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Title: Chromosome size in diploid eukaryotic species centers on the average length with a conserved boundary

Author
item LI, XIANRAN - KANSAS STATE UNIVERSITY
item ZHU, CHENGSON - KANSAS STATE UNIVERSITY
item LIN, ZHONGWEI - KANSAS STATE UNIVERSITY
item WU, YUN - KANSAS STATE UNIVERSITY
item ZHANG, DABAO - PURDUE UNIVERSITY
item Bai, Guihua
item SONG, WEIXING - KANSAS STATE UNIVERSITY
item MA, JIANXIN - PURDUE UNIVERSITY
item MUEHLBAUER, GARY - UNIVERSITY OF MINNESOTA
item SCANLON, MICHAEL - CORNELL UNIVERSITY
item ZHANG, MIN - PURDUE UNIVERSITY
item YU, JIANMING - KANSAS STATE UNIVERSITY

Submitted to: Molecular Biology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2011
Publication Date: 1/13/2011
Citation: Li, X., Zhu, C.L., Lin, Z., Wu, Y., Zhang, D., Bai, G., Song, W., Ma, J., Muehlbauer, G.J., Scanlon, M.J., Zhang, M., Yu, J. 2011. Chromosome size in diploid eukaryotic species centers on the average length with a conserved boundary. Molecular Biology and Evolution. DOI: 10.1093/molbev/msr011.

Interpretive Summary: Chromosomes are the basic unit for control of inheritance and evolution of living organisms. Although huge variation in chromosome number and size has been observed among organisms, knowledge of genome and chromosome evolution is important for understanding inheritance and evolution of these organisms. Using available genome sequence information, we show that chromosomes within a species do not change dramatically in their content of mobile genetic elements as the production of these elements increases from unicellular eukaryotes to vertebrates. Actually, variation in chromosome size in diploid eukaryotes with linear chromosomes has an upper limit. A single model can describe the variation in chromosome size for 886 chromosomes of 68 eukaryotic genomes. This model predicts that length (in base pairs) of the majority of chromosomes in a species is expected to range from 0.4035 to 1.8626 times the average chromosome length. This boundary of chromosome size variation is very conservative and fits a wide taxonomic range with only few exceptions. The results indicate that cellular, molecular, and evolutionary mechanisms, possibly together, confine the chromosome lengths around a species-specific average chromosome length. The research contributes novel knowledge for understanding the role of chromosome size variation in species evolution.

Technical Abstract: Understanding genome and chromosome evolution is important for understanding genetic inheritance and evolution. Universal events comprising DNA replication, transcription, repair, mobile genetic element transposition, chromosome rearrangements, mitosis, and meiosis underlie inheritance and variation of living organisms. Although the genome of a species as a whole is important, chromosomes are the basic unit subjected to genetic events that coin evolution to a large extent. Now as many complete genome sequences are available, we can address evolution and variation of individual chromosomes across species. For example, “how are the repeat and nonrepeat proportions of genetic codes distributed among different chromosomes in a multi-chromosome species?” “Is there a general rule behind the intuitive observation that chromosome lengths tend to be similar in a species, and if so, can we generalize any findings in chromosome content and size across different taxonomic groups?” Here we show that chromosomes within a species do not show dramatic fluctuation in their content of mobile genetic elements as the proliferation of these elements increases from unicellular eukaryotes to vertebrates. Furthermore, we demonstrate that, notwithstanding the remarkable plasticity, there is an upper limit to chromosome size variation in diploid eukaryotes with linear chromosomes. Strikingly, variation in chromosome size for 886 chromosomes in 68 eukaryotic genomes (including 22 human autosomes) can be viably captured by a single model, which predicts that vast majority of the chromosomes in a species are expected to have a basepair length between 0.4035 and 1.8626 times the average chromosome length. This conserved boundary of chromosome size variation, which prevails across a wide taxonomic range with few exceptions, indicates that cellular, molecular, and evolutionary mechanisms, possibly together, confine the chromosome lengths around a species-specific average chromosome length.