Sibling DNA Tests
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Test Details
Sibling DNA Testing is used to determine whether two (or more) individuals share one or both biological parents.
This test should only be used if other types of test have been ruled out, for example, Paternity/Maternity/Forensic/ Y – Chromosome Tests should all be considered first.
Sibling analysis is divided into two categories:
Full-Sibling Study
This test is ordered for clients who want to determine if they have both parents in common (share the same mother and the same father).
Half-Sibling Study
This test is ordered for clients who want to determine if they have one parent in common. (Share the same mother or the same father).
The price includes:
2 Individuals
The cost of the test also includes: Sample collection, all reports and correspondence.
Additional test participants should be charged at the rate specified.
The Sibling Test
As in a paternity test a DNA profile is produced for each person. The test analyses 16 genetic locations on the DNA strand. The allele (alternating form of DNA) at each location is identified by a number. The DNA profiles of the test participants are then compared.
The test is based on the fact that biologically related individuals should have more DNA in common than unrelated individuals. On average the alleles (numbers) of full siblings will match at more DNA locations than half siblings, and half siblings will match at more than unrelated people.
Test Limitations
Sibling analysis is not as conclusive as paternity testing. The results are based on statistical calculations that produce a probability of whether two individuals are true biological relatives.
The statistical analysis is based on factors such as:
- The number of allelic matches within the DNA profiles.
- How likely it is that the same allele would be found at that same DNA location, if testing a random, unrelated individual from the same ethnic background.
These calculations determine the most likely relationship between the individuals tested.
How the results are interpreted
The values from the calculations are used to generate a percentage probability value. Based on the question the client wants us to answer, this value tells us which scenario is more likely.
For example, if two individuals want to know if they are half or full siblings, the percentage probability will indicate which relationship is most likely to exists. This percentage value will fall into one of three categories:
0 – 10%: This is evidence that the relationship does NOT exist i.e. this would mean that the clients are unlikely to be full sibling, thus it is evidence that they are half siblings.
90 – 100%: This is evidence that the relationship DOES exist i.e. this would mean that the clients are likely to be full sibling.
10 – 90%: Tests falling within this range are deemed to be INCONCLUSIVE. This is because as an accredited laboratory, it is important that results are only given to the client when we can be confident that there is REAL and STRONG evidence that a certain relationship exists.
Sibling DNA Analysis is less accurate than Paternity/Maternity Testing
In a Paternity/Maternity test, exactly half of the child's DNA will match the biological father and the other half will exactly match the biological mother.
The DNA of siblings (except identical twins) will not match each other, as the inheritance of alleles (numbers) from biological parents is random. At each genetic location (part of the DNA) a person possesses two alleles (numbers). A person will only pass one of these alleles to their offspring. Which allele is passed on is completely random. Therefore, one child could inherit one allele from his father, while the child's brother or sister could inherit the other.
Inconclusive Results
While these tests can provide accurate results, there is the chance that the test will yield an INCONCLUSIVE result - Please see the Visual Representation of Relationship Analysis.
An INCONCLUSIVE result occurs in approximately 20% of sibling tests (i.e. 1 in 5).
Causes of inconclusive results include:
- The alleles shared between test participants are extremely common within the relevant general population. In these circumstances there is insufficient genetic evidence unique to the individuals being tested to confirm which biological relationship exists.
- Low level of allelic (number) matches in the DNA profile due to the chance nature of inheriting alleles within families (as explained above).
- Mutation causing mismatches at further locations within the DNA profile.
If an INCONCLUSIVE result is given, clients may be provided with the option of analysing further points on the DNA molecule. (This will incur an additional fee).
When should Sibling studies be used?
Usually, a Sibling test is only carried out as a last resort because the alleged mother and/or father are either deceased or unavailable for testing and other forms of test have been ruled out.
Due to the lengthy analysis, the cost of the test is higher than other forms of testing. This and the above risks mean other forms of test should be used first whenever possible.
Existence of other potential biological relationships
If other potential biological relationships exist between test participant, it is unlikely that this test will yield evidence strong enough to distinguish between them.
For example: if test participants believe they are either half sibling OR cousins, this test should not be performed.
What does the test NOT show?
The test result will not provide a conclusion on the identity of each test participants biological parents.
It will be for the client to decide what the result means to them taking into account the facts and circumstances surrounding the test.