BioEd Online

What do the elephant, the armadillo and the slime mould have in common? They are all about to have their genomes sequenced by researchers at the US National Human Genome Research Institute, according to plans unveiled on 4 August. In total, 18 species have been selected; they form an eclectic mix designed to shed light on both the human genome and the evolution of the entire tree of life.

It is the first time that species have been selected for genome sequencing in such numbers. Previous projects, most famously the decoding of the human genome, homed in on a single target organism. The roll-call runs from the gigantic to the microscopic: among the organisms selected are the African savannah elephant, the domestic cat, the nine-banded armadillo and a cadre of moulds, snails and worms.

The new strategy will allow scientists to fill gaps in our knowledge about how genomes evolve and which parts of the human sequence are most crucial, says Mark Guyer, a research director at the institute. "With each new genome that we sequence, we move closer to the goal of finding all the crucial elements of the human genome involved in development, health and disease," he says.

Wild bunch

The shortlist of mammalian species reflects this thinking. Seven of the animals chosen are from diverse branches of the mammalian evolutionary tree, so that their genomes can usefully be compared. These include the savannah elephant, which is from Africa; the common shrew, hedgehog and rabbit, which all originated in Europe; the guinea pig and nine-banded armadillo, from the Americas; and the lesser hedgehog tenrec (Echinops telfairi), which lives only in Madagascar.

Any sequences shared by all of these and by humans must surely contain important genes, the researchers reason. "Comparative analysis has emerged as an extremely powerful tool for deciphering the human genome sequence," says Guyer's colleague Jane Peterson.

Added to these seven are the domestic cat, which is an important model animal for studying human diseases, and our close cousin the orangutan. The orangutan's genome sequence will complement the projects to sequence the genetic codes of fellow primates the chimpanzee and the rhesus macaque, both of which are nearing completion.

Worms and slime

The second group of nine organisms will shine a light, hopefully, on the processes by which genomes are organized. The species, which come from far and wide on the evolutionary tree of life, include the slime mould Physarum polycephalum, the fish-like lamprey Petromyzon marinus, and the single-celled swimmer Monosiga ovata.

This group also includes two species with direct relevance to human disease. The roundworm Trichinella spiralis is transmitted in undercooked pork, and the snail Biomphalaria glabrata carries the parasite that causes the debilitating disease schistosomiasis.

The 18 species will be added to the institute's waiting list for genome sequencing, which currently features the kangaroo, cow, and a host of flies and fungi. Sequencing will be done at the five centres of the institute's Large-Scale Sequencing Research Network across the United States, using the high-speed 'shotgun' method developed for the Human Genome Project. Once work begins, the sequences should all take about a year to complete.