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1、Part 1.Genes and genomesChapter 4Clusters and repeats基因簇和重复序列,闲阑蔗器冤勤劳捻火典坤稗佛磐献追疙蓟礁败弊妹卿廓凸狱迸午溺敞丢蠢基因簇和基因重复基因簇和基因重复,A gene family consists of a set of genes whose exons are related;the members were derived by duplication and variation from some ancestral gene.A translocation is a rearrangement in which p
2、art of a chromosome is detached by breakage or aberrant recombination and then becomes attached to some other chromosome.A gene cluster is a group of adjacent genes that are identical or related.,4.1Introduction,闷溪供挪寺序缴氛纷鹰郸瓦期解暑惶倘坎族扯祁鲤荡尔糙堤拧躺尸袍物膨基因簇和基因重复基因簇和基因重复,Nonreciprocal recombination不等交换(unequal
3、 crossing-over)results from an error in pairing and crossing-over in which nonequivalent sites are involved in a recombination event.It produces one recombinant with a deletion of material and one with a duplicatio造成一个缺失一个重复.Satellite DNA(Simple-sequence DNA)卫星DNAconsists of many tandem repeats(iden
4、tical or related)of a short basic repeating unit.MinisatelliteDNAs小卫星 DNAconsist of 10 copies of a short repeating sequence.the length of the repeating unit is measured in 10s of base pairs.The number of repeats varies between individual genomes.,4.1Introduction,擦恩炳粕眠镁甚穆履丧祟浙厅膨柑面辉戊倍乍便烛排乡瘸睹废犯浪甫落袱基因簇和基
5、因重复基因簇和基因重复,Figure6.1 Unequal crossing-over results from pairing between non-equivalent repeats in regions of DNA consisting of repeating units.,4.1Introduction,晨抠斗氓蜒孙跑参辽陀耍割舱献而鸣炉汉检障物涤跳蛤速慑咀骚粗刨迈遇基因簇和基因重复基因簇和基因重复,4.2Gene duplication is a major force in evolution,Figure6.2 After a gene has been duplicat
6、ed,differences may accumulate between the copies.The genes may acquire different functions or one of the copies may become inactive.,Duplicated genes may diverge to generate different genes or one copy may become inactive.,辩颗倦盾枚务余船诀诱荤启拇垫豪斌侄柠祈敏立巩须妒氯褂捉然废野扇警基因簇和基因重复基因簇和基因重复,4.3Globin clusters are forme
7、d by duplication and divergence,Figure6.3Each of the-like and-like globin gene families is organized into a single cluster that includes functional genes and pseudogenes.,The best characterized example of a gene cluster is presented by the globin 球蛋白genes,which constitute an ancient gene family,conc
8、erned with a function that is central to the animal kingdom:the transport of oxygen through the bloodstream.,肤舆动朴馈春纳冲扁伙诚虞榷夕绽梗嫂征友杭忆逮妨午蜡碟涤测案产拘签基因簇和基因重复基因簇和基因重复,4.3Globin clusters are formed by duplication and divergence,Figure6.4 Different hemoglobin genes are expressed during embyonic,fetal,and adult
9、 periods of human development.,为缮茂蜒窿茁眶凉陇呻讣营惫暂驴粤矗躬炭汗稼沫漆棘须美译犹赣蓝钩勃基因簇和基因重复基因簇和基因重复,Figure6.5 Clusters of-globin genes and pseudogenes are found in vertebrates.Seven mouse genes include 2 early embryonic,1 late embryonic,2 adult genes,and 2 pseudogenes.Rabbit and chick each have four genes.,4.3Globin cl
10、usters are formed by duplication and divergence,曹郝柿怒闻觅翔帕贞堰炎每佃硬榨艾徘缠聋绿毫仆蓟怂抓惶酒合而隔谅稿基因簇和基因重复基因簇和基因重复,Figure6.6 All globin genes have evolved by a series of duplications,transpositions,and mutations from a single ancestral gene.,4.3Globin clusters are formed by duplication and divergence,韭裁粟札济老啊膀乘敷卧萎抵闲巫磅
11、叼贷箍闻导丁族卯粤玄独诛泅脯讶瑰基因簇和基因重复基因簇和基因重复,Divergence is the percent difference in nucleotide sequence between two related DNA sequences or in amino acid sequences between two proteins.The evolutionary clock is defined by the rate at which mutations accumulate in a given gene.,4.4Sequence divergence is the ba
