Evolutionary DNA variation in the genus Hypochaeris

The genome size and the base composition (GC%) of sight Hypochaeris species were determined by flow cytometry in order to establish the pattern of nuclear DNA variation within the genus. The species analysed showed an almost fivefold range of variation from 1.68 pg in H. cretensis to 8.10 pg in H. uniflora. This variation in DNA content is greater between taxonomic sections of Hypochaeris species than within a section. There was no correlation between 2C DNA content and GC% indicating that neither the GC fraction nor the AT fraction were preferentially associated with variation in genome size. Because there is little heterochromatin, these results show that it is interspersed repeated sequences that are most probably implicated in this variation. From phylogenetic analysis, it is likely that genome size has evolved by loss of DNA content in some lineages and by gain in one lineage from an ancestral genome which was probably similar to genomes of intermediate size in Hypochaeris.