Things You Should Know About DNA Profiling

Different Types of Forensic DNA Fingerprinting

Jan 25, 2009 Karen Lotter

DNA Profiling or Fingerprinting is one of the most useful and accurate of all forensic science tools especially as DNA analysis techniques are constantly evolving.

Modern forensic DNA techniques are powerful tools for all kinds of investigations. In any situation where DNA may be used, a DNA profile of fingerprint must first be created. DNA Profiling used to be called DNA fingerprinting, but to avoid confusion with actual skin fingerprints the name was changed. (Although they still seem to call it DNA fingerprinting in the UK).

Most of us are familiar with the use of DNA profiling in criminal cases and with the establishment of the DNA Databases by governments and crime fighting authorities across the world.

DNA is the Molecule of Life

Deoxyribonucleic Acid (DNA) is the molecule of life. To understand DNA profiling, it is important to understand that a large chunk of the DNA material we all share as humans is similar; after all that is what distinguishes us from animals or fish or birds. This bit of the DNA that is similar indicates that we have feet, not paws, or hooves for example and skin instead of scales or feathers. The rest of the DNA fragments are unique to each individual – these are the ones that are analyzed in a DNA Profile.

Dr Alec Jeffreys –Techniques for DNA Profiling (Fingerprinting)

DNA profiling is simply the collection, processing, and analysis of VNTR's- unique sequences on the loci (area on a chromosome). VNTR stands for variable number tandem repeats. After processing however, VNTR’s show up in bands that are unique enough to be used for identification. These differences were discovered in 1984 by Dr. Alec Jeffreys, when he had a “eureka” moment in his lab in Leicester, UK when looking at the results of an experiment, using DNA belonging to different family members of one of his lab technicians. DNA Profiling was born.

There are two main processes in use today - restriction fragment length polymorphism (RFLP) and allele-specific testing which although similar is quite different.

RFLP Analysis Requires a Large Sample of DNA

According to Dr Michael Baldwin on Dr Kathy Reichs’ Website, this form of DNA profiling can best be described as “extract it, chop it, sort it, photograph it”, but the drawback is that RFLP requires a relatively large sample of DNA, which is often a drawback or impossibility in criminal cases.

Allele Specific Testing

Allele Specific Testing, like RFLP, seeks out the alleles (a special type of polymorphic fragments). This process requires a much smaller sample and by using a process called Polymerase Chain Reaction (PCR) the smaller DNA sample can be amplified.

Short Tandem Repeats STR

One of the newer methods of producing a DNA Profile or DNA Fingerprint is testing for STR’s. This is a PCR based, allele specific test that manages to get results from samples that were previously regarded as too small or damaged to be usable. For this very reason, STR testing is very helpful to investigators and forensic scientists.

Y –STR DNA Profile

A variation on STR analysis is Y-STR. Only STR's found on the Y-chromosome (which only males have) are analyzed. STR analysis is useful if the sample has mixed DNA (from both men and women) or in sexual assault cases with a male assailant

Interpol DNA Unit

International criminal organization, Interpol recognizes the value of DNA profiling and supports this forensic investigative tool. An Interpol DNA Unit has been established.

Constantly Evolving Forensic Process

So, although it isn’t a one hundred percent failsafe guarantee, DNA profiling is still one of the more accurate tools forensic scientists can use in crime scene processing. As science advances, DNA analysis techniques are constantly evolving and over the past few years have provided the courts with interesting challenges like the cases concerned with Mitochondrial DNA, LCN DNA and Touch DNA.

Sources:

DNA Profiling by Dr Michael Baden

How DNA Profiling Works by Shanna Freeman

Sir Alec Jeffreys FRS - DNA fingerprinting - The Royal Society

Can DNA demand a Verdict? by Jacqui Wittmeyer - Genetic Science Learning Centre, University of Utah

The copyright of the article Things You Should Know About DNA Profiling in Forensic Science is owned by Karen Lotter. Permission to republish Things You Should Know About DNA Profiling in print or online must be granted by the author in writing.

Sir Alec Jeffreys -Discovered DNA Profiling.

Variations of VNTR Allele Lengths.

How Forensic DNA is Analyzed.

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Comments

Jan 26, 2009 1:32 PM

Guest :

When there are no fingerprints found or an eyewitness to a crime, should DNA alone be enough to convict?

'Beyond Reasonable Doubt' Available NOW! - the new novel by Dennis Gelbaum ('74) In my new novel, I question the validity of DNA Profiling. In 1962 Crick, Watson, and Wilkins received the Nobel Prize for their pioneering work on the structure of the DNA molecule. What if they were wrong? Think of all those we have set free based solely on DNA Profiling? Think of all those we have convicted solely on DNA Profiling? What do you think? Check out www.beyondreasonabledoubtbook.com and www.thegelbaumblog.blogspot.com to learn even more.

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