Fishy genome swims into view
The medaka fish (Oryzias latipes), a popular pet in Japan and model organism in the laboratory, has had its genome sequenced.
Shinichi Morishita and colleagues estimate that the small egg-laying freshwater fish’s genome contains approximately 20,000 genes, of which around 2,900 appear new and unique to medaka.
Teleosts (fish with bony skeletons), such as the medaka fish, make up more than half of all vertebrate species and have adapted to life in a variety of marine and freshwater habitats. The evolution and diversification of their genomes is therefore crucial to understanding how vertebrates evolved.
The team compared their high-quality draft sequence against human, pufferfish (Tetraodon) and zebrafish genomes. It’s already known that at some point in the past the whole teleost genome doubled. The new study shows that the last common ancestor of medaka, pufferfish and zebrafish experienced 8 major rearrangements between chromosomes within just 50 million years of this event. But where the zebrafish genome has changed considerably since it diverged from the last common ancestor some 320 million years ago, the medaka genome has remained remarkably unchanged for over 300 million years.

CONTACT
Shinichi Morishita (University of Tokyo, Chiba, Japan)
Tel: +81 47 136 3984; E-mail: moris@cb.k.u-tokyo.ac.jp