What is extended testing and when is it needed?

The below table shows the number of markers we used in a standard test vs. the number used in extended testing:


Type of test Standard number of markers Extended testing
Paternity testing 21 genetic markers (loci*) 25 genetic markers (loci)
Siblings testing 21 genetic markers (loci) 25 genetic markers (loci)

Extended testing allows us to provide you with more accurate results in the following scenarios:


  • You are carrying out a home paternity test where you suspect or know that the alleged fathers are brothers, you do not have the mother’s sample and can only test 1 of the alleged fathers.
  • You are carrying out a siblings DNA test.

*A genetic marker or a locus is a specific location of a gene (or of a significant sequence). When the laboratory carries out a DNA test, they extract the same genetic markers for every individual. Each person typically has two alleles for every one of the genetic markers extracted (alleles are alternate forms of the DNA which may have different repeats), one inherited from the biological mother and one inherited from the biological father. In a paternity test, we extract the set of genetic markers from the alleged father and the child and then see if the child has inherited the alleles from the alleged, tested biological father.

A note about siblings testing

Siblings’ testing compares the DNA of the individuals tested to confirm if they share a common parent. The test is based on a probability of relationship which essentially establishes the amount of common/shared DNA between the siblings. The amount of common DNA between siblings can vary – in some cases biological siblings can sometimes share a lot of DNA whilst in other cases, share far less common DNA making them appear unrelated. This is due to the nature of DNA inheritance. This is why with siblings testing we would suggest using additional markers as it can help you get a more conclusive result.

A note about paternity testing

In a paternity test we extract 21 genetic markers from the DNA of the alleged father. For any alleged father tested, the laboratory extracts the same exact markers (loci). The issue with both alleged fathers being brothers is that brothers may sometimes share common markers. This could affect the accuracy of the test.

If the alleged fathers are brothers (or you suspect they may be) you can:


  • Test both alleged fathers and the child. This means we need DNA samples from both brothers (and alleged brothers) and the DNA sample of the child.
  • Test just one of the alleged fathers and the child. In this case, you will need to select extended testing using additional markers to provide a conclusive result.
  • Test just one of the alleged fathers, the child’s mother and the child.

Testing the mother

Testing the mother is recommended in all paternity testing scenarios although not mandatory. The mother’s sample will always help towards getting stronger and more accurate result. However, the only time we would strongly not recommended doing a paternity test without the mother’s sample is if the alleged fathers are brothers (or suspected to be brothers) and you only have the DNA sample from one brother; in this case we would need the mother’s sample.

Other Tests
Relationship Tests
Paternity Tests