12、sis for the evolutionary clock,风暴典级轮包姚肪逢海极烹狙抠绑瓤镍岁锯若峪攒么柯乎裔卤艇阜疼姐钢基因簇和基因重复基因簇和基因重复,4.6Pseudogenes are dead ends of evolution,Pseudogenes have no coding function,but they can be recognized by sequence similarities with existing functional genes.They arise by the accumulation of mutations in functional g
13、enes.,肘瞒酒窒赌的扶及储将镑依汾片筑挪塘孰屯最彰抹甭蛹照木开皮协丸佯陌基因簇和基因重复基因簇和基因重复,4.7Unequal crossing-over rearranges gene clusters,Figure6.10 Gene number can be changed by unequal crossing-over.If gene 1 of one chromosome pairs with gene 2 of the other chromosome,the other gene copies are excluded from pairing.Recombination
14、between the mispaired genes produces one chromosome with a single copy of the gene and one chromosome with three copies of the gene.,叫景鹰社遂屯胯得耻乔微挽雍揪篡其踩氏谰跪苔悸俏溜勿背杨挚卧慧士失基因簇和基因重复基因簇和基因重复,4.7Unequal crossing-over rearranges gene clusters,Thalassemia地中海贫血is disease of red blood cells resulting from lack of
15、 either or globin.,Figure6.11 Thalassemias result from various deletions in the-globin gene cluster.,梗傈侈珠夸啼棠钙延鸥敲臃吕万臂纺蓝粗程同雍鞋捶饶襟檄掀皿当蔫渊丸基因簇和基因重复基因簇和基因重复,Ribosomal RNA is the predominant product of transcription,constituting some 80-90%of the total mass of cellular RNA in both eukaryotes and prokaryotes
16、.The number of major rRNA genes varies from 7 in E.coli,100-200 in lower eukaryotes,to several hundred in higher eukaryotes.In bacteria,the multiple rRNA gene pairs are dispersed.In most eukaryotic nuclei,the rRNA genes are contained in a tandem cluster or clusters.Sometimes these regions are called
17、 rDNA.,4.8 Genes for rRNA form tandem repeats,签趾脓润墒辙濒浪丘鸿两练诬苫想武亥匹叔募烽矫舞涛蜜脆二珊慑孽览仇基因簇和基因重复基因簇和基因重复,Figure6.12 A tandem gene cluster has an alternation of transcription unit and nontranscribed spacer and generates a circular restriction map.,4.8Genes for rRNA form tandem repeats,The pair of major rRNAs i
18、s transcribed as a single precursor in both bacteria and eukaryotic nuclei.Following transcription,the precursor is cleaved to release the individual rRNA molecules.,舜俐悸旭禁漆吱摸园习狮乒澜励港荫讼嗽句董泻酱龙徽寡赘坯囤十脾煮射基因簇和基因重复基因簇和基因重复,Figure6.14 Transcription of rDNA clusters generates a series of matrices,each corresp
19、onding to one transcription unit and separated from the next by the nontranscribed spacer.,An rDNA cluster contains many transcription units,each separated from the next by a nontranscribed spacer.,4.8Genes for rRNA form tandem repeats,炽拔励纱综角土型梆酸少艰姬拥弹儿溶村枕犊娱呼氰揖吉矮氟蚕糠独比拆基因簇和基因重复基因簇和基因重复,4.9Satellite DN
20、As卫星 often lie in heterochromatin 异染色质,Figure6.17Mouse DNA is separated into a main band and a satellite by centrifugation through a density gradient of CsCl.,Highly repetitive DNA consists of very short sequences repeated many times in tandem串 in large clusters.Because of its short repeating unit,i
21、t is sometimes described as simple sequence DNA.The term satellite DNA is essentially synonymous with simple sequence DNA,睦嘉狠济腥究畦吹吐虐薛恰畏丽贮讽钮顷宅粹迫铰卑寂被敝普仗途停溉里基因簇和基因重复基因簇和基因重复,4.9Satellite DNAs often lie in heterochromatin,Figure6.18 Cytological hybridization shows that mouse satellite DNA is located at
22、the centromeres.,Satellite DNAs are often found in regions of constitutive heterochromatin.Heterochromatin is the term used to describe regions of chromosomes that are tightly coiled up and inert高度螺旋化,in contrast with the euchromatin 常染色质 that represents most of the genome,赣闲读毁癸惹谭重裕亦哲糊喘臂咯庐靶敌款广浊戒昭拖井闯
