Pellicer and colleagues made an interesting observation that the rDNA loci were reduced in numbers in one group of Artemisia polyploids (Euroasian) while they were additively inherited from parents in another polyploids of New World origin. I wonder whether the different age of polyploids may account for this dramatical difference in the level of rDNA homogenisation. For example, American polyploids could be of more recent orgin compared to those of Euroasian. Loss of rDNA loci/copies might depedent on the time spent in the polyploid nucleus. There is some support for this hypothesis coming from evolutionary studies in Nicotiana allopolyploids (Clarkson et al.: New Phytologist 168: 241–252, 2005; Kovarik et al.: Biological Journal of Linnean Society 82: 615-625, 2004).Regards.Ales:-)

Article FISH mapping of 35S and 5S rRNA genes in Artemisia subgenus ...