The human body is composed of billions of cells of many different types i.e. blood cells, hair, skin, bone, muscle cells, heart, lung, spleen. Almost all cells contain a nucleus (except the red blood cell) and within the nucleus of each cell is an identical copy of a person’s DNA. Because of this DNA from a person’s blood will be the same as that found in their saliva or hair roots.
Half of our DNA is inherited from our mother and half from our father. Except for identical twins, each person’s DNA is unique. In fact, the chances of two people having the same profile within the Irish population is one in a thousand million.
Even though each person’s DNA is unique, with current technology it is not practical to look at each difference.
Currently in the laboratory we look at 16 different areas of DNA , which are known to have a wide variance within the Irish population.
We also examine the gender indicator. The 16 areas, represented by 32 of the peaks in the profiles below, contain short repeating sequences known as Short Tandem Repeats (STR). The number of these repeating sequences varies between individuals.
The technique of DNA profiling is centred on analysing and measuring the differences in length of these STRs. An additional two peaks on the profile (labelled X X or X Y) determines whether the person is male or female.
Technology has moved on vastly in recent years and many of the processes that were previously carried out manually can now be done by robotics. Essentially the technical process for DNA profiling involves the following main steps:
- Loading Puncher Preparation - Samples are first prepared so they are in a suitable form for extraction. The punching robot pictured on the right automatically dispenses reference samples into wells.
- Extraction - DNA is recovered from cells and cleaned in preparation for profiling.
- Quantification - The amount of DNA recovered is measured. An optimum amount of DNA is required for successful profiling.
- Amplification - The pieces of DNA targeted in profiling are copied many times. This makes profiling sensitive enough to generate a profile even from a barely visible blood stain.
- Capillary Electrophoresis - The sizes of the pieces of DNA targeted are measured and profiles are generated like those above.