TY1-COPIA GROUP RETROTRANSPOSON SEQUENCES IN AMPHIBIA AND REPTILIA

We have isolated sequences belonging to Ty1-copia group retrotransposo ns from the genomes of an amphibian (Pyxicephalus adspersa) and three reptiles (Conolophus subscristatus, Amblyrynchus cristatus and Pytas m ucosus). Two different seqences were found in the amphibian (Tpa1 and Tpa2). Each is present in several copies per genome and absent from th e genomes of two other amphibian species. The C. subcristatus sequence Tcs1 is present in multiple copies in both its host genome (Galapagos land iguana) and the genome of the related Galapagos marine iguana (A . cristatus). There is little or no polymorphism in Tcs1 insertions be tween different individual animals, suggesting that this sequence is n ot transposing rapidly in either iguana genome. The P. mucosus sequenc e Tpm1 shows a discontinuous distribution in snake species, suggesting that it has either been lost from many lineages during vertical germl ine transmission or has been transferred horizontally in some snake sp ecies. Phylogenetic comparisons of all these sequences with each other and with other members of this retrotransposon group from other anima ls and plants show that sequences within a particular vertebrate speci es are most closely related to each other, consistent with a vertical transmission model for their evolution.