LINE drive: L1 element orthologous loci

The L1Hs preTa subfamily is one of the youngest L1 families. It originated after the divergence of human and chimpanzee about 2.34 mya, and therefore is only found in the human genome. Some elements were inserted so recently that they are not fixed in the population. Thirty three of the 254 L1Hs preTa elements are polymorphic for the absence/presence of the insertion, making them useful markers for studying phylogenetics and human population genetics. However, the problem of homoplasy can diminish the value of using L1 elements as phylogenetic and population genetic markers. Examination of the L1Hs preTa orthologous insertion sites in a range of non-human primates revealed an assortment of events that altered the size of the pre-integration or “empty” sites. Only two cases of parallel mobile element insertions into the same pre-integration sites were discovered, one involves an AluY in green monkey and the other a L1PA8 element in owl monkey. However, both elements were clearly distinguishable from their human counterparts. No preTa L1 element gene conversion events were observed in any of the loci analyzed. Therefore, we conclude that L1 elements are homoplasy-free genetic characters.