Fig. 2. Spot intensity enhancement of macroarray clones after subtractive hybridization. Data for one filter are shown as a representative example. On the x-axis are the clone numbers and on the y-axis are the ranked spot intensity ratios of the after (I_sub) and before subtraction (I_unsub) screen. To select the putative pigment cell specific clones, an enrichment threshold value (broken line) was determined based on the range of enrichment values of the 24 phage clones spotted onto each filter. Most clones with enrichment values below threshold are clones the spot intensity of which is very close to the background both before and after subtraction. The spot intensity values of the selected group of enriched clones were checked on the dnN (driver) screen. The clones for which spot intensity was above background were discarded as false positive.