High-density microarrays were developed using spotted cDNA. At present, cDNA microarrays are still a major source for the production of valuable data, and they have the advantage that sequence analysis of the clones is not essential. If one would like to perform an array on some exotic creature, a cDNA library can be printed and significant clones can be sequenced afterward. However, cDNA microarrays have a number of disadvantages that prevent the development of high-density microarrays to perfection. First and most important, cDNA clones used for microarrays are not all verified by sequence analysis, resulting in up to 25% of clones not representing what they should. Such uncertainties are unacceptable for diagnostic microarrays. Second, cDNA clones have different lengths and basepair compositions resulting in different melting temperatures. Therefore it is impossible to achieve optimal hybridization conditions for all clones during a single hybridization experiment. Third, because most cDNA clones will have products of several hundreds of basepairs long, there is a major risk of cross-hybridization.
The best answer to these problems has proven to be the use of oligonucleotides to replace cDNA clones.[6,9,10] Oligonucleotides 50-70 nucleotides long have the advantage of being synthetically synthesized, thus they can be designed and customized for optimal performance (Com-pugen; www.cgen.com). They do not need to be sequence-verified and can be designed to minimize cross-hybridization and at similar melting temperatures. Furthermore, they can be designed to avoid known single nucleotide polymorphisms. Nowadays, most, if not all, of the commercial companies that offer high-density microarrays have platforms based on oligonucleotide technology.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.