SINE dimerization
Although the majority of SINEs are monomeric, numerous dimeric (and even trimeric) SINE families exist. According to the number of their genomic copies, dimerization is usually a progressive evolutionary event; however, dimeric SINEs are not necessarily more successful than the monomeric counterparts. For instance, the dimers of B1 and ID are much more ample in the genomes of squirrels and dormice, whereas the opposite pattern is observed in the guinea pig genome (Kramerov and Vassetzky, 2001).