Gene Ontology organizes gene function into hierarchical categories based on biological process, molecular function and cellular component. Fisher's exact test was applied for over representation of selected genes in GO biological categories. In order to assess the significance of a particular category by random chance, false discovery rate (FDR) was estimated for all of categories. After 5,000 re-samplings, FDR was defined as FDR=1-Nk/T, where Nk refers to the subtracted number which was from Fisher's test in random samples. We specified the threshold of significant GO as p-value<0.05, FDR<0.05 and enrichment parameters. Enrichment represents the degree of gene expression significance. The equation of enrichment is as following: Re=(nf/n)/(Nf/N) (14) , where nf is the number of significant genes within the particular category, n is the total number of genes within the same category, Nf is the number of significant genes in the entire microarray, N is the number of all genes tested.