Chapter 4 Linkage Inheritance and Mapping Gene on Chromosome 第四章 连锁遗传及染色体作图

1. Chapter 4 Linkage Inheritance and Mapping Gene on Chromosome 第四章 连锁遗传及染色体作图 4.1 Law of Linkage (连锁规律) 4.2 Frequency of cross-overs (交换值) 4.3 Mapping gene on chromosomes (基因定位) 4.4 Interference（干涉） 4.5 Linkage analysis in fungi (真菌的连锁分析)

2. 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 they 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。

3. 4.1.1 Complete linkage (完全连锁): 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1:1 b Vg b Vg B vg B vg B vg b Vg b vg b vg B vg b Vg b vg B vg b vg b Vg b vg

4. Complete 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。

5. 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% b Vg b Vg B vg B vg B vg b Vg b vg b vg B vg B Vg b vg b Vg b vg b vg b vg b vg b Vg B vg b vg B Vg b vg

7. Incomplete linkage 同源染色体上的基因既有连锁又有交换的遗传现象 —连锁互换律 presented in 1910 by Morgan

8. 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 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

9. 4.3 Mapping gene on chromosome 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 units (图距) between them. 1% recombination is equivalent to 1 map unit. (1%的重组率等于1个图距)

10. Two-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wx Crosses are set out below:

11. 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 cM 重组

12. 2. 糯性、饱满(wxwxShSh) ×非糯性、凹陷(WxWxshsh) F1 WxwxShsh × 糯性、凹陷 (wxwxshsh) W、Sh交换值20%, 20 cM

13. |-------------23.6-----------------------| |----------------20----------|----3.6----|wx sh c |-------------20------------| |-----3.6----|----16.4------|sh c wx

14. 3. 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?

15. Three-factor crosses (三点测验法): These are more accurate than two-factor crosses, in that they identify and utilize many of the double cross-overs that are missed by two-factor cross.

16. 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)

17. 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 + sh wx 107 cross-oversⅠ 有色、饱满、糯性 + + wx 672 single 无色、皱缩、非糯 c sh + 662 cross-oversⅡ 无色、饱满、糯性 c + wx 39 double 有色、皱缩、非糯 + sh + 19 cross-overs Total no. of F2 6033 no. 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 = 1334

18. Frequency 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

19. Frequency of double cross-overs (双交换值 ) =(39+19) / 6033 ×100% = 0.96% Frequency of single cross-overs I (单交换Ⅰ交换值) = (98+107) / 6033 × 100% + 0.96% = 3.4% + 0.96% = 4.36% Frequency of single cross-overs II (单交换Ⅱ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 I-----4.36-----I----------------23.07----------------I C Sh Wx

20. 4.4 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Ⅰ×单交换值Ⅱ =4.36% × 23.7%=1% The presense of one 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

21. Coefficient of coincidence （并发系数 S）： The extent of interference is calculated as the coefficient 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 = 0~1 S ，干涉 ； =1, single cross-overs independently, no interference; =0, complete interference, no double cross-overs. 1-S = 干扰值

22. 7 alleles Mendal researched situated on 7 individual chromosome?

23. I II III IV V VI VII A/a-0 Gp/gp - 21 F/f - 78 R/r - 60 Le/le -199 I/i - 204 V/v - 211

24. 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 groups

25. Application: 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%。 如何在F2代获得3-4株纯种矮竿抗病单株?

26. 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

27. 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. 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 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

28. Recombinant frequency between gene and centromere = ( no. of recombinant ascus / total no. of ascus ) × 100% × ½ 基因与着丝粒的重组率 = 交换型子囊数 × 100% × 1/2 总子囊数

29. Centromere mapping: 着丝粒为基因座, 分析染色体上基因的 连锁关系及分布 eg.1 甲硫氨酸（-）的链孢霉菌株(m)与野生型(+)菌株杂交，基因与着丝粒间距多远? 做图表示交换型子囊 产生过程? 子囊数 孢子 1+2 3+4 5+6 7+8 6 + m + m 5 m + + m 6 m + m + 7 + mm + 40 mm + + 36 + + m m 100

30. 交换型子囊 24%，一半重组，基因与着丝点间距12cM m m + + 子囊数 40/36 m + m + m + + m + m + m + m m + 子囊数 6 5 6 7