DNA

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every other persons, except for identical twins. DNA is contained in blood, semen, skin cells, tissue, organs, muscle, brain cells, bone, teeth, hair, saliva, mucus, perspiration, fingernails, urine, feces, etc. DNA collected from a crime scene can either link a suspect to the evidence or eliminate a suspect. It can also identify a victim through DNA from relatives, even when no body can be found. And when evidence from one crime scene is compared with evidence from another, those crime scenes can be linked to the same perpetrator. ("Popular Science" 417 )






Fig. 1 The chemical structure of DNA (“DNA 101”)
The Mechanics of Genetic Testing
DNA evidence can be collected from anywhere. DNA has helped solve many cases when investigators collected evidence from nontraditional sources. Numerous cases have been solved by DNA analysis of saliva on cigarette butts, postage stamps, and the area around the mouth opening on ski masks. Here are the steps that are required to identify a person from the DNA sample:
First, the DNA must be extracted from the tissues or cells of the sample.
Next, restriction enzymes are used to cut the DNA sequences at specific sites,
which provide a large number of DNA fragments.
The DNA fragments are then sorted according to size in a technique called gel
electrophoresis. The DNA pieces are poured into a positively charged gel made
from seaweed, which is called agarose. The slightly negative DNA strands are
attracted to the bottom of the gel a...