Microarray hybridized to muscle first strand cDNA vs. end-labeled oligo(dT) This figure shows the background-subtracted images of a single Research Genetics #GF200 array membrane, hybridized successively with two different probes. The first hybridization image, labeled as "Muscle", was performed using a first strand cDNA probe prepared from the skeletal muscle mRNA of a Zucker rat. The second hybridzation image, labeled as "PolyA", was performed after stripping the filter and rehybridizing it with end-labeled oligo(dT), in order to measure the spots' polyA content. The array consists of sixteen individual matrices. They are arranged in two fields (1 and 2, shown in Fig. 1(a) and Fig. 1(b), respectively), each of which contains eight matrices labeled with a letter from a to h. Each matrix consists of 12 columns and 30 rows of spots, which are indexed as indicated. The identity of the gene at each spot, indexed as described here, is available at http://www.resgen.com. Spots in column 1 of each array matrix contain reference genomic DNA (in rows 1, 3, 5, 7, 9, 11, 25, 27, and 29) and reference cDNA for "housekeeping" genes (in rows 13 through 24). Spots in rows 1, 3, and 5 of column 2 of each array matrix also contain reference genomic DNA. Spot locations between the genomic DNA are empty, resulting in the landmark patterns seen in the upper-right and lower-right corners of each of the matrices.