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Two different DNA tests exist, the
RFLP and the PCR. Both are very accurate, but they’re
conducted in different ways.
The restriction fragment length polymorphism
or RFLP (sometimes called DNA fingerprinting or
profiling) is considered to be the more accurate
of the two. This test examined sequences of base
pairs in a section of a DNA strand with a high probability
of being entirely unique to the donor. When a match
is found, there is no question that the donor was
at the scene of the crime. It’s very conclusive
and finalizing. Unfortunately, the RFLP requires
many sample cells from the crime scene like several
strands of hair or large splatters of blood. The
cells have to be “fresh”, too--that is, undamaged
and recently dead. The test takes anywhere from
3 weeks to three months to complete, also.
Although the PCR test, or polymerase
chain reaction test, isn’t quite as accurate, it
takes much less time to complete--a week at most.
The test can be performed with minute crime scene
samples, to, which helps investigators who have
little physical evidence. The DNA doesn’t have to
be recently collected, either; the PCR test can
still be performed even years after--decades after--the
fact, and still be just as accurate. This is because
the PCT method involves copying the available DNA
and analyzing only one specific gene, oftentimes
the gene called HLA DQ alpha. Geneticists look for
certain types of the gene (alleles) to determine
matches. If no match is found, the donor was not
at the crime scene. Matches are not conclusive,
though, because many people may have--and are more
than likely to have--the same alleles as the donor.
Still, juries have convicted suspects based on PCR
test results.
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