Understanding Your Results
Paternity testing
Samples are required from both individuals to confirm (or disprove) a biological relationship between a child and an alleged father. These samples are collected using a simple mouth (buccal) swab to painlessly scrape off a few cheek cells containing a full set of the individual’s genetic information in the form of DNA (deoxyribonucleic acid).
Each of us inherit half of our DNA from our mother and half from our father. As a result, half of a child’s DNA will match to half of the DNA from each parent. At the laboratory, we extract DNA from cheek cells and amplify specific regions using a process known as PCR (polymerase chain reaction). Our test analyzes up to 27 specific regions designated short tandem repeats (STRs). STRs are regions of DNA in which a short DNA sequence is repeated multiple times. They are highly variable, providing an accurate way to confirm or refute biological relationships.
For every STR, the result will show two numbers, indicating the number of repeats. This is known as the “STR profile”. At each STR, it may show the same number twice if the child inherited the same size repeat from each parent, or it may be two different numbers.
After we have obtained the STR profiles of the child and alleged father, we compare the two profiles. This allows us to state whether or not there is a biological father-child relationship.
For a father-child biological relationship (paternity inclusion), the repeat number will match between the two samples at every single STR marker tested. This means that the probability of paternity is >99.99%.
If there is no father-child biological relationship (paternity exclusion), there will be “mismatches” where some of the STR markers will not match between the two samples. The resulting probability of paternity will be 0%.
Other relationship tests
Each of our relationship tests are conducted just the same as the paternity test. We analyze up to 27 STR markers from each of the individuals being tested, to determine if there is a match.
- For Maternity Testing, half of a child’s STR profile will be an exact match to half of their mother’s STR profile (just like for a child-father relationship).
- For Twin Testing: Identical twins will have the exact same STR profile, while fraternal twins will be more like a sibling relationship profile and only share approximately 50% of their DNA in common.
- Statistical analysis involved in the other relationships are more complex. This is because the further apart two individuals are biologically, the less DNA they have in common. In these circumstances, we will determine an “index value” that is a good indicator of whether or not a biological relationship exists between two individuals.
- Remember, wherever possible, it is best to test for a parent-child biological relationship, as this enables us to provide completely conclusive results.
Our other tests
Many of our other tests detect other DNA changes known as single nucleotide polymorphisms or SNPs (pronounced “snips”). These occur when just one of the DNA building blocks (nucleotides) has been changed to something different. SNPs occur throughout the genome. Thousands of SNPs are linked to different attributes, from disease risk, to hair color, athletic ability, and food response. Some SNPs are detrimental to human health, others can provide an advantage, while others just contribute to differences in our appearance.
Other DNA changes that we can detect include VNTRs and large deletions or insertions. VNTRs (variable number tandem repeats) are similar to STRs (described above in the paternity testing), but the repeated region is larger. Larger deletions or insertions can occur when large sections of DNA are “missing” or “added” to a person’s genome. The affect of these bigger changes depends where in the genome the change has occurred.
