Genetic affinities of the Andaman Islanders, a vanishing human population.

BACKGROUND: The Andaman Islands in the Bay of Bengal are inhabited by hunter-gatherers of unknown origin, now on the verge of extinction. The Andamanese and other Asian small-statured peoples, traditionally known as "Negritos," resemble African pygmies. However, it is generally believed that they descend from the early Australo-Melanesian settlers of Southeast Asia and that their resemblance to some Africans is due to adaptation to a similar environment, rather than shared origins. RESULTS: We analyzed mitochondrial DNA (mtDNA) sequences and RFLP polymorphisms, and Y chromosome biallelic markers and microsatellites, in present-day Andamanese of the Onge, Jarawa, and Great Andamanese tribes, and of inhabitants of the neighboring Nicobar Islands. We also analyzed mtDNA sequences from Andamanese hair samples collected by an ethnographer during 1906-1908. Living Andamanese exhibit low genetic variability that is consistent with their small population size and reproductive isolation. CONCLUSIONS: Our data indicate that the Andamanese have closer affinities to Asian than to African populations and suggest that they are the descendants of the early Palaeolithic colonizers of Southeast Asia. In contrast, the Nicobarese have genetic affinities to groups widely distributed throughout Asia today, presumably descended from Neolithic agriculturalists.

Xena, a full-length basal retroelement from tetraodontid fish.

Mobile genetic elements are ubiquitous throughout the eukaryote superkingdom. We have sequenced a highly unusual full-length retroelement from the Fugu fish, Takifugu rubripes. This element, which we have named Xena, is similar in structure and sequence to the Penelope retroelement from Drosophila virilis and consists of a single long open reading frame containing a reverse transcriptase domain flanked by identical direct long terminal repeat (LTR) sequences. These LTRs show an organization similar to the terminal repeats already described in the Penelope retrotransposon of Drosophila but are structurally and functionally distinct from the LTRs carried by LTR-retrotransposons. In view of their distinctness, we refer to these repeats as PLTRs (Penelope-LTRs). Whereas the element contains a reverse transcriptase, no other domains or motifs commonly associated with retroelements are present. In the full-length Fugu element, the 5' direct PLTR is preceded by an inverted PLTR fragment. Additional elements, many showing various degrees of deletion, are described from the Fugu genome and from that of the freshwater pufferfish Tetraodon nigroviridis. Many of these additional elements are also preceded by inverted PLTR sequences. Xena-like elements are also described from the genomes of several other organisms. The Penelope-Xena lineage is apparently a basal group within the retrotransposons and therefore represents an evolutionarily important class of retroelement.