L1 (LINE-1) RETROTRANSPOSABLE ELEMENTS PROVIDE A FOSSIL RECORD OF THEPHYLOGENETIC HISTORY OF MURID RODENTS

The single most difficult problem in phylogenetic analysis is deciding whether a shared taxonomic character is due to common ancestry or one that appeared independently due to convergence, parallelism, or rever sion to an ancestral state. Mammalian LI retrotransposons undergo peri odic amplifications in which multiple copies of the elements are inter spersed in the genome. Because these elements apparently are transmitt ed only by inheritance and are retained in the genome, a shared L1 amp lification event can only be an inherited ancestral character. We prop ose that L1 amplification events can be an excellent tool for analyzin g mammalian evolution and demonstrate here how we addressed several re fractory problems in rodent systematics using L1 DNA as a taxonomic ch aracter.