Ag-NOR chromosomal association patterns in Rattus rattus (Rafinesque, 1814) and Rattus norvegicus (Berkenhout, 1796) from the southern Iberian peninsula

A high frequency of satellite association phenomena in a number of specimens of Rattus rattus and R. norvegicus, captured on the coastal fringe of Málaga province (Southern Spain), was found. Only Ag-NOR bearing chromosomes participated in associations in both species. R. rattus is characterized by 14/18 heterologous and R. norvegicus by 5/5 and 13/13 homologous association types.