The choice of DNA extraction method is determined by several factors; DNA yield and quality, convenience, cost and individual preferences. Although PCR can yield results from very poor specimens, e.g. forensic material, the use of poor quality specimens will compromise accurate and sensitive diagnosis. The exception to this is the use of paraffin embedded tissues for the extraction of nucleic acids. This valuable diagnostic resource can yield DNA suitable for analysis; however, the quality of the isolated DNA is dependent on the treatment of the tissue prior to and during fixation. The DNA will be of lower molecular weight, however due to the smaller amplicons suited to real-time PCR, good results can be obtained. Many commercially available kits produce high-quality DNA preparations that are good templates for real-time PCR, however one drawback is the low concentration of the DNA produced. Whilst these amplify very efficiently; there may be too few DNA molecules to ensure maximal sensitivity.
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