A number of questions regarding sibling relationships can be can be solved by doing sibling DNA testing. Siblings may sometimes doubt the nature and extent of their sibling relationship. Are we full siblings? half siblings? Are we even related? Do we really share a common father? Is he really my brother or sister?

Sibling relationships

• Full siblings- these siblings have both their biological parents in common and share far more DNA than siblings with only one parent in common. Full siblings share around 50% of their DNA. Twins are still siblings- be they identical twins or fraternal twins. Identical twins will share 100% of their DNA but there never is question of the relationship between identical twins.

• Half siblings- half siblings can share either a mother, in this case, they may be referred to as uterine siblings or may share the same father and sometime referred to as agnate siblings in this case.
Sibling DNA testing is used in cases where siblings are not share about whether they actually share biological parents. Typically, it is the father that is in question and not the mother.

Important: relationship testing (a general term which encompasses many tests to determine familial relationship including sibling tests) is often carried out to establish whether people have biological parents in common without actually testing the person they question their relationship with. This means that sibling DNA testing is less accurate and will not always give a definite answer; a paternity test on the other hand boils down to: “yes this man is the biological father of these children” or “no this man is not the biological father of these children”.

Sibling DNA testing: what information do you need to give?

A sibling DNA test falls under relationship testing but itself consists of a number of tests.
• Y chromosome testing- when males are involved, for example brothers wishing to know if they share the same father.
• X chromosome testing- when females are involved; sisters wanting to know if they have a biological father in common
• Full sibling test- brother and sister need to know whether they have a parent in common

Sibling DNA testing is reliable and a great way of establishing the nature of the sibling relationship.


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