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Paternity testing- From Blood Groups to PCR

Paternity testing has undergone many changes over the decades. We can trace its course beginning with the most simple technique in which blood groups of father and child where compared and move on to the present day method which involves using DNA.

Paternity testing with Blood Groups

The blood grouping system was used for a while to determine paternity. This was one of the earliest methods used but has today been phased out completely. Blood groups cannot be used to pin point a father as the biological father of a child. A child cannot have a blood group antigen that one or both of his parents does not have. But a father and child sharing the same blood group does in no way indicate that that man is the real father of the child- millions of men would in fact, have the same blood group and could all be potentially the child’s real dad. The blood group system to determine paternity is thus, only useful to exclude individuals as being the biological dads.

Moreover, with the ABO blood group system, there are only 4 different blood groups and groups A and O are very common. The implications of this are clear: even if the father’s blood group matches that of the child, it does not conclusively mean he is the biological father unless the mother is certain there is no other possibility.

DNA Paternity testing in the 1970s and 1980s

The 1970s brought on HLA typing, which does not require DNA. This test eliminated 80% of the male population but cannot distinguish between related alleged fathers. HLA (Human Leukocyte Antigen) is a protein found in white blood cells and any individual has quite a unique set of HLA proteins inherited from their parents. This testing had drawbacks: very large amounts of blood were needed meaning that babies had to be over 6 months old to be tested.
Using DNA to establish paternity was logically only possible after the discovery of the structure of DNA in the 1950s. It was not however, until the 1980s that DNA was used to establish paternity.

In the 1980s DNA testing became available with the possibility of including a father as the biological dad with an accuracy of 80% or sometimes even 90%. The procedure is known as RFLP (restriction fragment Length polymorphism). The testing required blood samples but an issue was that considerably large DNA samples were needed for scientists to work with. The processing time was also lengthy and thus, the method has gradually become disused as a better method was invented.

DNA Paternity Testing in the 1990s

PCR (Polymerase Chain Reaction) is the method that is used nowadays for paternity DNA testing. Scientists can work with very small quantities of DNA because with PCR they are able to replicate and make thousands of copies of the DNA and thus, have lots to work with. The DNA sequencing process with this method takes only around 2 hours. The process involves a reaction in which DNA is heated to 94 Celsius. An enzyme is then used (DNA polymerase) to assist in the replication and amplification of the DNA. The enzyme reads the code and then uses it as template. This is essentially the process very simply put.

Paternity testing has become extremely accurate and can precisely determine whether an alleged man is the biological father of a child or not.



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