連鎖遺傳及染色體作圖

1、4.1 Law of Linkage (連鎖規(guī)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.連鎖 - 兩個或兩個以上等位基因一起從一代傳遞到下一代的現(xiàn)象。 e.g. 雄性果蠅的完全連鎖遺傳(測交后代表型與親本完全一致,無新類型產生)：親本 灰身殘翅 (male) 黑身長翅 (female)子一代 灰身長翅 (male) 黑身殘翅 (female)子代配子 配子比1:1測交后代 灰身殘翅 黑身長翅 表型比1:1BvgBvgbVgbVgBvgbVgbvgbvgBvgbVgbvgBvgbvgbVgbvg4.1.1 Complete linkage (完全連鎖):Compl

3、ete linkage 同源染色體上的基因隨其染色體一起進入到同一配子中去的遺傳方式。4.1.2 雌果蠅的不完全連鎖遺傳 (incomplete linkage)：親本 灰身殘翅 (male) 黑身長翅 (female)子一代 灰身長翅(female) 黑身殘翅(male)子代配子 配子比兩兩相等測交后代 灰身殘翅 灰身長翅 黑身殘翅 黑身長翅親本型83% 41.5% 8.5% 8.5% 41.5% 交換型 17% BvgBvgbVgbVgBvgbVgbvgbvgBvgbVgbvgBvgbvgbVgbvgBVgbvgBVgbvgbvgbvgIncomplete linkage 同源染色體上的基

4、因既有連鎖又有交換的遺傳現(xiàn)象 連鎖互換律 presented in 1910 by Morgan 4.2 Frequency of cross-overs (交換值)Frequency of cross-overs =重組配子數(shù)(交換型配子數(shù)) / 總配子數(shù)(交換型+親本型)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.* 發(fā)生交換的性母細胞比例為交換值的?倍單交換(single cross-overs)：基因間分別發(fā)生單個交換雙交換(double cross-overs)：同源染色體上的等位基因間同時發(fā)生兩次單交換。圖距：If the recombination frequency is 14%, they have a map distance of 14 map un

6、its (圖距) between them. 1% recombination is equivalent to 1 map unit. (1%的重組率等于1個圖距)4.3 Mapping gene on chromosomeTwo-factor crosses (兩點測驗法) eg. Maize: 有色C / 無色c 飽滿Sh / 凹陷sh 非糯性Wx / 糯性wxCrosses are set out below:重組有色、飽滿(CCShSh) 無色、凹陷(ccshsh)F1 CcShsh 無色、凹陷(ccshsh)C、Sh交換值3.6%3.6 cM2. 糯性、飽滿(wxwxShSh) 非

7、糯性、凹陷(WxWxshsh) F1 WxwxShsh 糯性、凹陷 (wxwxshsh) W、Sh交換值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、無色(wxwxcc) F1 WxwxCc 糯性、無色(wxwxcc)W、C 交換值22%，22cM 兩值為什么不完全一致?Three-factor crosses (三點測驗法): 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、飽滿、非糯 (+ + + ) 無色、皺縮、糯性(cc shsh wxwx) F1 有色、飽滿、非糯 (+c +sh +wx) 無色、皺縮、糯性(cc shsh wxwx)Phenotypes Genotypes no. of F2 assembled types有色、飽滿、非糯 + + + 2238 parental無色、皺縮、糯性 c sh wx 2198 無色、飽滿、非糯 c + + 98 single有色、皺縮、糯性 +

9、sh wx 107 cross-overs有色、飽滿、糯性 + + wx 672 single無色、皺縮、非糯 c sh + 662 cross-overs無色、飽滿、糯性 c + wx 39 double有色、皺縮、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% 單交換值 = (單交換個體數(shù)+雙交換個體數(shù)）/ 總數(shù) 100% = 單交換值I + 雙交換值Frequency of double cross-overs (雙交換值 ) =(39+19) / 6033 100% = 0.96%Frequency of single cross-overs I (單交換交換值) = (98+107) / 6033 100%

11、 + 0.96% = 3.4% + 0.96% = 4.36%Frequency of single cross-overs II (單交換交換值) = (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）： 交換在交叉處發(fā)生，一個單交換的發(fā)生，會影響另一個單交換的發(fā)生，即干涉。雙交換理論值=單交換值單交換值 =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.雙交換實際值 雙交換理論值 時 表明兩個單交換間有干涉Coefficient of coincidence （并發(fā)系數(shù) 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. 并發(fā)系數(shù) S = 實際雙交換值 / 理論雙交換值 = 01 S ，干涉 ； =1, single cross-overs independently, no interference; =0, complete interference, no double cross-overs.1-S = 干擾值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基因連鎖群： 同一染色體上基因處同一連鎖群，同類生物有n對染色體就有n個連鎖群。e.g. Tomato 2n=24 12 linkage groups Drosophila 2n=8 4 linkage groupsApplication: 大麥 (barley) 高竿(B)/矮竿(b)，抗條銹病(T)/不抗條銹病(t)BT/BT bt/bt 兩對基因連鎖遺傳，交換值為12%。如何

15、在F2代獲得3-4株純種矮竿抗病單株? 4.5 Linkage analysis in fungi (真菌的連鎖分析): Ascomycete (粗糙鏈孢霉): Monoploid and sexual reproduction - Good material for genetic analysis Tetrad analysis (四分體分析): 減數(shù)分裂形成的四個線性排列的 子囊孢子 (ordered tetrad) 的分析 p112, p144 決定孢子顏色的基因和著絲粒間沒有發(fā)生交換，被稱為第一種分裂分離 (4:4的線性比) p112決定孢子顏色的基因和著絲粒之間發(fā)生了交換，兩種顏色

16、 表型在第二次減數(shù)分裂時被分開，出現(xiàn)其他分離類型，稱為第二種分裂分離 (2:2:2:2或2:4:2線性比) 子囊中僅一半的孢子發(fā)生重組. 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% 基因與著絲粒的重組率 = 交換型子囊數(shù) 100% 1/2 總子囊數(shù)eg