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Chapter 10 Gene mutations 基因突变 10.1 Mutant types 突变类型 10.2 Detection 基因突变的检出

Chapter 10 Gene mutations 基因突变 10.1 Mutant types 突变类型 10.2 Detection 基因突变的检出 10.3 Mechanisms 基因突变机理 10.4 DNA Repair 基因损伤的修复 10.5 Mutant part 突变的部位. Mutation 突变 Excision repair 切除修复 Point mutation 点突变 Direct repair 直接修复

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Chapter 10 Gene mutations 基因突变 10.1 Mutant types 突变类型 10.2 Detection 基因突变的检出

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  1. Chapter 10 Gene mutations 基因突变 10.1 Mutant types 突变类型 10.2 Detection 基因突变的检出 10.3 Mechanisms 基因突变机理 10.4 DNA Repair 基因损伤的修复 10.5 Mutant part 突变的部位

  2. Mutation 突变 Excision repair 切除修复 Point mutation 点突变 Direct repair 直接修复 Gross mutation 大片段突变 Nonsense 无义突变 Transversion 颠换 Frameshift 移码突变 Silent mutation 同义(沉默)突变 Missense 错义突变 Transition 转换 Mutagen 诱变剂 Recombination repair 重组修复

  3. 10.1 Gene mutations Gene mutations: Mutations are alterations to the usual DNA sequence of an organism that result from the action of chemical and physical agents or errors of DNA replication. Mutations are perpetuated by the genotype and phenotype. Organisms may have wild-type or mutant phenotypes. Point and gross mutations exist. Only mutations in the coding regions of genes are likely to affect protein function. 基因突变：具有遗传效应的DNA分子上特定的核苷酸的序列发生改变，导致遗传效应发生相应变化。

  4. 10.1.1 突变类型： • 根据产生原因： • 1. Spontaneous mutation (自发突变）: 在自然状态下，生物体起因不明自发产生的一类突变 2. Induced mutation（诱发突变）: 经各种人为因素处理后引起的突变。 • 根据基因突变的表型效应分： • Morphological mutation（形态突变）：生物体外形可见的突变。如植株的高矮、种子的形状、翅的长短、眼睛的颜色等 2. Lethal mutation （致死突变）： 显性：一产生即导致个体死亡，不可能传递给后代 隐性：二倍体生物中纯合时导致死亡，杂合时被掩盖，在后代 中传递

  5. 3. Conditional lethal mutation （条件致死突变）：改变生物体 适应性的突变。 4. 生化突变：生物体形态未发生改变，代谢的生化过程发生了变 化 • 根据基因突变的遗传密码分： • Samesense (or silent) mutation（同义突变）：Mutations may occur at the third base of a codon and do not change the encoded amino acid. Silent mutations have no effect on the encoded protein and do not result in a mutant phenotype. 密码子的第三个碱基突变，不改变编码氨基酸 • e.g. 亮aaCUU CUA UUA 对应的DNA GAA GAT AAT • CUC CUG UUG GAG GAC AAC

  6. 2. Missense mutation （错义突变）：These point mutations involve the alteration of a single base which changes a codon such that the encoded amino acid is altered. 密码子的第一、二位碱基改变导致对应的aa改变

  7. 3. Nonsense mutation（无义突变）： Nonsense mutation create stop codons （UAA/UAG/UGA） and produce shortened polypeptides 蛋白质合成提前终止，产生不完整的、无正常 活性肽链

  8. 4. Frameshift mutation（移码突变）：Frameshift mutations involve insertion or deletion of a base producing an altered reading frame. Frameshift mutations usually have a serious effect on the encoded protein and are associated with mutant phenotypes.

  9. e.g.ATG TTT CCC AAA GGG TTT --- CCC TAG TAC AAA GGG TTT CCC AAA --- GGG ATC mRNA AUG UUU CCC AAA GGG UUU --- CCC UAG(终止) Pro. Met—Phe—Pro— Lys—Gly—Phe ----- Pro 甲硫 苯丙 脯 赖 甘 苯丙 -----脯 增加A/T bp ATG ATT TCC CAA AGG GTT T----------------- TAC TAA AGG GTT TCC CAA A---------------- mRNA AUG AUU UCC CAA AGG GUU U---------------- Pro. Met—Ile—--Ser—Gln— Arg—Val-------------- 甲硫 异亮 丝 谷氨酰胺 精 缬----------

  10. 根据基因突变的碱基类型分： • Transition mutation（转换突变）：基因DNA分子上嘌呤碱之间或嘧啶碱之间的变化 A G T C 2. Transversion mutation（颠换突变）：嘌呤碱与嘧啶碱之间的变化 A/G T/C

  11. 10.2 基因突变的检出 • 生产实践中诱变剂处理作物，后代出现变异，需要检测这些变异是否遗传变异？是显性突变还是隐性突变？ e.g. 纯种种子诱变处理，若F1出现与亲本不同性状，F2性状分离：3/4与F1一致, 1/4与亲本一致，单株自交F3不分离株 (与F1同)，为显性突变纯合株，亲本为隐性纯种dd。 纯种 诱变Dd F1 自交 1DD 2Dd 1dd F2 严格单株自交 显性突变纯合株DD 2DD 4Dd 2dd dd F3

  12. 若诱变后 F1 与亲本一致，F2 3/4与亲本一致，1/4非亲本即隐性突变体纯合株 纯种 F1 Dd 自交F2 1DD 2Dd 1dd（非亲本类型的隐性突变纯合株, 亲本为DD） 若 F1 新性状，F2消失， F3 未出现，则为不遗传变异 2. 现代遗传学发展，通过直接测定多肽链上aa序列和mRNA、DNA中的碱基序列，定性定量分析分子水平上的突变

