Interpreting the DNA Paternity Test Result

Although the analysis behind DNA testing is extremely complex, there rarely are complications and paternity DNA tests results will provide, in the majority of cases, conclusive answers. The results will clearly state whether there is an inclusion of paternity or an exclusion. There may be cases where results might not be clear-cut but we will advise you well should this issue arise and you should not overly concern yourself given that these cases are seldom.

Your result in detail

Once you have sent in you oral swabs, our scientists will then analyze and locate precise regions on the DNA. These specific locations are referred to as loci and form the basis of DNA paternity testing. We opt for an analysis of a total of 21 loci as this is the number we must test if we wish to retain our accreditation. Studies have shown that within a given population there are variations in these loci from one individual to another; these variations are referred to as alleles.

The DNA test will report results as follows:

• The left hand column will display all 21 loci analyzed. Each individual has paired chromosomes, one chromosome from each pair inherited from each parent. Each locus on your results will have two numbers (or one number if the 2 loci have the same number) which represent the size of the allele.

• The numbers given on each locus will be compared between people taking part in the test. The greater the number of matches the more likely the possibility of a biological relationship between individuals.

An example: A child may have the following two alleles: 12, 16. The mother’s DNA test shows alleles 12, 19. By comparing this simple data, we can say that the child inherited the 12 allele from the mother. The child’s allele with number 16 must have been inherited from the father. If we are talking about a paternity DNA test, then the father’s DNA must show the allele with number 16 to have an inclusion of paternity.

What is the Combined Paternity Index?

Your DNA test results will show the 21 genetic loci analyzed. For each one of the loci, analysts calculate a paternity index and then through a calculation combine all these indexes together to derive that Combined Paternity Index (CPI).  The CPI will ultimately determine the probability of the alleged father being the biological father and is thus very important. The CPI will represent paternity as a percentage which will be 99.99% or higher for an inclusion. The statistical probability relies on working out how likely the tested father is of being the paternal father as opposed to any other unrelated male in a given group of the same ethnic origin.

If the father is totally unrelated to the child, this will clearly be represented as a 0% probability of paternity.

You can read more and acutally view a sample DNA test result by clicking here.

The Amelogenin Sex gene

As mentioned under the subheading ‘Your Result in Detail’, the total number of loci tested for maternity and paternity tests is 21. One of these markers is the sex gene, known as the amelogenin gene. The testing of this gene plays no role in determining paternity (therefore, statistical analysis in a paternity test relies on 20 loci) but just acts as a quality control measure in the testing process. Scientists analyzing your DNA can make sure that there was no contamination of swabs and that all swabs where placed in the correct envelope and labeled properly by the client.

A word about test results using forensic samples

Forensic samples include hair, semen or cigarette ends. Using such samples offers varying success rates; some samples can have DNA extracted from them with more ease than others. However, once the DNA is extracted the testing process is as reliable as the standard oral swab test.

Should you have any problems interpreting your DNA paternity test results, please contact us on [email protected]


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