A Multiple probes are used to quantify the expression value for a gene in GeneChip® technology. Currently the probe design has a 3' bias, i.e. probes are selected from the sequence at the 3'end of the gene. In the Hu6800 array, twenty probes are used for a single gene. 1 B Intensities of the twenty probes are plotted for both tissues 1 and 2. 1 C The twenty probes are clustered into three groups based on the similarity of probe intensity and probe adjacency. Each cluster, called a pseudo-exon in this paper, represents a sub-region of the gene.