Paternity testing

A paternity test is conducted to prove paternity, that is, whether a man is the biological father of another individual. This may be relevant in view of rights and duties of the father. Similarly, a maternity test can be carried out. This is less common, because at least during childbirth and pregnancy, except in the case of a pregnancy involving embryo transfer or egg donation, it is obvious who the mother is. However, it is used in a number of events such as legal battles where a person's maternity is challenged, where the mother is uncertain because she has not seen her child for an extended period of time, or where deceased persons need to be identified.

Although not constituting completely reliable evidence, several congenital traits such as attached earlobes, the widow's peak, or the cleft chin, may serve as tentative indicators of (non-)parenthood as they are readily observable and inherited via autosomal-dominant genes.

A more reliable way to ascertain parenthood is via DNA analysis (known as genetic fingerprinting of individuals), although older methods have included ABO blood group typing, analysis of various other proteins and enzymes, or using HLA antigens. The current techniques for paternity testing are using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). For the most part however, DNA has all but taken over all the other forms of testing. Genetic testing usually has a 99.999% accuracy rate, or 99,999 out of 100,000.

DNA testing
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).

Prenatal paternity testing
Scientific tests can now determine paternity at 12 weeks into a pregnancy using non-invasive testing methods in many cases. This involves a simple blood sample taken from the pregnant woman's arm. The pregnant female's blood carries the fetus' DNA which can be compared to the DNA of the alleged father. Professor Dennis Lo Yuk-ming is the Dr. Li Ka Shing Professor of Medicine and Professor of Chemical Pathology at The Chinese University of Hong Kong. He is one of the world's foremost researchers on this technology.

Legal issues
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 Department for Constitutional Affairs accredits bodies which can conduct this testing. The Department of Health is also in the process of updating its voluntary code of practice on genetic paternity testing.

Disproving paternity by use of blood types
A comparison of the blood type of both alleged parents and the child can disprove paternity in some cases. Only certain blood type combinations are possible and a mismatch may prove that the alleged biological father is, in fact, not the father of the child. See the Parent/Child Blood Type Comparison Chart on the website of the Canadian Children's Rights Council.