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1、Xunchao Xiang Southwest University of Science and TechnologyChapter12 Population Geneticsn n12.1 Populations and Gene Pools12.1 Populations and Gene Poolsn n12.2 Calculating Allele Frequencies12.2 Calculating Allele Frequenciesn n12.3 The Hardy-Weinberg Law12.3 The Hardy-Weinberg Lawn n12.4 Extensio
2、ns of the Hardy-Weinberg Law12.4 Extensions of the Hardy-Weinberg Lawn n12.5 Using the Hardy-Weinberg Law: Calculating 12.5 Using the Hardy-Weinberg Law: Calculating Heterozygote FrequencyHeterozygote Frequencyn n12.6 Factors That Alter Allele Frequencies in Populations12.6 Factors That Alter Allele
3、 Frequencies in Populationsn n12.7 Natural Selection12.7 Natural Selectionn n12.8 Origin of life and theory of biological evolution12.8 Origin of life and theory of biological evolutionn n12.9 Species formation12.9 Species formationXunchao Xiang Southwest University of Science and Technology遗传与进化遗传与
4、进化Xunchao Xiang Southwest University of Science and Technologyn群体遗传学群体遗传学(population genetics)：研究群体：研究群体的遗传结构及其变化规律的遗传学分支学的遗传结构及其变化规律的遗传学分支学科。科。n nPopulation Genetics: Scientific discipline that studies what happens in whole populations at the genetic level.n nTheoretic foundation:n nCharles Darwins
5、 natural selection and the Mendels laws.Xunchao Xiang Southwest University of Science and Technology12.1 Populations and Gene Poolsn nPopulation: A local group of individuals belonging to the same species, which are actually or potentially interbreeding.n有相互交配关系、能自由进行基因交流的有相互交配关系、能自由进行基因交流的同种生物个体的总和
6、。同种生物个体的总和。n遗传学、进化论中的遗传学、进化论中的群体、种群、孟德尔群体、种群、孟德尔群体群体为同一概念。为同一概念。Xunchao Xiang Southwest University of Science and Technology Gene pool: The total of all alleles possessed by reproductive members of a population. 基因库基因库(Gene pool): 一个群体内全部个体共一个群体内全部个体共有的全部基因称为基因库。有的全部基因称为基因库。A gene pool consists of a
7、ll gametes made by all A gene pool consists of all gametes made by all the breeding members of a population in a the breeding members of a population in a single population. single population. Xunchao Xiang Southwest University of Science and Technology 基因型频率(genotype frequency）：一个群体内某种特定基因型所占的比例。 基
8、因频率(gene frequency)：一个群体内某特定基因座(locus)上某种等位基因占该座位等位基因总数的比例，也称为等位基因频率也称为等位基因频率( (allele frequencyallele frequency) )。基因型频率与基因频率都是用来描述群体遗传结构(性质)的重要参数。从群体水平看：生物群体进化就表现为基因频率的变化，也就是群体配子类型和比例变化(对一个基因座位而言)，所以基因频率是群体性质的决定因素。基因型频率与基因频率Xunchao Xiang Southwest University of Science and Technology12.2 Calculati
9、ng Allele Frequenciesn nOne example: n nHIV-1, the virus responsible for the bulk of AIDS cases worldwide. Of particular interest to AIDS researchers is the small number of individuals who make high-risk choices, yet remain uninfected.Xunchao Xiang Southwest University of Science and Technologyn nCC
10、R5 gene, located on chromosome 3, encodes a protein called the C-C chemokine(趋化因子趋化因子趋化因子趋化因子) receptor-5 (CCR5).HIV-1EnvCD4Host CellEnv of changed shapeCCR5Second binding siteXunchao Xiang Southwest University of Science and Technologyn nThe mutant allele of the The mutant allele of the CCR5CCR5 ge
11、ne contain a gene contain a 32-bp deletion in one of its coding regions. As a 32-bp deletion in one of its coding regions. As a result, the protein encoding by the mutant allele result, the protein encoding by the mutant allele is shortened and made nonfunctional. The is shortened and made nonfuncti
12、onal. The protein never makes it to the cell membrane, so protein never makes it to the cell membrane, so HIV-1 cannot enter these cells.HIV-1 cannot enter these cells.n nThe geneThe genes normal allele is called s normal allele is called CCR51CCR51 (or (or 1 1) ) and its allele with the 32-bp delet
13、ion is called and its allele with the 32-bp deletion is called CCR5-CCR5-3232 (or (or 3232) )Xunchao Xiang Southwest University of Science and Technologyn nThe uninfected individuals had the genotype The uninfected individuals had the genotype 32/ 32/ 32. 32. As a result, they had no CCR5 on the As
14、a result, they had no CCR5 on the surface of their cells, and were resistant to surface of their cells, and were resistant to infection by strains of HIV-1 that require CCR5 infection by strains of HIV-1 that require CCR5 as a co-receptor.as a co-receptor.Organization of the CCR5 gene in region 3p21
15、.3Xunchao Xiang Southwest University of Science and TechnologyCCR5 Genotypes and PhenotypesGenotypeGenotypephenotypephenotype1/11/1Susceptible to sexually transmitted strains of Susceptible to sexually transmitted strains of HIV-1 HIV-1 1/1/ 3232Susceptible, but may progress to AIDS Susceptible, but
16、 may progress to AIDS slowly.slowly. 32/ 32/ 3232Resistant to most sexually transmitted strains Resistant to most sexually transmitted strains of HIV-1of HIV-1Xunchao Xiang Southwest University of Science and Technology Allelic Allelic variation variation in the in the CCR5CCR5 gene.gene.Xunchao Xia
17、ng Southwest University of Science and TechnologyMethods of Determining Allele Frequenciesn nA. From Data on GenotypesA. From Data on GenotypesGenotypeGenotype1/11/11/1/ 3232 32/ 32/ 3232TotalTotalNumber of Number of individualsindividuals797920201 1100100Number of Number of 1 1 allelesalleles158158
