Polymerase chain reaction 5 -nuclease method

Another class of readout measures RNA expression levels, with the three most common methods being chip-based hybridization/fluorescence techniques, realtime polymerase chain reaction (RT-PCR) and quantitative nuclease protection assays (QNPA) [48, 49]. Chip-based methods are widely used for whole-genome scans (discussed in more detail below), but have a disadvantage that they are relatively expensive and so are not really high throughput. The quantitative reproducibility and dynamic range of these chip-based methods are also lower than for the other RNA readout techniques. RT-PCR is a more quantitative technique for measuring transcript levels, and is typically run for up to 40 transcripts at a time. QNPA is another... 

Related mRNAs encoding various proteins can be detected by different types of in situ hybridization. For this method, the number of specific mRNAs detectable per tumor sample is limited. However, the advantage of in situ hybridization is the same as in immunohistochemistry where the morphology of the tumor is still visible. Specific mRNA-species can be detected by northern blot, nuclease protection assay or reverse transcription (RT) combined with polymerase chain reaction (PCR). Using the modern real-time PCR protocols, reliable quantification of PCR targets is possible. A more complex approach is possible by using the micro-array technology, where hundreds or even more of mRNAs can be detected simultaneously in a semi-quantitative fashion. 

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