Chapter 12 GENETICS AND EVOLUTION

1. Chapter 12GENETICS AND EVOLUTION 地球 - 生命的摇篮 生命 - 物质运动的最高级组织形式 自我复制、自我更新 遗传进化 - 了解遗传物质在地球上的形成变化和发展过程。

2. 12.1 原始生命遗传物质的诞生： • 生物大分子的起源 • - 生命前化学进化假说 (奥巴林生命起源假说): • 1200亿年前宇宙大爆炸 银河系 太阳系 太阳系星云 • 各大行星 地球(46亿年前) CH4、CO 、CO2、HCN等还原性气体 宇宙辐射供能 火山供热 无机小分子N2、H2S、NH3等 无机小分子 简单有机小分子 复杂有机分子 生物高分子 聚合 能自我复制、自我更新的原始生命 还原性大气 氧化性大气(O2) O3生命进一步进化

3. 2. 原始生命的诞生 具催化活性的大分子胶体，界膜包裹 团聚体小球 自我更新、复制 原始生命体模型 类蛋白微球 双膜结构（半透膜），膜内聚集多糖

4. 3. 原始生命中的遗传物质 • DNA and RNA exist together and they can be a pair of twin molecules. It seems that the earliest era of life origin is referred to as the ‘nucleic acid world’, afterwards DNA and RNA were generated separately by differentiation. The discovery of RNA interference shows that the change of phenotype of the gene can be controlled by RNA. The post-transcriptional processing of RNA is probably a reflection of the procedure of RNA evolution.

5. RNA优势： 1. C2 -OH，比DNA反应活性强。通常活性强的比弱的先发生 2.细胞中DNA合成需要RNA引物 3. RNA既可指令合成蛋白质又能自我复制或反向转录成DNA， 许多病毒仅含RNA DNA优势：现代生命体中的主要遗传物质 1.碱基位于 DNA双螺旋内部受保护，稳定性好 2.C2 –H，更具稳定性 3.复制时子链配对出错，在聚合酶作用下具纠错作用

6. 12.2 蛋白质分子进化 The rate at which amino acid changing mutations accumulate in genes for specific proteins tends to be constant over time. Similarly, changes in ribosomal RNA sequence, synonymous changes in coding sequences (silent mutations) and changes in non-coding sequences all have particular rates. These can all be used as molecular clocks. The degree of divergence between two species reflects the duration in time of their independent evolution. 在编码特定蛋白质的基因上发生氨基酸变化的突变的积累速率是恒定的。同样，核糖体RNA序列变化，编码序列的同义变化（沉默突变）以及非编码序列的变化都有特定的速率，这都可被用作分子钟。 两个物种间的分化程度反映了它们独立进化的时间历程。

7. 1. 血红蛋白分子的进化 Different species of animals can carry different types of hemoglobins in their blood. Animals have large molecular weight hemoglobins that are carried in the plasma. In contrast, other species, such as birds and mammals, have small molecular weight hemoglobins that are packaged in red blood cells. Red blood cells were thought to have evolved to package the small hemoglobins and prevent slower blood flow. 蛋白质分子的多样性 - 遗传性状的多样性 物种间进化上共同起源 遗传物质上同源 同源蛋白质 一级结构（aa序列）分析比较，揭示亲缘关系

8. 2. 细胞色素 c 分子的进化 • Rates of change at different time in several structural-functional areas of cytochrome c were also investigated in order to test the Darwinian hypothesis that during periods of rapid evolution, functional sites accumulate proportionately more substitutions than areas with no known functions. • This analysis revealed a significant increase in the rate of evolution for sites associated with the regions of cytochrome c oxidase and reductase interaction during the period between the emergence of the eutherian (真哺乳亚纲-动) ancestor to the emergence of the anthropoid (类人猿) ancestor.

9. 人 与黑猩猩完全一致 与猕猴差1个（第102位） 与酵母菌差45个 真核、原核生物中2/3 aa相异（变异区），1/3相同(恒定区)

10. 生物体中越是共同的蛋白质，其保守性越强，进化速率越慢 越是趋异性蛋白质，其保守性越弱，进化速率越快 e.g.纤维蛋白、血红蛋白、细胞色素c、组蛋白，这四种蛋白质中，每改变1%的aa残基，所需时间分别为： 纤维蛋白120万年 血红蛋白 610万年 细胞色素c 2140万年 组蛋白 6亿年

11. 12.3 核酸分子的进化 • 细胞中DNA数量的增加： • 生物进化过程中DNA含量逐渐增加。 e.g. φx174病毒DNA含量约6000 nts, 6-8基因，E.coli 为4×106 bp, 哺乳动物生殖细胞中基因组DNA 3.2×109bp DNA含量高不一定进化程度高, 因有许多不编码的重复序列。基因数量与复杂程度相关。如血红蛋白、免疫球蛋白基因仅存在于高等生物中。

12. 2.原有基因数量的扩增： 染色体加倍，导致整个基因组加倍 个别染色体重复 同源染色体配对时，不对等交换 ABCDEFADEF ABCDEF ABCBCDEF 3.新基因的增加 碱基对的替换突变（转换与颠换） 等位基因之间的不对等交换 非等位基因间的重组交换

