title: Conserved microstructure of the Brassica B Genome of Brassica nigra in relation to homologous regions of Arabidopsis thaliana, B. rapa and B. oleracea.
abstract: BACKGROUND
  The Brassica B genome is known to carry several important traits, yet there has been limited analyses of its underlying genome structure, especially in comparison to the closely related A and C genomes. A bacterial artificial chromosome (BAC) library of Brassica nigra was developed and screened with 17 genes from a 222 kb region of A. thaliana that had been well characterised in both the Brassica A and C genomes.
  
  
  RESULTS
  Fingerprinting of 483 apparently non-redundant clones defined physical contigs for the corresponding regions in B. nigra. The target region is duplicated in A. thaliana and six homologous contigs were found in B. nigra resulting from the whole genome triplication event shared by the Brassiceae tribe. BACs representative of each region were sequenced to elucidate the level of microscale rearrangements across the Brassica species divide.
  
  
  CONCLUSIONS
  Although the B genome species separated from the A/C lineage some 6 Mya, comparisons between the three paleopolyploid Brassica genomes revealed extensive conservation of gene content and sequence identity. The level of fractionation or gene loss varied across genomes and genomic regions; however, the greatest loss of genes was observed to be common to all three genomes. One large-scale chromosomal rearrangement differentiated the B genome suggesting such events could contribute to the lack of recombination observed between B genome species and those of the closely related A/C lineage.
authors.affiliation: Agriculture and Agri-Food Canada, 107 Science Place, Saskatoon, SK S7N 0X2, Canada. isobel.parkin@agr.gc.ca.
authors.forename: Zahra-Katy
authors.initials: ZK
authors.lastname: Navabi
authors.forename: Terry
authors.initials: T
authors.lastname: Huebert
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Sharpe
authors.forename: Carmel M
authors.initials: CM
authors.lastname: O'Neill
authors.forename: Ian
authors.initials: I
authors.lastname: Bancroft
authors.forename: Isobel A P
authors.initials: IA
authors.lastname: Parkin
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D001483:Base Sequence; D029741:Brassica rapa / Q000235:genetics*; D022202:Chromosomes, Artificial, Bacterial / Q000235:genetics; D017124:Conserved Sequence; D020451:Contig Mapping; D019143:Evolution, Molecular; D018628:Gene Dosage; D020440:Gene Duplication; D015321:Gene Rearrangement; D049810:Genetic Speciation; D018745:Genome, Plant; D009149:Mustard Plant / Q000235:genetics*; D017422:Sequence Analysis, DNA