When the Joint Genome Institute decided to sequence a frog genome, however, the Xenopus research community recommended X. tropicalis over X. laevis because tropicalis has half the genome size. While X. tropicalis is diploid, with two copies of each gene on 10 pairs of chromosomes, the X. laevis genome has undergone duplication and could have four copies of every gene on 18 pairs of chromosomes. Sequencing X. laevis would have been not only more costly, but also harder, because of the difficulty of matching genes to the proper chromosome.
Nevertheless, the high quality draft sequence will provide a "scaffold upon which to assemble the X. laevis genome," Harland said. Harland and Daniel Rokhsar, co-lead of the Xenopus genome project, UC Berkeley biology professor, JGI scientist and QB3 member, have applied for a National Institutes of Health grant to sequence the X. laevis genome. Harland said that, because of faster and cheaper sequencing machines, the cost would be about $1 million – about 20 times less than the cost of sequencing the X. tropicalis genome over a three-year period starting in 2002.
Though the draft genome sequence has been available to scientists for several years, the new paper is the first analysis of the full genome. According to Hellsten, a comparison of regions around specific genes in the frog, chicken and human genomes shows that they are amazingly similar, indicating a high level of conservation of organization, or structure, on the chromosomes.
Read more on QB3's news site.