生物学导论biology12

1、Chap.12. Natural Selection and Evolution12.1 The role of natural selection in evolution12.2 What influence natural selection12.3 Common misunderstandings about natural selection12.4 Processes that drive natural selection12.5 Gene-frequency studies and Hardy-weinberg equilibrium (self-learning)12.6 A

2、 summary of the causes of evolutionary change Acquired characteristics 获得性特征 Evolution 进化 Expressivity 表现度 Fitness 适合度 Genetic drift 遗传漂移 Genetic recombination 基因重组 Natural selection 自然选择 Penetrance 外显率 Selection agent 选择因素 Spontaneous mutation 自发突变 Theory of natural selection 自然选择学说 Cultural meanin

3、g of evolution is progressive change. Evolution 进化 is the continuous genetic adaptation of a population of organisms to its environment over time Only populations can involve in evolutionTo determine how a species changes over time: Environmental factors that affect organisms Sexual reproduction amo

4、ng the individuals in the gene pool The generation of genetic variety 遗传差异within gene pool Natural selection refers to various mechanisms that encourage the passage of beneficial genes to future generations and discourage harmful or less valuable genes from being passed to future generations Was fir

5、st proposed by Charles Darwin in On the origin of species，1859HMS Beagle，1831-1836 Theory of evolution 进化论 states that populations of organisms become genetically adapted to their surroundings over time. Natural selection is the process that brings about evolution by “selecting” which genes will be

6、passed to the next generation. More individuals are born than can survive to reproduce. Individuals vary in most traits Individuals with certain traits are more likely to survive and reproduce Variation is at least partly heritable Survival for the fittest Fitness 适合度 is the concept that those who a

7、re best adapted to their environment produce the most offspring这种0米长的带翅膀的Phasmagigas竹节虫原产于巴布亚新几内亚。美国科学家称，基因分析显示，某些竹节虫在进化过程中至少4次失去又恢复了翅膀。这种280厘米长的Leprocaulinus竹节虫原产于巴布亚新几内亚，今天竹节虫家族中的许多成员都像Leprocaulinus一样失去了翅膀，而它们的一些亲戚却仍然拥有翅膀。 科学家发现，某些种类的昆虫在进化过程中，失去又重新获得了飞行的能力。这一现象表明，达尔文的进化论本身也许需要进化了。研究者曾经认为，进化过程是不可以逆

8、转的，因此像翅膀一类复杂特征不可能失而复得。但是根据最新出版的一份研究报告，一种类似小树枝的竹节虫(walkingsticks)可能证明事实正好相反。 某种复杂生物特征的消失可能只是表面上的，实际上这一特征将在基因中潜伏相当长时间。http:/ Mutations produce new genes Spontaneous mutation 自发突变 are changes in DNA that can not be tied to a particular causative agent 致病因子 Cosmic radiation 宇宙射线 or naturally occurring m

9、utagenic 诱变 chemicals might be cause of these mutations. Sexual reproduction produces new combinations of genes Through crossing-over, independent assortment of homologous chromosomes Penetrance 外显率is how often an allele express itself when present Expressivity 表现度 is situations in which gene expres

10、ses itself but not equally in all individuals that have it Some genes express themselves only during specific periods in life of an organism. Many genes require an environmental trigger to initiate their expression. When both dominant and recessive alleles are present for a characteristic, the reces

11、sive alleles must be present in a homozygous 纯合子 condition before they have an opportunity to express themselves Some genes may have their expression hidden because the action of a completely unrelated gene is required before they can express themselves.Albinism白化病 The ability of a population to rep

12、roduce greatly exceeds the number necessary to replace those who die. If the species is living in harmony 协调地 with its environment, it does not experience dramatic increases in population size. Colorado potato beetles Green peach aphid1) Survival of the fittest 适者生存Not survival alone, but survival a

13、nd reproduction of more fit organisms2) Struggle for life Not necessarily refer to open conflict and fighting3) Significance of phenotypic characteristics that are not caused by genes Acquired characteristics are gained during the life of organism, are not genetically determined. Selecting agents: s

14、pecific environmental factors that favor certain characteristics Differential survival 差别生存 Differential reproductive rates Differential mate selection The peppered moth（Biston betularia）桦尺蛾The peppered moth Kettlewell, 1955 , Darwins Missing Evidence, Scientific American, vol. 200, no. 3, pp. 48-53

15、 First, the environment or background on which the moths rested played an important role. Second, there was variation in the appearance of the moths: both dark colored and light colored. Third, predators ate a large proportion of the moths in each generation so that only a few would survive to have

16、offspring, but depending on the environment, predators did not capture an equal proportion of dark-colored and light-colored moths. Fourth, the traits (dark or light color) were passed on from generation to generation. Finally, the combination of environment, variation, predation, and inheritance le

17、d to unequal survival of the moths.1) The tone of the article. Kettlewells article reads more like a piece of Darwinian propaganda than a scientific article.2) The unnatural positioning of the moths.3) The experiments conclusions are unjustified. 4) Bird predation as a major factor was not demonstra

18、ted. 5) Bird predation is contradicted by the facts.6) Other possible factors are ignored. /archive/evolution/199904/0112.html More insects are developing resistance to insecticide Organisms which have much offspring pass more copies of its genetic information on to next generation than does the organisms which have few offspring. Selection for shortness in clover苜蓿 Within animal populations, some individuals may be chosen as mates more frequently than others. Peacock EvolutionNatural selectionFactors infl