ABSTRACT
The chromosome complement of the genus Aloe has long been considered to be exceptionally stable. All species have a single basic chromosome number (x=7) and a large, strongly bimodal karyotype always comprising three short chromosomes and four much longer ones in the haploid set. Nevertheless, major and minor changes in chromosome morphology occur frequently, together with a two-fold range of interspecific variation in overall nuclear DNA amount, with the low values in primitive species. Polyploidy is now known to be more frequent than was believed earlier, with a record of triploidy (2n=21) and several of tetraploidy (2n=28) added recently to the single well-known example of hexaploidy in the genus (2n=42). The evolutionary significance of these numerical and structural changes in the chromosomes of Aloe will be discussed in this chapter.
