DNA FINGERPRINTING http://news.bbc.co.uk/media/images/38250000/gif/_38250230_dna_generic300.gif
DNA: Deoxyribonucleic Acid - biological equivalent of fingerprints - < 1% of nonviolent crimes yield DNA - < 50% of violent crimes yield DNA http://www.cnn.com/us/9903/01/dna.expansion/dna.jpg
BACKGROUND: 1868 DNA discovered found in every cell Early 1950 s Rosalind Franklin & Maurice Wilkins Crystallized DNA and obtained X-ray pattern showing helix http://www.dna50.org.uk/history_of_dna/featured_scientists/r_franklin.shtm http://www.simr.org.uk/images/nobel/watson-crick.jpg 1953 James Watson & Francis Crick Created double-helix model of DNA 1962 Nobel Prize to Watson, Crick, Wilkins Franklin had died of cancer at age 37 4 years earlier
DNA STRUCTURE Polymer: large molecule made by linking series of repeating units Repeat unit: nucleotide - 5 carbon sugar deoxyribose - phosphate group - nitrogen containing base Bases: attach to sugar unit A - T C - G 3 billion base pairs or rungs Double-stranded: held together by H bonds DNA --> Genes --> Chromosomes http://www.rsnz.govt.nz/news/dna50/history.php
WHY USE DNA? 1. No 2 individuals have same DNA except - Humans have large sections of DNA in common: coding sections (99.9%) -.1% junk DNA : tandem repeats of non-coding sections http://www.northside.com/online_pubs/womenfirst/winter2k/pg10.htm - DNA fingerprinting focuses on differences in junk sections 2. Genetic continuity: same DNA at death 3. Sensitivity: small samples needed Cell nucleus of skin, saliva, hair root, blood, semen Case example: World Trade Center bombing 2/26/93 4. Stability: molecule can withstand changes in environment
METHODS OF DNA FINGERPRINTING I. Restriction Fragment Length Polymorphism (RFLP) A. Process 1. DNA cut into fragments by restriction enzymes 2. Fragments suspended in agarose gel 3. Exposed to electric current: electrophoresis 4. Radioactive probe added 5. X-ray development 6. Bar code B. Sir Alec Jeffreys Developed in 1984 Used in 1985: immigration case First forensic use 1986 Case example: 1998 Impeachment of Bill Clinton Semen stained dress of Monica Lewinsky http://www.menzelphoto.com/gallery/big/dnafingerprinting1.htm
II. Polymerase Chain Reaction (PCR) 1. Use of thermal cycler to amplify DNA by heating and cooling 1 million copies in 1 hour! Uses 5 or 6 genetic markers Used in OJ Simpson trial http://www.ib.usp.br/evolucao/qtl/marcadores.html 1985 by Kary Mullis 1993 Nobel Prize in chemistry Found lab work routine and tedious http://www.keynotespeakers.com/mullis_kary.html
III. Short Tandem Repeats Repeats of 2-6 bases long Advantages of PCR & RFLP Gel or capillary electrophoresis Automation possible http://mapageweb.umontreal.ca/waldronk/
PROS CONS RFLP original sample tested 3-10 weeks time highly specific need large sample size odds: 1 in 10,000 s to doesn t work well on 1 in 1,000,000 degraded samples PCR small sample size; only need less specific than RFLP a few cells fast - only a few days odds: 1 in 100 to 1 in 2000 works well on degraded samples amplification step can cause concern with jurors; contamination STR very small sample size amplification step can cause concern with jurors very fast; automation works on degraded samples gel is problematic very specific: 1 in 260 billion no radioactive probes or x-ray
IV. Single Nucleotide Polymorphism (SNPs) - a single nucleotide in the sequence is altered - must occur in at least 1% of population - can occur in both coding and non-coding regions - many have no effect on cell function; others could predispose to disease or influence response to toxins, chemicals, drugs, etc. V. Mitochondrial DNA (mtdna) - only DNA present outside cell nucleus - only have maternal mtdna - 16,569 base pairs in length - reliability of 1 in 1000 Famous cases: http://www.bacbarcodes.com/images/ products_and_services/extracting.jpg 1. Argentinean children of disappeared parents 2. Sally Hemmings: slave mistress of Thomas Jefferson 3. Anna Anderson: claimed to be Anastasia
USES FOR DNA FINGERPRINTING 1. Forensics: CODIS (Combined DNA Indexing System): FBI s national database of felons from all 50 states http://cwx.prenhall.com/horton/medialib/me ia_portfolio/text_images/fg19_34.jpg
2. Parentage Testing http://www.dnaforensicconsultants.com /DNA%20Paternity.htm 3. Identification: a. Armed Services samples http://www.homeofheroes.com/moh/m emory/tomb.html
b. Old or archaeological remains In 2005 the attempts to identify those lost in the September 11 tragedy was suspended. At that time 1585 http://www.mindspring.com/~mike_rob inson/olympics.html d. Mass disasters http://www.cnn.com/2000/world/africa/05/ 23/sierra.leone.03/link.skeletal.remains.jpg individuals had been identified of the c. Sports testing 2792 known fatalities. In 2007 do to improved techniques that could use smaller sample sizes several more individuals were identified. The process continues today. http://image.guardian.co.uk/sysimages/guardian/pix/pictures/2002/04/15/crash372.jpg