Gene structure. Example of exons of gene SSX4 and SSX4B isoforms, annotated to illustrate the grammar of graphics extensions used. The filled rectangle represents exons and the chevron represents introns. They are grouped by transcript ID and the y axis shows the stepping levels, which stacks transcripts to avoid overplotting. Color is mapped from strand direction.
Yin et al. Genome Biology 2012 13:R77 doi:10.1186/gb-2012-13-8-r77