Paternity Test

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).

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).