Duplicate and diverge: the evolution of plant genome microstructure

The use of positional approaches for the isolation of genes from most crop species is difficult due to the large size of their genomes. If the order o f genes in segments of the genomes is similar in different plants, it might be feasible to use smaller genomes as templates upon which to base strateg ies for the positional cloning of genes from other species. Comparative gen etic mapping, using markers such as restriction-fragment length polymorphis ms, has revealed extensive conservation of long-range genome organization ( macrostructure) between related species. But is the organization of the ten s or hundreds of genes between the genetic markers also conserved? Recent r esults suggest that the fine-scale structure (microstructure) of plant geno mes is more dynamic than previously assumed from investigations of the macr ostructure.