Parental testing is the use of genetic fingerprinting to determine whether two individuals have a biological parent-child relationship. A paternity test establishes genetic proof whether a man is the biological father of an individual, and a maternity test establishes whether a woman is the biological mother of an individual. Though genetic testing is the most reliable standard, older methods also exist including ABO blood group typing, analysis of various other proteins and enzymes, or using human leukocyte antigen antigens. The current techniques for paternal testing are using polymerase chain reaction (PCR) and restriction fragment length polymorphism.
DNA testing is currently the most advanced and accurate technology to determine parentage. In a DNA parentage test, the probability of parentage is 0% when the alleged parent is not biologically related to the child and the probability of paternity typically greater than 99.9% when the alleged parent is biologically related to the child.
The DNA of an individual is almost exactly the same in each and every somatic (non reproductive) cell. Sexual reproduction brings the DNA of both parents together randomly to create a unique combination of genetic material in a new cell, so the genetic material of an individual is derived from the genetic material of both their parents in roughly equal amounts. This genetic material is known as the nuclear genome of the individual, because it is found in the nucleus.
Comparing the DNA sequence of an individual to that of another individual can show if one of them was derived from the other or not. Specific sequences are usually looked at to see if they were copied verbatim from one of the individual's genome to the other. If that was the case, then this proves that the genetic material of one individual could have been derived from that of the other (i.e.: one is the parent of the other). Besides the nuclear DNA in the nucleus, the mitochondria in the cells also have their own genetic material termed the mitochondrial genome. Mitochondrial DNA comes only from the mother, without any shuffling.
Proving a relationship based on comparison of the mitochondrial genome is much easier than that based on the nuclear genome. However, testing the mitochondrial genome can only prove if two individuals are related by common descent through maternal lines only from a common ancestor and is thus of limited value (for instance, it could not be used to test for paternity).
In testing the paternity of a male child, comparison of the Y chromosome can be used since it is passed directly from father to son.
In the US, AABB regulates DNA paternity and family relationship testing industry. Only the DNA test results produced by an AABB-accredited laboratory  are legally admissible and accepted by government child support agencies, welfare benefits offices and immigration authorities such as USCIS and U. S. embassies overseas in a family-based immigration petition.
The DNA parentage test that follows strict chain of custody can generate legally admissible results that are used for child support, inheritance, social welfare benefits, immigration, or adoption purposes. To satisfy the chain-of-custody legal requirements, all tested parties have to be properly identified and their specimens collected by a third party professional who is not related to any of the tested parties and has no interest in the outcome of the test.
In recent years, immigration authorities in various countries such as U.S., U.K., Canada, Australia, France and others have been requesting immigration petitioners and beneficiaries in a family-based immigration case to voluntarily take the DNA parentage test when primary documents such as birth certificate to prove biological relationship are missing or inadequate.
In the U.S., immigration applicants bear the responsibility of arranging and paying for DNA testing. The U.S. immigration authorities require that the DNA test, if pursued, be performed by one of the laboratories accredited by the AABB (formerly American Association of Blood Banks).
Although paternity tests are more common than maternity tests, there may be circumstances in which the biological mother of the child is unclear. Examples include cases of an adopted child attempting to reunify with his or her biological mother, potential hospital mix-ups, and in vitro fertilization where the laboratory may have implanted an unrelated embryo inside the mother.
Other factors such as new laws regarding reproductive technologies using donated eggs and sperm and surrogate mothers can mean that the female giving birth is not necessarily the legal mother of the child. For example, in Canada, the federal Human Assisted Reproduction Act provides for the use of hired surrogate mothers. The legal mother of the child may, in fact, be the egg donor. Similar laws are in place in the United Kingdom and Australia.
In the UK, there were no restrictions on paternity tests until the Human Tissue Act came into force in September 2006. Section 45 states that it is an offence to possess without appropriate consent any human bodily material with the intent of analyzing its DNA. Legally declared fathers have access to paternity testing services under the new regulations, provided the putative parental DNA being tested is their own.
Tests are sometimes ordered by courts when proof of paternity is required. In the UK, the Ministry of Justice accredits bodies which can conduct this testing. The Department of Health produced a voluntary code of practice on genetic paternity testing in 2001, this document is currently under review and responsibility for it has been transferred to the Human Tissue Authority.
If parental testing is being submitted for legal purposes in the U.S. including immigration, testing must be ordered through a lab that has AABB accreditation for Relationship DNA testing. All accredited labs are listed on the AABB's website. In the state of New York, only legally admissible testing is allowed by law and requires either a physician prescription or court order, labs must also have NYSDOH accreditation.