Siblings are referred to as being half or full siblings. Siblings can be brothers or sisters. Siblings that have one of their biological parents in common are in common are half siblings. From a genetic perspective, half siblings have about 25% of their genetic material in common. Half siblings can be of two types:
- Uterine siblings: these are half siblings that have a biological mother in common
- Agnate siblings: these are half siblings that share the same biological father
Full siblings have both biological parents in common. This means that full siblings share much more of their DNA than half siblings; around 50%. On very rare occasions, due to random chance in chromosome distribution, full siblings may share almost none of the genetic makeup and sometimes share well-over the expected 50%. Sibling DNA testing can help confirm whether siblings share a common biological parent. It is usually the father who the siblings question but in some instances it may be the mother. It is not always easy to know what the outcome of a sibling ship test result can be . We can generally reply on the assumption that full siblings will have much more DNA in common the half siblings but the amount of common DNA between siblings does vary. Sometimes half siblings may share more common DNA than full siblings. Ultimately, whenever parentage is in question, we suggest a DNA test that directly involves the sample of the parent in question (a paternity test or a maternity test).
Relationship DNA testing, particularly a sibling DNA test, is a good way of testing for sibling relationships. Any of the following tests might be useful: X chromosome test, Y chromosome test or an STR test.