Affymetrix announced this week the availability of mouse and rat expression microarrays. The GeneChip mouse expression set 430, and the rat expression set 230, each a two-chip product, are expected to ship by the end of the month. No pricing information was pro-vided. The mouse chip has 34,000 mouse genes among its 39,000 transcripts taken from public mouse genome databases. The rat chip has 28,000 substantiated genes among 30,200 transcripts taken from public rat genome databases.