['Alternative splicing is an important mechanism for generating functional and evolutionary diversity of proteins in eukaryotes. Here, we studied the frequency and functionality of recently gained, rodent-specific alternative exons.', 'We projected the data about alternative splicing of mouse genes to the rat, human, and dog genomes, and identified exons conserved in the rat genome, but missing in more distant genomes. We estimated the frequency of rodent-specific exons while controlling for possible residual conservation of spurious exons. The frequency of rodent-specific exons is higher among predominantly skipped exons and exons disrupting the reading frame. Separation of all genes by the rate of sequence evolution and by gene families has demonstrated that rodent-specific cassette exons are more frequent in rapidly evolving genes and in rodent-specific paralogs.'] Are rodent-specific alternative exons more frequent in rapidly evolving genes and in paralogs?