Sibling DNA Tests
Relationship Testing: Same Parent?

Genetic Tests

Sibship DNA Tests

Sibling DNA Tests


What Are Sibling DNA Tests?
How Do They Work?
Why Aren't Results Always Conclusive?
How Much Do They Cost?

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Genetic Testing

What Are Sibling DNA Tests?

Also known as siblingship and sibship tests, these complex tests are used to determine if two people share one or both biological parents. A full sibship DNA test analyses if 2 people share the same biological mother and father. A half sibship version checks if they share one parent, more commonly it is paternal line, or father who is in question. While paternity testing is a better alternative because it usually provides conclusive results, if the father is dead or missing this is not always an option. Where possible it is also important to test the mother's DNA so that her genetic material can be excluded in the sibship analysis process and results will be more accurate.

How Do They Work?

The lab will analyze up to 46 STR DNA markers of each of the potential siblings. This will help them obtain a full genetic profile of each individual. The profiles are then compared and the results are expressed as a likelihood ratio and converted into a probability sibship index. The results will depend on the number of markers the individual’s share, the rareness of those markers and the patterns they make. If 2 people are full siblings, their sibship index will be higher than if they were half siblings. What these tests do NOT do, is provide any information on possible genetic disorders. These are entirely different tests and should ideally be discussed with genetic counselors.


If you wish to carry out a test for curiosity-sake rather than legal purposes, then a non-legal test is perfectly adequate. You can order these online or they are available in some pharmacies or stores. A direct to consumer sibship testing kit usually includes mouth swabs for up to 3 people. Simply run the swab along the inside of your cheek and place in an envelope provided with the kit. Post all samples back to lab for analysis, and wait! Results are usually available by post, email or over the phone within 3 to 5 business days. If the mother's DNA is not available, results may take longer and the test is usually more expensive.


In many instances people take this test to establish relationships for legal purposes. This may be for inheritance or immigration reasons. Only a legal test will be accepted in a court of law. With regards to immigration, the Department of Homeland Security requires DNA tests for most visa applications to prove claimed relationships with citizens already residing in the United States. A so-called chain of custody needs to be established which means the test needs to be carried out in the presence of certified collector. Adults will have to present a government issued proof of identity or if children are involved a birth certificate or social security card will be required. All parties are finger printed and photographed and required to complete a consent form. Companies such as DDC (DNA Diagnostic Center) offer this service. Obviously, given the extra administration involved legal tests are more expensive than non-legal ones (although both involve taking a simple buccal cheek swab).

Why Aren't Results Always Conclusive?

Although DNA testing is generally accurate, in this case people are trying to determine a shared relationship without actually testing the DNA of that shared parent. This can never be as accurate as testing the alleged parent's actual DNA. While sibling testing can give a strong indication of probability of a relationship between two people, it is rarely conclusive. This is because although 2 people can share the same parent, they may only share a few of their recognizable DNA markers. The more markers tested however, the more accurate the results may be. If both people are male, an alternative option includes Y Chromosome DNA Tests. These can conclusively conclude if 2 men share the same father or not.

How Much Do They Cost?

The average cost will depend on which type of relationship is being tested and if the mother's DNA is also available.

Type Non Legal Legal
Full Sibship with Mother $600 $675
Full Sibship w/o Mother $700 $875
Half Sibship $700 $875

Other Types Of Genetic Tests

Ancestry Gene Tests
Grandparent DNA Testing
Twin DNA Testing

  Related Articles on DNA Tests

For more on genes and DNA, see the following:

Genetic Testing During Pregnancy
Paternity Test Kit
Can a paternity test be done without the father?
Genetic Testing Before Pregnancy
Paternity Testing Research

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