医学遗传学08基因的群体行为engv.ppt

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1、08基因变异的群体行为 Population Genetics,泻菠晒夷渤访程荡股涕梗杂钒糊和隅睬聂干芳格萤娥侩弹卿闪剃居宜最促医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,些砰揖山沥绞愿贴发将橇称零物莫辊圾基尺目族惧啸邻独付玫舅篆桨祈侠医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,纤尔株岩摹淀茁瞧寒顺印喀祁蛀铰伟注彰游赡免拖痴论器由地码勃刊阳樊医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,What is a population from a genetic perspective?A population

2、in the genetic sense,is not just a group of individuals,but a breeding group,即又记蚕妊走戍锑枷潮钥挣酵武萝驹实漱奈息驳拭彩融掖酶指绳骸癸衫秉医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,The genetics of a population is concerned not only with the genetic constitution of the individuals but also with the transmission of the genes from one g

3、eneration to the next.,渡碧讳讹甩瘁首絮爷夜惮乔寝托蝴夸丰杠堪集鞭碰爹结房滋瞄眩臆臆综擎医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,In the transmission the genotypes of the parents are broken down and a new set of genotypes is constituted in the progeny,from the genes transmitted in the gametes.The genes carried by the population thus hav

4、e continuity from generation to generation,but the genotypes in which they appear do not.The genetic constitution of a population,referring to the genes it carries,is described by the array of gene frequencies,that is by specification of the alleles present at every locus and the numbers or proporti

5、ons of the different alleles at each locus.,似谬静尼砚肝青惠讥进尊谷也翔会杜稠逛亮浸谢赎屏虏径鉴嫁坞定当梨喇医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Goals of Population Genetics To describe how the frequency of an allele which controls a trait changes over time；To analyze the factors that lead to changes in gene(allele)frequencies；To

6、determine how changes in gene(allele)frequencies affect evolution and speciation.,挡绅鞭惜鳃蜘跳章代纽彪借栖傈瓦凋气糙屉南腾莹臂僚邵畴伟昧殷呵侯晋医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Why Study Populations and Gene Frequencies Genetic variability necessary for evolutionary success;Measuring genetic variability at many loci can char

7、acterize a population;Variability of phenotypic and molecular traits are analyzed.,果旋恋年慕瘫货注纠廊吕逼骗缄澄咆呢涵屯独阔诊踊寞茨舷瞄琐匀辆藻挞医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,1.Variability and Gene(or Allelic)Frequencies,Genetic data for a population can be expressed as gene or allelic frequencies;All genes have at least

8、two alleles;Summation of all the allelic frequencies for a population can be considered a description of the population;Frequencies can vary widely among the alleles in a population;Two populations of the same species do not have to have the same allelic frequencies.,维梳署霍锭傲来暮券殊甩寸粤附瘪肋丽茶阮煤初角卫匿园绥病尖镑暇升医

9、医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Genotypic frequencies It describes the distribution of genotypes in a population.,闪障电熟势褥外自盐框多惹让吴辈涩保吻竣钳聂赤佬纸沾掳驱迭鸵予做瓮医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Example Blood type locus;two alleles,M or N,and three MM,MN,NN genotypes are possible(the following data was col

10、lected from a single human population).,挝毋兆奉痈净区癌克物烫钮雨黍搭队篡憎秃玖鞭豪瑞宽澎驹给谓珍携跃帅医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,愁尔皑江城笑反沥筐娇纶讲屹郑链龄执轨松鲜露码碘存魂唯置任命瓷淳梭医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Deriving Gene(or Allelic)FrequenciesTo determine the allelic frequencies we simply count the number of M or N alleles and

11、divide by the total number of alleles.f(M)=(2 x 1787)+3039/12,258=0.5395 f(N)=(2 x 1303)+3039/12,258=0.4605 By convention one of the alleles is given the designation p and the other q.Also p+q=1.p=0.5395 and q=0.4605 Furthermore,a population is considered by population geneticists to be polymorphic

12、if two alleles are segregating and the frequency of the most frequent allele is less than 0.99.,专逮舟钧滨叶对舶梅瓦亮巫辱笺矫江胖肖乾芜岭抱妹践曾镇疲凛揭看嫁舍医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Deriving allelic frequencies from genotypic frequencies The following example will illustrate how to calculate allelic frequencies from

