title: Intra- and intergenomic homology of B-genome chromosomes in trigenomic combinations of the cultivated Brassica species revealed by GISH analysis.
abstract: Intragenomic chromosome homology in the B genome of Brassica nigra and their homoeology with the chromosomes of the A-genome of B. rapa and C-genome of B. oleracea was investigated in triploids (ABC, n = 27) of different origins obtained following hybridizations between natural B. napus (AACC, 2n = 38) x B. nigra (BB, 2n = 16) [AC.B], synthetic B. napus x B. nigra [A.C.B] and B. carinata (BBCC, 2n = 34) x B. rapa (AA, 2n = 20) [BC.A]. A relatively high percentage of pollen mother cells (PMCs) with at least one B-genome chromosome paired allosyndetically with A/C chromosomes was evident in all three combinations. A maximum of three B-genome chromosomes undergoing allosyndesis per cell was observed in AC.B and A.C.B combinations. A maximum of two autosyndetic bivalents within the B genome appeared at diakinesis in all combinations. The accurate analyses of auto- and allo-syndetic pairing for B genome in trigenomic combinations provided further evidence for the hypothesis that the three basic diploid genomes of the cultivated Brassica species evolved from one common ancestral genome with a lower chromosome number. The results showed that Brassica diploids may not be ancient polyploids but may have undergone chromosomal duplications instead of whole-genome duplication. The relevance of these results along with genetic changes of progenitor genomes which occurred during the evolution of Brassica polyploids is discussed.
authors: National Key Laboratory of Crop Genetic Improvement, National Center of Crop Molecular Breeding Technology, National Center of Oil Crop Improvement (Wuhan), Huazhong Agricultural University, Wuhan, 430070, PR China.
authors: Xian-Hong
authors: XH
authors: Ge
authors: Zai-Yun
authors: ZY
authors: Li
mesh_terms: D005075:Biological Evolution; D001937:Brassica / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D023902:Chromosome Pairing; D032461:Chromosomes, Plant / Q000235:genetics*; D003433:Crosses, Genetic; D018744:DNA, Plant / Q000032:analysis / Q000302:isolation & purification; D018745:Genome, Plant; D017403:In Situ Hybridization / Q000379:methods*
chemical_list: D018744:DNA, Plant