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About this Article
Written by: Kristopher Kubow
Written on: November 1st, 2001
Tags: biomedical engineering, health & medicine
Thumbnail by: National Human Genome Research Institute/Wikimedia Commons
About the Author
In November 2001, Kristopher was a senior majoring in Biomedical (Biochemical) Engineering. When he's not thinking about biotechnology, he likes to backpack, bicycle, and pursue his interests in music composition.
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Volume II Issue I > DNA Fingerprinting
DNA fingerprinting has established itself as an efficient and highly accurate means of determining identities and relationships. It has practically revolutionized the field of forensics, especially concerning rape cases. DNA profiling, as the process is more appropriately called, involves the visualization of special segments of the human genome, which are unique to each individual. These special segments, called Standard Tandem Repeats (STR), can be cut out and separated from the rest of the DNA by two processes: mapping Restriction Fragment Length Polymorphisms (RFLP) and Polymerase Chain Reaction (PCR). After being separated from the other DNA, we can visualize these STR segments and separate them by size using gel electrophoresis. STR sequences can also be directly sequenced using DNA sequencing machines, but this method has yet to move into mainstream usage and is used primarily within the research community.

Introduction

It can exonerate a falsely accused person, while undeniably implicating a guilty party. It allows scientists to identify the remains of victims of highly disfiguring accidents or soldiers lost in battle. It can even settle child custody cases by identifying the child's true biological parents. This amazing technology is DNA fingerprinting, and it is arguably the most powerful and accurate form of human identification currently used. DNA profiling, as it is more accurately called, is the process whereby we visualize a sample of DNA and determine its relationship to other DNA samples. This sounds simple in theory, but how we get from several people's genomes-each of which contains over three billion elements-to a final conclusion is a complex process. There are currently two popular methods for DNA profiling, which use different elements of the DNA for identification: RFLP (Restriction Fragment Length Polymorphisms) and STR (Short Tandem Repeats). In this article we will examine the engineering and scientific basis behind these two powerful techniques as well as the future of identification by DNA profiling.

DNA: The Ultimate "How To" Guide

To understand the complicated technology behind DNA fingerprinting, we first need to understand some important background information about DNA structure and function. DNA molecules are tightly wrapped, like bundles of rope, into packages called chromosomes. Most humans have 23 chromosomes-collecti​vely referred to as the human genome-which can be found in almost all of your living cells. Because almost every cell in your body contains a copy of your genome, it is very easy to sample, or in the case of criminals, leave behind copies of your DNA for profiling. DNA samples suitable for profiling have been retrieved from blood, urine, semen, saliva, hair roots, bone, and many other kinds of biological tissue [1].
DNA molecules are very long and consist of two strands in a configuration resembling a zipper, except that the "teeth" of the two strands join head-to-head rather than interlock. The "teeth" of DNA molecules are called bases. There are four different biochemical bases, represented by four letters: adenine (A), thymine (T), guanine (G), and cytosine (C). These bases, arranged in a specific order along the two strands, are the letters of the genetic code (Fig. 1).
Wikimedia Commons
Figure 1: Diagram of DNA molecule showing bases.
On a functional level, we can think of our DNA molecules as very long instruction manuals for making humans, with the bases (A, T, G, and C) as the words and sentences. The exception to this analogy is the presence of non-coding DNA in the human genome. Non-coding DNA does not contain instructions and, as far as today's scientists can tell, serve no apparent function. An application of our analogy would look something like this: The foot bone's connected to dknjbie andmnanofib sofbo ansoiyz boln the leg bone. These non-coding regions, though they do not serve any currently known biological purpose, are actually what make DNA profiling possible [2].