18、20200 0178178Number of Number of 32 alleles32 alleles0 020202 22222Total number Total number of allelesof alleles15815840402 2200200Frequency of Frequency of CCR51CCR51 in sample: 178/200=0.89=89% in sample: 178/200=0.89=89%Frequency of Frequency of CCR5 CCR5 - - 32 32 in sample: 22/200=0.11=11%in s
19、ample: 22/200=0.11=11%Xunchao Xiang Southwest University of Science and TechnologyMethods of Determining Allele Frequenciesn nB. From Genotype Frequencies B. From Genotype Frequencies GenotypeGenotype1/11/11/1/ 3232 32/ 32/ 3232TotalTotalNumber of Number of individualsindividuals797920201 1100100Gen
20、otype Genotype FrequencyFrequency79/100=0.7979/100=0.7920/100=0.2020/100=0.201/100=0.011/100=0.011.001.00Frequency of Frequency of CCR1 CCR1 in sample: 0.79+(0.5)0.20=0.89in sample: 0.79+(0.5)0.20=0.89Frequency of Frequency of CCR5CCR5- - 32 32 in sample: (0.5)0.20+0.01=0.11 in sample: (0.5)0.20+0.0
21、1=0.11 Xunchao Xiang Southwest University of Science and Technology芬芬兰兰瑞瑞典典立陶宛俄俄罗罗斯斯法国西班牙西班牙Xunchao Xiang Southwest University of Science and TechnologyGenotype frequencyn n在一个个体数为在一个个体数为N N的二倍体生物群体的二倍体生物群体( (居群居群) )中，一对中，一对等位基因等位基因( (A, aA, a) )的三种基因型的频率如下表所示：的三种基因型的频率如下表所示：基因型基因型个体数个体数基因型频率基因型频率AA
22、AAD D D=DD=D/N/NAaAaH H H=HH=H/N/NaaaaR R R=RR=R/N/NN N1 1Xunchao Xiang Southwest University of Science and TechnologyAllele frequency在一个个体数为在一个个体数为N N的二倍体生物群体中，一对等位基因的二倍体生物群体中，一对等位基因( (A, aA, a) )的共有的共有2N2N个基因座位，两种基因的频率如下表所示：个基因座位，两种基因的频率如下表所示：等位基因等位基因基因座数基因座数基因频率基因频率A A2D+H2D+Hp=(2D+H)/2Np=(2D+H)/
23、2ND+HD+Ha a2R+H2R+Hq=(2R+H)/2Nq=(2R+H)/2NR+HR+H2N2N1 11 1Xunchao Xiang Southwest University of Science and Technology12.3 The Hardy-Weinberg Lawn nIdeal population of Hardy-Weinberg:Ideal population of Hardy-Weinberg:n n1. Individuals of all genotypes have equal rates of 1. Individuals of all genoty
24、pes have equal rates of survival and equal reproductive success; that is no survival and equal reproductive success; that is no selection.selection.n n2. No new alleles are created or converted from one 2. No new alleles are created or converted from one allele into another by mutation.allele into a
25、nother by mutation.n n3. Individuals do not migrate into or out of the population.3. Individuals do not migrate into or out of the population.n n4. The population is infinitely large, which in practical 4. The population is infinitely large, which in practical terms means that the population is larg
26、e enough that terms means that the population is large enough that sampling errors and other random effects are negligible.sampling errors and other random effects are negligible.n n5. Individuals in the population mate randomly.5. Individuals in the population mate randomly.Xunchao Xiang Southwest
27、University of Science and TechnologyThe Hardy-Weinberg Lawn nThe principle that both gene and genotype frequencies will remain in equilibrium in an infinitely large population in the absence of mutation, migration, selection, and nonrandom mating.n n在一个完全随机交配的大群体内，如果没有其他因素干扰时，群体的基因频率与基因型频率在生物世代之间将保持
28、不变。Xunchao Xiang Southwest University of Science and Technology 遗传平衡定律(哈德-温伯格定律)的要点：Key Points of Hardy-Weinberg Lawn n1. The frequency of alleles does not change from generation to generation; in other words, the population does not evolve.在随机交配的大群体中，如果没有其他因素干扰，群体将是一个平衡群体；Key Points of Hardy-Weinbe
29、rg Lawn n 2. After one generation of random mating, After one generation of random mating, offspring genotype frequencies can be predicted offspring genotype frequencies can be predicted from the parent allele frequencies. Genotype from the parent allele frequencies. Genotype frequency and allele fr
30、equency had relationship frequency and allele frequency had relationship as follows:as follows: D=p D=p2 2，H=2pqH=2pq，R=qR=q2 2群体处于平衡状态时：各代基因频率保持不变，且基因频率与基因型频率间关系为： D=p2，H=2pq，R=q2Xunchao Xiang Southwest University of Science and TechnologyKey Points of Hardy-Weinberg Lawn n3. Nonequilibrium great p
31、opulation (Dp2，H2pq，Rq2) can change for equilibrium population as long as random mating one generation. 在任何一个大群体内，不论其等位基因频率和基因型频率如何，只要一代的随机交配，这个群体就可达到平衡；Xunchao Xiang Southwest University of Science and TechnologyXunchao Xiang Southwest University of Science and TechnologyWhat makes the Hardy-Weinbe
32、rg law useful?What makes the Hardy-Weinberg law useful?n nBy specifying the assumptions under which the population cannot evolve, the Hardy-Weinberg law identifies the real-world forces that cause allele frequencies to change. n nIn other words, by holding certain conditions constant, the Hardy-Wein
33、berg law isolates the forces of evolution.Xunchao Xiang Southwest University of Science and TechnologyA Demonstration of the Lawn nAn example, n na single locus with two alleles, A and a.n nImagine a population in which the frequency of allele A, in both eggs and sperm, is 0.7, and the frequency of
