title: Genes on B chromosomes: old questions revisited with new tools.
abstract: BACKGROUND
  B chromosomes are supernumerary dispensable parts of the karyotype which appear in some individuals of some populations in some species. Often, they have been considered as 'junk DNA' or genomic parasites without functional genes.
  
  
  METHODS
  Due to recent advances in sequencing technologies, it became possible to investigate their DNA composition, transcriptional activity and effects on the host transcriptome profile in detail. Here, we review the most recent findings regarding the gene content of B chromosomes and their transcriptional activities and discuss these findings in the context of comparable biological phenomena, like sex chromosomes, aneuploidy and pseudogenes.
  
  
  CONCLUSIONS
  Recent data suggest that B chromosomes carry transcriptionally active genic sequences which could affect the transcriptome profile of their host genome.
  
  
  CONCLUSIONS
  These findings are gradually changing our view that B chromosomes are solely genetically inert selfish elements without any functional genes. This at one side could partly explain the deleterious effects which are associated with their presence. On the other hand it makes B chromosome a nice model for studying regulatory mechanisms of duplicated genes and their evolutionary consequences.
authors.affiliation: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Corrensstr. 3, 06466 Stadt Seeland, Germany.
authors.forename: Ali M
authors.initials: AM
authors.lastname: Banaei-Moghaddam
authors.affiliation: Helmholtz Center Munich, Dept. Plant Genome and Systems Biology, 85764 Neuherberg, Germany.
authors.forename: Mihaela M
authors.initials: MM
authors.lastname: Martis
authors.affiliation: Biology Centre ASCR, Institute of Plant Molecular Biology, Ceske Budejovice, Czech Republic.
authors.forename: Jiří
authors.initials: J
authors.lastname: Macas
authors.affiliation: Helmholtz Center Munich, Dept. Plant Genome and Systems Biology, 85764 Neuherberg, Germany.
authors.forename: Heidrun
authors.initials: H
authors.lastname: Gundlach
authors.affiliation: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Corrensstr. 3, 06466 Stadt Seeland, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Himmelbach
authors.affiliation: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Corrensstr. 3, 06466 Stadt Seeland, Germany.
authors.forename: Lothar
authors.initials: L
authors.lastname: Altschmied
authors.affiliation: Helmholtz Center Munich, Dept. Plant Genome and Systems Biology, 85764 Neuherberg, Germany.
authors.forename: Klaus F X
authors.initials: KF
authors.lastname: Mayer
authors.affiliation: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) Gatersleben, Corrensstr. 3, 06466 Stadt Seeland, Germany. Electronic address: houben@ipk-gatersleben.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Houben
mesh_terms: D000818:Animals; D002875:Chromosomes / Q000235:genetics*; D021901:DNA, Intergenic / Q000235:genetics*; D056890:Eukaryota / Q000235:genetics; D019143:Evolution, Molecular; D005786:Gene Expression Regulation / Q000235:genetics; D016678:Genome; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D011544:Pseudogenes / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D021901:DNA, Intergenic
keywords: Gene regulation; Genome evolution; Junk DNA; Pseudogene; Supernumerary chromosome; Transcription