中親值正向的基因型

20、加性假定的理論值，即cc的加性效應(yīng)；的加性效應(yīng)；-a表示中親值負(fù)向的基因型加性假定的理論值，表示中親值負(fù)向的基因型加性假定的理論值，即即cc的加性效應(yīng)；的加性效應(yīng)；d表示由顯性作用的影響所引起的與中親值表示由顯性作用的影響所引起的與中親值的偏差，即的偏差，即cc的顯性偏離。的顯性偏離。則：cccccc0(中親值中親值)dc+ ac- acxunchao xiang southwest university of science and technology 對(duì)于c，c cc，ac； cc ， dc； cc，- acac是基因的加性效應(yīng)，即累加效應(yīng)，可在自交純合過(guò)程中保存并傳遞給子代，也稱(chēng)為可固

21、定的遺傳效應(yīng)； dc是基因的顯性效應(yīng)，不能在自交過(guò)程中保持 c，c不是習(xí)慣上的顯隱性含義，而是增、減效基不是習(xí)慣上的顯隱性含義，而是增、減效基因因無(wú)顯性時(shí)，dc=0；c基因?yàn)轱@性時(shí)， dc為正；c基因?yàn)轱@性時(shí)， dc為負(fù)；完全顯性時(shí)， dc = +ac或 - ac ；顯性度為 dc/ac加性 -顯性遺傳模型xunchao xiang southwest university of science and technology f2的遺傳效應(yīng)與遺傳方差的遺傳效應(yīng)與遺傳方差在f2群體中，不考慮環(huán)境影響時(shí)， f2群體的方差(遺傳方差)為：xunchao xiang southwest univers

22、ity of science and technology f2的遺傳效應(yīng)與遺傳方差的遺傳效應(yīng)與遺傳方差n無(wú)環(huán)境作用、無(wú)連鎖、無(wú)互作(vi=0)n若p1, p2間性狀受k對(duì)基因控制，k對(duì)基因間作用具有累加性，則有f2的方差分量為：22222212222124121)(41)(21dadddaaavkkfa2是各對(duì)基因加性效應(yīng)方差的總和 a=a2 ;d2是各對(duì)基因顯性效應(yīng)方差的總和 d=d2. vf2 = a/2 + d/4xunchao xiang southwest university of science and technology f2的遺傳效應(yīng)與遺傳方差的遺傳效應(yīng)與遺傳方差n在考慮

23、環(huán)境效應(yīng)方差時(shí)：n vf2 =a/2 + d/4 +e (e=ve)n可見(jiàn)：n要估計(jì)f2代加性方差，必需剔除vf2中的d和e；n三個(gè)不分離世代均只能估計(jì)環(huán)境效應(yīng)方差(ve)，而無(wú)法進(jìn)一步剔除vd；n因此僅有p1, p2, f1, f2四個(gè)世代還不夠，需要引入b1, b2兩個(gè)世代xunchao xiang southwest university of science and technology 兩個(gè)回交世代的方差分量n回交與回交世代：n回交(back cross)：雜種f1與兩個(gè)親本之一進(jìn)行雜交的交配方式。n回交世代：一次回交獲得的子代群體。通常將雜種f1與兩個(gè)親本回交得到的兩個(gè)群體可分別記

24、為b1, b2。n在后述分析中：n b1為f1與純合親本cc回交子代群體；n b2為f1與純合親本cc回交子代群體。n回交世代方差分量:xunchao xiang southwest university of science and technology 兩個(gè)回交世代的方差分量vb1 = (a2 +d2)/2 - ( a+d)/2 2 = (a2- 2ad+d2) /4vb2 = (a2 +d2)/2 - ( d - a)/2 2= (a2 + 2ad+d2) /4xunchao xiang southwest university of science and technology n則:

25、 vb1 +vb2 = (a2- 2ad+d2) /4+ (a2 + 2ad+d2) /4n = (a2+d2) /2n若 k對(duì)基因并考慮到環(huán)境：n vb1 +vb2 =a/2+d/2+2en因?yàn)椋?vf2 =a/2 + d/4 +en顯然： 2vf2 -（ vb1 +vb2 ）n = 2（ a/2 + d/4 +e ）-（ a/2+d/2+2e ）n =a/2n所以：h2=va / vp100%n = 2vf2 -（ vb1 +vb2 ） / vf2 100%xunchao xiang southwest university of science and technology ve = (

26、vp1+vp2)/2=10.68 h2=73.5% ve = vf1=5.24 h2=87.0%ve = (vp1+vp2+ vf1)/3=8.87 h2=78.0%ve = (vp1 +2 vf1 +vp2)/4=7.96 h2=80.3%h2= 2 40.35 -(17.35+34.29)/40.35 100%=72.0%xunchao xiang southwest university of science and technology n遺傳率可作為雜種后代性狀選擇的指標(biāo)，其高低反映：性狀傳遞給子代的能力、選擇結(jié)果的可靠性、育種選擇的效率；n通常認(rèn)為遺傳率：n50%高；=2050%中

27、； 20%低.xunchao xiang southwest university of science and technology n一般來(lái)說(shuō)，凡是狹義遺傳率較高的性狀，在雜種的早期世代進(jìn)行選擇，收效比較顯著；而狹義遺傳率較低的性狀，則要在雜種后期世代進(jìn)行選擇才能收到較好的效果。 n相關(guān)選擇：對(duì)遺傳率比較低的性狀可以利用與之相關(guān)程度高(由性狀間相關(guān)系數(shù)指示)且遺傳率較高的性狀進(jìn)行間接選擇。xunchao xiang southwest university of science and technology xunchao xiang southwest university of sci

28、ence and technology m2 - mm1- mdefining (m2 - m) as the response (r), and (m1- m) as the selection differential (s),rsxunchao xiang southwest university of science and technology heritabilityxunchao xiang southwest university of science and technology xunchao xiang southwest university of science and technology molecular m