Plant Genome IV Conference Plant Genome IV Conference
The Brassicaceae include a wide range of cultivated species and their wild relatives as well as the model species, Arabidopsis thaliana. Short-range genome collinearity is strongly conserved throughout this family and a high proportion of interspecific hybrids are fertile, particularly after chromosome doubling. However, there are two barriers to the interspecific transfer of beneficial genes via sexual crosses: 1) the large number of gross chromosomal rearrangements that cause strictly homoeologous chromosomes to be rare, even when comparing closely related species, and 2) the control of chromosome pairing that prevents homoeologous recombination in certain interspecific hybrids. A combination of marker technology and cytology is being used to position Brassica centromeres and current work is confirming that whole arm exchanges are a prevalent form of rearrangement. Examples of the use of genetic markers to select recombinant chromosomes, in which homoeologous crossovers have introduced donor genes into appropriate intervals of recipient chromosomes, will be presented. Genetic variation in the system that controls the stringency of chromosome pairing will be described. The triplicated nature of the genomes of "diploid" Brassica species introduces additional complexity into the analysis of genome collinearity but homoeologous recombination only occurs between a limited range of potential homoeologues presumably indicating that the control of chromosome pairing distinguished between homoeologues with differing degrees of collinearity and/or homology.