Abstract

The application of DNA-based phylogenies to the study of chromosome evolution has allowed the direction of many of the changes that give rise to the chromosome variation to be analysed objectively for the first time. Dysploid changes in chromosome number, differences in the degree of karyotype symmetry, the loss or gain of chromosome bands, changes in genome size and variation in the number of ribosomal RNA gene clusters can all be shown to undergo a variety of changes, suggesting that there are no universal rules governing karyotype evolution. Phylogenetic studies as well as chromosome mapping and the analysis of chromosome pairing patterns using genomic in situ hybridization also demonstrate that cryptic or ancient polyploids may be more widespread in angiosperms than previously thought.