Cytotaxonomy: The end of childhood

Abstract

Detailed comparative karyotype analyses have proved to be an important tool for taxonomy and for understanding chromosome evolution. The basic principle of cytotaxonomy is that closely related species share a more similar karyotype than less related ones. However, phylogenetic studies have demonstrated that some karyotype features are more often recurrent than previously thought, meaning that similarity is not all. Two other criticisms to the cytotaxonomical interpretation are intraspecific variation, traditionally neglected, and the interpretation of chromosomal alterations based only on classical structural changes, without any investigative support. Chromosome numbers and nuclear DNA content are among the most reliable and practical characters for cytotaxonomical analyses involving a large number of species, whereas chromosome mapping with molecular probes is more recommended for a restricted number of species. In both cases, a robust phylogenetic tree is necessary to understand the relationships between species and their karyotype evolution. Evolutionary inferences based only on putative karyological trends are no longer sustainable.

Keywords:

• Basic chromosome numbers
• holokinetic chromosomes
• karyotype
• rDNA sites
• plant cytotaxonomy
• polyploidy

Acknowledgments

The author wishes to thank the Brazilian agency CNPq for financial support, and Liliane Dantas and André Marques for improving the English of the manuscript.