G-banding homologies of some Australian rodents

G-banding comparisons of 26 species in 10 genera of three tribes of Australian rodents show that at least one representative of each of the three tribes has autosomal complements that are indistinguishable on G-banding, implying unusually high conservation of karyotypes. Three genera (Pseudomys, Notomys, and Mastacomys) are distinguished karyotypically by a reciprocal translocation, one genus (Uromys) by a tandem fusion, and one genus (Zyzomys) by a radically altered karyotype. The only other rearrangements identified from G-banding are pericentric inversions, all 12 of which involve breaks in the proximal area.     

Chromosomal homoeologies in hamster species of the genus Phodopus (Rodentia, Cricetinae)

The karyotypes of the two hamster species Phodopus sungorus and P. roborovskii were analyzed with several banding techniques and compared. The homoeologies found between all chromosomes led to the proposal of the most likely common ancestral karyotype of these two species. The differences in the karyotypes were found to be a result of seven independent centric fusions, three inversions, and one possible telomeric fusion, as well as changes in the quantity and DNA-base pair composition of the constitutive heterochromatin.     

Chromosomal evolution in the Brazilian lizards of genus Leposoma (Squamata, Gymnophthalmidae) from Amazon and Atlantic rain forests: banding patterns and FISH of telomeric sequences

An extensive karyotype differentiation was found among three species of gymnophthalmid lizard genus Leposoma which occur in the tropical forest areas of Brazil. We examined the chromosomes of the Amazonic species L. guianense (LOU) and L. oswaldoi (LOS) and the Atlantic forest species L. scincoides (LSC) after conventional and differential staining, and FISH of telomeric sequences. Both Amazonic species shared very similar 2n = 44 karyotypes, including 20 biarmed macrochromosomes and 24 microchromosomes (20 M + 24 m). However, the location of Ag-NORs and the amount of constitutive heterochromatin differed in these karyotypes. The Atlantic forest species L. scincoides has a very distinct karyotype with 52 acrocentric and subtelocentric chromosomes of decreasing size. Comparative R-banding analysis revealed complete homeology of the macrochromosomes of LGU and LOS and correspondence of banding patterns between LSC acrocentrics and subtelocentrics and some arms of biarmed LGU and LOS chromosomes. Pair 1 had similar banding patterns in the three species, implying the occurrence of a pericentric inversion. Interstitial telomeric bands (ITBs) detected by FISH at the pericentromeric region of some biarmed LGU and LOS chromosomes could be remnants of chromosomal rearrangements occurred during the differentiation of the karyotypes. Robertsonian rearrangements as well as pericentric inversions events probable were involved in the karyotype evolution of these Amazon and Atlantic forests species of Leposoma.     

Autosomal and sex chromosomal polymorphisms with multiple rearrangements and a new karyotype in the genus Rhipidomys (Sigmodontinae, Rodentia)

Two diploid numbers and five karyomorphs were found in ten specimens of Rhipidomys (Sigmodontinae, Rodentia) from three states in Brazil: 2n = 50 from Amazonas, and 2n = 44 from Mato Grosso and Bahia. CBG, GTG, and RBG-banding and Ag-NOR analyses were performed, as well as fluorescence in situ: hybridization with (T2AG3)7 probes. The new diploid number of 2n = 50 was associated with two different fundamental numbers (FN = 71 and 72) as a result of pericentric inversions and addition/deletion of constitutive heterochromatin. The samples from two localities (Aripuan? and Vila Rica) in the state of Mato Grosso shared 2n = 44 and FN = 52, but their karyotypes differed because of pericentric inversions. Although the single specimen from Bahia had the same diploid number as the samples from Mato Grosso, its karyotype and FN were completely distinctive. Karyological comparison of GTG-banding patterns revealed total homology between the karyotypes of the specimens from Bahia and Mato Grosso, implying the occurrence of 14 autosomal pericentric inversions. Homologies between ten of the autosomes in the karyotypes with 2n = 50 (FN = 72) and 2n = 44 (from Vila Rica, MT) were demonstrated. The differentiation between 2n = 44 and 2n = 50 involved five pericentric inversions, addition/deletion of constitutive heterochromatin in both autosomes and sex chromosomes, at least one Robertsonian rearrangement and other not detected rearrangements. Despite the remarkable number of rearrangements, interstitial telomeric sites (ITS) were not detected. Sex chromosomes also exhibited polymorphism in size and morphology.     

