About our Siblings DNA Test

If siblings (male and female) question whether they share the same father or mother, they can choose to carry out sibling DNA testing. The test can be done with any number of siblings and the results will provide a clear indication of whether or not the siblings have a parent in common.

GTL Australia offers sibling testing for 2 alleged siblings for the cost of $589.Results are ready in 7-10 working days.

What about Testing the Parents?

If siblings have decided to keep the DNA test strictly between themselves it is probably because they have already considered testing the mother’s sample in a maternity test or the father’s sample in a paternity test and discarded these options due to the unavailability of DNA samples. The test that will give you the most accurate results is a DNA test where the samples of the alleged mother or father are compared directly with the samples of the child/children.

Genetic Testing Laboratories always recommend a sibling test as a second option in cases where out clients are unable to provide us with DNA samples from the alleged mother or father.

Although the results of a sibling test will not be as conclusive as a paternity or maternity test, they can still provide very accurate results and help find definitive closure. To increase the accuracy of a sibling test, try providing GTL with a sample from any of the known parents. It would also help us to know which parent you are certain you share, if any.

Sibling testing: The Results

Siblingship test results do not follow the same template as a maternity or paternity test. The test will compare the genetic profiles and calculate a siblingship index. The laboratory then combines multiple siblingship indexes to derive a combined siblingship index. We take an index of 1.00 as our benchmark – a figure below this number would indicate that the tested parties are not siblings. The higher the value is above 1.00, the higher the chances that the tested parties are blood siblings.

Basing ourselves on the laboratory analysis, we then give our clients a clear interpretation of the results, scientifically assessing the most likely relationship between the tested parties in terms of whether they are full siblings (having both mother and father in common), half siblings (having either just their father or just their mother in common) or not siblings (and thus having no common parent).

Samples for a sibling test are usually collected using our kit. GTL provides a home sample collection kit with which clients can collect their saliva samples using buccal swabs.

Testing between Male Siblings

If Siblings are male and want to know if they have the same father, GTL Australia suggests Y-STR DNA testing or Y chromosome testing. The Y chromosome is exclusively found in males and it encodes maleness in a region known as sex-determining region Y. Unlike sibling tests, a Y chromosome test is not made more accurate with the sample of the mother and gives highly accurate yes/no results. A Y chromosome test can even be used to trace patrilineal ancestry.

Please note: In some cases, a Y-STR DNA Test can provide more conclusive results for males determining common paternal lineage.


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