• Understanding a DNA Sibling Test

    Posted on September 30, 2013 by in Uncategorized
    Sibling DNA testing: Are they really blood siblings?

    Sibling DNA testing: Are they really blood siblings?

     DNA Sibling tests are a type of relationship test that is specifically designed to determine the type of relationship between siblings. Siblings can share either one parent, both parents; a test can establish either or may show them to be totally unrelated and share neither of their parents. In many instances, a sibling test is used instead of a paternity test as it may not be possible to carry out the latter test due to the father being unavailable or unwilling to take part in the test.

    How do I go about a Sibling DNA Test ?

    You will be asked the following questions so as to help choose the testing methodology most suited to your case:

    • What do you want to establish? ; for example, ‘we are two siblings and want to establish whether we share the same father’
    • What is the gender of the siblings that require testing?
    • Are any of the parents available for testing?

    In the above given example in which siblings want to establish whether they share the same father, carrying out a paternity DNA test with the father’s DNA samples is always the first option to consider- a paternity test result is more definite and conclusive. But when this is not possible, then a sibling paternity test is the next option. Also, it is always recommended that the mother’s samples be included for testing as this will help clarify with certainty which genetic markers where inherited from which parent. For more information about how to understand your paternity test results, visit this webpage.

    Can a Sibling Test be used for Immigration ?

    Yes, you can definitely use the results of a sibling test to help support you case with the immigration authorities. An immigration DNA test becomes a scientific proof of relationship between two people and is in some cases (depending what country the people are emigrating from) indispensable as authorities might question the authenticity of any records for marriage or birth presented.

    Testing methodologies for Sibling DNA Tests
    There are quite a few methodologies that can be used in this case:

    • If the testing involves male siblings trying to establish whether they share the same father they can do a Y chromosome test. The Y chromosome is only found in males and in fact this chromosome encodes all the genes the mark maleness and male characteristics. The Y chromosome contains far fewer genes than the X. To be noted, that males even have an X chromosome which they inherit from their mother. The Y test is an extremely accurate test providing a Yes or No answer.
    • If the siblings are two sisters who wish to establish whether they share the same father they will need an X chromosome test (if they share the same mother, they will need to include the mother’s DNA sample). The X test is also very accurate- this test, just like the Y test, provides a very accurate result. The result should be a perfect match if the two females share the same father. If the siblings are of different sexing they will need a full siblings test

    The sibling test result will tell you the likelihood that you are full siblings in terms of a percentage (referred to a probability of relationship)- the higher the percentage, the stronger the likelihood of a biological sibling relationship. However, different DNA testing companies may take different percentages as their benchmark and may even take a 50% probability of relationship as being enough to say there is a sibling relationship. For other DNA testing companies this is far too low.

    Genetic mutations and DNA Sibling Tests

    A mutation results in different regions of the DNA profile being mismatched. Genetic mutations on the Y chromosome are extremely and this chromosome rarely undergoes mutations. The X chromosome also rarely presents genetic mutations. When mutations do arise, these mismatches present difficulties when establishing what might actually be a paternity/ true biological relatedness. If there are 2 mismatches between the DNA profiles of the 2 people taking part in the test, this will not be enough to exclude paternity but the results will nevertheless be inconclusive. 3 or more mismatches in definitely an exclusion.

    Sibling DNA tests can definitely guide you and help you find the answers to the lingering questions you may have about the relationship with your siblings. However, you need to bear in mind that you will not, as stated, get a clear yes or no answer, but simply an indication of the degree of genetic relatedness between you.