TOKYO, June 7 (UPI) -- Japanese scientists have sequenced the genome of the medaka fish (Oryzias latipes) -- a popular pet in Japan and an often-used organism in the laboratory.
Shinichi Morishita and colleagues at the University of Tokyo estimate the small egg-laying freshwater fish's genome contains 20,000 genes, of which about 2,900 appear new and unique to medaka.
Teleosts -- fish with bony skeletons -- make up more than half of all vertebrate species and have adapted to life in a variety of marine and freshwater habitats, making their genomes crucial to understanding how vertebrates evolved.
The team compared their 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 suggests the last common ancestor of medaka, pufferfish and zebrafish experienced eight major rearrangements between chromosomes within just 50 million years of that event. But while the zebrafish genome has changed considerably since it diverged from the last common ancestor some 320 million years ago, the scientists found the medaka genome has remained remarkably unchanged for approximately 300 million years.
The data are reported in this week's issue of the journal Nature.
