1800s: Paternity by Eye Color
During the 1800s, paternity was doubted when a child had physical features that were significantly different from their parents. It was understood the children got some traits from their mother and the rest from their father. Gregor Mendel first proposed this theory in 1865. However, several genes contribute to eye color, and it is difficult to determine the eye color of an organism from the eye color of its parents.
1920s: Blood Typing
Human blood types were discovered in the early 1900s. Scientist discovered the blood type was genetically inherited, and they used this information to determine blood types in children. However, there are up to four different outcomes for a blood type pairing, and so specific parentage can only be determined by elimination: if the child has a blood type that can't be produced by the mother and a suspected father, that man is not the father.
1930s: Serological Testing
Scientists discovered other blood proteins that could identify humans. They used the Rh, Kell, and Duffy blood group systems. These system, like the ABO system, use the presence of antigens in the blood. These antigens are also genetically inherited, so scientists can predict the blood group of a child based on the blood groups of its parents. They tried to determine paternity based on the blood groups of the mother and the child, but serological tests are only up to 40 percent conclusive.
1970s: HLA Testing
Scientists discovered the human leukocyte antigen (HLA) in the mid 70s. This protein is prevalent in all body cells, except red blood cells. HLA types are genetically inherited. Each person has two types of HLA in their cells, and if the child does not have one type from th mother and the other from the suspected father, then that man is not the father of the child. This technology had a power of exclusion of up to 80%, and when combined with serotyping and blood typing, the power of exclusion was close to 90%. However, HLA testing requires a lot of freshly drawn blood, making it dangerous for young children.
1980s: RFLP DNA Testing
RFLP (restriction fragment length polymorphism) was discovered in the mid-80s. Scientists discovered that while you inherit your DNA from your parents, there are highly differentiated sections in each individual that can be used for identification. RFLP testing takes DNA from blood samples and makes profiles for each person sampled. Scientists can then compare these profiles to see if their a match between the parents and the child. DNA markers used in RFLP are highly diferential, so this procedure has a power of exclusion of 100%.
1990s-Present: PCR Testing
PCR (polymerase chain reaction) techniques became the standard for paternity testing in the 1990s. This technology lets scientists amplify a small amount of DNA into billions of copies. This produces enough DNA to test when only a small sample is given. The machine used for PCR allows this procedure to happen quickly. Samples are collected non-invasively and painlessly, so this technology is safe for the youngest of children. Genetic scientists can even test amniotic fluid from an embryo to determine paternity before the child is born. Like the RFLP technique, this procedure is very accurate, with a power of exclusion of 100%.
(paternity-answers.com)
