Using computational approaches we have identified 2017 expressed intronless 
genes in the mouse genome. Evolutionary analysis reveals that 56 intronless 
genes are conserved among the three domains of life--bacteria, archea and 
eukaryotes. These highly conserved intronless genes were found to be involved in 
essential housekeeping functions. About 80% of expressed mouse intronless genes 
have orthologs in eukaryotic genomes only, and thus are specific to eukaryotic 
organisms. 608 of these genes have intronless human orthologs and 302 of these 
orthologs have a match in OMIM database. Investigation into these mouse genes 
will be important in generating mouse models for understanding human diseases.