34、allele a is 0.3. n n(Note that 0.7+0.3=1, indicating that all the alleles Note that 0.7+0.3=1, indicating that all the alleles for gene for gene A A present in the gene pool are present in the gene pool are accounted for.accounted for. )Xunchao Xiang Southwest University of Science and TechnologyXun
35、chao Xiang Southwest University of Science and Technologyn n Imagine a gene pool in which the frequency of allele A is p and the frequency of allele a is q, such that p+ q=1.Xunchao Xiang Southwest University of Science and Technologyn nWhat the allele frequencies in the new gene pool will be when t
36、hese zygotes develop into adults and reproduce?n nThe frequency of allele A in the new gene pool will ben nP2+(1/2)2pq=p2+pq=p (p+q=1)n nThe frequency of allele a in the new gene pool will ben nq2 +(1/2)2pq=q2+pq=q (p+q=1)Xunchao Xiang Southwest University of Science and Technologyn nHardy-Weinberg
37、equilibrium:n nA population in which the allele frequencies remain constant from generation to generation and in which the genotype frequencies can be predicted from the allele frequencies is said to be in a state of Hardy-Weinberg equilibrium.Xunchao Xiang Southwest University of Science and Techno
38、logyConsequences of the Lawn n1. It shows that dominant traits do not 1. It shows that dominant traits do not necessarily increase from one generation to the necessarily increase from one generation to the next.next.n n2. It demonstrates that genetic variability can be 2. It demonstrates that geneti
39、c variability can be maintained in a population since, once maintained in a population since, once established in an ideal population, allele established in an ideal population, allele frequencies remain unchanged.frequencies remain unchanged.n n3. If we invoke Hardy-Weinberg assumptions, 3. If we i
40、nvoke Hardy-Weinberg assumptions, then knowing the frequency of just one genotype then knowing the frequency of just one genotype enables us to calculate the frequencies of all enables us to calculate the frequencies of all other genotypes.other genotypes.Xunchao Xiang Southwest University of Scienc
41、e and TechnologyTesting for Equilibriumn nOne way we establish whether one or more of the Hardy-Weinberg assumptions do not hold in a given population is by determining whether the populations genotypes are in equilibrium.Xunchao Xiang Southwest University of Science and TechnologyTesting for Equili
42、briumn nProcedure:1. Determining the frequencies of the genotypes, either directly from the phenotypes (if heterozygotes are recognizable) or by analyzing proteins or DNA sequences.2. Calculating the allele frequencies from the genotype frequencies, as demonstrated earlier. 3. Using the parents alle
43、les frequencies to predict the offsprings genotype frequencies.Xunchao Xiang Southwest University of Science and TechnologyTesting for Equilibriumn nAccording to the Hardy-Weinberg law, the genotype frequencies are predicted to fit the p2+2pq+q2=1 relationship. If they do not, then one or more of th
44、e assumptions are invalid for the population in question.Xunchao Xiang Southwest University of Science and TechnologySample 1n nA population in Britain includes 283 individuals, A population in Britain includes 283 individuals, of which 223 have genotypeof which 223 have genotype1/11/1, 57 numbers ,
45、 57 numbers represent genotype represent genotype 1/1/ 3232, 3 have genotype , 3 have genotype 32/ 32/ 32. 32. Please to determine whether this Please to determine whether this population is in equilibrium?population is in equilibrium?Genotype frequency :Genotype frequency :223/283=0.788, 57/283=0.2
46、01, 3/283=0.011.223/283=0.788, 57/283=0.201, 3/283=0.011.From the genotype frequencies, we compute the From the genotype frequencies, we compute the CCR51 CCR51 allele frequency as 0.89 and the allele frequency as 0.89 and the frequency of the frequency of the CCR5-CCR5- 3232 allele as 0.11. allele
47、as 0.11.Xunchao Xiang Southwest University of Science and Technologyn n We know: We know: n nfrequency of frequency of CCR51CCR51= =p p=0.89=0.89n nfrequency of frequency of CCR5-CCR5- 32 =q=32 =q=0.110.11n nTherefore:Therefore:n nExpected frequency of genotypeExpected frequency of genotype1/11/1= =
48、p p2 2=0.89=0.892 2n nExpected frequency of genotype Expected frequency of genotype 1/1/ 32 32 =2=2pqpq=20.890.11=0.196=20.890.11=0.196n nExpected frequency of genotype Expected frequency of genotype 32/ 32/ 32 32 = =q q2 2=0.11=0.112 2=0.012=0.012n n2=0.00023=0.0002320.05,2=5.99=5.99n n this popula
49、tion is in equilibrium.this population is in equilibrium.Xunchao Xiang Southwest University of Science and TechnologySample 2n nFrequencies of Frequencies of CCR51CCR51 and and CCR5-CCR5- 32 32 alleles in a alleles in a hypothetical population composed of 500 hypothetical population composed of 500
50、1/11/1 individuals and 500 individuals and 500 32/ 32/ 32 32 individualsindividualsAllele FrequenciesAllele FrequenciesGenotype FrequenciesGenotype FrequenciesPopulationPopulationCCR51CCR51CCR5- CCR5- 32 32 1/11/11/ 1/ 32 32 32/ 32/ 3232Source populationsSource populationsEast IslandEast Island1.01.