13. 12.4 进化学说 1. 拉马克 (1744-1829) 的获得性遗传假说 Historical perspective Previous theories of evolution supposed that organisms improve their status by their own efforts (inheritance of acquired characteristics), a theory now known as ‘Lamarkian’ after its last great proponent. It was supposed that there was a progression from slime up to humans. 拉马克进化理论认为有机体通过它们自身的努力才得以提高其自身的进化地位（获得性遗传），它认为从粘菌到人类是一个不断进步的过程。

14. 2. 达尔文（1809-1882）自然选择学说 Evolution by natural selection Natural selection is the constraint that natural conditions put on the size of populations, forcing individuals of the same species to compete for limited resources. Those types which use the resources most successfully in order to reproduce, pass on their genetic material to their offspring, and are selected for. Inefficient or unsuccessful types fail to reproduce and are selected against. Natural selection was first proposed as the cause of evolution by Charles Darwin, but he did not know how inheritance worked.

15. Observations were: 1. The potential numbers of descendants from any species is infinite. Many more offspring are produced than can survive; 2. This potential population growth is prevented by limited resources; populations are relatively constant in size; 3. There are many differences between individuals which affect their ability to survive and reproduce. 观察发现：1.物种产生的子代数量是无限的；2.有限的资源阻止了群体增长; 3.个体间差异影响生存和繁殖能力。

16. Darwin deduced that therefore: 1. There is a struggle for the limited resources 2. Those individuals which survive and reproduce successfully will pass on to their offspring the characteristics which helped them to survive and reproduce 3. The inherited characteristics which help in the competition to reproduce will become more frequent in the population. This gradual change is evolution. 推论：1. 争夺有限资源；2. 生存与繁殖特性传给后代；3. 竞争中繁殖的遗传特性发生频率增加。渐变 进化。 自然选择的基础 自然选择的主体 自然选择的原因 自然选择的结果

17. 缺陷与贡献: 过分强调自然选择作用 过筛、分类 基因突变 自然选择动因 宏观解释生物进化与物种起源

18. 3. 现代达尔文主义 New-Darwinian evolution considers evolution in terms of changes in allele or gene frequencies over time, and the average action of selection on genotypes (particular alleles), rather than on individuals. This combines an understanding of the mechanism of inheritance with the action of Darwinian natural selection. 进化 等位基因或基因频率随时间的变化 对基因型（特定等位基因）的平均选择作用 突变生物进化原料 选择定向保留有利突变 隔离 有利突变得以巩固 新种形成 （杜布赞斯基 ）

19. Species isolation mechanisms Isolation prevent species interbreeding or exchanging genetic material (gene flow). This is the most important requirement for speciation, because populations can only diverge into species if they stop exchanging genes.

20. 4. 中性突变学说：突变非有利非有害 自然选择不发生作用 日积月累影响种的形成。 e.g. 细胞色素 c，20亿年，aa差异不影响功能，构成种、属 间特征。 这种在自然选择不发生作用的情况下，且生物大分子照样进化的方式为非达尔文式进化—中性突变

21. Genetic diversity (遗传多样性): There is a lot of genetic variation in most populations. It originates from mutations and is the essential raw material for selection, however, it is difficult to account for its quantity. There are two alternative explanations - natural selection and chance Too much death from natural selection would be required to maintain all the variation by selection. There is debate about the relative importance of selection and drift in maintaining variation. 群体中存在大量遗传变异源于突变 - 供选择的基本素材。 两种解释：自然选择和随机漂变

22. Human mitochondrial DNA suggests that all humans are descended by the female line from one woman who lived in Africa 140 000-290 000 years ago. Conserved proteins (e.g. cytochrome c) and ribosomal RNA are useful for studying the whole period of life on earth. Phylogenies reveal discrepancies in evolutionary rates in particular lineages. 人线粒体DNA表明，人类由一位生活在140 000-290 000年以前非洲的妇女繁衍而来的。保守蛋白（如细胞色素 c）和核糖体RNA可以用来研究地球上的整个生命周期。系统发生揭示了各个谱系在进化速率上的不同。

23. 12.5 现代人群中的基因突变和自然选择 All current human populations are the same species. Humans are clearly mammals, and are closely related to chimpanzees and gorillas. Hominid separated from the apes about 4 million years ago. Bipedalism was an early development, freeing hands to use tools and weapons for hunting and defense, and seems to have been a key evolutionary step.

24. The first humans almost certainly evolved in Africa, where stone tools were in use for cutting up big game 2.5 million years ago. Homoerectus appeared 1.5 million years ago in Africa with a larger brain and more sophisticated tools. Homo erectus colonized Eurasia around 700 000 years ago, to be replaced by modern humans, homo sapiens, again from Africa, about 120 000 years ago.

25. 基因突变和自然选择从古至今在人类中一直发挥着作用，其对人类基因的性质和频率、人类健康、体征及生理、病理过程的影响长期存在。基因突变和自然选择从古至今在人类中一直发挥着作用，其对人类基因的性质和频率、人类健康、体征及生理、病理过程的影响长期存在。

26. 优生优育： 1. 避免近亲婚配 2. 胚胎期遗传病诊断 3. 基因疗法—基因工程研究