医学遗传学课件：Chapter6-8 多态性与突变

1、Chapter 6 Genetic Variation in Individuals: Mutation and Polymorphism 1 Mutation and Polymorphism 2 MUTATION（1） Mutation: is defined as any changes in the nucleotide sequence or arrangement of DNA Neutral mutation, Pathogenic mutations 3 MUTATION（2） vThe categories of Human Mutation 1. Genome Mutati

2、ons 2. Chromosome Mutations 3. Gene Mutations 4 The Origin of Mutations 5 The origin of Genome Mutations 6 Genome Mutations arising from error in chromosome segregation during meiosis or mitosis, such as Down syndrome, cancer cells 缺失缺失 缺失环缺失环 The origin of Chromosome Mutations 7 Chromosome Mutation

3、s changes involving only a part of a chromosome including: deletion,duplication, translocation, inversion Chromosome Mutations Inversion translocation 8 The origin of Gene Mutations 9 Gene Mutations changes in DNA sequence of the nuclear or mitochondrial genomes DNA replication errors Strict base-pa

4、iring rules and molecular proofreading replication errors 10-10/bp/cell division threshold，resulting in diseases, such as Huntington disease 26 Huntington disease 36/17 21/16 50/16 38/16 21 41/21 Mutant gene is IT5, which has a (CAG) repeated polymorphism at the first exon, 27 POLYMORPHISM 28 POLYMO

5、RPHISM vGenetic polymorphism: The alleles are found in more than 1% of chromosomes in the general population. v Rare variants: 1% of chromosomes of the general population function polymorphism non-function ploymorphism 29 Types of DNA polymorphism vRFLP (Restriction Fragment Length Polymorphisms) vS

6、TRP (Short Tandem Repeat Polymorphism) vSNP (Single Nucleotide Polymorphism) 30 RFLP 31 RFLPs RFLP (Restriction Fragment Length Polymorphisms) 限制性酶切多态性 DNA-based variations at restriction sites 用某种限制性内切酶酶切基因组DNA，得 到的长度 不同的DNA片段，遵循孟德尔遗传规律，共显性遗传方式 detecting method: Southern blotting 32 PAH 11.0kb9.7kb

7、 sph1 sph1 sph1 PAH 11.0kb7.0kb sph1 sph1 sph1sph1 2.7kb 33 11.0kb 9.7kb 7.0 kb F M P N T F:father M:mother P:proband N:normal control T: fetus 34 STRP vMinisatellite Polymorphisms vMicrosatellite Polymorphisms vShort tandem Repeat（STR ） 35 Minisatellite Polymorphisms VNTR (variable number of tandem

8、 repeat) Insertion of multiple copies of a DNA sequence 10 to 100 base pairs in length, known as a minisatellite, due to variations in the number of copies of minisatallite that are repeated in tandem. Co- dominant inheritance DNA fingerprinting 36 Co-dominant inheritance of an autosomal DNA polymor

9、phism caused by VNTR Detecting method: PCR -PAGE37 Microsatellite Polymorphisms vMicrosatellite Polymorphisms (Short tandem Repeat) Microsatellite are stretches of DNA consisting of repeating units of two, three or four nucleotides, such as TGTGTG, CAACAACAA, or AAATAAATAAAT. Detecting method :PCR f

10、ragment analysis 38 STR (Short tandem Repeat) ACACAC Primer 1 Primer 2 ACACACAC ACACACACAC ACACACACACAC 39 STR markers in human DNA 40 SNP 41 Single nucleotide polymorphism (SNP) vSNPs: usually have only two alleles corresponding to the two different bases occupying a particular location in the geno

11、me. the simplest and most common of all the polymorphisms 个体间基因组DNA序列同一位置单个核苷酸 变异(替代、插入或缺失)所引起的多态性 42 SNPs 43 Inherited variation and polymorphism in proteins vBlood Groups and Their Polymorphism 1. the ABO System 2. the Rh System 3. the serum 1-antitrypsin 44 Inherited variation and polymorphism in

12、 proteins 45 Uses of Polymorphisms in Medical Genetics vMapping a gene to a particular region of a chromosome by linkage analysis vPrenatal diagnoses of genetic disease vDetection of heterozygous carrier of genetic disease 46 Chapter 10 Gene Mapping and the Human Genomic Project 47 GENE MAPPING vGen

13、e mapping: Assigning a gene to a particular band of particular chromosome and its relationship to other genes with different methods. 1911， Wilson first mapped red and green colorbindness gene on ChrX 48 GENE MAPPING vGene Mapping of Human Genes by Linkage Analysis 1968, Donahue mapped Duffy gene on

14、 chr1 vPhysical Mapping of Human Genes 49 Genetic Linkage Analysis 50 Genetic Linkage Analysis vGenetic Linkage Analysis A method of mapping genes that uses family pedigrees analysis to determine whether two genes show linkage when passed on from one generation to the next. 应用系谱分析确定被定位的基因与另一已 知位置的基因

