A sibling DNA test is often performed instead of a Paternity Test when the alleged father is deceased, unavailable or unwilling to take part but the child’s brother or sister is available. A paternity test would give more conclusive results but can only be carried out if we can obtain DNA samples from the alleged father. A Sibling Test is a good option to consider if you are unable to carry out a paternity test.

PLEASE NOTE: In the event of a possible pre-existing relationship the laboratory would NOT be able to run a sibling test if you believe your cousin could be your sibling. Please contact us to help you find the right test for you.

A sibling DNA test is based on a very simple principle in genetics: heredity. All siblings will share common genetic markers with each other which they have inherited from their biological parents. If we analyse the samples of alleged siblings, we would expect to find these common maternal or paternal genetic markers.

Once DNA samples are at the laboratory, a DNA profile is generated for each of the individuals and a siblingship DNA index is determined. If the siblingship DNA index is less than 1.00, this would indicate that the siblings are unlikely to be related. If the siblingship DNA index is greater than 1.00, this indicates that the individuals tested are more likely to be true biological siblings. The higher the value of the siblingship DNA index, the greater the likelihood that the two individuals are true biological siblings. To analyse the possibility that the siblings share only one common parent versus two common parents (mother and father), a half siblingship DNA index is also obtained. The ratio of the half siblingship DNA index versus the full siblingship DNA index would provide you with an indication of whether the two individuals are more likely to share only one common parent (e.g. mother only) or two common parents (mother and alleged father).

Sibling DNA testing provides indications as to whether the individuals tested are full siblings, half siblings or not siblings at all. Including a sample from a known parent will help increase the accuracy of this test.

To increase the accuracy of a sibling DNA test and provide the most accurate result, we ask that samples of a known parent should be included when possible. If the child’s mother takes part in the test it enables the laboratory to identify the mother’s DNA inherited by the child and take it out of the equation, leaving only the DNA inherited from the father to be compared against the other test participant(s). There is no additional fee for including a known parent.

All males from the same paternal line will share the same Y chromosome which makes Y Chromosome Testing a very accurate and conclusive test. This test will accurately confirm if the male siblings tested share the same biological father. AffinityDNA offers Y chromosome testing for both legal and peace of mind purposes. Please Contact Us for more information.

Siblings who want to establish whether they share the same mother can do so by carrying out an X-SV test. This test is also known as a Mitochondrial DNA Test and will confirm with a Yes-or-No answer whether the tested parties share a common maternal line. With an X-SV test, both males and females can take part. X-SV maternal lineage testing can be carried out for legal or peace of mind purposes. Please Contact Us for more information.
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