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

http://www.pbs.org/wgbh/nova/education/body/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