Chromosome breaks and translocations mold the trimodal karyotype of a hexaploid population of Milla biflora (Asparagaceae) from Reserva Ecológica del Pedregal de San Ángel, Distrito Federal, Mexico

Abstract

Thirty individuals from one population of Milla biflora from Reserva Ecológica del Pedregal de SanÁngel, Distrito Federal, Mexico were sampled to analyze the architecture and behavior of mitotic chromosomes inmeristematic root cells. The use of the splash technique allowed the corroboration of the chromosome number 2n=6x= 42 (x= 7), and to propose the karyotype formula (6m+24sm+12st), to obtain the total haploid chromosome length(106.92 μm) mean chromosome size (5.09 μm) and chromosomal length range (2.54-9.07 μm). The asymmetry index(TF%= 32.45) correspond to asymmetric karyotype exhibiting 3 differentiated chromosomal types by their shape andsize (trimodal). The NOR regions were associated to st chromosomes bearing a secondary constriction and satellite.Chromosome fragments and heterochromosomes show an active mechanism of chromosomal rearrangements thatmold the karyotype of M. biflora and play an important role in the evolution of the species. Its autohexaploide originis discussed in function of the presence of chromosome subgroups, absence of nucleolar dominance and the role ofgene redundancy.