Chromosomal homologies between Cebus and Ateles (primates) based on ZOO-FISH and G-banding comparisons

ZOO-FISH (Fluorescent "in vitro" hybridization) was used to establish the chromosomal homology between humans (HSA) and Cebus nigrivitatus (CNI) and Ateles belzebuth hybridus (ABH). These two species belong to different New World monkey families (Cebidae and Atelidae, respectively) which differ greatly in chromosome number and in chromosome morphology. The molecular results were followed by a detailed banding analysis. The ancestral karyotype of Cebus was then determined by a comparison of in situ hybridization results, as well as chromosomal morphology and banding in other Platyrrhini species. The karyotypes of the four species belonging to the genus Cebus differ from each other by three inversions and one fusion as well as in the location and amounts of heterochromatin. Results obtained by ZOO-FISH in ABH are in general agreement with previous gene-mapping and in situ hybridization data in Ateles, which show that spider monkeys have highly derived genomes. The chromosomal rearrangements detected between HSA and ABH on a band-to-band basis were 27 fusions/fissions, 12 centromeric shifts, and six pericentric inversions. The ancestral karyotype of Cebus was then compared with that of Ateles. The rearrangements detected were 20 fusions/fissions, nine centromeric shifts, and five inversions. Atelidae species are linked by a fragmentation of chromosome 4 into three segments forming an association of 4/15, while Ateles species are linked by 13 derived associations. The results also helped clarify the content of the ancestral platyrrhine karyotype and the mode of chromosomal evolution in these primates. In particular, associations 2/16 and 5/7 should be included in the ancestral karyotype of New World monkeys.     

Karyotype, C-banding, and Ag-NOR analysis in Diplodus bellottii (Sparidae, Perciforms). Intra-individual polymorphism involving heterochromatic regions.

A karyotype analysis was carried out in nine specimens of the Sparid species Diplodus bellottii using conventional staining, as well as C-banding and Ag-NOR banding techniques, showing, respectively, 2n = 46 and fundamental number (FN) = 54, and scarce heterochromatic areas irregularly distributed and up to four NOR active regions that were C positive. When compared with the karyotypes of other related species, one centric fusion giving rise to a large metacentric pair and several pericentric inversions seem to have been involved in the karyotype evolution. An intra-individual polymorphism was detected in one specimen, resulting in two karyotypic forms in roughly identical proportion, owing to a larger C-band by the NOR regions, appearing either in a terminal position of the short arms of pair 2 or in telomeric position of pair 3. These findings suggest that the extra heterochromatic segment responsible for the heteromorphism apparently only involves associated heterochromatin and not the NORs themselves. This C-positive block seems to have eventually been transferred between heterologous NOR chromosomes by a somatic event, facilitated by the physical proximity of NOR pairs in the nucleolus.     

Chromosomal evolution in Malagasy lemurs: X. chromosomal banding studies of Propithecus diadema edwardsi and Indri indri and phylogenic relationships between all the species of the Indriidae

The R-banded karyotypes of two Indriidae, Propithecus diadema and Indri indri, are described and compared with each other and with those of the other species of this family, previously reported, Avahi laniger and Propithecus verreauxi. These comparisons show that 30 chromosomal rearrangements, including 21 Robertsonian translocations and eight pericentric inversions, differentiate these karyotypes. A phylogenic diagram is proposed, showing the early separation of Avahi and the relatively late divergence of the three other species. A populational evolution has occurred between the three other species, but Indri is clearly separated from the two other species by at least five complex rearrangements, although it shares four Robertsonian translocations with P. verreauxi but not P. diadema.     

Chromosome polymorphism and C-banding variation of the brachypterous grasshopper Podisma sapporensis Shir. (Orthoptera, Acrididae) in Hokkaido, northern Japan

The grasshopper Podisma sapporensis consists of two main chromosome races in Hokkaido. The western group of populations of P. sapporensis, belonging to the XO race, has a diploid number of chromosomes 2n = 23 in the male and 2n = 24 in the female (sex determination XO male/XX female). The eastern group of populations of this species, belonging to the XY race, differs from the western one as a result of Robertsonian translocation between the originally acrocentric X chromosome and M5 autosome in homozygous state, having resulted in the forming of chromosome sex determination neo-XY male/neo-XX female (2n = 22). These races are geographically isolated by the mountainous system consisting of the Mts Daisetsu and Hidaka range, occupying the central part of the island. The hybrid zones between the races have not so far been discovered. Various levels of polymorphism for the pericentric inversions and C-banding variation exist in different chromosomes throughout populations in both chromosome races. In some solitary populations (the population at the summit of Mt Yotei, populations in the vicinity of Naganuma, Oketo, and Tanno) pericentric inversions are fixed in some pairs of chromosomes, which enables marking of the discrete karyomorphes. In the Mt Daisengen population all chromosomes are two-armed as a result of fixing the pericentric inversions. These facts contradict karyotypical conservatism of the tribe Podismini. The level of diversity of P. sapporensis karyotypes could provide a new perspective on the evolutionary process of different karyotype in Orthoptera. The considerable occurrence of polymorphism in chromosomes suggests that karyotypic diversification is undergoing in P. sapporensis. The authors also proposed that P. sapporensis would be divided into four chromosome subraces in the XO chromosome race and two chromosome subraces in the XY race, on the basis of karyotypic features. These races may have been established by fundamental climatic changes during the glacial epoch.     

