Chromosomes' Big Picture: Similarities Found in Genomes Across Multiple Species; Platypus Still out of Place
Their discovery, "Chromosome Size in Diploid Eukaryotic Species Centers on the Average Length with a Conserved Boundary," was recently published in the journal Molecular Biology and Evolution. It details a project that compared 886 chromosomes in 68 random species of eukaryotes -- organisms whose cells contain a nucleus and are enclosed by cellular membranes. The researchers found that the chromosome sizes within each eukaryotic species are actually similar rather than drastically different as previously believed. They also found that the chromosomes of these different organisms share a similar distribution pattern.
In a new study, researchers found that the chromosome sizes within each eukaryotic species are actually similar rather than drastically different as previously believed. They also found that the chromosomes of these different organisms share a similar distribution pattern. (Credit: Image courtesy of Kansas State University)
Because chromosomes are the genetic building blocks for an organism and its traits, the information will be beneficial to understanding the core components of biological evolution -- especially in genetics and genome evolution, said Jianming Yu, associate professor of agronomy at Kansas State University. With this data, scientists can now better predict the evolutionary adaptations of an organism.
"Basically what this all means is that if the chromosome number of a species can be given, the relative sizes of all the chromosomes can instantly be known," Yu said. "Also, if you tell me the genome size in the chromosome base pair, I can tell you the base pair length of each chromosome."
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Chromosome Size in Diploid Eukaryotic Species Centers on the Average Length with a Conserved Boundary
Xianran Li†,1, Chengsong Zhu†,1, Zhongwei Lin†,1, Yun Wu1, Dabao Zhang2, Guihua Bai1,3, Weixing Song4, Jianxin Ma5, Gary J. Muehlbauer6, Michael J. Scanlon7, Min Zhang*,2 and Jianming Yu*,1
Author Affiliations
1Department of Agronomy, Kansas State University
2Department of Statistics, Purdue University
3United States Department of Agriculture-Agricultural Research Service (USDA-ARS), Hard Winter Wheat Genetics Research Unit, Manhattan
4Department of Statistics, Kansas State University
5Department of Agronomy, Purdue University
6Department of Agronomy and Plant Genetics, University of Minnesota
7Department of Plant Biology, Cornell University
*Corresponding author: E-mail: jyu@ksu.edu; minzhang@purdue.edu
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 units subjected to genetic events that coin evolution to a large extent. Now 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 multichromosome 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 the vast majority of the chromosomes in a species are expected to have a base pair 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.
Key words
chromosome size, genome evolution, evolutionary modeling
Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution 2011.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License
(http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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