基因組大小,，是指一個(gè)基因組中所擁有的DNA含量,，是生物進(jìn)化中最基本的,、同時(shí)也是最復(fù)雜的遺傳特征之一,。例如，生物的復(fù)雜度并不與基因組大小有顯著相關(guān),，即C值悖論,。作為模式物種的紅旗東方鲀和斑點(diǎn)綠河鲀是目前已知的具有最小基因組大小的脊椎動(dòng)物（<400Mb，僅相當(dāng)于人基因組大小的八分之一）,，對它們的全基因組測序分析發(fā)現(xiàn),，它們卻具有與人相近的基因數(shù)目。正因?yàn)槿绱?，河鲀基因組大小變化的研究引起關(guān)注,。
在中國科學(xué)院水生生物研究所何舜平研究員的指導(dǎo)下，博士研究生郭寶成等通過構(gòu)建刺河鲀（基因組大小為780Mb）的BAC文庫和隨機(jī)挑取克隆測序,，在基因組水平對河鲀基因組大小變化進(jìn)行了研究,。對10個(gè)BAC克隆、長度776 kb的刺河鲀基因組測序分析發(fā)現(xiàn),，河鲀基因組大小變化同時(shí)表現(xiàn)為基因組同源區(qū)域和非同源區(qū)域長度的變化,；基因組注釋結(jié)果表明，內(nèi)含子長度與河鲀基因組大小變化呈正相關(guān),，刺河鲀的內(nèi)含子長度為566bp,，統(tǒng)計(jì)上顯著大于紅旗東方鲀和斑點(diǎn)綠河鲀的內(nèi)含子長度（435bp）；轉(zhuǎn)座子序列的含量和家族在不同河鲀基因組表現(xiàn)出明顯的不同,，并且轉(zhuǎn)座子序列在不同河鲀基因組內(nèi)的非等速積累是造成河鲀基因組大小變化的主要機(jī)制,。
這一結(jié)果被國際同行評價(jià)為是對在河鲀基因組大小變化傳統(tǒng)研究的重要補(bǔ)充和證明。(生物谷Bioon.net)
生物谷推薦原文出處：
BMC Genomics doi:10.1186/1471-2164-11-396
Genome size evolution in pufferfish: an insight from BAC clone-based Diodon holocanthus genome sequencing
Baocheng Guo , Ming Zou , Xiaoni Gan and Shunping He
Background
Variations in genome size within and between species have been observed since the 1950s in diverse taxonomic groups. Serving as model organisms, smooth pufferfish possess the smallest vertebrate genomes. Interestingly, spiny pufferfish from its sister family have genome twice as large as smooth pufferfish. Therefore, comparative genomic analysis between smooth pufferfish and spiny pufferfish is useful for our understanding of genome size evolution in pufferfish.
Results
Ten BAC clones of a spiny pufferfish Diodon holocanthus were randomly selected and shotgun sequenced. In total, 776 kb of non-redundant sequences without gap representing 0.1% of the D. holocanthus genome were identified, and 77 distinct genes were predicted. In the sequenced D. holocanthus genome, 364 kb is homologous with 265 kb of the Takifugu rubripes genome, and 223 kb is homologous with 148 kb of the Tetraodon nigroviridis genome. The repetitive DNA accounts for 8% of the sequenced D. holocanthus genome, which is higher than that in the T. rubripes genome (6.89%) and that in the Te. nigroviridis genome (4.66%). In the repetitive DNA, 76% is retroelements which account for 6% of the sequenced D. holocanthus genome and belong to known families of transposable elements. More than half of retroelements were distributed within genes. In the non-homologous regions, repeat element proportion in D. holocanthus genome increased to 10.6% compared with T. rubripes and increased to 9.19% compared with Te. nigroviridis. A comparison of 10 well-defined orthologous genes showed that the average intron size (566 bp) in D. holocanthus genome is significantly longer than that in the smooth pufferfish genome (435 bp).
Conclusion
Compared with the smooth pufferfish, D. holocanthus has a low gene density and repeat elements rich genome. 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.
