Chromosomal description of the rodent generaOecomys andNectomys from Brazil

We analysed karyotypes of five taxa of the rodent generaOecomys andNectomys, trapped in 14 localities in an area ranging from 8° to 29°S on Brazilian territory.Oecomys cf.concolor, collected in the Amazon and in two localities of the Cerrado biome, showed a 2n=60 karyotype constituted by a pair of large subtelocentric chromosomes, a small metacentric pair and 27 acrocentric pairs. The X chromosome was a large submetacentric and a subtelo-submetacentric, the morphology of the latter showing variable C-banding patterns. In all three localities the Y chromosome was a medium size heterochromatic acrocentric. Two individuals from the Cerrado had a heterochromatic acrocentric B-chromosome.Oecomys cf.bicolor presented two cytotypes, 2n=80 in the specimens from the Cerrado biome and 2n=82 in individuals trapped in the Amazon. The 2n=80 cytotype 1 showed a large subtelocentric, 22 biarmed pairs (medium to small) and 16 acrocentric autosomal pairs. The karyotype of the 2n=82 cytotype 2 is constituted by 15 biarmed chromosomes (median to small) and 25 acrocentric pairs with heterochromatic blocks at pericentromeric regions. The sexual pairs were the same (large submetacentric X and median acrocentric Y) in both cytotypes. InO. cf.concolor and in both cytotypes ofO. cf.bicolor the nucleolar organizer regions were observed in 1-3 pairs, located in the short arms.Nectomys genus presented two cytotypes, 2n=52–55 (N. rattus, with 0–3 biarmed heterochromatic accessory chromosomes) and 2n=56–59 (N. squamipes, bearing 0–3 biarmed, heterochromatic, B-chromosomes). These 2 cytotypes occupy disjunct regions of South America, with overlapping areas in the Brazilian states of Pernambuco, Bahia, and Mato Grosso do Sul.     

G-, R- and C-band patterns of goral (<Emphasis Type="Italic">Nemorhaedus caudatus</Emphasis>) and comparison to goat (<Emphasis Type="Italic">Capra hircus</Emphasis>)

The karyotype of goral (Nemorhaedus caudatus, 2n = 56) was prepared using lymphocytes and its chromosomal band patterns were compared with those of goat (Capra hircus, 2n = 60) by CBG-, GTG- and RBG-banding techniques. The standard karyotype of goral was composed of 54 acrocentric autosomes, submetacentric X chromosome, and acrocentric Y chromosome. C-bands were prominent in all autosomes except the X chromosome. G- and R-band patterns of goral were dissimilar to those of goat. The data support the idea that the goral did not originate from a common ancestor of bovid, or that there were numerous complicated chromosomal interchanges during goral evolution, in contrast to other bovids.     

Supernumerary chromosomes,Robertsonian rearrangement and variability of the sex chromosomes inNectomys squamipes (Cricetidae,Rodentia)

Chromosomes were analyzed in 91 specimens ofNectomys squamipes, collected in three distinct geographic regions of Brazil. Chromosomal polymorphism due to supernumerary chromosomes, Robertsonian rearrangement and variation of sex chromosomes is reported. Samples collected in the northeastern region had 2n=52, FN=52; 2n=53, FN=54; 2n=54, FN=56; 2n=55, FN=56; 2n=56, FN=56; 2n=57, FN=57. The specimens from the southeastern and southern regions showed 2n=55, FN=56; 2n=56, FN=56; 2n=57, FN=58; 2n=58, FN=60; 2n=59, FN=62. Seven different types of supernumeraries were observed. These vary in size, morphology and C-banding characteristics.The Brazilian populations ofNectomys squamipes are composed of at least two basic entities, one with 2n=52 and its increasing series up to 2n=55, the other with 2n=56, increasing to 2n=59. Both entities are characterized by variation from 0 to 3 supernumeraries. The X and Y chromosomes present polymorphisms in terms of the size, shape as well as the distribution of constitutive heterochromatin.This research was supported by CNPq-PIG (Projeto Integrado de Genética) and is part of the Rodent Cytogenetic Colaborative Study, developed by different Laboratories in Brazil.     