51、00 01.01.00 00 0West IslandWest Island0 01.01.00 00 01.01.0New population on Central IslandNew population on Central IslandObservedObservedP P=0.5=0.5q q=0.5=0.50.50.50 00.50.5ExpectedExpectedP P2 2=0.25=0.252 2pqpq=0.5=0.5q q2 2=0.25=0.25Xunchao Xiang Southwest University of Science and Technologyn
52、 nThese expected frequencies obviously differ These expected frequencies obviously differ from the observed frequencies; there are no from the observed frequencies; there are no heterozygotes at all on Central Island. heterozygotes at all on Central Island. Therefore, population is not in Hardy-Wein
53、berg Therefore, population is not in Hardy-Weinberg equilibrium (a equilibrium (a 2 2 test would confirm this).test would confirm this).n nTwo assumptions are violated in the new Two assumptions are violated in the new population:population:n n1. Everyone living on Central Island is a migrant;1. Eve
54、ryone living on Central Island is a migrant;n n2. Central Island s population are not the 2. Central Island s population are not the products of random mating.products of random mating.Xunchao Xiang Southwest University of Science and Technologyn n If mating is random in the population, If mating is
55、 random in the population, equilibrium will be reached in one generation.equilibrium will be reached in one generation.Xunchao Xiang Southwest University of Science and Technology12.4 Extensions of the Hardy-Weinberg Lawn nThe ABO blood group in human, three blood group A, B, O, three allele IA,IB,
56、IOn nLet p, q and r represent the frequencies of allele IA,IB and IO ,respectively, n np+ q+ r =1n nThe frequencies of genotypes:n n(p+ q+ r )2=p2+q2+r2+2pq+2pr+2qr=1Xunchao Xiang Southwest University of Science and TechnologySample 1n nIn one population, the following blood-type frequencies are obs
57、erved: A=0.53, O=0.26. Please calculating the allele frequencies.n nO allele is recessive, r2=0.26n n r =0.51Xunchao Xiang Southwest University of Science and Technologyn nIA allele is present in two genotypes, AA and AO, the combined frequency of type A blood and type O blood is given byn np2+2pr+r
58、2=0.53+0.26n n(p+r)2=0.79 p=0.38 q=0.11n nIf calculating the genotype frequency of B?n nfrequency of B=q2+2qr=0.112+2*0.11*0.51n =0.12Xunchao Xiang Southwest University of Science and Technology Example 2n n设一个初始群体（尚未达到设一个初始群体（尚未达到设一个初始群体（尚未达到设一个初始群体（尚未达到Hardy-Weinberg Hardy-Weinberg 平衡）平衡）平衡）平衡），其初
59、始基因型频率为：，其初始基因型频率为：，其初始基因型频率为：，其初始基因型频率为：P P11(0)11(0) =0.6 =0.6，P P12(0)12(0) =0.4 =0.4， P P22(0)22(0) =0.0 =0.0，则初始基因频率为：，则初始基因频率为：，则初始基因频率为：，则初始基因频率为：n nP P1(0)1(0) = P = P11(0)11(0) 1/2 P1/2 P12(0)12(0) 0.60.61/2*0.41/2*0.40.80.8，n nP P2(0)2(0) = P = P22(0)22(0) 1/2 P1/2 P12(0)12(0) 0.00.0 1/2*0
60、.4=0.21/2*0.4=0.2n n随机交配第一代的基因型频率为随机交配第一代的基因型频率为随机交配第一代的基因型频率为随机交配第一代的基因型频率为 ：n nP P11(1) 11(1) = P= P1(0)1(0) 2 2 = 0.8 = 0.8 2 2 =0.64=0.64n nP P12(1) 12(1) = 2P= 2P1(0) 1(0) P P2(0) 2(0) =2*0.8*0.2=0.32=2*0.8*0.2=0.32n nP P22(1) 22(1) = P= P2(0)2(0) 2 2 = 0.2 = 0.2 2 2 =0.04=0.04Xunchao Xiang Sou
61、thwest University of Science and TechnologyExample 2n n则随机交配第一代的等位基因频率为：则随机交配第一代的等位基因频率为：n nP1(1) = P11(1) 1/2 P12(1) 0.64 1/2*0.320.8n nP2(1) = P22(1) 1/2 P12(1) 0.04 1/2*0.32=0.2n n随机交配第二代的基因型频率：随机交配第二代的基因型频率：n nP11(2) = P1(1) 2 = 0.8 2 =0.64n nP12(2) = 2P1(1) P2(1) =2*0.8*0.2=0.32n nP22(2) = P2(1
62、) 2 = 0.2 2 =0.04Xunchao Xiang Southwest University of Science and TechnologyExample 2n n随机交配第二代的等位基因频率：随机交配第二代的等位基因频率：n nP1(2) = P11(2) 1/2 P12(2) 0.64 1/2*0.320.8n nP2(2) = P22(2) 1/2 P12(2) 0.04 1/2*0.32=0.2n n由上可见，基因型频率，虽然由上可见，基因型频率，虽然P11(1) P11(0) ， P12(1) P12(0) ， P22(1) P22(0) ，n n但是，经过一代随机交配
63、，但是，经过一代随机交配， P11(1) P11(2) ， P12(1) P12(2) ， P22(1) P22(2) Xunchao Xiang Southwest University of Science and TechnologyExample 2n n至于等位基因频率，则始终保持不变：至于等位基因频率，则始终保持不变：n nP1(0) = P1(1) = P1(2) ， P2(0) = P2(1) = P2(2) 。 Xunchao Xiang Southwest University of Science and Technology12.5 Using the Hardy-We
64、inberg Law: 12.5 Using the Hardy-Weinberg Law: Calculating Heterozygote FrequencyCalculating Heterozygote FrequencyThe frequency of a recessive trait can usually be The frequency of a recessive trait can usually be determined by counting such individuals in a determined by counting such individuals
65、in a sample of the population. With this information sample of the population. With this information and the Hardy-Weinberg law, we can then and the Hardy-Weinberg law, we can then calculate the allele and genotype frequencies.calculate the allele and genotype frequencies.In one application, the Har
66、dy-Weinberg law allows us to estimate the frequency of heterozygotes in a population. Xunchao Xiang Southwest University of Science and TechnologySamplen nCystic fibrosis(囊性纤维化囊性纤维化, ,属遗传性胰腺病属遗传性胰腺病), an autosomal recessive trait, has an incidence of about 1/2500=0.0004 in people of European ancestr
67、y. What are the frequency of heterozygotes for cystic fibrosis?n nq2=1/2500, q=0.02n n the frequency of heterozygotes =2pq=2(1-0.02) 0.02=0.04Xunchao Xiang Southwest University of Science and Technologyn nThe incidence of cystic fibrosis=1/2500=0.04%,The incidence of cystic fibrosis=1/2500=0.04%,n n
68、The frequency of heterozygotes=0.04=4%The frequency of heterozygotes=0.04=4%n nIt indicates that heterozygotes for recessive genetic diseases are rather common in some population.Xunchao Xiang Southwest University of Science and Technologyn nIn general, the frequencies of all three genotypes can be
