Sibling DNA testing: testing between brothers and sisters

If both male and female siblings need to take part in the same test, we suggest a full sibling STR test. Testing starts from R4995 for testing 2 individuals.

This DNA test will establish whether you have a common biological parent and is carried out between two or more individuals. Sibling testing is recommended when the people taking part in the test are male and female.

We strongly suggest including the sample of a known mother to provide stronger results.

What we seek to establish in a test between brother and sister


  • Do the individuals tested share both their biological mother and father
  • Just one biological parent in common
  • No common biological parents

The result will enable inferences about the most likely relationship between the two siblings – for example, X and Y are more likely to be half siblings than full siblings. Test results are intended to provide a statistical likelihood that gives evidence to support the tested relationship in question. Providing additional parties to be tested (for example, a known parent’s sample) or performing direct relationship testing may provide additional evidence.

A full siblings test is recommended when the individuals taking part in the test are male and female. A sibling test determines the amount of common DNA between the people tested. It is a test that relies on a statistical probability. Unlike a paternity test, however, sibling tests do not need to have genetic profiles that match at every genetic marker. A sibling test simply seeks to determine whether the individuals tested share one common parent, both common parents or have neither their mother or father in common. In a sibling ship test, we calculate siblingship index. If the siblingship index is less than 1.00, this indicates non-relatedness. If the siblingship index is greater than 1.00, this indicates that the two tested individuals are more likely to be true full sibling or half siblings.

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.

In cases where siblings are male

Are the test participants males? Do they need to establish whether you have the same father or paternal line? In such instances, EasyDNA offers Y chromosome testing. This test is highly accurate and results are ready in 5-7 working days from the moment we receive samples at the laboratory. This test is extremely accurate. Male siblings that share the same father will also have the same Y chromosome profile. If females wish to establish whether they have a common paternal line they can ask a direct male blood relative to take a Y chromosome test on their behalf. Testing starts from R4995 for testing 2 individuals.

Note: We can only guarantee standard result turnaround time when testing takes place solely using oral swab samples. Using a forensic sample for your test may lead to an increase in turnaround time.

We suggest you return samples by courier directly at the office because the local postal system has proved unreliable and we cannot be responsible for samples that do not reach us.

In cases where siblings are female

Are test participants females? Do they wish to establish whether they have the same father? Do they have different mothers or the same biological mother? If test participants are female and their scope is to find out if they have the same biological father, we suggest that you get in touch with our team to discuss your case and find the best solution for your testing requirements.

Twin siblings: Are they monozygotic or dizygotic?

Twins can be either monozygotic or dizygotic. The best way to find out whether twins are identical or fraternal is by doing a twin zygosity test. Twin siblings that are monozygotic will have the same DNA profile whilst twin siblings that are dizygotic will have different DNA profiles.

What is STR analysis?
Understanding your relationship test results

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