Present/absent characteristics of two hybridizations. Left part: The Yeast Genome 2.0 (YG 2.0) array contains about 50% probe sets designed for S. cerevisiae and S. pombe each. The hook refers to a chip hybridized with RNA taken from S. cerevisiae . The hooks are calculated either for all probes or masking the probes of one of the two yeast species. The lower part shows the respective signal-density distributions. The added transcripts of S. cerevisiae give rise to virtually absent probes of S. pombe in the N-range of the hook curve. The relative amount of S. cerevisiae-probes called absent (red) and of S. pombe-probes called present (blue) are given within the figure. Right part: Hook curves for a DG1-chip taken from the Golden Spike series which has been hybridized with a definite collection of "spiked"-transcripts. The selective masking of the spikes and of the remaining "empty" probes shows that these probes accumulate in the S- and N-region, respectively. The relative amounts of empty probes called present and of spiked probes called absent are given in the figure.