连锁遗传及染色体作图

1、4.1 Law of Linkage (连锁规律)Linkage is the tendency for alleles of two or more genes to pass from one generation to the next in the same combination. Only genes situated on the same chromosome can show linkage. That means the closer together any two genes lie on the same chromosome the more linkage the

2、y are to show linkage and the stronger that linkage will be.连锁 - 两个或两个以上等位基因一起从一代传递到下一代的现象。 e.g. 雄性果蝇的完全连锁遗传(测交后代表型与亲本完全一致,无新类型产生)：亲本 灰身残翅 (male) 黑身长翅 (female)子一代 灰身长翅 (male) 黑身残翅 (female)子代配子 配子比1:1测交后代 灰身残翅 黑身长翅 表型比1:1BvgBvgbVgbVgBvgbVgbvgbvgBvgbVgbvgBvgbvgbVgbvg4.1.1 Complete linkage (完全连锁):Compl

3、ete linkage 同源染色体上的基因随其染色体一起进入到同一配子中去的遗传方式。4.1.2 雌果蝇的不完全连锁遗传 (incomplete linkage)：亲本 灰身残翅 (male) 黑身长翅 (female)子一代 灰身长翅(female) 黑身残翅(male)子代配子 配子比两两相等测交后代 灰身残翅 灰身长翅 黑身残翅 黑身长翅亲本型83% 41.5% 8.5% 8.5% 41.5% 交换型 17% BvgBvgbVgbVgBvgbVgbvgbvgBvgbVgbvgBvgbvgbVgbvgBVgbvgBVgbvgbvgbvgIncomplete linkage 同源染色体上的基

4、因既有连锁又有交换的遗传现象 连锁互换律 presented in 1910 by Morgan 4.2 Frequency of cross-overs (交换值)Frequency of cross-overs =重组配子数(交换型配子数) / 总配子数(交换型+亲本型)100% = (No. of recombinant / Total no. of progeny) 100% = 50% = 0 50% = 0 The closer the two genes are together the less likely it is that a cross-over will take

5、place between them. The frequency of recombinants give an indirect measure of how close the two genes lie to each other.* 发生交换的性母细胞比例为交换值的?倍单交换(single cross-overs)：基因间分别发生单个交换双交换(double cross-overs)：同源染色体上的等位基因间同时发生两次单交换。图距：If the recombination frequency is 14%, they have a map distance of 14 map un

6、its (图距) between them. 1% recombination is equivalent to 1 map unit. (1%的重组率等于1个图距)4.3 Mapping gene on chromosomeTwo-factor crosses (两点测验法) eg. Maize: 有色C / 无色c 饱满Sh / 凹陷sh 非糯性Wx / 糯性wxCrosses are set out below:重组有色、饱满(CCShSh) 无色、凹陷(ccshsh)F1 CcShsh 无色、凹陷(ccshsh)C、Sh交换值3.6%3.6 cM2. 糯性、饱满(wxwxShSh) 非

7、糯性、凹陷(WxWxshsh) F1 WxwxShsh 糯性、凹陷 (wxwxshsh) W、Sh交换值20%, 20 cM |-23.6-|-20-|-3.6-|wx sh c |-20-|-3.6-|-16.4-|sh c wx3. 非糯性、有色(WxWxCC) 糯性、无色(wxwxcc) F1 WxwxCc 糯性、无色(wxwxcc)W、C 交换值22%，22cM 两值为什么不完全一致?Three-factor crosses (三点测验法): These are more accurate than two-factor crosses, in that they identify a

8、nd utilize many of the double cross-overs that are missed by two-factor cross. P 有色、饱满、非糯 (+ + + ) 无色、皱缩、糯性(cc shsh wxwx) F1 有色、饱满、非糯 (+c +sh +wx) 无色、皱缩、糯性(cc shsh wxwx)Phenotypes Genotypes no. of F2 assembled types有色、饱满、非糯 + + + 2238 parental无色、皱缩、糯性 c sh wx 2198 无色、饱满、非糯 c + + 98 single有色、皱缩、糯性 +