15、是否有连锁关系。 51 Genetic Linkage Analysis 52 Some Concepts vLinkage and Recombination(连锁与重组) vHaplotype(单体型） vGenetic markers(遗传标记） vGenetic maps and physical maps(遗传图和 物理图） 53 Linkage Linkage The tendency for alleles close together on the same chromosome to be transmitted together, as a intact unit, thr

16、ough meiosis 减数分裂时，同一染色 体上的基因作为一个整体 传递的紧密程度。 54 Recombination Frequency of recombination as a measure of how far apart two loci are 重组值：基因定位时，两个基因 间遗传图距的量度，即基因间的 遗传距离。 55 56 0.10（10cM) tightly linked； 0.100.20moderately linked； 0.20 loosely linked =0.5 unlinked :recombination frequency 1% recombinat

17、ion Frequency=1cM Linkage and recombination frequency 57 Meiotic behavior of alleles at two loci on the same chromosome The smaller the recombination frequency, the closer together two loci are . The recombination frequency 0-50%, 1% recombination frequency = 1cM 58 Supposed: DM from father dm from

18、mother Meiotic behavior of alleles at two loci on the separate chromosome 59 Haplotype vDefinition：the linked phase of two or more genetic polymorphisms (alleles) on the same chromosome. 一条染色体上两个或两个以上的多态性位点 状态（等位基因）的组合叫作染色体单体型。 vNot the haploid. 60 Genetic Markers vRFLPs, Microsatellites, STR,SNP et

19、c can be used as genetic markers vMarker does not necessarily code for something functional vEach chromosome has several genetic markers vAccording to Mendelian inheritance. 61 Genetic maps and physical maps vGenetic maps (linkage maps): The maps of the relative position and genetic distance on the

20、chromosome of Alleles or genetic markers. 也叫连锁图,是指基因或DNA标记物在染色体上的 相对位置与遗传距离。以cM为单位 vPhysical maps: The maps of the position of a genetic marker on a particular band of particular chromosome and its relationship to other genes in terms of numbers of base pairs. 以DNA碱基对数目为距离单位标明遗传标记在 DNA分子或染色体上所处位置的图谱

21、。 62 The goal of Genetic Linkage Analysis 1.The null hypothesis :H0 =1/2 H1 1/2 2.To estimate the recombination 63 vLikelihood Odds (Lod)= Likelihood of data if loci are linked at a particular Likelihood of data if loci are unlinked =0.50 Likelihood odd 64 Lod Scores (Z) L( 0.5) k(1- )n-k nZ = log10

22、= log10 L( = 0.5) ()n n Z 3 is considered definitive evidence that two loci are linked( equivalent to greater than 1000:1 odds in favor of linkage) n Z 1 suggest that the two loci are linked n Z 1 suggest that the two loci are unlinked 65 example 66 Genetic linkage analysis 21 436 5 86, 8890, 92 86,

23、 9086, 9088, 9086, 92 7 94, 96 9811 10 86, 9486, 94 92, 96 86, 96 标记: D8S1130 D, dd, d D, dD, dd, dD, d D, dd, dd, dD, d d, d NRNRNRNR NRRNRNR LOD calculating: 1)Calculate combination 2)LOD = log10 qRx(1-q)N-R/0.5(R+N-R) = log (0.11x0.97)/0.58 = log (12.25) = 1.09 67 Model-based linkage analysis of

24、Mendelian Diseases vA best estimate of max between a marker locus and the disease locus v an assessment of how strong the evidence is for linkage at that values of max. the LOD score above 3 are considered strong evidence. vGenetic diagnosis for Mendelian Diseases with linkage analysis. 68 Short tan

25、dem Repeat -for Prenatal Diagnosis vF：father P：proband T：fetus M：mother Selected Polymorphism site must be heterozygous site 69 Physical mapping 70 71 72 Methods n Somatic cell hybrids (cell fusion) nFluorescence in situ hybridization (FISH) 73 Somatic Cell Hybrids _Gene mapping Mixtures of cell typ

26、es from two same or different specie Monochromosomal assignment Regional assignment 74 Somatic Cell Hybrids Isolate cells from affected patient Make cell lines Make hybrids，formed hybrids cells. Select and Isolate hybrids cells (HAT selecting system) Retain hybrids with the disease (phenotype) Ident

27、ify chromosomes 75 HAT selecting system vHPRT- human mutate cell lines vTK- mouse mutate cell lines vCell fusion, formed HAT selected system vCultured in the HAT (Hypoxanthine, Aminopterin, Thymidine) 76 Fluorescence in situ hybridization _Gene mapping 77 Human Genome Project vWhat did they do? vWhy did they do it? vWhat will it mean for humankind?