Cousin DNA Test
A cousin DNA test seeks to establish whether first degree cousins are biologically related. International Biosciences receives many requests for cousin testing but does not currently offer it. The reason for this is that a cousins DNA testing will invariably provide a very inconclusive result.
Why is cousin DNA testing inaccurate?
Cousin’s DNA testing is inaccurate due to the inheritance pattern of genes in a family. For example, we know that children share around 50% of their genes with their biological mother or father. Aunts and uncles will share around 25% of their genes with their nieces or nephews. When it comes to first cousins, these share only about 12.5% of their genes. This means that 87.5 % of the genetic makeup between first cousins is different. Already tests such as aunt/uncle testing, where test participants share 25% of their genetic makeup, can be challenging for laboratories because of the relatively low percentage of common DNA between aunts and uncles and their nieces or nephews. With just 12.5% of common DNA between first cousins, a test result showing common DNA between the two is likely just due to chance. Genetically speaking, we actually share a lot of DNA with any random individual and if cousins have any common DNA, it would be impossible to determine whether this is due to random chance or to inheritance.
Although some companies do offer cousin DNA testing, these companies cannot offer a conclusive results as current DNA testing technologies have not made this possible. We do not recommend carrying out a cousins test with any company.
What are the testing options between cousins?
There are many better tests available to determine the relationship between alleged relatives. The following tests will offer more accurate results:
Paternity and Maternity Testing: Often cousins seek a cousin DNA test because they wish to establish whether their parent (their mother or father) is actually their biological parent. The idea behind this is that any common genes shared between the cousins are due to these being inherited from their common blood relative (the biological parent of one cousin would be the biological aunt or uncle of the other). If individuals really want to know whether their mother or father is actually their biological parent, before considering testing any other relatives, they should consider a Paternity Test or a Maternity Test.
DNA Testing between Male Cousins: If cousins are male and want to see if they are related through their paternal line, they can carry out a Y Chromosome Test. This test is highly accurate and if the tested males share the same Y chromosome profile, then they also share a paternal blood line.
Aunt Uncle testing:Testing uncles or aunts with their nieces of nephews can determine whether there is a shared biological relationship between the tested parties. An avuncular test result will show what is called an avuncular index. An index which is higher than 1.00 suggests the individuals tested are related whilst an index that is lower than 1.00 suggests non-relatedness. An index that is exactly 1.00 would be an inconclusive result. Click here for more information about aunt/uncle DNA testing.
Cousins and their maternal lineage
Cousins who wish to know whether they share a common maternal relative can carry out what is called an X SV test. This test analyses the maternally inherited mtDNA and if the tested parties have the same mtDNA profile they also share a common maternal relative.
mtDNA or mitochondrial DNA is passed on from a mother to her male and female children. All females, in turn, pass on their mtDNA to their children. However, males do not pass their mtDNA and this is a very important point. The birth of a male interrupts the mitochondrial DNA line. In other words, the people tested must have an unbroken, traceable maternal line in order to be able to carry out an mtDNA test.