Wednesday, September 1, 2021
Megan Briley, DNA Solutions Senior Administrator, with Dr. James Anstead, Laboratory Director
We understand the importance of understanding the results you receive. Available upon request, are handouts explaining results for both paternity and secondary tests. For those interested in a technical explanation behind the statics used to obtain your results, insight into the science of these analyses can be found below.
The 24 relationship markers we are testing are known as STR autosomal DNA markers and originate from the nucleus of a cell. Other than identical twins, no two people have the same autosomal DNA. Each system indicated on your report reflects a specific locus, which is the physical site or specific location on a chromosome. Each locus has repeated motifs, which is a sequence or recurring pattern of the nucleotides found in DNA. The four nucleotides are Adenine, Thymine, Cytosine, and Guanine. The allele number indicated in your report is a value determined by the number of repeats of these four nucleotides (or five for Penta D and E) at each system.
For example, if your DNA represents the following base pairs: ATCG with a repeat of that system five times (ATCG, ATCG, ATCG, ATCG, ATCG) then your report would indicate a value of 5 at that system.
So why are there values for two alleles at each system?
There is a value for each chromosome you inherited from your parents. The report does not indicate which value falls on which chromosome (paternally inherited or maternally inherited) as the values are simply reported with the smallest number first. If you see a blank allele with no value listed, this indicates that you inherited the same number of repeats from each parent, such as 16 and 16 for D3S1358, shown in the example table.
The Relationship Index (RI Value) is a statistical value determined by the likelihood you inherited that allele by descent due to a shared relationship versus the likelihood you inherited that allele from a random person of the same race group. Rare or uncommon alleles will give a higher RI value. Common markers commonly shared among individuals of a specific population, will result in a lower RI Value. RI values of 1 or less can contribute to a low CRI Value. Each RI value is then multiplied together to provide the Combined Relationship Index (CRI). The CRI value will then be converted to a probability of relationship percentage using a statistical equation.