If we take a sample of tissue or blood or other substancefrom a person or a crime scene, and this is found to have complete unbroken strands of DNA in it, then ordinary DNA analysis can be done.
This is carried out by a process that strips the DNA strands and allows scientists to identify particular short lengths of DNA with a recognisable pattern of complex chemical elements attached in certain places.
It has been shown that these chosen areas (a different number and different locations in different jurisdictions) contain sufficient variety of structure to make rational decisions about whether different samples do in fact match to a level of probability suitable to make a scientifically and forensically valid conclusion.
This complexity is because these twenty sites (In current usage) have a variety of chemical structures (called here 'markers' (elsewhere alleles) which are associated with these particular locations. Each area has a series of possible markers associated with it, and some markers may attach to more than one different sites. The number of markers for each site totals between 3 and 20 or so. Some are very rare and some are very common associations, but with 20 possible areas and several hundred in total markers there is sufficient information to exclude everyone else from identification to very high levels of probability.
Different jurisdictions make different assessments of how many markers are required for such identification to be legally valid.
Anything contentious so far?
