A DNA siblings test is used to establish the type of relationship between siblings. We know that siblings may be either full siblings (in this case siblings have both father and mother in common), or they can be half siblings (in this case, have either just their mother or just their father in common). A sibling test can also determine whether siblings share not common parents; in this case, they are not siblings at all.
Siblings are of Two Types
As mentioned, siblings can either share the same father; in this case, they are known as agnate siblings. Agnate siblings will have different mothers.
Uterine siblings are siblings that share the same mother but have different fathers.
First cousins whose parents are identical twins will have their genetic makeup which is very close to that of siblings despite being first cousins rather than siblings.
How Much DNA do Siblings Share?
It is difficult to say with accuracy how much DNA is in common between two full siblings and thus predict the accuracy of a sibling DNA test. Normally, scientists would expect to see around 50% of common DNA. However, there can be cases where full siblings have hardly any DNA in common- in this case the result of the sibling test would be inconclusive despite the people tested being full siblings; also, in other instance, siblings can have so much common DNA that it may show as high as 95% or higher- in this case, the siblings test would clearly show the people tested are siblings.
When to do the Sibling test?
Sibling testing is a type of relationship test. Most often than not it is siblings themselves who wish to do the test. Very often, they do the DNA test to know if they share a common father. In most cases, the mother is known and rarely disputed; but paternity is another issue. It is often difficult for siblings to do a paternity DNA test with the DNA sample of their father; this because they would not want their father to know about the DNA test or in other instances the alleged father has passed away. The sex of the siblings involved is also an issue because different tests might actually be suited to siblings depending on whether they are male or female. Females wishing to know if they have the same father can do an X chromosome test; males wishing to know if they have the same father can do a Y chromosome test.
Sibling DNA testing is just one means of knowing paternity; the test is often conclusive but the randomness of genetics means that sometimes you might get that inconclusive result. Other tests might be available or options to help get a stronger result. For your sibling DNA test.