Understanding my DNA paternity test results

Everything you need to know to interpret your test results.

Casey Randall Alphabiolabs

By Casey Randall, Head of Genetics at AlphaBiolabs
Last reviewed: 05/07/2023

What are DNA markers?

Specific locations on a chromosome are made up of sequences of repeated DNA. These DNA markers that AlphaBiolabs examines are highly variable in length between individuals. Each individual has two copies of each DNA marker, known as alleles: one is inherited from the father and the other from the mother.

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Which DNA markers are examined?

AlphaBiolabs tests up to 45 DNA markers including two sex-specific markers as standard. These are:

DNA markers D3S1358, vWA, D1S1358, D16S539, CSF1PO, TPOX, D8S1179, D21S11, D18S51, Penta E, D2S441, D19S433, TH01, FGA, D22S1045, D5S818, D13S317, D7S820, D6S1043, D10S1248, D1S1656, D12S391, D2S1338, D7S1517, D3S1744, D2S1360, D6S474, D4S2366, D8S1132, D5S2500, D21S2055, D10S2325, SE33 and Penta D.

Two sex markers: Amelogenin and Yindel (Y chromosome specific) Differences between the X chromosome and Y chromosome versions of the amelogenin gene (AMELX and AMELY, respectively) enable it to be used in sex determination.

How does the DNA paternity test work?

The two alleles observed at each DNA marker are compared between the tested individuals. A full match of these alleles between individuals provides evidence of a relationship between them. Each allele is represented by two numbers.

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For example, if a father displays numbers 17.3 and 13 for one specific genetic marker (in this case D16S539), the child will need to display either the 17.3 or the 13 on the same genetic marker to show it has been inherited from the father. There will need to be a match with all the DNA markers tested for an inclusion of paternity (A).

DNA Test Relationships

In example A, you can see that the child’s DNA footprint is made up from half the mother and half the father.

Example B shows that the possible father does not share a marker with the child and is therefore excluded from paternity. In other words, he cannot be the father.

DNA marker Mother Child Possible father
D3S1358 11 17 11 14 8 14
vWA 16 16 15 16 15 15
D16S539 14 15 15 17.3 13 17.3
CSF1PO 10 10 10 10 10 10
TPOX 13 14 14 14 14 16

What is the probability of paternity?

DNA testing relies on the statistical probability of the possible father being the child’s biological father and not any other man from the same ethnic group who may share a similar DNA profile by random chance.

DNA marker Mother Child Possible father
D3S1358 11 17 11 14 8 14
vWA 16 16 15 16 15 15
D16S539 14 15 15 17.3 13 17.3
CSF1PO 10 10 10 10 10 10
TPOX 13 14 14 14 14 16

What is the combined paternity index?

The probability of a relationship is calculated by comparing the DNA profiles obtained to an untested random individual within the general population.

For example, when the probability of paternity is 99.99%, this means that the tested man is 99.99% more likely to be the biological father of the child than any other man chosen at random from the same ethnic group. The combined paternity index is a calculation that helps us arrive at the probability of paternity.

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Could the DNA result be incorrect?

AlphaBiolabs tests all exclusion results twice so you can be confident of getting an accurate DNA test result.

Most illnesses will not affect the DNA result.

All tests are performed assuming that a close male relative of the potential father is not the biological father. If this is not the case, we recommend that any such relative is also tested as the result provided may be invalid. This information should be provided in section 3 of your DNA Test Request Form, so that it can be taken into consideration when analyzing your results.

Still have questions? Visit our Frequently Asked Questions or lots more information can be found on the Learning Center pages.


Casey Randall AlphaBiolabs

Casey Randall

Head of Genetics at AlphaBiolabs
Casey joined AlphaBiolabs in 2012 and heads up both the Genetics and Health testing teams. An expert in DNA analysis and a member of the International Society for Forensic Genetics (ISFG), Casey holds an MS degree in DNA Profiling and a BS degree in Forensic Science. Casey is responsible for maintaining the highest quality testing standards, as well as looking for ways to further enhance the service that AlphaBiolabs provides and exploring new and innovative techniques in DNA analysis.

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