In the event of siblings needing confirmation of their biological relationship, researching your family history will only tell you so much. In the absence of the biological parents for testing, the only definitive way to prove a biological relationship is through a DNA sibling test.
The most common use for this test is to determine the likelihood of individuals having the same parents in common. In situations where one or both parents are unavailable or unwilling to be tested, the next option is to analyse DNA and make direct comparisons. The genetic laws of inheritance are made up in such a way that there can be big differences in sibling genetic profiles. Whilst it is possible to share many genes in common it is also possible to have inherited different genes from each parent, which would explain situations where the DNA results show a lack of genes in common.
Sibling testing can be used to determine the likelihood of two or more individuals being full siblings, half siblings or sharing no biological relationship meaning being not related. Full siblings by definition have two biological parents in common (the mother and father), whereas half siblings have only one parent in common (either the mother or the father). It is impossible to determine which parent they share without further DNA samples.
Determining Biological Relationships
By examining the number of shared genetic markers between individuals tested, the test can determine the probability of a biological relationship existing between the people. The aim of the DNA test is to analyse the amount of shared DNA and, by using scientific statistical analysis, to deduce any possible biological relationship. The stronger the commonality of the DNA shared means the greater the probability of a biological relationship existing.
It is strongly recommended when undergoing sibling analysis, especially a half sibling test, to include any parent (normally the mother) as this will help improve in the comparison and interpretation of the results. However, as it is common for parents to be absent from this process, a DNA laboratory is still able to provide accurate results due to the testing methodology now used.
This includes testing the Y-chromosome, which is suitable for male-to-male siblings; Y chromosome is transferred through the direct male lineage whilst the X-chromosome is suitable for female-to-female siblings with the same potential father and different mothers. (Mitochondrial DNA can also test both male and female siblings through the maternal lineage).
Common Cases for DNA Sibling Testing
There are many different reasons for siblings resorting to DNA test to prove a biological relationship. In some cases, siblings have been separated from young, and find their alleged siblings later in life, often after parents are deceased. Sometimes a sibling will have doubts as to who their real father is. They will feel sure they share the same mother but have concerns over their biological father. As mentioned above, a sibling test will clarify whether siblings are full or half, possibly eliminating any doubts over paternity. Last but not least, during inheritance disputes or claims, it can often be of importance for siblings to prove their relationship and whether they are full or half siblings can greatly affect the outcome of a will.
Before embarking on a DNA Siblings Test it is important to identify who is available for testing as this will assist the DNA laboratory to decide which DNA test is most applicable to your case. There can also be various stages of testing with additional people included in the testing if the first results do not yield a satisfactory result. Also in the case of minors (16 or 18 years of age depending on country of location) permission from the legal guardians may be required.
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