Figure 9.

Semantic zooming and other functionality implemented in the Integrated Genome Browser, version 5.3. The top view shows a region of human chromosome 21 with gene annotations and mRNA alignments. The display also shows plots of expression array data from Jurkat and HepG2 cell lines, represented as a score for each tiling array probe chromosomal position. The bottom view shows a "sliced" subset of the same data, in which exons for selected annotations (outlined in red) along with flanking sequence have been spliced to form a virtual sequence and all annotations remapped to the virtual sequence. There are roughly 50,000 data points per expression array plot in the region displayed in the top view, averaging 50 data points per pixel along the horizontal axis. The graph Glyph object used to render these plots appears in both views. The display uses semantic zooming to render them differently according to the different resolutions. In the lower resolution top view, for each horizontal pixel position a vertical line is drawn representing the score range for data points whose genomic coordinates fall within that pixel. A slightly brighter dot is also drawn for the scores' average. In the sliced view at the lower part of the display, the resolution is high enough that each scored position is rendered as a simple bar. These rendering techniques can allow real-time visualization of more data than is shown here. For example, the two plots shown each have greater than 3 million data points on chromosome 21.