Our DNA is the building blocks of our cells and 99.9% of all humans are the same. The 0.1% that is different, however, is enough to ensure that everybody’s internal and external characteristics will be completely unique. Identical twins, because they shared an egg, are the only people that can have the exact same DNA composition.
A DNA profile is a specific DNA pattern that is unique to each individual. The forensic technique of DNA profiling, also known as DNA fingerprinting, was introduced in 1985. Its aim is to use the characteristics of a person’s DNA in order to identify them. Most people have only one distinct set of DNA, except in the very rare cases of ‘chimeras’ who have two, as a result of two fertilized eggs fusing together in the womb. This makes DNA profiling a very accurate process and it is used in three main circumstances to discover an individual’s identity:
Criminal Investigation – Using DNA fingerprinting, forensic science is extremely helpful in proving whether or not the person that is accused of a crime is actually guilty.
Locate Family Members – Members of the same family always have parts of their DNA that are identical. This is because we all get half our DNA from either parent. DNA profiling can be used in family situations to determine the father of a child, as well as to find long lost relatives.
Disaster Victims – There are instances when a natural disaster, or a crime, obliterate all fingerprint and dental information from the victim. This leaves DNA profiling as the only option of identifying them.
DNA profiling is most prolific in criminal investigations and the process that is currently used, was developed in 1988. A simplified version of it is shown below:
Step 1: A reference sample is required in order to begin proving the identity of the person who committed the crime. The easiest way to obtain this is by taking a swab from the inside of their cheek. This is only possible if there is a court order demanding it, and at other times different ways of obtaining a sample may be required. Blood, semen, saliva, or any other source of cells can be used, such as hair and nail clippings.
Step 2: The DNA is extracted from the nucleus of the cell, using specific chemicals, and then copied to make a strand long enough to test via a process called Polymerase Chain Reaction (PCR).
Step 3: STRs (Short Tandem Units), which are short units of DNA, are made and repeated numerous times to determine somebody’s identity. The repetitions vary widely in each person and for criminal investigative purposes 13 STR regions are analyzed, and the repeated units in each counted. A suspect is only convicted if all 13 STR regions match. This means that the process is incredibly accurate and there is only a 1 in a billion chance of mistaking someone’s identity using it.