DNA profiling
Each of us has a unique DNA profile or fingerprint. A technique called electrophoresis is used to obtain DNA profiles, relying on sections of our DNA that are known as non-coding DNA – DNA that does not code for a protein.
We have many sections of non-coding DNA in our genome. Within this non-coding DNA are areas called short tandem repeats (STRs). For example, you may have a stretch of DNA made up of the following base sequence:
ATCTTCTAACACATGACCGATCATGCATGCATGCATGCATGCATGCATGCATGCATGCATGCATGTTCCATGATAGCACAT
This sequence starts off looking random and then has repeats of the sequence CATG towards the middle and then becomes random again. The repetitive section of the sequence is what is referred to as an STR.
For a given STR, you will have inherited different numbers of the repeated sequence from each of your parents. For example, you may have inherited 11 repeats of the CATG sequence, as shown above, on a chromosome from your mother, and 3 repeats of this sequence within the STR on the matching chromosome from your father.
Because the number of repeats within an STR will create different lengths of DNA for that STR, electrophoresis can be used to show how many repeats you have.
Generating a DNA profile usually involves analysing an individual's DNA for ten different STRs on different chromosomes. Statistically, no two people (except identical twins) are likely to have the same numbers of repeats in all of these STRs.
Polymerase chain reaction (PCR) is used first to produce many copies of the ten STRs before they are analysed using electrophoresis. The different lengths will show up as bands at different spots on the electrophoresis gel. The banding pattern produced is called a DNA profile or fingerprint, and can be analysed.
You can produce a DNA profile using a DNA sample from a crime scene - interactive