Homotypic hybridizations. (a) A typical hybridization where a single RNA pool was split and labeled with Cy3 and Cy5. For each element, intensities in each channel are plotted against each other. The central diagonal line represents equivalent intensities and the flanking lines twofold differences in intensity. (b) Data points from four such homotypic hybridizations were used to construct the histogram, which shows the distribution or 'bandwidth' of gene elements (as a percentage of the total) around the natural logarithm of the expected ratio of 1.0. As relative fluorescence can vary with laser power, spectral line and bandwidth and other detector parameters, it is more useful to express results as ratios, a unit-less term. (c) The ratio plotted against position of the element on the array. The parallel lines are at equivalent intensities and at twofold differences in intensity.