Understanding your
Paternity Test Result

Analysis details in your test results

Ideally, we recommend sending in the father, mother and child’s DNA. However, we understand that this is not always possible. Most paternity DNA tests we carry out (80%) are done without the mother’s sample. The mother’s DNA sample will not make your results more accurate but they will help strengthen it.

Your paternity test will show you each of the 20 loci analyzed. These loci are the locations on chromosomes which vary in length between individuals and which are taken as the subject of analysis in a paternity DNA test. On the DNA test report, all 21 loci will be shown. For each locus you will see 2 separate numbers; this is because we inherit half our genetic material from one parent and half from the other parent. We can thus say we inherit one of the two numbers from each of our parents. (If the locus numbers are the same, then only one number will be displayed). Scientifically, we refer to these numbers as alleles. For example, the results will show a locus for the child’s DNA with numbers 21, 9. The same locus for the mother will show alleles with numbers 14, 9. This means that the child has inherited the 9 from the mother and the 14 from the father.

If the alleged father tested is the biological father of the child then he will have to have the allele numbered 14. For every locus, the father, mother and child’s alleles are compared. Normally, 15 alleles would need to match between father and child to confirm paternity.

Using all this information, our scientists work out the probability of relationship. They work out what the statistical chances are that the tested father is the true biological father of the child as opposed to another random person in the father’s same ethnic group.

They will report an inclusion rate of 99.99% if the tested father is the child’s paternal father. If he is not the inclusion rate will be 0%.

The paternity index and combined paternity index (CPI)

We analyze 20 loci on the DNA sample you provide us with. A locus (plural loci) is a particular location on the DNA strand taken under analysis. There is one added locus tested which is the amelogenin sex gene, but this locus does not actually play a part in the paternity test result. For each locus analyzed, scientists calculate a paternity index. When they have worked out 20 paternity indexes, one for each locus, they combine all these to work out the Combined Paternity Index (CPI). The CPI will enable scientists to calculate an extremely high inclusion of paternity of 99.99%. Your results will cite both the CPI and the percentage for the inclusion or exclusion of paternity.

The 21st locus tested

The 21st locus tested is the amelogenin sex gene. This is primarily tested as a means of ensuring the quality of your results since clients do sometimes make mistakes when placing the swabs into the envelopes; they might for example, place the mother’s swabs in the father’s envelopes.

Standard samples vs. Forensic samples

The majority of our tests are done using a simple mouth swab. However, we do offer the possibility to use forensic samples such as semen, hair, a licked envelope and many others such samples referred to as forensic or non-standard samples. With such samples we will always advise you on the success rate of each; this is because extracting the DNA from forensic samples may not always be successful, depending on the sample.

The sampling process for non-forensic samples may require very strict guidelines. Make sure to be fully aware of how to collect your forensic sample.

Once the DNA has been extracted, DNA testing proceeds as with any other sample and with equal accuracy.