Have you ever watched an episode on CSI and wondered, "Just HOW do they always manage to identify and catch the criminals using DNA"?

Well, that question as well as the method for using DNA in criminal investigations will be answered today! You'll be working in an exciting career in criminal investigation before you know it!

Well,Maybe not, but you'll definitely learn how all those big time scientists identify suspects in criminal investigations.

To start off, you must first know what exactly DNA is. DNA stands for deoxyribonucleic acid. It is the fundamental thing that determines whether we are human, male, female, or anything that makes us who we are. Your DNA determines what you look like, or whether or not you look more like your mother or your father. DNA profiling can be used both in real life circumstances when trying to determine paternity or maternity of a parent to a child, and in some cases, it can be used to differentiate between suspects in a criminal investigation.

Although human DNA is basically the same, they are small differences in each and every person that separate us from being the carbon copy of a complete stranger. It is these differences in DNA that scientists manipulate in order to either exonerate or convict a suspect of a crime. In these cases, scientists use the method of DNA profiling in order to determine whether or not a suspect committed a crime. DNA profiling is the process of testing to identify DNA types. In forensic investigations, it can be used to indicate parentage or to convict or exonerate suspects.

So, now that the basics are out of the way, we can get on to the DNA profiling 101!

Now, DNA fingerprinting is the technique used to distinguish between different people of the same species using samples of their DNA. Where can scientists obtain this DNA? Well, DNA is present in every fiber of our being. All bodily fluids like saliva, blood, and semen contain DNA, and scientists use these factors in order to do DNA profiling. In DNA profiling, scientists use highly variable repeat sequences in DNA called VNTRs, which stands for variable number tandem repeats. Now, in English this is simply a location in our genes where nucleotides (parts of DNA) repeat. The repeating VNTRs vary in length, and each variant acts as an inherited trait. These variations in length show differences in different individuals.

If these VNTRs are variable enough, then it can be determined that the individuals being compared are unlikely to share common traits, and therefore prove which one of them committed the crime or action.

Let's use this scenario as an example: A young woman is raped, and the investigators find semen samples on the young woman's clothes. If there are two suspects in the case, then how do we find out who is the perpetrator?

Well, when using DNA profiling, scientists usually use restriction enzymes to cut the DNA at certain places in the DNA sequence. Depending on the VNTRs in a suspect's DNA, the enzymes will cut in different places. The process is actually quite long and laborious, but put simply, if the cuts found in the DNA match the cuts found on the evidence, than most likely the suspect committed the crime. Using this method, one suspect will be convicted, and the other sent home.

I hope this helped you all to better understand what those CSI people are talking about!

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