Understanding Your Paternity Test Results

Reading and understanding the results of a DNA test can sometimes be confusing. There are lots of numbers, unfamiliar terminology, and coupled with an emotional situation, can result in frustration.

There are only two possible results that can come from a DNA paternity test.

  1. The tested male is the biological father of the tested child. The results will show the probability of paternity is 99.99%.
  2. The tested male is not the biological father of the tested child. The results will show the probability of paternity is 0%.

Your results will contain a range of information pertaining to the DNA samples provided, and the relationship (if any) between the people tested.

First, we isolate the DNA from the provided swabs, then test this DNA to locate certain regions of chromosomes. These chromosomes vary in length in each individual, and are known as ‘locus’ or if more than one, ‘loci’.

Genetic Markers Explained

An allele is a genetic marker that is used in determining if a person is the biological parent of a child. During a DNA test, 21 plus loci are analysed, to determine a genetic relationship between two people.
The analysis of many loci across the population has taught us that there are many different sized fragments, known as alleles that are associated with each locus. Everyone has two alleles at each locus, one inherited from the mother, and one from the father. Measuring the length of each allele at each locus is the key to determining parentage.

 

How to Read your Results

When you receive your DNA test results, they will be in the form of a tabled report.

  • The first column of the report will indicate the 21 plus loci that have been analysed.
  • The columns marked ‘Alleles Called’ contain numbers indicating the two alleles found at each locus. If the alleles are the same size, then only one number will be recorded.

    For example, a tested child has two alleles at a locus numbered 12.1 and 18. The mother has 2 alleles at the same locus, numbered 12.1 and 16. The child and the mother obviously share the 12.1 allele, which means that the allele numbered 18 is inherited from the father. If the tested male has the same number allele, then he is generally the biological father.


If the tested male does not have matching allele at the tested loci, then he is generally not the biological father of the child. Conversely, if the tested male matches with all tested loci, then he is generally the biological father of the child.

 

Combined Paternity Index

We calculate the probability of the tested male being the biological father of a child using data from all tested alleles. This calculation is expressed as a percentage of probability that the tested man is the biological father, compared to an untested, unrelated man.
If the DNA of the tested father is consistent with the DNA of the child in question, then the report will indicate that the tested father cannot be excluded as the biological father.
Conversely, if the DNA of the tested father does not match that of the child’s DNA, then the report will indicate that the tested father is excluded from as the biological father.