Chapter 7 DNA Fingerprinting By the end f this chapter yu will be able t: Explain hw crime scene evidence is cllected and prcessed t btain DNA Describe hw radiactive prbes are used in DNA fingerprinting Explain hw DNA evidence is cmpared fr matching Explain hw t use DNA fingerprinting t identify DNA frm a parent, child, ther relative, r a nnrelated individual 1 All Rights Reserved Suth-Western / Cengage Learning 2012, 2009 Frensic Science: Fundamentals & Investigatins, Chapter 7
Histry f Bilgical Evidence in Frensics 2 DNA fingerprinting Als knwn as DNA prfiling Used with a high degree f accuracy Bilgical evidence (skin, bld, saliva, urine, semen, hair) is examined fr the presence f inherited traits Sme frensics labratry techniques were riginally develped fr ther purpses. Can yu name any? Frensic Science: Fundamentals & Investigatins, Chapter 7
Bilgical evidence 3 Karytyping analysis f chrmsmes 23 pairs Distinguish between male and female (xy r xx) Bld typing techniques develped fr transfusins Can exclude suspects, paternity testing, number f individuals at a crime scene DNA fingerprinting determine identity and parentage Very accurate Frensic Science: Fundamentals & Investigatins, Chapter 7
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The Functin and Structure f DNA DNA cntains the genetic material f a cell Chrmsmes are lcated in the cell nucleus Chrmsmes cntain lng DNA strands wrapped arund prteins Duble helix Backbne = sugar and phsphates Rungs = nitrgenus bases 5 Frensic Science: Fundamentals & Investigatins, Chapter 7
The Functin and Structure f DNA Base-Pairing Rules adenine (A) binds nly with thymine(t) Cytsine (C) binds nly with guanine (G) 6 Frensic Science: Fundamentals & Investigatins, Chapter 7
Genes and Alleles 7 Genes segments f DNA that have instructins (eye clr) Allele ne f tw r mre alternative frms f a gene (blue, brwn, green, hazel) One allele cmes frm mther, ther allele cmes frm father Genme ttal amunt f DNA in cell Exn DNA cntaining genes (1.5%) Intrns DNA nt cntaining genes but imprtant fr gene regulatin (98.5%)
DNA Identificatin 8 Plymrphisms: Nn-cded DNA that cntain unique patterns f repeated base sequences that that are unique t individuals DNA Fingerprinting (Prfiling) islates and analyzes plymrphisms DNA fingerprints appear as a pattern f bands n X-ray film. Frensic Science: Fundamentals & Investigatins, Chapter 7
DNA Prfile 9 Tw types f repeating DNA sequences Variable Numbers f Tandem Repeats (VNTR) The number f repeats varies frm persn t persn 9 t 80 bases in length Shrt Tandem Repeats (STR) 2 t 5 bases in length Shrter lengths make STRs easier t use than VNTRs VNTR and STR data are analyzed fr tissue matching inheritance matching Frensic Science: Fundamentals & Investigatins, Chapter 7
DNA Prfile Matching Tissue Matching Tw samples that have the same band pattern are frm the same persn Inheritance Matching Each band in a child s DNA fingerprint must be present in at least ne parent 10 Frensic Science: Fundamentals & Investigatins, Chapter 7
DNA Ppulatin Databases 11 Ppulatin genetics: the study f gene variatins amng grups f individuals Analyze the prbability f a randm persn with the same alternative frm f a gene (an allele) Database is created frm many samples Helps calculate the prbability f having the same bld type r allele when: Identifying the suspect in a crime Identifying an alleged father in a paternity case Frensic Science: Fundamentals & Investigatins, Chapter 7
Surces f DNA Bilgical evidence: examples include saliva, bld, skin, hair, seminal fluid Individual evidence is capable f identifying a specific persn. Small amunts may be nly trace evidence Plymerase chain reactin (PCR) technique generates multiple cpies f DNA evidence 12 Frensic Science: Fundamentals & Investigatins, Chapter 7
Cllectin and Preservatin f DNA 1. Use dispsable glves and cllectin instruments 2. Avid physical cntact, talking, sneezing, and cughing in the evidence area 3. Air-dry evidence and put it int new paper bags r envelpes 4. Dry r freeze the evidence 5. Keep evidence cl and dry during transprtatin and strage 1. Direct sunlight, heat and mld damage DNA 13 Frensic Science: Fundamentals & Investigatins, Chapter 7
Preparing DNA Samples fr Fingerprinting Extractin 1. Cells are islated frm bilgical evidence such as bld, saliva, urine, semen, and hair 2. The cells are disrupted t release the DNA frm prteins and ther cell cmpnents 3. The DNA can be extracted frm the cell nucleus 4. Restrictin enzymes cut DNA at specific places 14 Frensic Science: Fundamentals & Investigatins, Chapter 7
Preparing DNA Samples fr Fingerprinting 15 1. DNA is mixed with special enzymes 2. Enzymes cut apart the DNA in specific places frming different sized fragments 3. DNA is separated within an agarse gel 4. An electric current is passed thrugh the gel separating the fragments by size 5. DNA fragments line up in bands alng the length f each gel Frensic Science: Fundamentals & Investigatins, Chapter 7
Electrphresis An electrphresis apparatus running five sample f DNA Arrws shw the mvement f the negatively charged DNA fragments thrugh the gel matrix 16 Frensic Science: Fundamentals & Investigatins, Chapter 7
Prbes DNA prbes identify the unique sequences in a persn s DNA are made up f different synthetic sequences f DNA bases cmplimentary t the DNA strand bind t cmplimentary bases in the strand (see the fragmentary DNA bands abve) In mst criminal cases, 6 t 8 prbes are used 17 Frensic Science: Fundamentals & Investigatins, Chapter 7
Analysis f DNA Fingerprints and Applicatins Bands and widths are significant in matching samples f DNA 18 Frensic Science: Fundamentals & Investigatins, Chapter 7
Analysis f DNA Fingerprints and Applicatins DNA fingerprinting can match crime scene DNA with a suspect determine maternity, paternity, r match t anther relative eliminate a suspect free a falsely imprisned individual identify human remains 19 Frensic Science: Fundamentals & Investigatins, Chapter 7
.............. Summary.... DNA cntains the infrmatin needed fr replicatin in a sequence f nitrgenus bases. DNA analysis allws even a small sample f tissue t be identified with a single individual. DNA cntains, in nn-cding regins called junk DNA, many repeated sequences that vary in number between individuals. These differences between individuals can be used t prduce a DNA fingerprint fr an individual. 20 Frensic Science: Fundamentals & Investigatins, Chapter 7
................. Summary Plymerase chain reactin (PCR) fr DNA amplificatin has largely eliminated the prblem resulting frm the tiny samples usually available. DNA evidence must be cllected carefully t avid cntaminatin with ther DNA. DNA analysis invlves extractin, electrphresis, and visualizatin. DNA prfiles are kept by plice agencies in electrnic databases. 21 Frensic Science: Fundamentals & Investigatins, Chapter 7
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