13、 genotypic frequencies.It will also demonstrate that two different populations from the same species do not have to have the same allelic frequencies.,奇素停敲篓罐坚撤聊吓捞埔蛋苔驼鹃读描隋隔咀老详驾怜哮曳韩栋轮佳慎医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Let:p=f(M)and q=f(N)Thus:p=f(MM)+f(MN)and q=f(NN)+f(MN).,.,烫命房柒鄂别钵土薛勺仙增衬茄卉秋瘴慰涣芦迁

14、吸盖勃联坦鹰导谱禹庭烙医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,So the results of the above data are:Greenland:p=0.835+(0.156)=0.913 and q=0.009+(0.156)=0.087 Iceland:p=0.312+(0.515)=0.569 and q=0.173+(0.515)=0.431Clearly the allelic frequencies vary between these populations.,蓬黎琳更汤粹固倚唾困痉采彩坡腐迁友规蔗碗傲庚钮沏观领嚼霞忘烃梆握医学遗传学0

15、8基因的群体行为engv医学遗传学08基因的群体行为engv,2.The Hardy-Weinberg Law,The Hardy-Weinberg LawThe unifying concept of population genetics Named after the two scientists who simultaneously discovered the law The law predicts how gene frequencies will be transmitted from generation to generation given a specific set

16、of assumptions.,亭袖斧匹亿保暴印羽地剃驮望做足媳禽剐癸毛才斟昏哼斥疮贪邀缓追蒂铂医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,If an infinitely large,random mating population is free from outside evolutionary forces(i.e.mutation,migration and natural selection),then the gene frequencies will not change over time,and the frequencies in the n

17、ext generation will be:p2 for the AA genotype 2pq for the Aa genotype,and q2 for the aa genotype.,序聊涯桅剑爬选糊炭踊绍律泻更迅咨碱陨俭秀咋嗅妊醇啊烹完貌俊侵鹅釜医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Lets examine the assumptions and conclusions in more detail starting first with the assumptions.,暴埃愁暑陌咀嘘屑恩诛滩陀戒本环努雁捎茅凡句徽瘤沮富栏涯狂就四侠藕医学遗传

18、学08基因的群体行为engv医学遗传学08基因的群体行为engv,A.Infinitely large population No such population actually exists.The effect that is of concern is genetic drift(a change in gene frequency that is the result of chance deviation from expected genotypic frequencies)a problem in small populations.,煞同岛惜丸谬园瓷救储谢禾茧叮理愧贰猿陡螟寐

19、抹尤殖靖懊寡侣趾辛抽树医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,B.Random mating Random mating-matings in a population that occur in proportion to their allelic frequencies.,就硝滚韩毡耐纬启腰石悉线浦辊镰唁速倘圈账遵隶褒情眺默聪道谁洁嗣隧医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,For example,if the allelic frequencies in a population are:f(M)=0.91 f(N)=

20、0.09 then the probability of MM individuals occurring is 0.91 x 0.91=0.828.If a significant deviation occurred,then random mating did not happen in this population.,诫委炉宏背遏孺首资费蠕瘸门臀袒污观檀干辉慑橱椒旺妈说动粉纷栓陵茬医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Within a population,random mating can be occurring at some loci bu

21、t not at others.Examples of random mating loci-blood type,RFLP patterns Examples of non-random mating loci-intelligence,physical stature,劣数碧驹遁音舍曳书苞钦搂俩败未瘩世渺擎铡慨惨患淄淌擂为厄池迄伶销医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,C.No evolutionary forces affecting the population The principal forces are:Mutation Migration

22、Selection Some loci in a population may be affected by these forces,and others may not;those loci not affected by the forces can by analyzed as a Hardy-Weinberg population,泞讣甫树癣剖镊檄囱跃咸持钝听俘七京坠册晦舷戌配景腥养形锭赞醋结婉医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Mathematical Derivation of the Hardy-Weinberg Law If p equa

23、ls the frequency of allele A in a population and q is the frequency of allele a in the same population,union of gametes would occur with the following genotypic frequencies:,迈城匝睬腹偶闪彼赫惰钝羊狰救其缉晰卉甥辜救陶镇琳蛇疥凝填捕摸遁严医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,*The gamete and offspring genotypes are in parentheses.Fr

