Genetic databases
There are several databases containing DNA profiles maintained by different agencies around the world.
These concentrate on a number of gene loci spread amongst the human genome which have been shown to contain variable numbers of alleles - STR microsatellites.
The proportions of each of these alleles in the general population have been determined, so that an estimate of the probability of matching two samples (such as crime scene
vs suspect, or in a paternity dispute) can be calculated by multiplying all the individual allele freqencies.
Some countries maintain a number of versions of the database corresponding to different racial groups, in order to make allowances for differences in the distribution of different alleles, and the probability of making a match.
There are a number of supply companies producing kits to be used in these analyses and the details of their techniques (primers,etc) are considered commercial secrets.
Some loci are named after specific enzymes, others after the specific location on the chromosome (number after D in these cases)
Check out the NIST Standard Reference Database (link below).
Image courtesy PD-USGov-NIST
The American version of this - Combined DNA Index System (CODIS) - was set up with 13 loci but it has now been expanded to include 20 loci.
Originally it focussed on those accused of sex offences but it has been extended to cover those accused of felonies.
There is also a missing persons database.
The UK National Criminal Intelligence DNA Database (NDNAD) is based on 16 loci. It was set up in 1995 and has gone through a number of upgrades based on improvements in analytical techniques. In 2020 It contained 6.6 million profiles - approximately 10% of the population.
Anyone arrested in England and Wales on suspicion of involvement in any recordable offence will have had their DNA sample taken and profile data will be stored in the database, whether or not they are subsequently charged or convicted. However, those not charged or not found guilty must (or may?) have their DNA data deleted within a certain period of time.