<P> The bulk of identifications using CODIS rely on short tandem repeats (STRs) that are scattered throughout the human genome and on statistics that are used to calculate the rarity of that specific profile in the population . STRs are a type of copy - number variation and comprise a sequence of nucleotide base pairs that is repeated over and over again . At each location tested during DNA analysis, also known as a locus (plural loci), a person has two sets of repeats, one from the father and one from the mother . Each set is measured and the number of repeat copies is recorded . If both strands, inherited from the parents, contain the same number of repeats at that locus the person is said to be homozygous at that locus . If the repeat numbers differ they are said to be heterozygous . Every possible difference at a locus is an allele . This repeat determination is performed across a number of loci and the repeat values is the DNA profile that is uploaded to CODIS . As of January 1, 2017, requirements for upload to national level for known offender profiles is 20 loci . </P> <P> Alternatively, CODIS allows for the upload of mitochondrial DNA (mtDNA) information into the missing persons indexes . Since mtDNA is passed down from mother to offspring it can be used to link remains to still living relatives who have the same mtDNA . </P> <P> Prior to January 1, 2017, the national level of CODIS required that known offender profiles have a set of 13 loci called the "CODIS core". Since then, the requirement has expanded to include seven additional loci . Partial profiles are also allowed in CODIS in separate indexes and are common in crime scene samples that are degraded or are mixtures of multiple individuals . Upload of these profiles to the national level of CODIS requires at least eight of the core loci to be present as well as a profile rarity of 1 in 10 million (calculated using population statistics). </P> <P> Loci that fall within a gene are named after the gene . For example, TPOX, is named after the human thyroid peroxidase gene . Loci that do not fall within genes are given a standard naming scheme for uniformity . These loci are named D + the chromosome the locus is on + S + the order in which the location on that chromosome was described . For example, D3S1358 is on the third chromosome and is the 1358th location described . The CODIS core are listed below; loci with asterisks are the new core and were added to the list in January 2017 . </P>

Who came up with the idea for codis