13 CODIS Core STR Loci

The choice of the 13 marker profile is the result of scientific research going back more than a decade. It was determined in the early 1980’s that there were locations in the human genome that are highly polymorphic. These locations (loci) contain many alleles detected initially as restriction fragment length polymorphisms (RFLPs) and later as short tandem repeats (STRs). Using population genetic principles, it was determined that a standard set of 13 genetically independent loci was sufficient to provide suitable information regarding biological relationships and to uniquely identify an individual (except for identical twins).

The mutation rate at these loci has been studied and found to be higher than single SNP (single nucleotide polymorphism) changes. This is possibly due to the nature of the mutational changes that typically differ by a single repeat unit of four base pairs and may be a result of slippage of the polymerase molecule during replication.

Most of the databases developed meet the assumptions of the Hardy-Weinberg equation and the alleles appear to be in equilibrium. Thus, even though there is a high mutation rate, generally about 1/1000, the impact on the allele frequency is small.

The databases contain allele frequencies only, and do not contain any genotypes or genotype frequency. Since these alleles can occur in combinations in a genotype without restriction, any combination of allele(s) is possible. We simply use the alleles observed in a person’s profile and can calculate a frequency of occurrence of each genotype with the databases available. These types of calculations are performed routinely in the forensic community to provide DNA information.

Since Connect My DNA is not an ancestry test, the associations you might have anticipated based on personal knowledge of your family will likely not be present in the ConnectMyDNA™ results. ConnectMyDNA™ looks at a number of locations in your DNA that are useful for identification purposed, i.e. paternity and forensic analysis. Since the individual markers at each location (alleles) are found in all populations tested, the frequency they occur determines order of the country matches.

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3 thoughts on “13 CODIS Core STR Loci

  1. My birth was the result of an affair. My (dad) and mom raised me together but my Bio dad never was told of me but had a suspision. I have never been given a name and address but have some clues. Will this test give me any idea of the geographical location of the closest resembling DNA? I do not think Bio dad is alive but I would like to know if their are siblings? I’m curious. Thank you, Desiree

    Posted by
    • Wow Desiree, I just read your post and it was like reading my own life… I too have the same scenario, with the exception of having meet my bio Dad 3 times only…. I wish you luck on your search.

  2. Only one major surprise which was Norway as #2; Ireland #1.
    When did Norwegians stop plundering Ireland?

    Posted by Green Nose

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