(T(2)AG(3))(n) telomeric sequence hybridization suggestive of centric fusion in karyotype marsupials evolution

It has been suggested that the karyotype of the marsupials derived from a l ow diploid number (2n = 14) which originated, through fissions of biarmed c hromosomes, the karyotypes with a higher 2n. The telomeric sequence (T(2)AG (3))(n) was in situ hybridized to the chromosomes of Gracilinanus microtars us and G. emiliae, Micoureus demerarae and Marmosa murina, species with 2n = 14, in Monodelphis sp., M. domestica, M. kunsi and M. brevicaudata with 2 n = 18, and Lutreolina crassicaudata, Didelphis albiventris, Chironectes mi nimus, Philander opossum and P. frenata, all of them with 2n = 22. The prob e hybridization occurred in the telomeric regions of both arms, short and l ong, of all chromosomes of the complement of all individuals of all species analysed. However, in some pairs of the karyotypes of Gracilinanus microta rsus and Micoureus demerarae (with 2n = 14), and in Monodelphis sp., M. dom estica, M. kunsi and M. brevicaudata (2n = 18) ectopic signs of hybridizati on were detected proximal to the centromeres, suggesting the retention of t his telomeric sequence in the centromeric regions of some chromosomes of th ese species. Based on these results, it is proposed that the karyotype of m arsupials evolved from a 2n = 22 to a 2n = 14, by means of chromosomal fusi ons.