Researchers from Trinity College Dublin have uncovered the evolutionary mechanisms that have caused increases or decreases in the numbers of chromosomes in a group of yeast species during the last 100-150 million years. The study, to be published on July 21st in the open-access journal PLoS Genetics, offers an unprecedented view of chromosome complement (chromosome number) changes in a large group of related species.
A few specific cases of chromosome number changes have been studied in plants and animals, for example the fusion of two great ape chromosomes that gave rise to chromosome 2 in humans, giving humans a chromosome count of 23 pairs compared to 24 pairs in great apes. The family of yeasts studied in this new research spans a similar evolutionary distance to that of vertebrates. The availability of completely sequenced genomes facilitated the reconstruction of ancestral genome structures at different evolutionary time points. Tracing the positions of essential parts of chromosomes (centromeres and telomeres) through time allowed for the identification of specific genome rearrangement events that resulted in chromosome complement changes.
The addition of large numbers of genes is not often tolerated by cells, and neither are deletions of large numbers of genes. This restricts the types of possible changes in chromosome complement to rearrangements of genes on chromosomes that maintain the same number of genes.
The researchers show that, in yeasts, chromosome complement has decreased in all except one notable event, a whole genome duplication – an event that doubled the complement of an ancestor of several of the species from 8 chromosomes to 16. The decreases in chromosome number were mostly by the fusion of whole chromosomes, similar to the one that gave rise to chromosome 2 in humans. One exception to this mechanism was the breakage of a chromosome and the subsequent fusion of the two broken edges to two different chromosome ends.
Although some aspects of the research are specific to yeast, many of the mechanisms of chromosome number change in yeast are similar to those found in other organisms and therefore shed light on how chromosome complements evolve.
FINANCIAL DISCLOSURE: This study was supported by Science Foundation Ireland (07/IN1/B911). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
COMPETING INTERESTS: The authors have declared that no competing interests exist.
CITATION: Gordon JL, Byrne KP, Wolfe KH (2011) Mechanisms of Chromosome Number Evolution in Yeast. PLoS Genet 7(7): e1002190. doi:10.1371/ journal.pgen.1002190
PLEASE ADD THIS LINK TO THE FREELY AVAILABLE ARTICLE IN ONLINE VERSIONS OF YOUR REPORT (the link will go live when the embargo ends): http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1002190
CONTACT: Jonathan Gordon
This press release refers to an upcoming article in PLoS Genetics. The release is provided by journal staff, or by the article authors and/or their institutions. Any opinions expressed in this release or article are the personal views of the journal staff and/or article contributors, and do not necessarily represent the views or policies of PLoS. PLoS expressly disclaims any and all warranties and liability in connection with the information found in the releases and articles and your use of such information.
About PLoS Genetics
PLoS Genetics (http://www.plosgenetics.org) reflects the full breadth and interdisciplinary nature of genetics and genomics research by publishing outstanding original contributions in all areas of biology. All works published in PLoS Genetics are open access. Everything is immediately and freely available online throughout the world subject only to the condition that the original authorship and source are properly attributed. Copyright is retained by the authors. The Public Library of Science uses the Creative Commons Attribution License.
About the Public Library of Science
The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit http://www.plos.org.
AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert! system.