9、sh wx 107 cross-overs有色、饱满、糯性 + + wx 672 single无色、皱缩、非糯 c sh + 662 cross-overs无色、饱满、糯性 c + wx 39 double有色、皱缩、非糯 + sh + 19 cross-oversTotal no. of F2 6033no. of F2 from double cross-overs： 39+19 = 58; no. of F2 from single cross-overs I: 98+107 = 205; no. of F2 from single cross-overs II: 672+662 = 1

10、334Frequency of single cross-overs = (no. of single cross-overs + no. of double cross-overs) / total no. of progeny 100% 单交换值 = (单交换个体数+双交换个体数）/ 总数 100% = 单交换值I + 双交换值Frequency of double cross-overs (双交换值 ) =(39+19) / 6033 100% = 0.96%Frequency of single cross-overs I (单交换交换值) = (98+107) / 6033 100%

11、 + 0.96% = 3.4% + 0.96% = 4.36%Frequency of single cross-overs II (单交换交换值) = (672+662) / 6033 100% + 0.96% = 22.11% + 0.96% = 23.07%Map unit of C、Sh: 4.36 cM，Sh、Wx: 23.07 cM I-27.43-I C Sh Wx4.4 Interference（干涉）： 交换在交叉处发生，一个单交换的发生，会影响另一个单交换的发生，即干涉。双交换理论值=单交换值单交换值 =4.36% 23.7%=1% The presense of one

12、chiasmata in a particular chromosome region can reduce the frequency of others forming close to it. This can result in a reduction in the number of double cross-overs observed.双交换实际值 双交换理论值 时 表明两个单交换间有干涉Coefficient of coincidence （并发系数 S）： The extent of interference is calculated as the coefficient

13、of coincidence, the observed number of double cross-overs divided by the expected number of double cross-overs. 并发系数 S = 实际双交换值 / 理论双交换值 = 01 S ，干涉 ； =1, single cross-overs independently, no interference; =0, complete interference, no double cross-overs.1-S = 干扰值7 alleles Mendal researched situated

14、on 7 individual chromosome? I II III IV V VI VIIA/a-0I/i - 204R/r - 60Gp/gp - 21V/v - 211Le/le -199 F/f - 78基因连锁群： 同一染色体上基因处同一连锁群，同类生物有n对染色体就有n个连锁群。e.g. Tomato 2n=24 12 linkage groups Drosophila 2n=8 4 linkage groupsApplication: 大麦 (barley) 高竿(B)/矮竿(b)，抗条锈病(T)/不抗条锈病(t)BT/BT bt/bt 两对基因连锁遗传，交换值为12%。如何

15、在F2代获得3-4株纯种矮竿抗病单株? 4.5 Linkage analysis in fungi (真菌的连锁分析): Ascomycete (粗糙链孢霉): Monoploid and sexual reproduction - Good material for genetic analysis Tetrad analysis (四分体分析): 减数分裂形成的四个线性排列的 子囊孢子 (ordered tetrad) 的分析 p112, p144 决定孢子颜色的基因和着丝粒间没有发生交换，被称为第一种分裂分离 (4:4的线性比) p112决定孢子颜色的基因和着丝粒之间发生了交换，两种颜色

16、 表型在第二次减数分裂时被分开，出现其他分离类型，称为第二种分裂分离 (2:2:2:2或2:4:2线性比) 子囊中仅一半的孢子发生重组. p113 In ascomycete fungi, first and second division segregation patterns can be used to determine distance between a gene and the centromere. A similar approach can be used to estimate distances between genes. Recombinant frequency between gene and centromere = ( no. of recombinant ascus / total no. of ascus ) 100% 基因与着丝粒的重组率 = 交换型子囊数 100% 1/2 总子囊数eg