DNA Fingerprinting Sotheavy Vann

What is DNA Fingerprinting?  “The generation of a set of distinct DNA fragments from a single DNA sample”  Aka DNA profiling, forensic DNA analysis, DNA testing, genetic fingerprinting, and DNA typing  Invented by Alec Jeffreys in 1985

Historic Cases  In 1988, the first criminal to be convicted based on supporting evidence of DNA fingerprinting was Colin Pitchfork.  In 1995, O. J. Simpson was acquitted based on sloppy DNA fingerprinting technique.  DNA fingerprinting was used to identify Abraham Lincoln with Marfan’s Syndrome.

Common Uses  More often use to exclude suspects than to identify criminal (CODIS and NDIS)  Paternity test  Identifying genetic disorder  Ancestry analysis  Identifying a body

Types of Samples  Blood  Hair  Saliva  Semen  Vaginal canal swab  Body tissue

Types of DNA Fingerprinting Technique 1. RFLP analysis 2. VNTR analysis 3. PCR analysis 4. STR analysis 5. RAPD analysis 6. AFLP analysis 7. Mitochondrial analysis 8. Y-chromosome analysis

Types of DNA Fingerprinting Technique 1. Restriction Fragment Length Polymorphism (RFLP) analysis  The sequence between between two restriction sites varies in length  Southern Blotting  Requires more DNA  More specific than PCR method  Time consuming  Need prior knowledge of genome

Types of DNA Fingerprinting Technique 2. Variable number tandem repeats (VNTR)  PCR  9-80 or more nucleotide sequence repeated as compared to RFLP which is 1-2 kilo base pairs  Both are reproducible

Types of DNA Fingerprinting Technique 3. PCR analysis  DQA1  For older samples  Determine presence or absence of certain alleles  Less DNA is needed  Less specific  Simple and fast

Types of DNA Fingerprinting Technique 4. Short Tandem Repeats (STR) analysis  A type of VNTR  2 to 6 nucleotides sequence repeated multiple time  PCR  Requires prior knowledge of genome to create primer

Types of DNA Fingerprinting Technique 5. Random Amplified Polymorphic DNA (RAPD) analysis  Uses low-stringency PCR conditions  Prior genomic knowledge is not needed  Interpreting results can be challenging

Types of DNA Fingerprinting Technique 6. Amplified Fragment Length Polymorphism (AmpFLP or AFLP) analysis  Detect absence or presence of polymorphism  Highly specific  Capable of amplifying 50 to 100 fragment simultaneously  Prior genomic knowledge is not needed  Highly reproducible

Types of DNA Fingerprinting Technique 7. Y-chromosome analysis  Examines genetic markers in Y chromosomes (males only)  Used in sexual assault cases that involves more than one male suspects

Types of DNA Fingerprinting Technique 8. Mitochondrial analysis  Use mtDNA, sample does not need to have nucleated cells  Old samples

Step 1 of DNA Fingerprinting  Collect sample of DNA  Isolate DNA - Centrifuge - Detergent

Step 2 of DNA Fingerprinting  Cut  Restriction enzymes  Sort  Gel electrophoresis or size fractionation

Step 3 of DNA Fingerprinting  Denature DNA  Transfer DNA to nitrocellulose membrane

Step 4 of DNA Fingerprinting  Add radioactive probe  Allow to hybridize

Step 5 of DNA Fingerprinting  Autoradiography  Analyze DNA profile by comparison

Southern Blot Virtual Lab  y/create-dna-fingerprint.html y/create-dna-fingerprint.html

Problems  High probability for sample to be contaminated  Fake DNA evidence  Chimerism  Two different set of genes  VNTRs are not distributed evenly throughout racial population