Chromosomes of five artiodactyl mammals

Somatic chromosomes of six specimens belonging to the following five species of artiodactyls (Artiodactyla: Mammalia) are described: A female nilgai (Boselaphus tragocamelus), 2n=46; male baresingha (Rucervus duvauceli), two specimens, 2n=56; a female Himalayan tahr (Hemitragus jemlahicus), 2n=48; a female Kirk's dik-dik (Rhynchotragus kirki), 2n=46; and a male sambar (Cervus unicolor), 2n=58. In the baresingha and the sambar, one or more acrocentric chromosomes carried satellites on their long arms. ³H-thymidine radioautographs of cultured cells of the Himalayan tahr showed a long acrocentric chromosome to be late-replicating, suggesting that it is an X chromosome.     

Constitutive heterochromatin variation in two species of rattus with apparently similar karyotypes

Rattus blanfordi and R. cutchicus medius both have a chromosome complement of 2n=36 and all chromosomes except the submetacentric Y of R. blanfordi are acrocentric. The apparently similar karyotypes of the two species, however, show variations in the nature and quantity of C-band-positive constitutive heterochromatin (C-heterochromatin) as revealed by C- and G-banding and Hoechst 33258 fluorescence. R. blanfordi with large-sized X and Y chromosomes and conspicuously larger centromeric heterochromatin in all the autosomes as compared to that of R. cutchicus medius has much more C-heterochromatin in its genome than the latter. The variation in the quantity of C-heterochromatin has been accomplished without altering the morphology of the acrocentric chromosomes unlike other mammals in which variations have been reported to result generally in the addition or deletion of a totally heterochromatic second arm.     

Cytogenetic characterization and description of an XX/XY1Y2 sex chromosome system in catfish Harttia carvalhoi (Siluriformes, Loricariidae)

Karyotypic and cytogenetic characteristics of catfish Harttia carvalhoi (Paraíba do Sul River basin, S?o Paulo State, Brazil) were investigated using differential staining techniques (C-banding, Ag-staining) and fluorescent in situ hybridization (FISH) with 18S and 5S rDNA probes. The diploid chromosome number of females was 2n = 52 and their karyotype was composed of nine pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric and four pairs of acrocentric chromosomes. The diploid chromosome number of males was invariably 2n = 53 and their karyotype consisted of one large unpaired metacentric, eight pairs of metacentric, nine pairs of submetacentric, four pairs of subtelocentric, four pairs of acrocentric plus two middle-sized acrocentric chromosomes. The differences between female and male karyotypes indicated the presence of a sex chromosome system of XX/XY1Y2 type, where the X is the largest metacentric and Y1 and Y2 are the two additional middle-sized acrocentric chromosomes of the male karyotype. The major rDNA sites as revealed by FISH with an 18S rDNA probe were located in the pericentromeric region of the largest pair of acrocentric chromosomes. FISH with a 5S rDNA probe revealed two sites: an interstitial site located in the largest pair of acrocentric chromosomes, and a pericentromeric site in a smaller metacentric pair of chromosomes. Translocations or centric fusions in the ancestral 2n = 54 karyotype is hypothesized for the origin of such multiple sex chromosome systems where females are fixed translocation homozygotes whereas males are fixed translocation heterozygotes. The available cytogenetic data for representatives of the genus Harttia examined so far indicate large kayotype diversity.     

Cytogenetic study on Microtus guentheri (Danford and Alston, 1880) (mammalia: rodentia) from Turkey: constitutive heterochromatin distribution and nucleolar organizer regions

Conventionally stained, C- and Ag-NOR banded karyotypes of Guenther's vole, Microtus guentheri were studied from Turkey. The species possesses a karyotype of 2n = 54, NFa = 52 and NF = 54 in specimens from Kahramanmara? and Gaziantep provinces, whereas NF = 56 in females and NF = 55 in males were found in individuals from Kirikkale and Nev?ehir provinces. The X chromosome was a large acrocentric (NF = 54) or submetacentric (NF = 55, 56) while the Y chromosome was a small telocentric in all specimens examined. Blocks of constitutive heterochromatin were located in the pericentromeric areas of autosomes including the X chromosome. Nucleolar organizer regions (NORs) were located at the telomeric regions of the short arms of five acrocentric pairs and centromeric regions of two telocentric pairs in the Nev?ehir and Kirikkale specimens.     

