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Comparative studies among four species--Akodonazarae (2n = 38), A. lindberghi (2n = 42), A. paranaensis (2n = 44) and A. serrensis (2n = 46)--employing classic cytogenetics (C- and G-bands) and fluorescence in situ hybridization with telomeric (TTAGGG)n sequencesare reported here. Non-telomeric signals in addition to the regular telomeric sites were detected in three species:A. azarae, A. lindberghi and A. serrensis. One interstitial telomeric site (ITS) was observed proximally at the long arm of chromosome 1 of A. azarae. The comparison of G-banding patterns among the species indicated that the ITS was due to a tandem fusion/fission rearrangement. Non-telomeric signals of A. lindberghi and A. serrensis were not related to chromosomal rearrangements; instead, the sequences co-localized with (i) heterochromatic regions of all chromosomes in A. serrensis; (ii) some heterochromatic regions in A. lindberghi, and (iii) both euchromatic and heterochromatic regions in the metacentric pair of A. lindberghi. These exceptional findings revealed that ITS in Akodon can be related to chromosomal rearrangements and repetitive sequences in the constitutive heterochromatin and that the richness of TTAGGG-like sequences in the euchromatin could be hypothesized to be a result of amplification of the referred sequence along the chromosome arms., (Copyright 2006 S. Karger AG, Basel.)

In this article we review the existing cytogenetic information on the polymorphic dot-like chromosomes in Trinomys iheringi, the only species in the family Echimyidae harboring them, and provide new data on the frequency, banding properties, meiotic behavior and DNA composition of these minute chromosomes. Since no individuals lacking these chromosomes have hitherto been found, one of the main properties of B chromosomes, i.e. dispensability, has not yet been tested, so that some reasonable doubt might exist on whether they are true B chromosomes. The dot-like chromosomes were also present in the twelve new individuals analyzed, showed intraindividual variation in number, most likely due to mitotic instability during development, failed to show C-bands, showed late-replication, paired among them in meiosis, but not with the large chromosomes, and appeared to be mainly composed of telomeric DNA. These results suggest that these dot-like chromosomes might actually be mitotically unstable micro B chromosomes showing very high frequency in the natural populations thus far analyzed. But, to be confident of this conclusion, individuals lacking the dot-like chromosomes should actively be searched in future research to test their dispensability., (Copyright 2004 S. Karger AG, Basel)

The karyotypes of the bat species Molossus ater, M. molossus (2n = 48; NF = 64) and Molossops planirostris (2n = 34; NF = 60) were analyzed by G-, C-banding, silver nitrate staining (AgNO3), base-specific fluorochromes and fluorescent in situ hybridization (FISH). The two species of Molossus presented the constitutive heterochromatin (CH) in the pericentromeric regions of all autosomes and in the X chromosome, while the Y chromosome was completely heterochromatic. Molossops planirostris showed conspicuous CH blocks in the pericentromeric regions of the pairs 4, 5, 8, 15, 16 and in the short arm of the X chromosome, while the Y did not present any CH block. Pretreated slides for C-banding stained with DAPI (CB-DAPI) revealed a similar pattern of C-banding (CBG) for these species. Sequential staining (AgNO3/CMA3/DAPI) in M. planirostris showed that the nucleolus organizer regions (NORs) are weakly CMA3 positive and DAPI negative. In the three species, triple staining with CMA3/DA/DAPI revealed R-banding with CMA3 and uniform staining with DAPI. The ribosomal cistrons detected by FISH were present only in the pair 5 in both species of Molossus, and in two pairs of medium sized chromosomes (pairs 9 and 10) of Molossops planirostris. The results obtained by FISH, compared with those by AgNO3 staining, indicated that all NORs in these species are transcriptionally active.

This paper provides new data on chromosomes of Brazilian vampire bats Desmodus rotundus and Diphylla ecaudata. These species were analyzed by GTG, CBG- and CB-DAPI banding, AgNO3/CMA3 sequential staining, base-specific fluorochrome dyes and in situ hybridization with 18S rDNA probe. C-banding (CBG) revealed constitutive heterochromatin in the pericentromeric regions in all autosomes and the X and Y chromosomes appeared entirely heterochromatic in both species. CB-DAPI revealed a coincident banding pattern to that obtained by CBG. Triple staining CMA3/DA/DAPI revealed an R-banding and a weak G-banding pattern in the karyotypes. Sequential AgNO3/CMA3 staining showed a NOR located interstitially on the long arm of pair 8 in D. rotundus and on the short arm of pair 13 in D. ecaudata. FISH with a rDNA probe confirmed the location and number of NORs; a difference neither in intensity nor in size of hybridization signal was detected between homologues for both species.

Akodon cursor is an exceptional example of high chromosomal variability, displaying diploid numbers from 14 to 16 and fundamental numbers (FN) from 18 to 26 as the result of a complex rearrangement in par 1 and pericentric inversions in three autosomal pairs. The difference in the diploid number is due to the presence of a large metacentric pair 1 in the 2n=14 karyotype, a large metacentric 1 and two different submetacentrics (1a and 1b) in 2n=15 and 1a and 1b submetacentric pairs in homozygosis in the 2n = 16 karyotype. Chromosomes 1a and 1b share homology with the short and long arms of the large metacentric 1 respectively. In this paper, evidence based on fluorescence in situ hybridization (FISH) with telomeric sequences and G-banding indicates that pericentric inversions and fusion of chromosomes 1a and 1b are the probable rearrangements giving rise to the large metacentric 1.