69、estimated once the frequency of either allele is known and Hardy-Weinberg assumptions are invoked.Xunchao Xiang Southwest University of Science and TechnologyThe relationship between genotype and allele The relationship between genotype and allele frequencies derived from the Hardy-Weinberg equation
70、frequencies derived from the Hardy-Weinberg equationXunchao Xiang Southwest University of Science and Technologyn nThe observation confirms the conclusion that when a recessive trait such as cystic fibrosis is rare, the majority of those carrying the allele are heterozygotes. Xunchao Xiang Southwest
71、 University of Science and Technology12.6 Factors That Alter Allele Frequencies in Populationsn nIdeal population: n nRandom mating, absence of selection and mutation, and equal viability and fertility hold. n nNatural population:n nDynamic, and changes in size and gene pool.Xunchao Xiang Southwest
72、University of Science and Technology改变基因平衡的因素A.突变B.选择C.遗传漂变(又称遗传漂移)D.迁移Xunchao Xiang Southwest University of Science and TechnologyA. Mutationn nMendelian assortment and recombination produce new genotypic combinations, but not produce new alleles. n nMutation alone acts to create new alleles.n nMut
73、ation rate: The frequency with which mutations take place at a given locus or in a population.Xunchao Xiang Southwest University of Science and TechnologySamplen nIn humans, a dominant form of dwarfism known In humans, a dominant form of dwarfism known as achondroplasia(as achondroplasia(软骨发育不全软骨发育不
74、全软骨发育不全软骨发育不全), in a survey of ), in a survey of almost 250,000 births, the mutation rate (almost 250,000 births, the mutation rate ( ) for ) for achondroplasia has been calculated asachondroplasia has been calculated asn n =1.4 =1.41010-5-50.50.51010-5-5n nWe represent the normal allele as We repre
75、sent the normal allele as d d, and the , and the allele for achondroplasia as allele for achondroplasia as D D. .n nImagine a population of 500,000 individuals in Imagine a population of 500,000 individuals in which everyone has genotype which everyone has genotype dddd. The initial . The initial fr
76、equency of frequency of d d is 1.0, and the initial frequency of is 1.0, and the initial frequency of D D is 0. is 0. Xunchao Xiang Southwest University of Science and Technologyn nIf each individual contributes 2 gametes to the If each individual contributes 2 gametes to the gene pool, the gene poo
77、l will contain 1,000,000 gene pool, the gene pool will contain 1,000,000 gametes, all carrying allele gametes, all carrying allele d d. While the gametes . While the gametes are in the gene pool, 1.4 of every 100,000 d are in the gene pool, 1.4 of every 100,000 d alleles mutate into a alleles mutate
78、 into a D D allele. allele.n n The frequency of allele The frequency of allele d dn n(1,000,000-14)/1,000,000=0.999986(1,000,000-14)/1,000,000=0.999986n nThe frequency of The frequency of D Dn n14/1,000,000=0.00001414/1,000,000=0.000014Xunchao Xiang Southwest University of Science and TechnologyXunc
79、hao Xiang Southwest University of Science and TechnologyB. Migrationn nVarious evolutionary forces, including selection can establish different allele frequencies in different population. Migration occurs when individuals move between the populations.Xunchao Xiang Southwest University of Science and
80、 TechnologySamplen nImagine a species in which a single locus has Imagine a species in which a single locus has two alleles,two alleles, A A and and a a. There are two populations . There are two populations of this species, one on a mainland, and one on of this species, one on a mainland, and one o
81、n an island. The frequency of an island. The frequency of A A on the mainland is on the mainland is represented by represented by p pmm and the frequency of and the frequency of A A on the on the island is island is p pi i. Under the influence of migration from . Under the influence of migration fro
82、m the mainland to the island, the frequency of the mainland to the island, the frequency of A A in in the next generation on the island (the next generation on the island (p pi i ) is given by ) is given by n np pi i=(1-=(1-mm) )p pi i+ +mpmpmmn nWhere Where mm represents ratio that migrants from th
83、e represents ratio that migrants from the mainland to the island on the all of island.mainland to the island on the all of island.Xunchao Xiang Southwest University of Science and Technologyn nIf either m is large or if pm is very different from pi, then a rather large change in the frequency of A c
84、an occur in a single generation.n nIf migration is the only force acting to change the allele frequency on the island, then an equilibrium will be attained only when pi = pm.Xunchao Xiang Southwest University of Science and Technologyn nThe B allele of the ABO locus in present in a gradient The B al
85、lele of the ABO locus in present in a gradient from east to west. The gradient parallels the waves of from east to west. The gradient parallels the waves of Mongol migration into Europe.Mongol migration into Europe.Xunchao Xiang Southwest University of Science and TechnologyXunchao Xiang Southwest U
86、niversity of Science and TechnologyC. Genetic Driftn nLarge interbreeding populations are essential to Large interbreeding populations are essential to maintain Hardy-Weinberg equilibrium.maintain Hardy-Weinberg equilibrium.n nIn small populations, significant random In small populations, significan
87、t random fluctuations in allele frequencies are possible by fluctuations in allele frequencies are possible by chance deviation.chance deviation.n nGenetic drift(Genetic drift(遗传漂变遗传漂变遗传漂变遗传漂变): Random variation in allele ): Random variation in allele frequency from generation to generation. Most fr