Karyotype, centric fusion polymorphism and chromosomal aberrations in captive-born mountain reedbuck (Redunca fulvorufula)

Chromosomes of fourteen captive-born mountain reedbucks (Redunca fulvorufula) have been investigated. The diploid chromosome number was 2n = 56 (FN = 60). The mountain reedbuck karyotype consists of 26 acrocentric and two biarmed chromosome pairs resulting from two centric fusions involving chromosomes 2 and 25, and 6 and 10, respectively. In some animals, 57 chromosomes were detected. Variation in the diploid number was found to be due to polymorphism for the centric fusion 6;10. Both X and Y chromosomes are large and acrocentric. The entire Y chromosome and the proximal part of the X chromosome consist of heterochromatin. The chromosomes X, 9 and 14 appeared to be of caprine type. Chromosome aberrations have been detected in two of the 14 animals investigated. A de novo formed Robertsonian translocation rob(6;13) was found in one female heterozygous for the fusion 6;10. CBG-banding revealed one block of centromeric heterochromatin in the de novo formed translocation rob(6;13) and also in the evolutionarily fixed centric fusions 6;10 and 2;25. One examined male homozygous for fusion 6;10, had a mosaic 56,XY/57,XYY karyotype, with 11% of analyzed cells containing two Y chromosomes. The findings were confirmed by cross-species fluorescence in situ hybridization (FISH) with bovine (Bos taurus L.) chromosome painting probes. The study demonstrates the relevance of cytogenetic screening in captive animals from zoological gardens.     

Genetic studies in representatives of genusRhipidomys (Rodentia, Sigmodontinae) from Brazil

Karyotypic polymorphism of five taxa of the rodent genusRhipidomys from the Brazilian Amazon and Cerrado biomes was analysed.Rhipidomys nitela Thomas, 1901 from Amazon has 2n=48, FN=68. The other species, all have 2n=44, but can be separated into two groups, one with high FNs (76, 80) and the other with low FNs (48, 52). Two cytotypes ofR. mastacalis (Lund, 1840) with high FNs were trapped in four localities of the Cerrado, showing 19 and 17 biarmed autosomes, respectively. A low FN (48) was observed inR. leucodactylus (Tschudi, 1844) in two localities of the Cerrado and FN=52 in one locality in the Cerrado and the Amazon. All taxa with 2n=44 have a medium-sized acrocentric X chromosome and a small Y.Rhipidomys nitela is different from the species with 2n=44 by presenting a heterochromatic short arm of the X chromosome. In all karyotypes analysed, the nucleolus organizer regions were located in the short arms of two to six pairs and the (T₂AG₃)_n telomeric probes hybridizedin situ in both the short and long arms of all pairs of the karyotypes.     

SOME PIECES OF THE AFRICAN GENOME PUZZLE IN HIBISCUS SECT. FURCARIA (MALVACEAE)

New chromosome counts are reported for four African diploid species of Hibiscus L. sect. Furcaria DC: H. greenwayi Bak. f., H. hiernianus Exell et Mendonça, and H. mechowii Garcke, n = 18; and H. berberidifolius A. Rich., 2n = 36. Chromosome behavior is described in seven new hybrid combinations. Hibiscus greenwayi is shown to carry an A genome. Hibiscus hiernianus and H. mastersianus have similar genomes which are not homologous with that of H. mechowii. New and earlier data are integrated to elucidate genome relationships among 13 taxa–each of the four tetraploid species has a different formula encompassing 2 of 6 mutually nonhomologous genomes, A, B, G, H, X and Y (H. acetosella Welw. ex Hiern = AABB; H. meeusei Exell = AAXX; H. sabdariffa L. = AAYY; H. rostellatus Guill. et Perr. = GGHH). Diploid donors of A, B, G, X and Y are proposed on the basis of plant, flower and pollen morphology. Diploid carriers of A (H. asper Hook. f., H. cannabinus L., H. greenwayi), B (H. surattensis L.) and G (H. sudanensis Hochr.) have been verified cytologically. Cytological confirmation of X (H. hiernianus, H. mastersianus Hiern) and Y (H. mechowii) carriers is incomplete. No putative diploid carrier of H is at hand. Genome affinities of H. berberidifolius are unknown.     

