Chaper 8 Genetic recombination

1. Chaper 8 Genetic recombination Types of genetic recombination Molecular mechanism of homologous recombination Bacteria homologous recombination Site- specific recombination Illegitimate recombination Transposition mechanism and genetic effect

2. 第八章 遗传重组 • 一、遗传重组的类型 • 二、同源重组的分子机制 • 三、细菌的同源重组 • 四、位点专一性重组 • 五、异常重组 • 六、转座机制与遗传效应

3. Section 1 Types of DNA recombination There is DNA where there is genetic recombination. The organism variation was from the gene mutation and genetic recombination 1. Generalized or homologous recombination It is dependent on the synapsis by a large range of homologous DNA sequences, whereby two chromosomes or DNAs equally exchange each other 2. Site-specific recombination It is dependent on the synapsis by a small range of homologous DNA sequences. without exchanging equally, it is also called integrative recombination 3. Illegitimate recombination Without homologous DNA sequences, a DNA fragment inserts another DNA fragment

4. 第一节 遗传重组的类型 • 只要有DNA就有重组，生物变异的来源是突变和重组 • 一、普遍性重组或同源重组 • 依赖大范围的DNA同源序列的联会，两条染色体或DNA互换对等部分 • 二、位点专一性重组 • 依赖小范围的DNA同源序列的联会，不交换对等部分，又称“整合式重组” • 三、异常重组 • 不依赖DNA同源序列，一段DNA插入另一段DNA中

5. Homologous recombination, generalized recombination, occurres in the cross over between non-sister chromatids in eukaryotic meiosis, transformation, transduction and conjugation in bacteria, and some genetic recombination in virus RecA protein: Responsible for DNA pairing and recombination The explanation for homologous recombination with Holliday model: Whether the neighboring genes exchange is dependent on the breakage mode of the Holliday structure. This indicated that the cross over is not consistent with the recombination while there existed a chiasma. However, the heterologous double strand DNA in non-sister chromatids, such as G-A and C-T, might lead to gene conversion Holliday model of homologous recombination

6. 同源重组的Holliday模型 • 同源重组又称普遍性重组，真核生物减数分裂中非姊妹染色单体之间，细菌的转化、转导、结合及某些病毒的重组 • RecA蛋白质：负责DNA配对及重组的蛋白质 • 同源重组的Holliday模型解释：Holliday结构因断裂方式不同而出现旁侧基因是否发生重组，并由此说明交叉结的出现（有交换），不能肯定有（所研究的基因）重组的发生。但由于非姊妹染色单体含有异源双链DNA区（G—C、A—T变成G—A、C—T ）为基因转变的发生创造了条件

7. Section 2 Molecular mechanism of homologous recombination第二节 同源重组的分子机制

8. Gene conversion Concept One gene changes to its allele due to abnormal interactive segregations in meiosis types Chromatid conversion Half-chromatid conversion 一、概念： 减数分裂出现非正常的交互式分离，一个基因变成了它的等位基因 二、类型： 染色单体转变 半染色单体转变

9. Section 3 Homologous recombination ofbacteria and bacteriophages第三节细菌及噬菌体的同源重组

10. Section 4Site- specific recombination第四节 位点专一性重组 The nucleotide acid sequence in site-specific recombination 位点专一性重组的核苷酸序列

11. λbacteriophage integration and excision λ噬菌体的整合和切除 BOB∕（细菌）+(POP ∕)（噬菌体）←→ BOP∕——POB ∕（原噬菌体）

12. Section 5 Illegitimate recombination- transponson • Barbara McClintock, a maize geneticist, made prominent contributions to the investigation on the heredity and variation in the kernel color of maize, the transponson heredity, and was crowned the Nobel Laureate in 1983 • The Ds-Ac system • A(anthocyan) to control color, C(color) to control red and purple • R(red) to control red, P(purple) to control purple • I(inhibitor) to inhibit C • R is dependent on A and C, and P is dependent on A, C, and R • The inhibitor I, referred to dissociator Ds, is a transposable element and able to insert into the color C. Another transposable element, the activator Ac, is to activate the inhibitor I to transfer into a gene such the color C or out, which results in a gene mutation or reverse mutation

