Differential repeat accumulation in the bimodal karyotype of Agave L.

Bimodal karyotypes have an ancient origin and are one of the most successful lines of chromosomal evolution, believing that the conservation of this type of karyotype, conserving the different chromosomal types, may be related to adaptive mechanisms. Differences in chromatin distribution and gene concentration between different chromosome types found in several species with bimodal karyotypes, show that the genomic structure is more complex than previously observed. Characterization of this genomic structure and the dynamics of DNA sequences within and between different chromosomal types may help to elucidate phylogenetic relationships between species with and without bimodal karyotypes within taxonomic groups. In addition, it may also contribute to the identification of the evolutionary mechanisms that reorganize the genomes that led to this particular and successful type of karyotypic and genomic structure. The genus Agave presents a bimodal karyotype with x = 30 (5L+25S). Bimodality within this genus is generally attributed to allopolyploidy in the ancestral of Agavoideae. However, alternative mechanisms, such as the preferential accumulation of repetitive elements at the macrochromo-somes, could also be important. The aim is to understand the role of repetitive DNA within the bimodal karyotype of Agave.