Comparative chromosome painting between two marsupials: origins of an XX/XY1Y2 sex chromosome system

Cross-species chromosome painting was used to investigate genome rearrangements between tammar wallaby Macropus eugenii (2n = 16) and the swamp wallaby Wallabia bicolor (2n = 10♀/11♂), which diverged about 6 million years ago. The swamp wallaby has an XX female:XY₁Y₂ male sex chromosome system thought to have resulted from a fusion between an autosome and the small original X, not involving the Y. Thus, the small Y₁ should represent the original Y and the large Y₂ the original autosome. DNA paints were prepared from flow-sorted and microdissected chromosomes from the tammar wallaby. Painting swamp wallaby spreads with each tammar chromosome-specific probe gave extremely strong and clear signals in single-, two-, and three-color FISH. These showed that two tammar wallaby autosomes are represented unchanged in the swamp wallaby, two are represented by different centric fusions, and one by a tandem fusion to make the very long arms of swamp wallaby Chromosome (Chr) 1. The large swamp wallaby X comprises the tammar X as its short arm, and a tandemly fused 7 and 2 as the long arm. The acrocentric swamp wallaby Y₂ is a 2/7 fusion, homologous with the long arm of the X. The small swamp wallaby Y₁ is confirmed as the original Y by its painting with the tammar Y. However, the presence of sequences shared between the microdissected tammar Xp and Y on the swamp wallaby Y₂ implies that the formation of the compound sex chromosomes involved addition of autosome(s) to both the original X and Y. We propose that this involved fusion with an ancient pseudoautosomal region followed by fission proximal to this shared region. Received: 16 October 1996/Accepted: 30 January 1997     

A note on chromosomes of two species of tree shrews (Tupaiidae)

Karyological studies of five tree shrews showed a diploid number 2n=60 forTupaia glis and 2n=66 forTupaia minor. The Y chromosome ofTupaia glis was found to be a medium-sized submetacentric chromosome in contrast to earlier data in the literature. The karyotype of a femaleTupaia minor showed five pairs of metacentric and submetacentric chromosomes and 28 pairs of acrocentric chromosomes.     

The founder effect theory: quantitative variation and mdg-1 mobile element polymorphism in experimental populations of Drosophila melanogaster

The chromosomes of 14 specimens of the genus Reithrodon from three different localities of Argentina and two localities of Uruguay were studied using G-and C-banding techniques. Specimens of Uruguay showed a karyotype of 2n=28 chromosomes having a large metacentric X, and a telocentric Y chromosome. This karyotype is very similar to that recently described in a sample from southern Brazil, differing only in the nature of the Y chromosome, which is metacentric in the Brazilian form. All specimens from Argentina showed a 2n=34 karyotype, differing from the Brazilian karyotype by two centric fusions, an acquisition of chromosome material, and at least one pericentric inversion, and by the telocentric nature of both the X and the Y chromosomes. G-and C-banding suggest that the metacentric gonosomes in the Brazilian form resulted from a double autosomal-X-Y Robertsonian translocation. The Uruguayan cytotype is interpreted as derived from a hypothetical neo-X/Y₁Y₂ ancestral form by the secondary loss of the Y₁ chromosome. The karyotypic differences between the Brazilian-Uruguayan and the Argentinian forms afford evidence of species differentiation. It is proposed to assign the former to Reithrodon typicus, and the later to R. auritus.     

