Blood Typing (1920)
Blood typing, which is based on the ABO blood group system, was the first method used for paternity testing and took place in the 1920s. This method was hardly accurate, being that it only eliminated 30% of the male population as being the biological father.

Each person’s blood type is determined from the proteins, called ABO antigens, found on the surface of the red blood cells. Because these ABO antigens are inherited from our mother and father, it is possible to predict a child’s blood type if the parents’ blood types are known. However, some circumstances can produce more than one possibility of a child’s blood type. Therefore, blood typing is a very inaccurate way to determine paternity.

Serological Testing (1930)
Serological testing, which is based on the Rh, Kell, and Duffy blood group systems, was the next method of testing used for paternity and took place in the 1930s. This method provided a bit more accuracy for paternity testing, eliminating 40% of the male population as the biological father, but still provided many inconclusive results.

Other proteins on the red blood cells cause reactions in blood transfusions and organ transplants between those with incompatible proteins. A person inherits these proteins more complicated than other proteins, so it was used to provide a slightly higher power of exclusion.

HLA Typing (1970)
Finally in the 1970s, a paternity testing method was discovered that was able to provide a probability of paternity of 80%, sometimes 90%. This method is known as HLA typing, based on proteins called Human Leukocyte Antigens. These cells are found in most cells in the body, except red blood cells. Mainly found in white blood cells, these antigens help the immune system detect foreign cells.

Each person inherits a small, unique set of HLA antigens from the biological parents. Determining paternity with these antigens depends on how rare the alleged father’s HLA type is in the population. The more rare the HLA type, the more conclusive the paternity test results would be. Also, if close relatives are tested as alleged fathers and have the same HLA type, this testing method could not determine paternity.

DNA Testing through RFLP (1980)
DNA testing became available in the 1980s through RFLP (Restriction Fragment Length Polymorphism). Because each individual has a unique DNA profile, this method provided a 99.99% or higher paternity result.

In RFLP, the DNA is purified from blood samples in a string-like molecule and placed into a mix of restriction enzymes, which cut the DNA into fragments. The size of these fragments was based on the type of DNA given from the biological parents. The sizes of the child’s fragments are compared to the mother and tested man, half of which should come from each biological parent.

This method is conclusive, however it requires a larger amount of sample and a longer time for processing.

DNA Testing through PCR (1990)
In the 1990s the Polymerase Chain Reaction (PCR) method became the standard form of DNA testing for determining paternity. An extensive amount of PCR testing has allowed a database to be created for DNA analysis that ensures PCR is the most accurate paternity testing process.

In PCR, the DNA must first be isolated from the specimen, which requires the removal of any proteins and other cell components. Once isolated, the DNA is placed into a thermocycler with 16 florescent primers which allow the Identifiler system to locate specific fragments of the DNA. Within each cycle of the thermocycler, the primer finds the specific fragments and amplifies those areas. After amplification, the DNA is placed in an ABI Prism Genetic Analyzer, which performs capillary electrophoresis. At this point, the DNA loci, or fragments, are mapped and a genetic profile is created. The individual profiles are then analyzed and compared and a paternity probability is calculated.