Intra- and intergenomic homology of B-genome chromosomes in trigenomic combinations of the cultivated Brassica species revealed by GISH analysis

Chromosome Res. 2007;15(7):849-61. doi: 10.1007/s10577-007-1168-4. Epub 2007 Oct 1.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Biological Evolution
  • Brassica / classification
  • Brassica / genetics*
  • Brassica / growth & development
  • Chromosome Pairing
  • Chromosomes, Plant / genetics*
  • Crosses, Genetic*
  • DNA, Plant / analysis
  • DNA, Plant / isolation & purification
  • Genome, Plant*
  • In Situ Hybridization / methods*

Substances

  • DNA, Plant