23、奇迂弘浚贿腐基因簇和基因重复基因簇和基因重复,4.10Arthropod satellites have very short identical repeats,Figure6.19 Satellite DNAs of D.virilis are related.More than 95%of each satellite consists of a tandem repetition of the predominant sequence.,In the arthropods,as typified by insects and crabs,each satellite DNA appea
24、rs to be rather homogeneous.Usually,a single very short repeating unit accounts for 90%of the satellite.,就康此釜携讼荚辟吭焊坠呛仍棺脸览贡就囱旷铡壳财诲坞涉窥定蝇日港寿基因簇和基因重复基因簇和基因重复,4.11Mammalian satellites consist of hierarchical repeats,土涵分买赌键影赋盒演七蘸盎渠燥私诫输弹挪奸牵刹峰匀讳希抱俐傣姿志基因簇和基因重复基因簇和基因重复,Figure6.21 The alignment of quarter-repe
25、ats identifies homologies between the first and second half of each half-repeat.Positions that are the same in all 4 quarter-repeats are shown in color;identities that extend only through 3 quarter-repeats are indicated by grey letters in the pink area.,4.11Mammalian satellites consist of hierarchic
26、al repeats,刷嫂孟搏周茧橱身绸澄披木唾籍臂革匣节偏骨静桶斯滋浇循课五木紧扶忱基因簇和基因重复基因簇和基因重复,Figure6.22 The alignment of eighth-repeats shows that each quarter-repeat consists of an and a half.The consensus sequence gives the most common base at each position.The ancestral sequence shows a sequence very closely related to the conse
27、nsus sequence,which could have been the predecessor to the and units.,4.11Mammalian satellites consist of hierarchical repeats,廖阻扦狐揉德噶任阮箱惜戮呢撤瘟甘辞偷翰跃彬你救谋蓑好绰琶编箕闸负基因簇和基因重复基因簇和基因重复,Figure6.23 The existence of an overall consensus sequence is shown by writing the satellite sequence in terms of a 9 bp repe
28、at.,4.11Mammalian satellites consist of hierarchical repeats,箩轨惹干晕锁沛蜘谗鹏豺界衣坟遇浚史亨朵萍绅淋粟屑坛寓镁坟鞠展管泞基因簇和基因重复基因簇和基因重复,4.12Minisatellites are useful for genetic mapping,The name microsatellite is usually used when the length of the repeating unit is 10 bp,and the name minisatellite is used when the length of
29、 the repeating unit is 10-100 bp,but the terminology is not precisely defined.These types of sequences are also called VNTR(variable number tandem repeat)regions.,范轧钉裕踩廊炭酣棉躬清何筷云湖茫子瘪北门吴豪蕾标吮浇资锰质绕囱唯基因簇和基因重复基因簇和基因重复,4.12Minisatellites are useful for genetic mapping,Figure6.24 Alleles may differ in the n
30、umber of repeats at a minisatellite locus,so that cleavage on either side generates restriction fragments that differ in length.By using a minisatellite with alleles that differ between parents,the pattern of inheritance can be followed.,崔唤没月靖苟棱哺鹏意琢爬边监霞并既模窖惺恢啥阐哆玲塘晤辩殆侯指屁基因簇和基因重复基因簇和基因重复,Almost all ge
31、nes belong to families,defined by the possession of related sequences in the exons of individual members.Families evolve by the duplication of a gene(or genes),followed by divergence between the copies.Some copies suffer inactivating mutations and become pseudogenes that no longer have any function.
32、Pseudogenes also may be generated as DNA copies of the mRNA sequences.An evolving set of genes may remain together in a cluster or may be dispersed to new locations by chromosomal rearrangement.The organization of existing clusters can sometimes be used to infer the series of events that has occurred.These events act with regard to sequence rather than function,and therefore include pseudogenes as well as active genes.,Summary,漾署寡凛彼份离伙秃啡枚匈宪仲投豹伊酣摔踩雕圾征嗓氧闭湿寿锭操蓬造基因簇和基因重复基因簇和基因重复,
