The rates and patterns of insertions, deletions and substitutions in mouse and rat inferred from introns

The rates and patterns of InDel (insertions and deletions) and substitution in rodent (mouse and rat) have been studied. The result reveals that deletions occur more frequently than insertions, and single nucleotide insertion and deletion are the most frequent in both mouse and rat. The frequencies of both deletions and insertions decrease rapidly with increasing InDels length, and the size distributions of both insertions and deletions can be described well by power-law. There are more AT→GC than GC → AT substitutions in the introns of rat. However, there are more GC→AT than AT→GC substitutions in the introns in mouse. The deletion bias found in introns in mouse and rat supports the prediction that intron insertions are more deleterious than deletions because of reduced transcription and splicing efficiency. The patterns of substitution suggest that both composition and GC content are not equilibrium in the introns in rodents.