Effects of masking of poorly performed probes during human and canine hybridizations to HG-U133A on "Present" calls, average probe set size and composition. Panel A. MAS 5.0 was applied to human (open triangles) and canine (open circles) hybridization profiles without masking (NM) and with masking of probes that poorly performed in 40, ≥35, ≥30, etc. hybridizations (x axis) and resulting numbers of total "Present" calls generated for each array were averaged and expressed in percentage values (y axis). Average sizes of human (solid triangles) and canine (solid circles) probe sets were computed for corresponding masking conditions and expressed in percentage values (y axis). Panel B. Distribution of probe set sizes after masking probes that failed to generate detectable hybridization signal during 15 or more hybridizations (~40%) of human (triangles) and canine (circles) samples. Panel C. Distribution of masked probes according to location on the target sequence.