About DNA Testing
A DNA test can be used to determine whether two or more individuals are biologically related. There are a variety of relationships that can be tested; the most common are described below.
Paternity and Maternity
Paternity and maternity tests compare a child to an alleged parent, either the father or the mother. In the majority of cases, one parent is sufficient for testing but we request that both parents participate if possible. In rare cases, a mutation may occur during the formation of the sperm or the egg that can lead to the false exclusion of a true parent; a mutation will sometimes bring the calculated likelihood of parentage below a conclusive reporting threshold but having both parents available for testing increases the probability that a conclusion can be generated based on the DNA profiles.
Grand-parentage testing is performed when an alleged parent is unavailable for testing but the alleged parent’s family still wishes to establish a biological relationship. Testing can be performed using one or both parents of the alleged parent who is not available for testing (grandparents of the child in question). If only one grandparent is available, it is strongly suggested that the known parent of the child be tested also. Due to the genetic separation in this type of relationship, grand-parentage testing with only one grandparent and no known parent can sometimes lead to inconclusive results.
Sibling tests can determine if potential siblings share one or both parents. Either a half-sibling relationship, wherein the participants would share a single parent, or a full-sibling relationship, wherein the participants would share both parents, can be tested. To determine a more conclusive probability of relatedness between two potential siblings, it is recommended at least one known parent should be tested as well.
Avuncular tests are conducted between a child and a known sibling of the alleged parent (the alleged aunt or uncle of the child). It is strongly recommended that the child’s known parent also be included in the testing to provide a more conclusive probability of relatedness between the child and the aunt/uncle.
DNA typing is the most powerful genetic testing method available. A variety of sample types can be used as a source of DNA. The most typical sample used is a mouth (buccal) swab that is quickly and painlessly collected using cotton-tip swabs much like Q-tips. We can arrange for buccal swab collection in locations across the U.S. and the world.
We are also able to use virtually any sample of biological origin as a source of DNA that is suitable for testing. Buccal swabs, blood and blood spotted on filter paper are common types of samples but we can also extract DNA from bone, teeth, tissue, paraffin embedded tissue, amniotic fluid/CVS, cord blood, semen and other biological samples or stains. Please contact the laboratory at 1-800-299-7919 to discuss your options when dealing with samples other than buccal swabs or blood.
The Science of DNA Testing - Questioned Family Relationships
The laws of genetic inheritance proposed by Mendel used in DNA testing can often establish or refute questioned family relationships such as parentage (paternity/maternity), sibling, grandparent, and aunt/uncle. The vast majority of questioned family relationships involve cases of parentage. In these cases, our lab will, in most instances, be able to produce a compelling result resolving the question either by excluding the alleged parent, or including the alleged parent with >99% probability. The same high probability is generally possible when testing questioned grandparents. However, as the questioned relationship moves farther from the first-degree parent to child, the likelihood of obtaining a compelling result decreases. Thus, sibling testing is less likely to produce a compelling result than is parent to child or grandparent to child, and half-sibling testing is less likely to produce a compelling result than full sibling testing and so on.
In relationship cases, either the relationship will be excluded, or, a likelihood ratio (LR) will be produced. The LR is a numerical statement that reflects the weight of the evidence either for or against the claimed relationship. This ratio, also known as the relationship index (RI), refers to the genetic odds in favor of the relationship. The size of this number is a reflection of how many genetic markers within the DNA are shared between the individuals involved in the test, and how those shared markers are expected to be distributed within a family group or pedigree. In general, the more elements of the DNA profile that are shared, a larger likelihood ratio will result. The likelihood ratio can also be expressed as a percentage probability. A larger likelihood ratio will produce a larger percentage probability that the relationship in question is a true relationship.