Abstract: A method is disclosed which can be used for the identification of one or more orthologous genes on a microarray, that utilises a microarray derived from a first animal that is used to analyse a corresponding nucleotide sequence from a second animal or a distinct variety of the first animal. The method comprises applying genomic DNA from the second animal, or distinct variety of the first animal, to a microarray derived from the first animal, measuring a background level of hybridisation intensity of the genomic DNA to probes of the microarray, and selecting probes on the microarray for which the hybridisation intensity is greater than a threshold value based on the background level of hybridisation intensity, whereby the selected probes are indicative of orthologous genes.