Comparative cytogenetics of the African elephant (Loxodonta africana) and Asiatic elephant (Elephas maximus)

G- and C-banded karyotypes of the two extant species of the mammalian order Proboscidea are presented for the first time. Chromosome complements were 2n = 56 in both Loxodonta africana and Elephas maximus. Comparisons between the species demonstrated a high level of chromosome band homology, with 26 conserved autosomal pairs. The normal diploid karyotype of L. africana had 25 acrocentric/telocentric and two metacentric/submetacentric autosomal pairs. E. maximus differed by having one less acrocentric and one additional submetacentric pair due to either a heterochromatic arm addition or deletion involving autosomal pair 27. Several acrocentric autosomes of L. africana exhibited small short arms that were absent in homologous chromosomes of E. maximus. The X chromosomes in both species were large submetacentric elements and were homologous. However, the small acrocentric Y chromosomes differed; in E. maximus it was slightly larger and had more distinct G-bands than its counterpart in L. africana. Extant Elephantidae appear to be relatively conservative in their rates of chromosomal change compared to some other mammalian families. The high-quality banded karyotypes presented here should prove useful as references in future chromosome analyses of elephant populations and in comparative cytogenetic studies with other ungulate orders.     

A remarkable autosomal heteromorphism in Pseudoryzomys simplex 2n = 56; FN = 54–55 (Rodentia,Sigmodontinae)

Pseudoryzomys simplex, the false rice rat, is a monotypic genus of the Oryzomyini tribe (Sigmodontinae) distributed in part of Bolivia, Paraguay, Argentina and Brazil. Its diploid number has been described as 56 acrocentric chromosomes decreasing in size and no karyotype figure has been depicted. Herein, we present karyotypic data on P. simplex, including chromosome banding and molecular fluorescent in situ hybridization using telomeric sequences and the whole X-chromosome of its sister clade Holochilus brasiliensis (HBR) as probes. A case of remarkable autosomal heteromorphism due to the presence of a whole heterochromatic arm leading to the variability of FN is reported, as well as the occurrence of regions of homology between the X and Y chromosomes (pseudoautosomal regions) after chromosome painting with the HBR X probe on P. simplex metaphases.     

A multiple sex-chromosome system in Antarctic ice-fishes

Summary We have studied the chromosomes of 11 of the 15 known species of the notothenioid family Channichthyidae, the specialized whiteblooded Teleosts endemic to the Southern Ocean (ice-fishes). In the female sex, all studied species have the same diploid number of forty eight mostly acrocentric (uniarmed) chromosomes; however there is an interspecific variability in the chromosome morphology, type and quantity of repetitious DNA (usually seen as heterochromatin) localization of silver-stained nucleolar organizers. At least five of the studied species show a multiple sex-chromosome system possibly originated by the translocation of an autosome on an early Y gonosome morphologically similar to the X: the digametic males (2n = 47) show a X₁Y X₂ and the homogametic females (2n = 48) a X₁X₁X₂X₂ gonosomic constitution. This peculiar sex determining mechanism, otherwise rare in Teleosts, can be considered apomorphic in the same way as other morphofunctional characters usually interpreted as adaptive in these fishes.Some of the data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

A new karyotype in Callicebus torquatus (Cebidae, Primates)

We describe a new karyotype of Callicebus torquatus using conventional staining, G-banding with Wright Stain, CBG, Ag-NOR staining and fluorescence in situ hybridization (FISH) with human telomere probes and comparative analysis with the previously reported karyotype of C. torquatus torquatus (2n = 20). We studied a female specimen maintained in captivity at the Centro Nacional de Primatas (Para, Brazil). This titi monkey presented 2n = 22, with four large biarmed and six acrocentric autosome pairs; the X chromosome is a medium submetacentric. C-bands were revealed at the centromeric region of all acrocentrics and X chromosome; punctual C-bands also are visualized at the centromeric region in the large biarmed pairs. The NOR site was located at the long arm of pair 4, at the position of a conspicuous secondary constriction. Hybridization signals were detected exclusively at the terminal region of all chromosomes. The karyotype described here has one acrocentric pair more than that found in the literature and also differs by amount and distribution of constitutive heterochromatin. Our data support the notion that the torquatus group may be composed of distinct species, each with its own karyotype.     

