SANTA CLARA, Calif.--Affymetrix has introduced a family of GeneChip expression arrays for the rat, and separately, its GeneChip HuSNP mapping assay, an integrated tool for generating genotypes needed for genetic linkage mapping. Central to the assay is a new GeneChip HuSNP probe array, containing oligonucleotides of known sequences enabling simultaneous interrogation of nearly 1500 single nucleotide polymorphisms covering all 22 autosomes and the X chromosome in a single experiment.