In genotype CFRA 157, five of the six 5S rDNA sites
are co-localized with 25S rDNA sites, which means loss
of one 25S rDNA site (if the latter hypothesis discussed
above is true) has occurred on one of the six “doublemarked”
chromosomes and the second one on a “singlemarked”
chromosome. These two chromosomes could
not be homologs, suggesting that elimination of 25S
rDNA sites could occur simultaneously on non-homologous
chromosomes. Therefore, in species with a high
site number, loss of rDNA copies could proceed very quickly simply because there are many opportunities for
occurrence of this event. This speculation gains support
from the cases of octo- and deca-ploid strawberries, in
which eight 5S and twenty-four 25S rDNA sites, and ten
5S and thirty 25S rDNA sites, respectively, would be
expected but much less are actually observed.