4 DNA Testing - How to understand a Parentage Test Report
The Report shows the results of laboratory tests that provide evidence regarding the alleged family relationship.
The laboratory tests the DNA isolated from buccal (cheek) swabs to locate certain regions of chromosomes that vary in length between individuals. 16 of these sites are tested, each site is called a "locus", ("loci" - plural). Analysis of these 16 loci in a large population has revealed many different sized fragments, or alleles, associated with each locus. These are the genetic markers used in parentage analysis.
Because each individual has 2 of each type of chromosome, 1 inherited from each parent, everyone has 2 alleles at each locus. These 2 alleles are sometimes identical, but usually they are not the same size. During parentage testing, the laboratory identifies the length of the 2 alleles found at each locus. The report you will be given shows numbers (in the 1st column) that indicate each of the 16 loci involved in the testing process.
The columns marked "allele" on the report contain numbers indicating the 2 alleles found at each locus (or 1 number if they are the same size).
If, e.g., a child has 2 alleles that are designated 12.1 and 18, and if the mother has alleles 12.1 and 16, then the child inherited the 12.1 allele from the mother. The child has to have inherited the 18 allele from the father. Generally, the alleged father must have this allele if he is the biological father of the child.
15 different loci are used as genetic markers in the tests, as well as one to confirm the sex of the person providing the sample. If the alleged father does not have the matching allele at every tested locus, then he usually cannot be the biological parent. If he does have it, they he could be the father. A "relationship index" (called the "Direct Index" in the report) for each locus is calculated based on information including the portion of the male population that has the obligate paternal allele at that locus. This index is reported for each DNA locus.
A combined relationship (or "Direct") index for all of the tested alleles is then calculated and appears below the chart. This number is used to calculate the "probability of relationship", which is the percentage likelihood that a man with the alleles of the alleged father is the biological parent of the child, as compared to an untested, unrelated man of the same race. If the DNA of the alleged father is consistent with that of the child, then the report will conclude that the alleged father can not be excluded as the biological father of the child. If the DNA is not consistent, it will conclude that the alleged father can be excluded as the biological father of the child.
Grandparent, Aunt or Uncle Test
This test determines the likelihood of a statistical probability that a person is the grandparent, aunt or uncle of a child. This type of testing is referred to as Avuncular Testing.
When the issue of an avuncular relationship is in question, the recommended method is to test the available parent of the child in question if at all possible. In situations where the child's parent is unavailable for testing, a DNA avuncular test can still be performed.
Unlike a DNA paternity test which will always provide a conclusive result, avuncular tests are different. When an avuncular test is conducted, the DNA laboratory will determine the genetic profile of the alleged relatives based on the type of genetic material exhibited by each person, an avuncular index is determined. If the avuncular index is less than 1.00, this indicates non-relatedness. If the avuncular index is greater than 1.00, this indicates that the 2 tested individuals are more likely to be true biological relatives. The higher the value of the avuncular index, the greater the likelihood the 2 individuals are true biological relatives. Although the avuncular test will not provide you with a conclusive answer, it may be able to provide you with an indication of whether you are more likely to be or not to be the true biological relative of the other tested individual.
Siblingship test
This type of test determines the statistical probability of whether siblings (brothers and sisters) share the same two parents or not.
The recommended method to determine whether individuals are true biological siblings is to test their parents.
Including one common parent greatly increases the accuracy of this type of analysis and is recommended if at all possible.
When a siblingship test is conducted, the DNA laboratory will determine the genetic profile of the alleged siblings. Based on the type of genetic material inherited by each sibling, a siblingship index is determined. If the siblingship index is less than 1.00, this indicates non-relatedness. If the siblingship index is greater than 1.00, this indicates that the two tested individuals are more likely to be true biological siblings. The higher the value of the siblingship index, the greater the likelihood that the two individuals are true biological siblings. To analyse the possibility that the siblings share only one common parent versus two common parents (mother and father), a half siblingship index is obtained. The ratio of the half siblingship index versus the full siblingship index would provide you with an idea of whether the two individuals are more likely to share only one common parent (eg mother only) or two common parents (mother and alleged father).
Although the siblingship test will not provide you with a conclusive answer, it may be able to provide you with an indication of whether you are more likely to be or not to be the true biological sibling of the other tested individual.
