How do I read my DNA Paternity Test results?

The technical terminology used in the DNA Paternity Test Report comes from regulatory and legal requirements. To demystify some of this terminology, here’s how to read and understand the different parts of your test report.

Overview

Your DNA Paternity Test Report will consist of the following 3 pages:

• Page 1 is a cover page that shows your Case Number (Order ID) and the first names of each person participating in the test.
• Page 2 is where you will find the results of your DNA Paternity Test and a chart with the genetic markers for each person tested (DNA profile).
• Page 3 is an educational page that includes a glossary for the terminology used in the report, as well as interpretation guidelines.

The Science

To understand the details of your test report, it is important to be familiar with the terminology and science behind how relationship DNA testing works.

In a DNA paternity test, the laboratory generates a DNA profile of specific genetic markers (also known as short tandem repeats, or “STR”) at a set of known sites (“loci”, or singular, “locus”) in your DNA. At each DNA locus, you will have two genetic variants (“alleles”), one of which is inherited from your mother, and the other from your father.

The laboratory technique used to amplify and study DNA is called polymerase chain reaction (PCR). In a relationship DNA test, such as the DNA paternity test, PCR analysis is used to determine the specific alleles that you have for each STR marker. In a true parent-child relationship, it is expected that at least one allele at each DNA locus in the child’s DNA profile will be found at the same DNA locus in the biological parent’s DNA.

Your Results

In your test report, you will find a chart displaying the DNA profiles for each person tested. The data displayed in the DNA profile chart may look something like:

The first column, DNA Locus, lists the genetic markers that were analyzed for your paternity test (e.g. D8S1179). At each genetic marker, the two alleles from the tested individuals are recorded in the Child and Alleged Father columns. You may have two identical alleles at a marker (e.g. “13”), or you may have two different alleles (e.g. “13,14”). If the same number is present in both columns, that means you “match” at the corresponding genetic marker.

At the D8S1179 locus in the example chart (above), the child’s alleles are “13” and “14”, and the alleged father has two copies of the “13” allele.  Since the “13” allele is present in both DNA profiles, that means the alleged father and child match at the D8S1179 locus.

The final column displays the Paternity Index (PI), which represents the statistical strength of a match at the corresponding genetic marker. Some alleles are more common than others in the population, so the PI calculation accounts for how likely it is that two random individuals share the same allele match.

If there is no allele match between the alleged father and child at a given DNA locus, the Paternity Index will display 0, as seen in the example below:

Combined Paternity Index

After the PI values have been determined for each DNA locus, the Combined Paternity Index (CPI) value is calculated by multiplying the calculated PI values together. The CPI value is a measure of the overall strength of the genetic evidence. It represents how many times more likely it is that the tested alleged father is the true biological father than a randomly selected man in the population.

Probability of Paternity

The probability of paternity is calculated from the CPI, and it is generally considered to be the final result of a paternity test. A CPI value of 0 corresponds to a probability of paternity of 0%. A CPI value that is greater than 1000 corresponds to a probability of paternity of greater than 99.99%.

Conclusion

In a DNA Paternity Test, your test report will indicate one of two possible outcomes:

If the alleged father IS NOT the true biological father, your report is expected to state:

PROBABILITY OF PATERNITY: 0

If the alleged father IS the true biological father, your report is expected to state:

PROBABILITY OF PATERNITY: >99.99%