DNA Profiling - An Investigative Report

3. Constructing a DNA Profile:

i. How the Profile is Done:

        When collecting the samples of DNA from a suspect, a mouth swab is usually used.  However, DNA can be collected from a crime scene from blood, semen, saliva, bones, or hair.  When the sample has been collected, and there is a enough DNA present to complete the profile, the DNA must be processed.  

        There are a number of techniques that are used by different labs, however we will be discussing one technique that is the most common.  This technique involves a process based on STR [(Short Tandem Repeat), short lengths, or sequences, of DNA which are repeated end to end. Different people will have different lengths of repeated DNA.].  This technique requires five steps.  The first step is to extract and purify the DNA.  This is done breaking down the proteins and other cellular material, yet not the DNA itself.  Once this is done, the next step comes into play:  Target and Amplify.  In this step they cut the DNA at specific places using enzymes.  Also copying the STR can do this.  Next, the DNA is tagged.  In the PCR (Polymerase Chain Reation.
A technique used to make numerous copies of a specific segment of DNA quickly and accurately) technique, fluorescent tags are added to each of the samples to help with the profiling of the DNA in later steps.  Next the DNA is sized and sorted.  The DNA is placed into a gel (such as agarose), then an electrical charge is applied into the gel, with positive at the bottom and negative at the top.  Since DNA is somewhat negatively charged, the DNA will be attracted to the bottom of the gel.  However, the smaller pieces of DNA will be able to more quickly to the bottom then the larger pieces.  Thus the different sized pieces of DNA will be separated by size, with the smaller pieces at the bottom and the larger pieces towards the top.  Finally the last step is actually doing the profile.  As the DNA moves through the gel, a laser excites the tags and a picture is made of the pattern of bands that represent the lengths of the STR.  This is then compared to other DNA profiles that have been previously conducted, by means of a computer.  

ii. Interpreting the Results:

        For each of the locus, a database, which contains frequencies of each type occurring in the population, is constructed.  This is then used to determine what frequency of a particular combination is expected to happen in the general population.

The results of DNA profiling that currently exist will never be able to give results that could have come from one person only.  The results will always be something like one in one million.  

4. What DNA Profiling Means for a Case:

        DNA profiling is not an absolute identification tool, yet it can be very strong evidence and is usually just one part of a case.  DNA profiling is presented to the court only as one thing that the jury can think about and draw their own conclusions about, like they do other evidence.  

        DNA profiling can be a very useful forensic tool.  Of the cases that it has been used in so far, approximately half of the results have placed the suspect somewhere other then the scene of the crime.  That is they were excluded as being the suspect of the crime in question.  Before a DNA profile can begin, the case has to be processed first.  It has to be submitted and prioritized to the individual articles that must be examined by a forensic scientist.  The examination may include many other factors, depending on the case.  The DNA profile may only be one part of the case.

        It is important to remember that in most cases, the DNA is not the only evidence.  Some of the consequences of the DNA evidence ranges from charges being withdrawn to defendants pleading guilty.  There have been no successful challenges to DNA profiling as being a valid technique.  Only the process in which the test is conducted has been challenged.  

5. Conclusions:

        DNA profiling as to date is an evolving science.  It is as of yet not one hundred percent accurate, however, it is accurate within a range (one in a million).  Since the idea of DNA profiling is relatively new, courts not as of yet accept it as core evidence.  It has been used to obtain many convictions, yet is not as solid as other forms of evidence.  This will, however, change as it begins to evolve and is used further.  The lengths at which this science can evolve are endless.