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fragments undergo electrophoresis using a gel that allows the separation of the fragmented DNA.
Because the gel is fragile, a thin nylon membrane, covered by a towel is laid over the gel. As mois-
ture is drawn to the towel from the electrophoresis gel, the DNA fragments are transferred to the
nylon membrane. This process is called blotting. The DNA bands are visible to the eye but they are
too numerous to be useful. Thus, a radioactive solution is washed over the nylon membrane that
binds to select fragments, generally to only 6–20 of the DNA clusters. A sheet of photographic fi lm
is placed on top of the nylon membrane that records these cluster sites. The film is then developed

producing a pattern of thick-and-thin bands. This pattern is the genetic pattern for that particular
sample. This process can take a month or more at commercial labs for routine analysis, but when
needed, the analysis can be made in only a day or two.
There are different restriction enzymes that cut DNA at different sites. The previous sequence
can be repeated several times for the same DNA sample. From a study of each restriction enzyme,
a probability that another person will have the same profile is assigned. Thus, one restriction

enzyme may have the possibility that another person has the same match of 1 in 100 or 1%. A sec-
ond restriction enzyme may have the probability of 1 in 1,000 or 0.1%. A third restriction enzyme
may have a probability for a match being 1 in 500 or 0.2%. If there is a match with all three restric-
tion enzymes, the probability would be 0.01 × 0.001 × 0.002 or 0.00000002 or 0.000002% or
1 part in 50,000,000. There is a caution to using the “multiplication rule,” in that DNA sequences
are not totally random. In fact, DNA sequence agreements generally diverge as one’s ancestors are
less closely related.
The RFLP method requires a sample about 100 times larger than that required for the PCR
approach, but with repeated sequences using different restriction enzymes, RFLP is more precise.
It must be noted that factors leading to DNA degradation, such as moisture, chemicals, bacteria,

heat, and sunlight will impact negatively on DNA profiling since the precise sequences and length
of the DNA and DNA fragments may be changed. While DNA, in general, is robust and can exist
“alive” more than thousands of years (such as the germination of seeds found in the pyramids of
Egypt), DNA degradation decreases the probability of precise matches. Also, DNA contamination
by addition of DNA from another source greatly confuses the fi nal results.
DNA sequencing has found importance in a wide range of areas. It is being used to identify indi-
viduals at greater risk for having certain diseases such as breast cancer. It is used for the screening
of certain diseases such as the presence of the sickle-cell gene.
The initial VNTRs were several hundred nucleotide units long requiring long lab periods for
the various segments to separate on the gel. Today, most tests employ shorter, 3–5 nucleotides long,
VNTRs that allow for more rapid movement on the gel resulting in faster and less costly results.
It also allows for the production of a greater number of sequences that are looked at and hence, a
greater ability to match/not match the results. These shorter sequences are called short tandem
repeats (STRs).
While DNA is more robust than often depicted in movies, age and extreme conditions such as a
fire can substantially degrade it. In such cases mitochondrial DNA (mtDNA) is best used. Unlike

nuclear DNA, mitochondrial genome exists in thousands of copies and is less apt to degrade and it
is inherited only from the mother. Here, STRs are not analyzed, but rather the focus is on variable
regions of the mitochondrial genome. Such analyses take much longer but are used for situations
where time is not essential.
This type of DNA profiling has allowed taxonomists to determine evolutionary relationships

among plants, animals, and other life forms. Currently it is a basis for the so-called Eve theory that
says all of us are related to a common women, called Eve after the Biblical Eve. It is also being used
to trace the (ancient) movement of people about Earth.

DNA profiling was used to determine whether bones unearthed that were said to be from Jesse
James were in fact his. DNA samples were taken from grandchildren and compared to those obtained
from the bone material and shown to be similar, so that while it cannot be absolutely said the bones
were or were not from Jesse James, DNA evidence was consistent with them being his bones. DNA

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