The idea of evolution as a principle for the origin of biodiversity fits all phenomena of life, including the carriers of nuclear inheritance, the chromosomes. Insights into the evolutionary mechanisms that contribute to the shape, size, composition, number and redundancy of chromosomes elucidate the high plasticity of nuclear genomes at the chromosomal level, and the potential for genome modification in the course of breeding processes. Aspects of chromosome fusion, as exemplified by karyotype evolution of relatives of Arabidopsis, have recently received special attention.