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05%20Normalization%20cDNA%201_24_07 - Normalization...

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1 1 Normalization Methods for Two-Color Microarray Data 1/24/2008 Peng Liu 2 Normalization Normalization describes the process of removing (or minimizing) non-biological variation in measured signal intensity levels so that biological differences in gene expression can be appropriately detected. Aim: Normalization does not necessarily have anything to do with the normal distribution that plays a prominent role in statistics. 3 Normalization The ideal procedure would reach some ‘universal’ measurement of mRNA copies per cell so that we can compare biological differences independent of genes, technology and experiments. However, this can not be done now. We just talk about normalization for a single experiment that include a set of slides. 4 Sources of non-biological variation Dye bias: differences in heat and light sensitivity, efficiency of dye incorporation Differences in the amount of labeled cDNA hybridized to each channel in a microarray experiment (here channel is used to refer to a particular slide/dye combination.) Variation across replicate slides Variation across hybridization conditions
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