title: Genes on B chromosomes of vertebrates.
abstract: BACKGROUND
  There is a growing body of evidence that B chromosomes, once regarded as totally heterochromatic and genetically inert, harbor multiple segmental duplications containing clusters of ribosomal RNA genes, processed pseudogenes and protein-coding genes. Application of novel molecular approaches further supports complex composition and possible phenotypic effects of B chromosomes.
  
  
  RESULTS
  Here we review recent findings of gene-carrying genomic segments on B chromosomes from different vertebrate groups. We demonstrate that the genetic content of B chromosomes is highly heterogeneous and some B chromosomes contain multiple large duplications derived from various chromosomes of the standard karyotype. Although B chromosomes seem to be mostly homologous to each other within a species, their genetic content differs between species. There are indications that some genomic regions are more likely to be located on B chromosomes.
  
  
  CONCLUSIONS
  The discovery of multiple autosomal genes on B chromosomes opens a new discussion about their possible effects ranging from sex determination to fitness and adaptation, their complex interactions with host genome and role in evolution.
authors.affiliation: Institute of Molecular and Cellular Biology SВ RAS, Novosibirsk, 630090 Russia ; Theodosius Dobzhansky Center for Genome Bioinformatics, St. Petersburg State University, St. Petersburg, Russia.
authors.forename: Alexey I
authors.initials: AI
authors.lastname: Makunin
authors.affiliation: Institute of Molecular and Cellular Biology SВ RAS, Novosibirsk, 630090 Russia.
authors.forename: Polina V
authors.initials: PV
authors.lastname: Dementyeva
authors.affiliation: Institute of Molecular and Cellular Biology SВ RAS, Novosibirsk, 630090 Russia ; Novosibirsk State University, Novosibirsk, Russia.
authors.forename: Alexander S
authors.initials: AS
authors.lastname: Graphodatsky
authors.affiliation: Museum National d'Histoire Naturelle, Origine, Structure et Evolution de la Biodiversite, Paris, France.
authors.forename: Vitaly T
authors.initials: VT
authors.lastname: Volobouev
authors.affiliation: Department of Animal Sciences, The University of Illinois at Urbana-Champaign, Champaign, USA.
authors.forename: Anna V
authors.initials: AV
authors.lastname: Kukekova
authors.affiliation: Institute of Molecular and Cellular Biology SВ RAS, Novosibirsk, 630090 Russia ; Novosibirsk State University, Novosibirsk, Russia.
authors.forename: Vladimir A
authors.initials: VA
authors.lastname: Trifonov
keywords: B chromosomes; Evolution of genomes; Proto-oncogenes; Segmental duplication; Vertebrates