Test for Normality of the Gene Expression Data

One of the main issues in statistical analysis of gene expression data is testing levels of differentially expressed genes. There are different approaches to address this issue. If in one case, given two probe sets of gene expression levels, we test whether they are differentially expressed or not, in other cases we just check whether the given sample is drawn from the prescribed distribution or not. Assuming that the prescribed distribution is normal we would like to test normality of gene expression data.