Chromosomal polymorphism caused by supernumerary chromosomes in Rattus rattus ssp. frugivurus (Rafinesque, 1814) (Rodentia, Muridae).

A chromosomal numeric polymorphism 2n = 38, 39, 40 and 41 in the species Rattus rattus ssp. frugivurus (Rafinesque, 1814) is reported for the first time for this subspecies. The numbers 2n = 39, 40 and 41 are new for the species. The polymorphism is due to the presence of 1, 2 or 3 B-chromosomes, which are all small metacentrics of the size and shaped vary close to the other autosomes of the normal complement, and whose character of being supernumeraries is shown in Meiosis.