Gene mapping of 28S rDNA sites in allotriploid Cobitis females (Pisces: Cobitidae) from a diploid-polyploid population

We performed cytogenetic analysis on triploid Cobitis hybrid specimens from a natural diploid-polyploid population in the Bug River (Poland). Chromosomes were examined by fluorescence in situ hybridization method (FISH) with 28S rDNA as a probe. The rDNA sites were commonly identified in the terminal position of p arms of two small submetacentric chromosomes, in the centromere area of two acrocentric chromosomes and in the terminal position of q arm of one acrocentric chromosome. Some of the observed signals were stronger than others. In few cases, one small acrocentric chromosome showing rDNA sites located terminally on both p and a q arm was observed. This study brings useful information about polymorphism of 28S rDNA sites regarding their number, location and size in triploid specimens. Moreover, it gives preliminary data for comparison with similar researches on the parental species of Cobitis hybrid females, viz. C. taenia, C. taurica and C. tanaitica , and other related Cobitis taxa of different ploidy level. The present study increases our knowledge about ribosomal genes inheritance between Cobitis species and their polyploid hybrids.