Hybridization signals of P. gingivalis strains - dead probes. A. The total intensity distribution of probe signals of W83 DNA hybridized to the W83 array. The density peak around 7.5 contains the negative controls (empty spots and A. thaliana probes). The peak around 12 should contain all present genes in strain W83. B Probe signal intensities of each P. gingivalis test strain are represented in light blue dots; medium blue dots, slightly below that, symbolize A. thaliana negative control genes. Dark blue dots represent P gingivalis probes, which show the same low intensity as the negative control probes. These 22 probes are called dead probes as they do not give any significant hybridization signal.