Do you share the same parents with your brothers and sisters? Are you really siblings? If these questions keep recurring in your mind, then you might want to consider doing a half sibling DNA test. This will confirm your biological relationship with your alleged siblings.
When the individuals taking part in the test are male and female, then a full sibling DNA test is recommended. The test establishes the levels of common DNA shared by the test subjects and largely relies on statistical probability. Sibling tests do not need to meet the threshold of a paternity test where the genetic profiles must match at every genetic marker. The goal is to determine whether the individuals share a common parent, have both parents in common, or have neither of their father or mother in common. The test is hinged on a siblingship index where anything less than 1.00 is considered non-relatedness. If the index is greater than 1.00, then there’s a chance that the individuals are half or full siblings. It is important to include the DNA sample of a known mother to make it easier to establish siblingship.
Half Sibling DNA Test Results
The test results provide a statistical likelihood in support of the tested relationship. Normally, additional parties related to the individuals being tested (for example known parents) are also tested to help provide additional evidence. The tests results may not be conclusive by themselves.
DNA Sibling Test Scenarios
If two individuals have the same biological parents, they are referred to as full siblings. Those who share only one biological parent are referred to as half-siblings. Full siblings usually share about 50% of their genes since they come from the same parents. Half siblings only share about 25%. There are 3 types of sibling DNA tests that depend on the parental relationship in question.
- Full Sibling vs Unrelated
In this kind of sibling test, the DNA of two individuals is compared in a bid to establish whether they have the same biological mother and father versus being totally unrelated. This type of test is normally requested by the U.S government in immigration cases where one individual is a US citizen who claims to be sponsoring an supposed sibling who has applied for an immigrant visa.
- Full Sibling Vs. Half Sibling
In this type of sibling test, two individuals with the same biological mother are tested to establish their likelihood of having the same biological father. For this type of test, it is mandatory to have DNA samples of the biological mother tested. This helps establish which genes the two children inherited from their supposedly shared biological father. This makes the test more conclusive.
- Half Siblings Vs Unrelated
In this scenario, the DNA of two people with different mothers is tested to find out if they have the same biological father. It is best to have DNA samples from both biological mothers if possible. This enables the DNA specialists to pinpoint the genes the two individuals inherited from their father(s) and make the test more conclusive.
- Half Sibling DNA Test Between Brothers
If the siblings are both male and want to find out whether they share a biological father, then the DNA test performed should be the Y chromosome test. The Y chromosome test is the most accurate for determining the paternal line. If the two are females, they can ask a male blood relative to take the Y chromosome test in their stead.
- Half Sibling DNA Test Between Sisters
If the siblings are both females who want to find out whether they have the same biological father, then an X chromosome test will do. With this test, the DNA of the biological mother might be tested if they share one. Talk to a professional at CRI genetics for more information on the requirements.
- Sisters and Brothers with the Same Biological Mother
Sisters and/or brothers who want to know if they share a maternal line can have their mitochondrial DNA (mtDNA) tested. This type of DNA is passed down to both males and females from the mother. Only females can pass on this gene to their offspring. If any two people have a common maternal ancestor, then they will have the same mtDNA profile. However, the mtDNA test is not conclusive as it only tells you if you share a maternal ancestor. This may be a mother, aunt, grandmother, great grandmother and so on.
It is important to note that half sibling DNA tests are not an exact science. This is because it is not always possible to obtain the DNA or all the parties involved (parents and the children) as would be the case with a paternity test. The pattern of inheritance and the extent to which genetic markers are shared between siblings is not the same as that of a parent and child. Normally, the accuracy of these tests rests solely on who is available for testing. The more the DNA information available the easier it is to get a conclusive test.