How does the genome arise and give origin to new species? This is our central question. The genome are variable in size, mainly in plants. But, what does give this difference in size of genomes? The answer to this question reside on repetitive sequences. There are many kind or families of repetitive sequences. They can be organized on in tandem or dispersed sequences. In the first we can find the satellite DNAs and in the second the retroelements, mainly. At least 95% of the genome are composed by these sequences and as a result, they are the major components of the chromosomes. Each species contain a specific number of chromosomes and moreover each chromosome has a morphology resulted of the centromere position. The characterization of the chromosomes morphology of a species result in the karyotype, that can be compared among related species and determine how the evolution has affected their structure. So, a species is characterized by the karyotype and it is a synonymous of genome.

In our group we have applied molecular cytogenetic techniques to study these aspects of karyotype evolution in the speciation process. Firstly, we are characterizing the karyotype structure by classic cytogenetics processes, measuring the chromosomes by morphometric analysis and obtaining the maps called idiogram. Hereafter, in the idiogram we can plot the positions of the sequences mapped through fluorescent in situ hybridization (FISH). To help us in the localize the heterochromatin (a repetitive sequence rich structure) we have used fluorocrome staining techniques and an idea about the AT or GC richness of the region can be inferred. The physical mapping of the rDNA genes by FISH has give us a major view about the alterations of the karyotypes during the evolution.