88、equency from generation to generation. Most often observed in small populations.often observed in small populations.n nIn small populations, significant random fluctuations in allele In small populations, significant random fluctuations in allele frequencies are possible by chance deviation. The deg
89、ree offrequencies are possible by chance deviation. The degree of fluctuation increases as the population size decreases, a situation fluctuation increases as the population size decreases, a situation known as genetic drift.known as genetic drift.n n在群体较小时，等位基因频率会发生显著的随机波动。随着在群体较小时，等位基因频率会发生显著的随机波动
90、。随着在群体较小时，等位基因频率会发生显著的随机波动。随着在群体较小时，等位基因频率会发生显著的随机波动。随着群体规模下降，波动程度也增加的情况称为遗传漂变。群体规模下降，波动程度也增加的情况称为遗传漂变。群体规模下降，波动程度也增加的情况称为遗传漂变。群体规模下降，波动程度也增加的情况称为遗传漂变。Xunchao Xiang Southwest University of Science and TechnologyPopulation size and genetic drift群体大小与遗传漂变群体大小与遗传漂变n nIf the frequencies of the allele A
91、and a in a population are p and q, If the frequencies of the allele A and a in a population are p and q, respectively, the standard deviationrespectively, the standard deviation in those samples composed of N in those samples composed of N induviduals is expressed as: induviduals is expressed as: =
92、(pq/2N)= (pq/2N)1/21/2, which indicates that the more , which indicates that the more the sampling err are and the less those samples arethe sampling err are and the less those samples aren nFounder effectFounder effect: The effect that genotypes of a few induviduals control : The effect that genoty
93、pes of a few induviduals control frequencies of their offspring.frequencies of their offspring.n nBottle neck effectBottle neck effect: Changes in allelic frequencies accidentally happen in : Changes in allelic frequencies accidentally happen in the few induviduals subjective to extinction.the few i
94、nduviduals subjective to extinction.n n群体大小与抽群体大小与抽样误样误差的关系差的关系n n奠基者效应：奠基者效应：奠基者效应：奠基者效应：由少数个体的基因频率决定了他们后代中的基因频率的由少数个体的基因频率决定了他们后代中的基因频率的效应。效应。n n瓶颈效应瓶颈效应瓶颈效应瓶颈效应：群体中个体数目急剧减少甚至灭绝的等位基因频率发生的：群体中个体数目急剧减少甚至灭绝的等位基因频率发生的偶然变异。偶然变异。Xunchao Xiang Southwest University of Science and TechnologyXunchao Xiang S
95、outhwest University of Science and TechnologyD. Nonrandom Matingn nNonrandom Mating itself does not directly alter Nonrandom Mating itself does not directly alter the frequencies of alleles. However, the frequencies of alleles. However, it can alter it can alter the frequencies of genotypes in a pop
96、ulation the frequencies of genotypes in a population and and thereby indirectly affect the course of evolution.thereby indirectly affect the course of evolution.n nThe most important form of nonrandom mating is The most important form of nonrandom mating is inbreeding (mating between closely related
97、 inbreeding (mating between closely related organisms). The most extreme form of organisms). The most extreme form of inbreeding , self-fertilization.inbreeding , self-fertilization.Non-random mating非随机交配非随机交配Xunchao Xiang Southwest University of Science and TechnologyXunchao Xiang Southwest Univers
98、ity of Science and Technology12.7 Natural Selectionn nThe first assumption of the law is that individuals The first assumption of the law is that individuals of all genotypes have equal rates of survival and of all genotypes have equal rates of survival and equal reproductive success. If not, allele
99、 equal reproductive success. If not, allele frequencies may change from one generation to frequencies may change from one generation to the next. To see,the next. To see,n n100 individuals of a population, 100 individuals of a population, A A=0.5, =0.5, a a=0.5.=0.5.n n fr(AA)=0.25, fr(Aa)=0.5, fr(a
100、a)=0.25Xunchao Xiang Southwest University of Science and Technologyn nNow suppose different genotypes have different Now suppose different genotypes have different rates of survival to reproduce:rates of survival to reproduce:n nRate of Rate of AAAA=100%, rate of =100%, rate of AaAa=90%, rate of =90
101、%, rate of aaaa=80%,=80%,n n When the survivors reproduce, each contributes When the survivors reproduce, each contributes two gametes to the new gene pool,two gametes to the new gene pool,n n225+ 290%50+ 280%25=180225+ 290%50+ 280%25=180 (gametes)(gametes)n nFrequency of allele Frequency of allele
102、A A=(225+90%50)/180=0.53=(225+90%50)/180=0.53n nFrequency of alleleFrequency of allele a a =(90%50+280%25)/180=0.47=(90%50+280%25)/180=0.47Xunchao Xiang Southwest University of Science and Technologyn nNatural selection: Differential reproduction of some members of a species resulting from variable
103、fitness conferred by genotypic differences.Natural selection is the principal force that shifts Natural selection is the principal force that shifts allele frequencies within large populations and is allele frequencies within large populations and is one of the most important factors in evolutionary
104、 one of the most important factors in evolutionary change.change.Xunchao Xiang Southwest University of Science and TechnologyFitness and Selectionn nFitness(Fitness(适合度适合度适合度适合度): A measure of the relative survival ): A measure of the relative survival and reproductive success of a given individual
105、or and reproductive success of a given individual or genotype.genotype.n n适合度：为成熟个体经自然选择后的生存率。适合度：为成熟个体经自然选择后的生存率。适合度：为成熟个体经自然选择后的生存率。适合度：为成熟个体经自然选择后的生存率。n nHardy-Weinberg analysis also allows us to Hardy-Weinberg analysis also allows us to examine fitness. By convention, the letter examine fitness.
