Genetics in Forensic Science for Non-scientists

By N. Alice Yamada

Chief of Staff

n the past decade or so, recombinant DNA technology and genetic engineering have experienced an explosion of knowledge and new discoveries. From early detection of defective birth to the O.J. Simpson trial, genetic technology is everywhere. We hear words like RFLP, PCR, and VNTR, but what exactly are they saying? How accurate are these results in forensic science and how do we know what we think we know?
Here's a quick and comprehensive introduction to recombinant DNA technology. In the near future, all this may become general knowledge much like how everyone knows that the earth revolves around the sun. But for now, this is a start.
Basically, your genes are comprised of DNA, which are these super condensed chains of chemicals. It's been stated over and over that your DNA is a double helix - two chains in a helical pattern . The chemicals in the chains have initials and they are A, G, T, and C. A and G are sisters and T and C are brothers; A and T are always paired up together and G and C are also hooked up. These chemicals may be lined up in different orders and repeat in many different patterns. The repeating sequence is called tandem repeats.
Each person has different numbers of tandem repeats. Let's say your repeat sequence is GCCC, and you have 3 of these copies, so your DNA looks like this: GCCCGCCCGCCC. These repeats bring individuality in your DNA pool. VNTR stands for Variable Number Tandem Repeats, and detects the length of tandem repeats in your DNA. VNTR's are especially useful in forensic science, because the chances of somebody else having the exact same VNTR results, if done in careful lab conditions, is less than one in a million .
In forensic science, it is common to have only a small amount of sample to use for lab work. This sample can be a tiny bit of blood, sperm, mucus, etc, because we have the PCR method. PCR is simply an amplification method of making a sufficiently big pool of DNA sample from a very small amount. Jurassic Park based its creation of dinos on this amplification method. Although PCR is a very simple and easy method, it is one of the most important techniques in genetic study. First, the double strand of DNA is denatured into single strands. Then, the strands are placed in a medium with all the chemicals needed for DNA replication. The single strands both become double strands. Now you have doubled the number of DNA sample you started. Then, the double strands are once again denatured to form single strands. The process is repeated until you have enough DNA sample to do whatever lab work necessary.
Unlike other tests where genes may change from recombination and deletion, which I may talk about in future articles, the VNTR is stable and accurate. More explanation is found in several Web sites, such as this clinical genetics page, but the most important factor for genetic knowledge to succeed in the world is for the general population to accept and understand the concepts beyond what the eye can see. If it is possible to reverse the belief that the sun revolved around the earth, it is possible to believe in the somewhat abstract concepts in genetics.