Determining the position of nucleosomes on genomic DNA with ChIP techniques. (a) Genome-wide analysis of the position of histones at all active promoter elements of yeast by the ChIP-Seq technique reveals a pattern of DNA accessibility at the promoter region. Peaks indicate regions of DNA bound to histones, and valleys indicate regions of DNA relatively free of histones. (b) Chip-Chip experiments define the location of nucleosomes positioned around an active gene.