Illustration of the specificity of the hybridization reaction on the AT microarray for genotyping of C. psittaci . Alignments of target (ompA gene segments) and probe sequences are shown on the left-hand side, and the respective hybridization signals (including internal staining marker) are given on the right-hand side. Upper part: The signal generated by duplex formation at genotype E-specific probe VD2-04 is reduced to approx. 20% when the target has a single mismatch, such as genotype B. This applies also to genotype B-specific probe VD2-03, when reacting with genotype E. Lower part: Signal is reduced to less than 10% in the case of two mismatches on the target sequence.