B chromosomes have a functional effect on sex determination in a species of cichlid fishes from Lake Victoria, according to a study by Japanese researchers to be published in open-access journal PLoS Genetics on August 18th, 2011. The researchers found sex-ratio distortions caused by B chromosomes in the breeding line of the cichlids, as well as several protein-coding genes in the B chromosomes. The resultant ratio was female biased, suggesting a role for B chromosomes in female sex determination.
The B chromosome was first identified by E. B. Wilson in 1907. B chromosomes (or accessory chromosomes) are additional to the standard set of chromosomes (autosomes and sex chromosomes) in an organism. They have been found in many species (more than 1,000) over the last hundred years. Although they are widely distributed, the effect of B chromosomes on host organisms has not been detected. Indeed, B chromosomes have been thought to be a selfish genetic element, lacking genes and having no effect on the organism. It has previously been proposed that the unique features shared by B chromosomes and sex chromosomes imply an evolutionary relation between them. However, research into B chromosomes has been limited to a few species and the question has not been resolved.
In the present study, the researchers performed an extensive analysis of B chromosomes in cichlid fishes from Lake Victoria to investigate their effect on cichlid evolution. Karyotype analysis of Lake Victoria cichlids suggested that, in one species, Lithochromis rubripinnis, there are female-specific B chromosomes. Crossbreeding experiments suggested that an effector of female sex determination in this species was the B chromosome. Furthermore, analyses of large-scale sequences of B chromosomes in Lake Victoria cichlids revealed multiple protein-coding genes in B chromosomes.
The sex determination gene was not found in this research. However, the researchers provide evidence that B chromosomes have a functional effect on sex determination and that they demonstrate a capacity to evolve into sex chromosomes.
FINANCIAL DISCLOSURE: This work was supported by Grants from the Ministry of Education, Culture, Sports, Science, and Technology of Japan 21227002 (NO), JSPS Asia-Africa Science Platform Program (NO), and Grant-in-Aid for JSPS Fellows 218867 (KY). 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: Yoshida K, Terai Y, Mizoiri S, Aibara M, Nishihara H, et al. (2011) B Chromosomes Have a Functional Effect on Female Sex Determination in Lake Victoria Cichlid Fishes. PLoS Genet 7(8): e1002203. doi:10.1371/journal.pgen.1002203
PLEASE ADD THIS LINK TO THE FREELY AVAILABLE ARTICLE IN ONLINE VERSIONS OF YOUR REPORT (the link will go live when the embargo ends):
CONTACT: Norihiro Okada
Graduate School of Bioscience and Biotechnology
Tokyo Institute of Technology
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.
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.