DNA Defined and Delineated

DNA is the carrier of genetic information. It is composed of two linear polymers held together by hydrogen bonds and arranged in a helical conformation, similar to a stepladder. These polymers or strands consist of repeat units of nucleotides which are composed of a sugar, deoxyribose, a phosphate group, and a purine or pyrimidine base. There are four main nucleotides, each defined by the base attached to the sugar moiety. The four nucleotides are: adenine, thymine, cytosine, and guanine. They represent the DNA alphabet.1

Klosinski and Mattson report that the investigation of DNA has spread of late, with a variety of applications available. Among these applications is fingerprinting microorganisms, which uses restriction enzyme analysis with agarose gel electrophoresis, pulsed-field electrophoresis and DNA-DNA hybridization.2 Edwards, Hunter, and Hankin concur that the use of restriction enzyme analysis proves superior to the organic extration of DNA.3 There are, however, several qualifications to the successful use of this technique. These qualifications include: the need to tilt the gel in the depurination solution; the choice of membrane; the need to use a hybridization solution; the need to modify stringency washes; and the use of sal

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n sample. Storage in a paper envelope appears best, so that the specimen is air dry and can be frozen. The specimen sample is to be as large as possible, with, for example, blood stains being at least 0.25 of an inch in diameter. For semen, one swab is needed at minimum via collection with the standard rape kit. While one hair follicle can prove sufficient for DNA testing, several are preferred due to the continuing experimentation with this type of specimen. Regarding blood that is, for example, on a wall, apply cotton swab that has been moistened with distilled water. Processing laboratories, however, would prefer to receive the original piece of material on which the specimen is located. Accuracy of DNA Fingerprinting The U. S. Department of Justice reports that, given the use of multiple probes (i.e., at least four), the laboratory technician can identify an individual to the degree of one out of a million.12 Koehler, however, reports different identification statistics for DNA testing.13 Koehler indicates that expert laboratory technicians who have been thoroughly trained in DNA testing can not positively identify a defendant or suspect to the degree of one out of a million. The expert can, with varied degrees o
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Approximate Word count = 2837
Approximate Pages = 11 (250 words per page)

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