title: Evolution and function of B chromosome 45S rDNA sequences in Brachycome dichromosomatica.
abstract: The origin and activity of 45S rDNA located on micro B chromosomes of the daisy Brachycome dichromosomatica were analysed. The internal transcribed spacer 2 (ITS2) of the 45S rRNA gene was sequenced for micro B, large B, and A chromosomes of B. dichromosomatica cytodeme A2, and conserved differences were identified between sequences originating from A and both types of B chromosomes. Phylogenetic analysis did not identify a species containing an ITS2 sequence more similar to either of the B chromosome sequences than the B. dichromosomatica A chromosome sequences. Thus, an origin of the B chromosomes from A chromosomes at a time prior to the divergence of the 4 cytodemes of B. dichromosomatica is suggested. The frequent (70%) nucleolar non-association of micro B chromosomes suggests inactivity of micro B 45S rDNA.
authors: Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), 06466 Gatersleben, Germany.
authors: Sylvia
authors: S
authors: Marschner
authors: Armin
authors: A
authors: Meister
authors: Frank R
authors: FR
authors: Blattner
authors: Andreas
authors: A
authors: Houben
mesh_terms: D019659:Asteraceae / Q000145:classification / Q000235:genetics*; D001483:Base Sequence; D002466:Cell Nucleolus / Q000378:metabolism; D032461:Chromosomes, Plant; D004275:DNA, Ribosomal / Q000737:chemistry* / Q000378:metabolism; D019143:Evolution, Molecular; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D012335:RNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D004275:DNA, Ribosomal; D012335:RNA, Ribosomal; C088179:RNA, ribosomal, 45S