A new allopatric lineage of the rodent Deltamys (Rodentia: Sigmodontinae) and the chromosomal evolution in Deltamys kempi and Deltamys sp

Deltamys Thomas 1917 is a poorly studied and rarely collected taxon of Akodontini (Sigmodontinae). The single described species, Deltamys kempi (DKE), has a basic karyotype with a diploid number of 2n = 37 in males and 2n = 38 in females, a fundamental number FN = 38 for both sexes, and an X(1)X(1)X(2)X(2)/X(1)X(2)Y sex determination system. Herein, a new allopatric form, Deltamys sp. (DSP), is reported, based on specimens from southern Brazil, with 2n = 40, FN = 40 and XX/XY sex chromosomes. We describe the karyotype and mechanism of chromosomal differentiation between both Deltamys complements. Phylogenetic analyses, based on the complete sequence (1,140 bp) of the mitochondrial cytochrome b gene, grouped Deltamys sp. as sister species to D. kempi, with up to 12% genetic divergence between them. The GTG-banding patterns show complete autosomal correspondence between D. kempi and Deltamys sp. and identify a tandem rearrangement involving DSP7, DSP19 and DKE4 that is responsible for the differences in 2n and FN. Chromosome painting with Akodon paranaensis chromosome 21 (a small metacentric akodont marker) paint revealed total homology with the smallest acrocentric Deltamys sp. chromosome, DSP19. This suggests the occurrence of a pericentric inversion or centromeric shift when compared to other akodontines, with a posterior tandem rearrangement giving rise to DKE4. In DKE, large blocks of pericentromeric constitutive heterochromatin are present on the autosomes and the X, and the Y/autosome has an entirely heterochromatic short arm. In DSP, small heterochromatic blocks are observed on autosomes and X, and the Y is a very small, mostly heterochromatic acrocentric. The cytogenetic analyses suggest that the Deltamys sp. karyotype is ancestral, with the derived condition resulting from a tandem fusion (DSP7 + DSP19) and the Y/autosome translocation giving rise to the multiple sex chromosome system. The autosomal rearrangements, the differences in CBG-banding patterns and Ag-NOR localization, as well as the presence of X(1)X(1)X(2)X(2)/X(1)X(2)Y and XX/XY sex determination mechanisms, possibly acting as a reproductive barrier, and the phylogenetic position within the Deltamys genus, with high genetic divergence, call for a taxonomic review of the genus.     

Polyploidy and new chromosome counts in Anaphalis (Asteraceae: Gnaphalieae) from the Qinghai‐Tibet Plateau of China

Abstract Anaphalis is one of the largest genera of the Asian Gnaphalieae (Asteraceae) and is most diversified on the Qinghai‐Tibet Plateau. The chromosome numbers and karyomorphology of six species from seven populations were investigated for the first time for this region. Chromosome numbers have been newly documented for four species: Anaphalis deserti (2n = 56 = 24 median [m]+ 24 submedian [sm]+ 8 acrocentric [st]); Anaphalis plicata (2n = 56 = 26m + 30sm); Anaphalis xylorhiza (2n = 28 = 2 median point [M]+ 14m + 12sm); and Anaphalis rhododactyla (2n = 56 = 32m + 24sm). Two further counts are in agreement with the previously reported numbers, that is, Anaphalis royleana (2n = 28 = 4M + 6m + 18sm) and Anaphalis margaritacea (2n = 28 = 12m + 16sm). A new polyploid cytotype (2n = 56 = 26m + 30sm) was found in the Zougong population of A. margaritacea. Polyploidy is for the first time reported for Anaphalis, with four out of seven counts being tetraploid. Our cytological results suggest that polyploids might have played an important role in the evolution of Anaphalis on the Qinghai‐Tibet Plateau.     

Unusual C-band patterns in three karyotypically rearranged forms of Scapteromys (Rodentia, Cricetidae) from Brazil

Chromosome studies of 30 specimens of the rodent Scapteromys collected at nine localities in southern Brazil revealed the occurrence of three karyotypic taxa with 2n = 36 (one locality), 34 (two localities), and 24 (six localities), although all three had 40 autosomal arms (AN). The G-band analysis indicated that this reduction in diploid number was mainly due to Robertsonian translocations which have occurred along a gradient, possibly in two independent evolutive routes. The C-bands occur on one autosomal pair and on the X and Y in the 2n = 36 and 34 forms and on the X and Y chromosomes only in the 2n = 24 taxon. The broad genomic reorganization which has occurred in this genus, in which the chromosomes do not have large amounts of constitutive heterochromatin, argues against the idea that a large amount of constitutive heterochromatin favors chromosome evolution and speciation.