EVOLUTIONARY CHANGE AT THE 5S-DNA LOCI OF SPECIES IN THE TRITICEAE

Previous studies have shown that two separate loci for 5S DNA sequences may exist within a species. Two size classes have been tentatively assigned in the ranges 327-468 bp (chromosome 1), and 469-500 bp (chromosome 5) and the entire data-base was subjected to various numerical taxonomic analyses. The results confirm the existence of two lineages of 5S DNA sequences represented by the two size classes. Hordeum vulgare is separate from the species known also as Critesion and, together with Dasypyrum, occupy an intermediate position between the two size classes. The 5S DNA units from Triticum spp. that have also been named Aegilops spp. in other classifications appear as a distinct group within Triticum spp. at both loci. The consensus 5S DNA sequence from Psathyrostachys is remote from Hordeum s.l. in contrast to opinions based on morphology. Other aspects are detailed and discussed, including the inadequacy of the computing methods used as well as the need for more data in view of the large amount of homoplasy. The merit of using the spacer for phylogenetic inference is also discussed.