PCR Technique
In 1983, Kary Mullis and members of the human genetics team at Cetus Corporation developed a genetic replication technique called polymerase
chain reaction (PCR). After several years of fine-tuning the process,
PCR
became the most popular DNA replication technique by the 1990s.
Kary Mullis was awarded the Nobel Prize in Chemistry for this work in 1993.
The popularity of PCR is based on both the sample size and the processing time it requires. DNA testing utilizing PCR can be performed
in a matter of hours with a very small DNA sample.
In PCR, scientists isolate a small amount of DNA (an amount easily obtained from a
buccal swab
). They then copy regions (or
loci
) on the DNA many
times to establish large quantities of DNA fragments from the copied regions. PCR can be used to copy any region of DNA.
For PCR use in paternity testing, scientists isolate a small amount of DNA and copy many specific DNA fragments (or loci) that help identify
and differentiate people. Fragments from one individual are compared to fragments from other individuals, as done in RFLP, and relationships are
determined based on the similarities and differences between the DNA fragments or genetic profiles.
DNA Comparison of Related Individuals
In the graphic above the child has one marker that matches the mother and one that matches the father. This means that the mother and father could be the child's biological
parents. To be biologically related to the child, the mother and father would have to match the child at several genetic loci. Most DNA testing companies will
compare 16 loci.
DNA Comparison of Unrelated Individuals
In the graphic above, the child has one marker that matches the mother. The child's second marker does not match either of the father's markers, meaning that the child and
the father may not be biologically related. Most testing laboratories require more than one non-match to exclude a relationship. The child in
this case could be biologically related to the mother.
(1900s) Blood Typing
(1930s) Serological Testing
(1970s) HLA Typing
(1980s and 1990s) RFLP Technique
(1990s) PCR Technique
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