| DNA
profiling is a biological tool which allows
the scientist to compare samples of DNA
material. With the exception of identical
siblings, the DNA of each person is unique.
That is why it is so valuable as a form
of identification. DNA analysis can reveal
the genetic profile of an individual and
compare this with samples from a relative
to determine whether or not he/she may be
the source of the biological material.
DNA
profiling is commonly in use for paternity
testing, usually to determine fatherhood
of a child when this is disputed. It may
also be used in helping to identify whether
objects have been handled by, or belonged
to, a missing person.
What
IS DNA?
The
initials DNA stand for "DeoxyriboNucleicAcid'',
found in the cells of all living things,
including the human body. The DNA is a threadlike
molecule and is found in the nucleus of
cells.( see "What is DNA?" )
Although
each person's DNA is unique (unless he/she
has an identical twin), the techniques for
identification only look at small parts
of the DNA. ( see "Why don't I look
like my brother?" )
It
is important to realize that a person will
have the same DNA throughout their body
in every cell with a nucleus. That is, the
same DNA profiling results for one person
will be obtained whether testing blood or
semen or muscle tissue.
How
is DNA typing done?
Only
one-tenth of a single percent of DNA (about
3 million bases) differs from one person
to the next. Scientists can use these variable
regions to generate a DNA profile of an
individual, using samples from blood, bone,
hair, and other body tissues and products.
In
paternity cases, this generally involves
obtaining samples from the individuals in
question, extracting the DNA, and analyzing
it for the presence of a set of specific
DNA regions (markers).
Scientists
find the markers in a DNA sample by designing
small pieces of DNA (probes) that will each
seek out and bind to a complementary DNA
sequence in the sample. A series of probes
bound to a DNA sample creates a distinctive
pattern for an individual. Forensic scientists
compare these DNA profiles to determine
whether the suspect's sample matches the
evidence sample. A marker by itself usually
is not unique to an individual; if, however,
two DNA samples are alike at four or five
regions, odds are great that the samples
are from the same person.
If
the sample profiles don't match, the person
did not contribute the DNA.
The
more probes used in DNA analysis, the greater
the odds for a unique pattern and against
a coincidental match, but each additional
probe adds greatly to the time and expense
of testing. |