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Jiang Qiang Department of Forensic Medicine

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Presentation on theme: "Jiang Qiang Department of Forensic Medicine"— Presentation transcript:

1 Jiang Qiang Department of Forensic Medicine
Forensic DNA Typing   Jiang Qiang Department of Forensic Medicine

2 Outline Introduction Application of forensic DNA typing
Process of forensic DNA typing Conclusion

3 Brief History of Forensic DNA Typing
Ray White describes first polymorphic RFLP marker Alec Jeffreys discovers multilocus VNTR probes first paper on PCR first STR paper UK DNA database 1998 – US CODIS database 2000 – Other countries database DNA parting standardization

4 Examples of DNA in the News
2004 Indian Ocean Tsunami 2001 “911”, New York 2008 Wenchuan Earthquake

5 What are we doing Identification Paternity testing

6 How to do DNA analysis STR,Y-STR,X-STR mtDNA,SNP

7 Methods for Human Identification
DNA Fingerprints since 1985 Fingerprints have been used since 1901

8 Applications for Forensic DNA Typing
Forensic cases - matching suspect with evidence Paternity testing - identifying father Historical investigations Missing persons investigations Mass disasters - putting pieces back together DNA database

9 Two main tasks of Forensic Biology
Individual Identification Paternity Testing

10 Polymerase Chain Reaction (PCR)
Basic Concepts Polymerase Chain Reaction (PCR) Locus Allele STR Homozygote Heterozygote

11 Individual nucleotides
DNA in the Cell chromosome cell nucleus Double stranded DNA molecule Individual nucleotides 11

12 ( Polymerase Chain Reaction)
P C R ( Polymerase Chain Reaction) 类似于DNA的天然复制过程，在体外试管内，以一对特异性的寡核苷酸为引物，四种脱氧核苷酸为底物，待测DNA为模板，在DNA聚合酶的催化作用下，通过高温变性——低温退火——中温延伸的温度循环，选择性扩增特异性目的DNA片段过程 。

13 1 2 3 1 2 3 4 5 22 55 72 94 时间（min） 温度 （℃） 高温变性 低温退火 适温延伸 重复1～3步
25～30轮 形成2条单链 DNA变性 目的DNA片段 扩增100万倍以上 子链延伸 DNA加倍 DNA单链 与引物复性 DNA双螺旋

14 principle Father’s Sperm Mother’s Egg Child’s Cell
For each inherited characteristic, an organism has two genes, one from each parent. We call these genes alleles. 14

15 基因座(locus) 基因在染色体上的特定位置称基因座。 等位基因(allele) 同一个基因座上的基因可以有多个，它们之间存在DNA一级结构差异，导致产生相对性状，这种有差异的基因互称为等位基因。

16 个体1 个体2 A B － ＋

17 Short Tandem Repeats (STRs)
number of repeat units Fluorescent dye label Fluorescent dye creates a labeled PCR product AATG AATG primer1 7 repeats primer2 primer1 8 repeats primer2 Locus is the region of the genome being examined Homozygote: Alleles are identical on each chromosome； both alleles are the same length Heterozygote: Alleles differ on each on each chromosome ； alleles differ and can be resolved from one another 17

18 Sources of Biological Evidence
Blood/Blood stain Semen/ Semen stain Saliva/Saliva stain Urine Hair Teeth Bone Tissue Blood stain Only a very small amount of sample is needed to obtain a DNA profile

19 Forensic STR Markers on Human Chromosomes
13 CODIS Core STR Loci CSF1PO D5S818 D21S11 TH01 TPOX D13S317 D7S820 D16S539 D18S51 D8S1179 D3S1358 FGA VWA AMEL Sex-typing

20 Steps in Forensic DNA Typing
Sample Obtained from Crime Scene or Paternity Investigation Biology DNA Extraction Quantitation PCR Amplification of Multiple STR markers Technology Separation and Detection of PCR Products (STR Alleles) Sample Genotype Determination Genetics Comparison of Sample Genotype to Other Sample Results If match occurs, comparison of DNA profile to population databases Generation of Case Report with Probability of Random Match

21 Polymerase Chain Reaction (PCR)
Separate strands (denature) 5’ 3’ Starting DNA Template 5’ 3’ Add primers (anneal) 5’ 3’ Forward primer Reverse primer 5’ 3’ Make copies (extend primers) PCR is a method of amplifying a specific region of the genome – go from 1 to over a billion copies in about several hours

22 Multiplex PCR Over 10 Markers Can Be Copied at Once
Sensitivities to levels less than 1 ng of DNA Ability to Handle Mixtures and Degraded Samples Different Fluorescent Dyes Used to Distinguish STR Alleles with Overlapping Size Ranges

23 Information is tied together with multiplex PCR and data analysis
AmpFlSTR® Identifiler™ (Applied Biosystems) D8S1179 D21S11 D7S820 CSF1PO TH01 D13S317 D3S1358 D16S539 D2S1338 D19S433 VWA TPOX D18S51 D5S818 AMEL FGA 1 integrated analysis vs. 16 separate runs

24 Capillary Electrophoresis Instrumentation
ABI capillary array ABI single capillary Not too much detail here 4 – 5 dye chemistry used

25 Genetic Inheritance Pattern of DNA Profiles
DAD CHILD MOM

26 Results of DNA Tests Impact Families
PATERNITY TESTING Family Inheritance of STR Alleles (D13S317) PCR product size (bp) 11 14 Father Results of DNA Tests Impact Families Me 12 14 Child #1 8 14 Child #2 11 12 Child #3 8 12 Mother

27 PATERNITY TESTING Family Inheritance of STR Alleles (D13S317) Amanda
PCR product size (bp) 11 14 Father Me Marshall 12 14 Child #1 8 14 Child #2 11 12 Katy Child #3 8 12 My Wife Mother

28 Crime Scene - Two Suspects
Evidence D3 vWA FGA S1 14, , ,24 S2 15, , ,24 E 15, , ,24

29 Individual Identification
Conclusion Main Tasks Individual Identification Paternity Testing

30 Forensic DNA Typing The genome of each individual is unique (with the exception of identical twins) Probe subsets of genetic variation in order to differentiate between individuals DNA typing must be done efficiently and reproducibly (information must hold up in court)

31 Reference STRBase Forensic DNA Typing， John Butler
NIST website: STRBase

32 谢谢各位同学! Thank you for your attention!

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