106、 By convention, the letter w w is is used to represent fitness.used to represent fitness.n nw wAAAA, , w wAaAa and and w waaaa represent the relative fitness of represent the relative fitness of genotype genotype AAAA, , AaAa and and aaaa, respectively. , respectively. Xunchao Xiang Southwest Univer
107、sity of Science and TechnologySamplen nBecause individuals with Because individuals with 32/ 32/ 32 32 genotype are genotype are resistant to most sexually transmitted strains of resistant to most sexually transmitted strains of HIV-1, we might expect AIDS to act as a HIV-1, we might expect AIDS to
108、act as a selective force causing the frequency of the selective force causing the frequency of the 32 32 allele to increase over time.allele to increase over time.n nImagine a population in which the current Imagine a population in which the current frequency of the frequency of the 32 32 allele = 0
109、.1,allele = 0.1,n n the genotype frequencies:the genotype frequencies:n n1/11/1=0.81, =0.81, 1/1/ 32 32 =0.18, =0.18, 32/ 32/ 32 32 =0.01=0.01Xunchao Xiang Southwest University of Science and Technologyn n If fitness levels to the genotypes as follows: If fitness levels to the genotypes as follows:
110、n nw w1/11/1=0.99, =0.99, w w1/1/ 3232 =0.99, =0.99, w w 32/ 32/ 3232 =1.0=1.0n nWhen the survivors reproduce, each contributes When the survivors reproduce, each contributes two gametes to the new gene pool,two gametes to the new gene pool,n n299%0.81+ 299%0.18+ 299%0.81+ 299%0.18+ 2100%0.01=1.9802
111、 2100%0.01=1.9802 (gametes)(gametes)n nFrequency of alleleFrequency of allele 3232 =(99%=(99% 0.18+20.18+2 100%100% 0.01)/1.9802=0.1000910.01)/1.9802=0.100091n nIn fact, it will take about 100 generations (about In fact, it will take about 100 generations (about 2000 years) for the frequency of the
112、2000 years) for the frequency of the 3232 allele allele to reach just 0.11.to reach just 0.11.Xunchao Xiang Southwest University of Science and TechnologyThe rate at which the frequency of the allele changes in The rate at which the frequency of the allele changes in hypothetical populations with di
113、fferent initial hypothetical populations with different initial frequencies and different fitnessesfrequencies and different fitnessesXunchao Xiang Southwest University of Science and TechnologySelection in Natural PopulationXunchao Xiang Southwest University of Science and TechnologyXunchao Xiang S
114、outhwest University of Science and TechnologyNatural Selection and Quantitative Traitsn nMost phenotypic traits are controlled not by Most phenotypic traits are controlled not by alleles at a single locus but by the combined alleles at a single locus but by the combined influence of the individuals
115、genotype at many influence of the individuals genotype at many different loci and the environment. Because different loci and the environment. Because selection is a consequence of the organisms selection is a consequence of the organisms genotypic/phenotypic combination, polygenic or genotypic/phen
116、otypic combination, polygenic or quantitative traits also respond to selection.quantitative traits also respond to selection.n nSelection for such traits can be classified as Selection for such traits can be classified as (1) directional, (2)stablizing, or (3)disruptive.(1) directional, (2)stablizin
117、g, or (3)disruptive.Xunchao Xiang Southwest University of Science and TechnologyDirectional selectionn nLong-term selection to alter the oil content of corn kernelsLong-term selection to alter the oil content of corn kernelsXunchao Xiang Southwest University of Science and TechnologyStabilizing Sele
118、ctionn nRelationship between birth and mortality in humanRelationship between birth and mortality in humanXunchao Xiang Southwest University of Science and TechnologyDisruptive Selection( (分裂选择分裂选择分裂选择分裂选择) ) The effect of disruptive selection on bristle number in drosophilaXunchao Xiang Southwest U
119、niversity of Science and Technologyn nThe impact of stabilizing, directional, and disruptive selection.Xunchao Xiang Southwest University of Science and Technology12.8 Origin of life and theory of biological evolution地球生命的起源是一个长达约35亿年的历史，经历了以下历程：有机物质与非细胞生命形式形成；非细胞生物细胞生物；原核细胞真核细胞、单细胞生物多细胞生物；水生生物陆生生物；