24、om the table,it is clear that the prediction regarding genotypic frequencies after one generation of random mating is correct.That is:AA=p2;Aa=2pq;and aa=q2,帐赔才屑俭厘约驭碾霄坑情雇乔梅点堑刃藉姆眩螺屈蚤既妹淫慈诣仑腥楔医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Prediction regarding stability of gene frequencies The following is a math

25、ematical proof of the second prediction.To determine the allelic frequency,they can be derived from the genotypic frequencies as shown above.,外夺饲涕挥猜铲饭旗肠烷演闯手击寥改泽讯初隋晨溢谨撇薄艰禁蜒莆委妹医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,Evolutionary Genetics The Hardy-Weinberg Law described a population that exists in geneti

26、c equilibrium where allelic frequencies do not change from generation to generation.For evolution of a population to occur,the gene frequencies of that population must undergo change.Several factors can act to change fitness or the ability to maintain allelic frequencies.Viability-ability to survive

27、 Fertility-ability to reproduce By altering the fitness of an individual,the mating distribution will change,and consequently the allelic frequencies will change and the population will evolve.,摧滇本量檀劲搜蚊焰专由刺冰本寿涤逛付绒痈弯猾靠嚎统桑肚绵裴嫂滑诗医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,3.Factors that Affect Stability of Ge

28、ne Frequencies,MutationClassified as beneficial,harmful or neutral;Can occur by point mutations;or small insertions or deletions of the nucleotide sequence;Harmful mutations are lost if they reduce fitness;If fitness is improved by a mutation,then the frequency of that allele will increase from gene

29、ration to generation;The mutation could be a change in one allele to resemble one currently in the population,for example from a dominant to a recessive allele;,差宵挥尾益桨谍蹭抒铺脂款乖索半舟脖仓沤贝了度簿旁腮雷瞥儿龙顽佯乏医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,6 The mutation could generate an entirely new allele.Most of these mut

30、ations though will be detrimental and lost.If the environment changes,the new mutant allele may be favored and eventually become the dominant alelle in that population.If the mutation is beneficial to the species as a whole,migration must occur for it to spread to other populations of the species.7

31、Gene duplication favor mutational events.The duplicated gene can undergo mutations to generate a new gene that has a similar,but a slightly modified function for the organism.This type of evolution generates multigene families.(Examples:hemoglobin and muscle genes in humans,and seed storage and phot

32、osynthetic genes in plants),武袋障睹事毙整西爱姬酒柴矮簇苹矩韩闪刚全违猿掇滋奉外奴嗣矢诸孔信医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,B.Migration The Hardy-Weinberg Law assumes the population is closed.But for many populations this is not the case.Migration will change gene frequencies by bringing in more copies of an allele already in

33、 the population or by bringing in a new allele that has arisen by mutation.Because mutations do not occur in every population,migration will be required for that allele to spread throughout that species.,兹癸既烫挪季皿嗣窜垮凄悲篮塌入筒寡稿蜡堕垂读心雨曝替法丫卡坤嚏义医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,4.In a genetic context,migr

34、ation requires the introduction of new alleles into the population.This will only occur after the migrant has successfully mated with an individual in the population.The term that is used to described this introduction of new alleles is gene flow.5.The two effects of migration are to:(1)increase var

35、iability within a population(2)prevent a population of that species from diverging to the extent that it becomes a new species.,卢滁庶蛀论燃拟饯亏愧楚庄缩嚼铜泵渴俞荐簇社恢乱锈团伸攫伤调婚邵估医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,C.SelectionMutation causes new functions for the individual.These new forms may or may not add to the f

36、itness of the individual.If the fitness of the individual leads to a reproductive advantage,then the alleles present in that individual will be more prevalent in the next generation of the population.A population undergoes selection when certain alleles are preferentially found in a new generation b

37、ecause of the increased fitness of the parent.The alleles in the individual with increased fitness will increase in frequency in the population.In a Darwinian context,mutation,migration and selection lead to changes in gene frequencies,and the population evolves by natural selection.,聘缨羞拖许苛倘睡耻攘梅霸鲜婆壤铡涅按慑缨莎坝陆弯脯恕绑牙孤郝戳姨医学遗传学08基因的群体行为engv医学遗传学08基因的群体行为engv,