Genome size, defined as the total amount of DNA contained within the haploid chromosome set of an organism, is not only one of the most fundamental genetic properties of living organisms, but also one of the most mysterious biological traits. A well-known phenomenon is the “C-value paradox” or “G-value/N-value paradox”, which is the long-recognized lack of correlation between genome size and organism complexity. Serving as model organisms, smooth pufferfish (Takifugu rubripes and Tetraodon nigroviridis) possess the smallest vertebrate genomes (<400 Mb), which is one-eighth the length of the human genome. However, genes which they have are as many as human. Therefore, genome size variation in pufferfish has been a hot study for a long time.   

Supervised by HE Shunping, Professor of Institute of Hydrobiology, Chinese Academy of Sciences (IHB), IHB PhD student GUO Baocheng et al. used comparative genomics method for further understanding of genome size evolution in pufferfish. A BAC library of the spiny pufferfish D. holocanthus with genome size 780 Mb was constructed and 10 clones, containing sequences of around 100 kb, were randomly selected, sequenced, and subsequently analyzed. In total, 776 kb of non-redundant sequences without gap representing 0.1% of the D. holocanthus genome were identified. Analysis results showed that genome size variation between D. holocanthus and the smooth pufferfish exhibits as length variation between homologous region and different accumulation of non-homologous sequences. The length difference of intron is consistent with the genome size variation between D. holocanthus and the smooth pufferfish. Different transposable element accumulation is responsible for genome size variation between D. holocanthus and the smooth pufferfish. Reviewers comment that this work is important in its field and is the first paper that directly compares the sequences among these species and provides sufficient information for publication. The results have been published on BMC Genomics 2010, 11:396doi:10.1186/1471-2164-11-396，http://www.biomedcentral.com/1471-2164/11/396