13. 第五节 异常重组-转座因子的发现 Barbara McClintock (1902) ：玉米遗传学家，突出表现在玉米籽粒颜色变异的遗传基础（转座因子的遗传性质）；1983年获“诺贝尔奖” Ac-Ds系统：A（anthocyan）决定颜色，C决定红色和紫色，R（Red）以A C 为条件，P（Purple）以A C R为条件，I（抑制基因）抑制C基因 I基因（Ds）即现称的解离因子，是一个“可移动的遗传因子”，可插入到C基因，另一个可移动的因子是“Ac激活因子”，它激活Ds转座进入C基因或其他基因，也能使Ds从基因中转出，使突变基因回复

14. Illegitimate recombination– transposon types DNA transposition: A certain DNA fragment is transposon element 1. Replicative transposition: A transposon is replicated and the transposon sequence a copy of the original transposon 2. Nonreplicative transposition: a transposon dircetly transfers to the target site of a receptor 3. Conservative transposition: A transposon inserts into a target site with all bases conserved Retrotransposition: With RNA-mediated transposition the transposon RNA is copied into cDNA integrated to a host genome by a reverse transcriptase, which is classified as retrotransposon and retro virus

15. 异常重组--转座因子的分类 • 一、DNA转座：以DNA序列某些区段作转座成分 • 1、复制型转座：转座子被复制，转座的DNA序列是原转座子的一个拷贝 • 2、非复制型转座：转座因子直接从一个位点移到受体的一个靶位点 • 3、保守型转座：转座因子插入到靶位点时，其所有碱基均被保留 • 二、反转录转座子：转座过程由RNA介导，通过反转录酶将转座子RNA拷贝为cDNA的再整合到宿主基因组，分反转录转座子和反转录病毒两类

16. 1. Transposable elements in prokaryote The classification of transposon elements in prokaryote based on their molecular structure and genetic character Insertion sequence (IS): Transferred DNA sequences without host genes Transposon (Tn): Transposable elements with anti-drug genes or other genes confer the host a specific character Mutator phage: A phage in E. coli can insert any site of a host chromosome 2. Transposable elements in eukaryote Transposon yeast(Ty): It consist of a DNA sequence with a length of 5900bp with a δ direct repetitive sequence in two ends Transposon in Drosophila: Hybrid dysgenesis factor in Drosophila called the P factor, in P male(P factor) x M female(non-P factor), a transposition, as in bacteria 3. Transposon in maize: Ds-Ac system 4. Transposon in the human genome Long interspersed nuclear element(LINE), Alu family Transposable elements in the organism

17. 生物中的转座因子 • 一、原核生物中的转因座子 • 据分子结构和遗传性质可将原核生物中的转座因子分为： • 1、插入序列(IS)：不含宿主基因的可转位的DNA序列；2、转座子（Tn）带有抗药基因及其他基因，使宿主菌获得有关基因特性；3、转座噬菌体(Mu)：E Coli 的一种温和噬菌体，可插入到宿主染色体的任一位置 • 二、真核生物中的转座子 • 酵母菌的转座子：Ty系列，一般长约5900bp，两端含有两个称为δ的正向重复序列 • 果蝇的转座子：在果蝇中造成杂种劣育（P品系）的细胞中有导致杂种劣育的遗传因子，称为P因子，P雄（P因子）x M雌（无P因子）出现转座，它与细菌中的转座子相似 • 三、玉米转座子：Ds—Ac系统 • 四、人类基因组中的转座子 • 长散在重复序列（LINE）、Alu家族成员等

18. Section 6 Transposition mechanism and genetic effect Transposition mechanism DNA transposition mechanism: replicative transposition and non-replicative transposition Retrotransposition mechanism Genetic effect and application of transposon elements 1. Chromosomal structure variation 2. Gene mutation and exon shuffling 3. Gene expression regulation 4. Induction of variation 5. Target gene marker 6. Genetic engineering vector

19. 第六节 转座机制与遗传学效应 • 一、转座机制 • 1、DNA转座机制：复制型转座和非复制型转座 • 2、反转录转座子的转座机制 • 二、转座因子的遗传学效应与应用 • 1、引起染色体结构变异 • 2、诱发基因突变与外显子混编 • 3、调节基因表达 • 4、产生新的变异 • 5、转座子标记目的基因 • 6、基因工程的载体