120、高等生物的形成与动植物分化。生命现象有四个最基本的特征：生长、生殖、新陈代谢与适应性Xunchao Xiang Southwest University of Science and Technology不定微小变异广泛存在，并且都是可遗传的；变异导致生物个体间(特别是同种个体间)表型和适应性差异；选择(人工与自然选择)保留符合人类要求、适应环境的类型(适者生存)；长期选择和变异积累导致物种演化、新物种产生(因而生物进化与物种形成是渐变式的)。达尔文的获得性状遗传达尔文的获得性状遗传Xunchao Xiang Southwest University of Science and Techno
121、logy狄弗里斯对普通月见草(Oenothera lamarckiana)进行研究时候发现：一些新类型是突然产生的，并且只要一代自交就达到遗传稳定。狄弗里斯据此提出了突变论。突变论认为：自然界新种的形成不是长期选择的结果，而是突然出现的；这一观点与达尔文选择学说和拉马克学说均不相符，并且有明确的试验证据。狄狄弗里斯的突变论弗里斯的突变论Xunchao Xiang Southwest University of Science and Technology选择只能将混合群体中已有变异隔离开来，并没有表现出创造性作用；所以选择可能并不是生物进化的动力。纯系内选择无效，由环境引起的变异是不可遗传，没
122、有进化意义，所以拉马克的获得性状遗传也是没有根据的。约翰生的纯系学说约翰生的纯系学说Xunchao Xiang Southwest University of Science and Technology基因论不仅能解释自然选择学说与突变论、纯系学说的矛盾，也解决了个体水平进化的遗传变异机制难题。变异分为：遗传变异和不可遗传变异；遗传变异主要由染色体和基因变异以及遗传重组产生。染色体数目、结构均可变异，基因突变则是基因化学结构改变；自然界巨大突变较少，而微小不定变异占大多数；微小突变必须通过选择积累才能形成新种。基因论将自然选择学说与遗传学统一起来，一般都将这一发展认为是新达尔文主义的继续。摩
123、尔根的基因论摩尔根的基因论Xunchao Xiang Southwest University of Science and Technology如今最广为人知的生物进化论仅限于上述内容。但是科学研究者从没有停止探索，生物进化机制与历程研究的发展即使不再象它创立时那么突出、辉煌，却从来也没有停止发展。探索的结果是发展、形成了生物进化的新理论，主要包括： 群体遗传水平的“进化综合理论”；分子遗传水平的“中性学说”。Xunchao Xiang Southwest University of Science and Technology群体是生物进化的基本单位，进化就是群体遗传结构(基因频率)的改变
124、；基因突变是偶然的、与环境无必然联系；突变、基因重组、选择和隔离是生物进化和物种形成的基本环节；自然选择是连接物种基因库和环境的纽带，自动地调节突变与环境的相互关系，把突变偶然性纳入进化必然性的轨道，产生适应与进化。自然选择存在多种机制和模式，并从群体水平与分子水平进行了阐述。进化综合理论进化综合理论(synthetic theory of evolution)Xunchao Xiang Southwest University of Science and Technology分子水平研究发现生物基因组中存在中性基因变异：不同等位基因间碱基序列存在差异，但无表型选择作用。中性基因频率改变不是
125、选择压引起，而主要是由遗传漂变引起。中性基因可能有以下几种情况：中性基因可能有以下几种情况：氨基酸序列改变、性状变异，但无选择意义(中性性状)；氨基酸序列改变，但蛋白质功能不发生改变(中性突变)；氨基酸序列不改变(同义突变)。分子水平进化分子水平进化的中性学说的中性学说Xunchao Xiang Southwest University of Science and TechnologyXunchao Xiang Southwest University of Science and TechnologyXunchao Xiang Southwest University of Science
126、 and Technology原原始始人人的的进进化化Xunchao Xiang Southwest University of Science and TechnologyXunchao Xiang Southwest University of Science and Technology12.9 Species formation1. 物种(species)的概念物种是具有一定形态和生理特征、分布在一定区域内的生物类群，是生物分类的基本单元，也是生物繁殖和进化的基本单元。判断不同的变种或居群间差异是否成为不同物种，也即界定物种的主要标准是：是否存在生殖隔离、能否进行相互杂交。这一标准最初
127、是由林耐所确立的；同种的个体间可以交配产生后代，进行基因交流从而消除群体间的遗传结构差异；不同物种的个体则不能交配或交配后不能产生有生殖力的后代，因此不能进行基因交流。Xunchao Xiang Southwest University of Science and Technology2. 隔离与物种形成隔离在生物进化尤其是新物种的形成过程中占有重要的地位。来自同一物种(遗传结构相同)的不同居群，如果形成了某种形式的隔离，居群间不能进行基因交流、群体遗传结构差异逐渐增大，最终产生生生殖隔离殖隔离；首先形成不同亚种，最后形成不同物种。群体内或群体间即使存在遗传结构差异，如果没有隔离，随机交配将
128、消除差异，而不会歧化形成新的物种。Xunchao Xiang Southwest University of Science and Technology3. 物种形成的方式渐变式渐变式：在一个长时间内旧的物种逐渐演变形成新的物种，是物种形成的主要形式。也是自然选择学说所描述的新物种形成方式。爆发式爆发式：短期内以飞跃形式形成新的物种，往往没有复杂的中间亚种阶段。主要在高等植物普遍存在。Xunchao Xiang Southwest University of Science and Technology渐变式 继承式继承式一个物种在各种改变基因频率因素(突变、选择等)作用下，变异累积导致群体
129、遗传结构改变，经过一系列中间类型过渡为新物种。(无需隔离作用)分化式分化式一个物种在变异累积和隔离(地理隔离与生态隔离)共同作用下，形成先形成两个或两个以上的地理亚种或生态亚种；亚种间遗传结构进一步分化形成生殖隔离，从而分化形成两个或两个以上的新物种。(需要隔离作用)Xunchao Xiang Southwest University of Science and Technology爆发式新物种的爆发形成机制：突变：一系列大突变相继产生。染色体结构变异：倒位与易位。染色体数目变异：同源多倍体化；远缘杂种染色体数目加倍。Xunchao Xiang Southwest University of
130、 Science and TechnologyXunchao Xiang Southwest University of Science and Technologyu知 识 点 群体和基因库；计算等位基因频率；Hardy-Weinberg定律及其扩展；用Hardy-Weinberg定律计算杂合体频率；群体中改变等位基因频率的因素；自然选择；生命起源和生物进化理论；物种形成。u重 点 计算等位基因频率；Hardy-Weinberg定律及其扩展。u难 点 用Hardy-Weinberg定律计算杂合体频率；群体中改变等位基因频率的因素。 Highlightsu基本要求n1. 识 记：群体遗传学（p
131、opulation genetics）、孟德尔群体（Mendel population）、基因库（gene pool）、等位基因频率（allele frequency）、基因型频率（genotype frequency）、Hardy-Weinberg平衡（Hardy-Weinberg equilibrium）、理想群体（ideal population）、自然群体（natural population）、遗传漂变（genetic drift）、自然选择（natural selection）、适合度（fitness）、物种（species） Highlightsn2. 领 会：等位基因频率和基因
132、型频率；Hardy-Weinberg定律；Hardy-Weinberg平衡；理想群体和自然群体。 n3. 简单应用：等位基因频率和基因型频率的计算；Hardy-Weinberg平衡的判定；改变等位基因频率的因素。 n4. 综合应用：非平衡大群体后代等位基因频率和基因型频率的计算；杂合体频率的计算。 Highlightsu 考核要求n1. 本章重点名词的英语词汇；n2. Hardy-Weinberg定律； n3. 等位基因频率和基因型频率的计算；n4. Hardy-Weinberg平衡的判定；n5. 改变等位基因频率的因素；n6. 非平衡大群体后代等位基因频率和基因型频率的计算；n7. 杂合体频率的计算。Highlights