  13. 10.3 基因突变机理： • Physical mutagens (物理因素): • 紫外线、X、γ射线。 • DNA突变与射线强度成正比 • （波长短、能量大、穿透力强、突变厉害） • X、γ射线穿透力强，直接损伤性细胞DNA • 紫外线危害上皮细胞，使DNA形成嘧啶二聚体，局部氢 • 键消失，结构变形，DNA复制出错，导致基因突变

  14. High energy ionizing radiation, such an χ-ray and γ-rays cause extensive damage to DNA molecules producing strand breaks and the destruction of sugars and bases. Nonionizing radiation in the form of ultraviolet (UV) light is absorbed by bases and can induced structural changes. In particular, UV light can cause the formation of structures called cyclobutyl dimers between adjacent pyrimidines, especially thymines. Dimerization causes the bases to stack closer together and can result in deletion mutations following DNA replication.

  15. 2. Chemical mutagens (化学因素): • 碱基类似物的诱发突变： • 结构相似的化合物替代天然碱基引起配对出错 • 碱基作用物诱发突变： 碱基作用物与碱基起化学反应，改变碱基结构 • 移码插入物诱发突变： • 吖啶类化合物的移码插入

  16. many different chemicals act as mutagens. Base analogs substitute for normal bases during DNA replication and cause mutation by having altered base-pairing patterns. Intercalating agents slip between the bases in the double helix. They cause the insertion of an extra base during replication producing a frameshift mutation. Many chemical mutagens modify bases, often by the addition of alkyl or aryl groups or by de-amination. DNA also undergoes spontaneous mutation by reaction with normal chemical species in cells. Reactive oxygen species present in aerobic cells also damage base.

  17. 亚硝酸氧化脱氨作用： A -氨基 H （次黄嘌呤） A/T H/C CG C -氨基 U C/G U/A AT 烷化剂：DNA碱基上H被烷基取代，复制时错配 G 硫酸二乙酯 G-C2H5（乙基） G-C2H5 / C G-C2H5 / T （GC GT TA） 羟胺还原剂： C-NH2 C-OH CG CT TA

  18. 3. Biological mutagens (生物因素)： 病毒或外源DNA 生物体细胞 DNA重组 表型改变 突变 • 转导诱发突变 噬菌体病毒侵染 • 动植物病毒侵入 • 转化诱发突变 外源DNA 受体细胞(真、原核） • 基因重组 • 转座诱发突变 • 1950年发现玉米胚乳颜色与9th染色体上一转入片段（Ac-Ds系统）有关。

  19. 10.4 DNA repair（基因损伤的修复) : The presence of numerous agents that mutate DNA has led organisms to develop extensive DNA repair mechanisms. 紫外照射受损形成嘧啶二聚体的三种修复方式： direct repair excision repair recombination repair

  20. Direct repair - Photoreaction（光复活修复）： • Enzymes called DNA photolyases are induced by visible light and repair pyrimidine dimers by breaking the links that form on dimerization. • 嘧啶二聚体 光复合酶 可见光中 解开，DNA分子恢复原状

  21. 2. Excision repair (切除修复或暗修复): This is a complex system which is probably the most common form of DNA repair: Initially, one of a number of enzymes recognizes nucleotides that are damaged and marks them for repair; The mark can take the form of a nick in one of the strands of the double helix adjacent to the area of damage; An nuclease removes the damaged base and adjacent bases leaving a gap.; The gap is then filled with new DNA by a DNA polymerase and closed by DNA ligase.

  22. a.内切酶识别二聚体：在二聚体一侧切开 b.DNA多聚体酶Ⅰ中5’—3’外切酶从切口5’起，一个个将二聚体及附近碱基切除 c.切口处以另一单链为模板，多聚酶Ⅰ作用下，5’—3’合成新互补单链 d. DNA ligase 片段连接 完成修复

  23. 3. Recombination repair (重组修复): Recombination is a process which makes new combinations of genetic information on a DNA molecule by cutting and splicing 1 2 复制 补2’ 缺 补1’ 缺 1 1’ 2 2’ 重组 1’ 2’ 野生型 缺陷型（失活）

  24. 10.5 突变的部位： DNA mutation is the underlying cause of genetic diseases and of cancer. Genetic disease are caused by inherited mutations. Usually a single gene is involved. The mutation arises in a germ cell which results in an individual who carries the mutation in all of their cells and will pass it on to subsequent generations. Mutations associated with the development of cancer occur in somatic cells and often in genes that control cell division. 突变为生物进化、良种选育提供原材料，但对人类健康产生很大危害，其程度与发生部位密切相关。

  25. 1. In somatic cells 体细胞基因突变 a. 动物体细胞突变： 组织、器官、细胞 DNA损伤（污染的自然环境中） 准确修复 体细胞恢复正常功能 DNA复制 基因突变 癌症、动脉粥样硬化、白内障、慢性病、衰老（突变积累）等 当代 表现

  26. b. 植物的体细胞突变（芽变）： 叶芽突变 枝条变异 嫁接、扦插 新表型/新基因型植株 花芽突变 花序变异 花、果形、色泽及分布上改变 （eg. 大丽菊半红半白头状花序）

  27. 2. In sexual cells 生殖细胞突变： 生殖细胞 污染环境（物理、化学、生物诱变剂） DNA损伤 未修复复制后 基因突变 显性突变 子代变异 修复 隐性突变 子代携带 纯合表现 恢复正常 遗传病发生 后代正常

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