The qualitative analysis of a single array to determine if a transcript is Present, Absent or Marginal. Affymetrix tab-delimited format of the probe sequence download file: The probe sequence download file in the Download Center is a tab-delimited file containing the following columns: Probe Set Name: For example, 1007_s_at Probe X: The X coordinate of the probe sequence on the GeneChip® probe array. Probe Y: The Y coordinate of the probe sequence on the GeneChip probe array. Probe Interrogation Position: The position of the 13th ("middle") nucleotide of the probe sequence as it aligns on the consensus/exemplar sequence. Probe Sequence: The 25-base perfect match sequence. Target Strandedness: The sense/antisense orientation of the target sequence that can hybridize with the probe sequence. Note: Probe Sequence databanks in the NetAffx(tm) Analysis Center have an additional column called, "Serial Order". This column provides the relative order of probe sequences as they align with the consensus/exemplar sequence.