Karyotype diversity and evolutionary trends in angiosperms

Karyotypic change constitutes an important evolutionary mechanism contributing to angiosperm diversification and speciation. Comparative analyses of the karyotype usually include numerical features (chromosome number) and their changes (dysploidy, aneuploidy, polyploidy), as well as morphological features (chromosome size, karyotype length and genome size, centromere position and karyotype symmetry, secondary constrictions, supernumerary chromosomal material). More detailed characterization of angiosperm karyotypes involves also analyses of the abundance, distribution, and organization of specific molecular landmarks of different types (heterochromatin, ribosomal DNA, telomeric sequences, transposable elements, tandemly repeated DNA) and sizes (ranging from small genomic blocks to entire chromosome sets). This chapter describes the above mentioned karyotypic features and discusses their variation and evolutionary trends within angiosperms with respect to, for instance, their phylogenetic distribution and significance, directionality of chromosome number changes, or the nature and function of genetic elements involved in genome diploidization.