Sample DNA Test Result | Interpret your Paternity Test Result | EasyDNA South Africa

Interpret Your DNA Paternity Test Result

EasyDNA carries out paternity testing exclusively in ISO 17025 accredited laboratories. Some DNA testing companies only test handful of genetic markers but at easyDNA we abide by the minimum accepted international standard for paternity testing which stipulates using a 20 marker genetic profile. Paternity testing is more than just a simple DNA extraction; it involves mathematical and statistical calculations which ultimately will conclude whether the tested alleged father is the biological father or not.

Your paternity test result can show one of two possibilities

  • If the genetic markers on the DNA profile of the alleged father and the child are a perfect match, then we issue what is known as a paternity inclusion DNA test report (meaning the tested man is the biological father of the child)
  • If the genetic markers on the DNA profile of the alleged father and the child do not match then we issue a paternity exclusion report (meaning the tested man is not the biological father)

The probability of paternity

The probability of paternity is the final calculation we carry out in your result. It basically sums up the result of the test in a simple percentage showing how likely the tested man is the biological father of the child. To be included as the biological father, the probability must be 99.9% or higher. To be excluded as the father, the probability of paternity is always 0%.

Paternity indexes

easyDNA tests 20 genetic markers or alleles; for each one of these 20 genetic markers we generate a paternity index once the alleles have been extracted and amplified. This paternity index basically shows how likely it is that the child tested has inherited that allele from the alleged tested father compared to another random man within the same ethnic / racial group. The calculation is highly complex and relies on the use of a data base which gives the frequency distribution of alleles in a population.

Taking all the paternity indexes and combining them together using multiplication, we can calculate the combined paternity index. This is a ratio that shows the likelihood that the man tested is the biological father. We can then convert the combined paternity index to the probability of paternity using the Baysian theorem.

A bit more about the 21 genetic markers

We actually compare 20 genetic markers and not 21. This is an important point because we do actually extract and amplify 21. So why 20 markers? The 21st genetic marker is the amelogenin sex gene which is one of the genes which can tell us the sex of the DNA sample submitted. The amelogenin sex gene is carried on both the X and the Y chromosome but we can distinguish a male sample from a female sample by the amelogenin peaks which are typically higher on the Y chromosome than on the X chromosome.

Inconclusive results

In some cases we do get an inconclusive result; this is very rare but the situation could arise and could be due to a number of reasons. If the alleged fathers are close relatives (typically brothers) one alleged father is the uncle and one is the biological father. If we only test one of the alleged fathers, the result will show genetic profiles between the alleged father and the child which are very similar. Normally, we would have a match of 13 or 14 markers and a probability of paternity of, for example, 98%. Such a result will not however, be strong enough to conclude that the tested man is the biological father of the child. If we do not have the sample of both fathers, it will be hard to confirm which alleged father is the biological father; to provide a conclusive result we would need to include the mother’s sample or test both fathers.