Theoretical study of inversions affecting human chromosomes

A theoretical study of inversions affecting human chromosomes is proposed. Taking into consideration the number of bands and the fact that breaks occur at interfaces between bands, it is concluded that: 7.659 different pericentric inversions might be detected in a prometaphasic 802-band karyotype; this number decreases to 917 in a metaphasic 273-band karyotype; 8.607 and 862 different paracentric inversions might be detected in the same karyotypes respectively, but these results are likely to be overestimated. These theoretical data are used for showing that the pericentric inversions detected in human cytogenetic laboratories, are too frequently recurrent and are not distributed at random.     

Unusually extensive karyotype reorganization in four congeneric Gerbillus species (Muridae: Gerbillinae)

Comparative analysis of the G- and C-banding patterns in four morphologically poorly differentiated Gerbillus species (G. pyramidum, G. perpallidus, G. tarabuli and G. occiduus) was carried out. These gerbils have similar karyotype morphology with 2n and NF equal to 38/76, 40/76, 40/78 and 40/80, respectively. Our study revealed that possibly 70 Robertsonian (Rb) fusions, two pericentric inversions, one tandem translocation and at least 13 non-identified rearrangements have occurred during the karyotypic evolution of these species. The number of chromosomal changes by which any of these species differ from each other ranges from 33 to 49. One Rb fusion was common to two of the species, with only a single autosome-gonosome translocation shared by all four, suggesting a monophyletic origin of these karyotypically highly divergent species. Based on the chromosomal data obtained here, the systematic and geographic implications for these North African species are also discussed.     

Cytogenetic study of Cercopithecus wolfi, Cercopithecus erythrotis and a hybrid Cercopithecus ascanius X Cercopithecus pogonias grayi

The karyotypes of two species of Cercopithecus, C. wolfi and C. erythrotis, as well as that of a hybrid C. ascanius X C. pogonias grayi, are described and compared. The karyotype of C. erythrotis is similar to that of C. ascanius and C. cephus described previously. The karyotypes of C. wolfi and C. p. grayi differ by a single inversion. The karyotype of the hybrid shows that the two parental species differ by five rearrangements, three fissions and two inversions, an observation in agreement with our previous interpretation.     

Karyotype polymorphism in the cycad Zamia loddigesii (Zamiaceae) of the Yucatan Peninsula, Mexico

The cycad %amia loddigesii Miq. forms a morphologically variable complex on the Yucatan peninsula, Mexico. Several diploid chromosome numbers have been found in the species: In = 17, 24, 25, 26 and 27. Differing karyotypes and chromosome numbers were found in individuals of the same population and die karyotypes differ widely in numbers of metacentric and telocentric chromosomes present. Centrometric fission as well as pericentric inversions and unequal translocations are suggested to be the probable mechanisms for this karyotype variation. There appears to be a correlation between high chromosome number and increasing dryness of the habitats. Coupled with the strongly asymmetrical karyotypes, this suggests that karyotype evolution in Z- loddigesii is recent.     

Karyology and karyotype analysis of diploid freshwater planarian populations of the Dugesia gonocephala group (Platyhelminthes,Tricladida) found in Sardinia

Karyology and karyotype analysis were carried out on freshwater planarian populations of the Dugesia gonocephala group. The strains studied were all diploid with chromosomic number 2n = 16; n = 8. They came from 12 sites mainly localized on the west of the island of Sardinia. Three karyotypes indicated with the letters A, B and C were found in which eight homomorphic pairs of chromosomes were easily identified. In karyotype A all chromosomes are metacentric. Ten populations of the twelve examined showed this karyotype which appears to be the most common. In karyotype B the seventh pair of chromosomes is submetacentric. This karyotype is quite common having been previously found in another eight Sardinian localities. Karyotype C differs from the others in having submetacentric third and seventh pairs of the chromosome complement. It was found in only one locality. The differences observed between these three karyotypes could be interpreted either as sign of differentiation at species level, or as an intraspecific variation due to chromosome mutations (pericentric inversions). This revised version was published online in July 2006 with corrections to the Cover Date.     

The chimpanzee-specific pericentric inversions that distinguish humans and chimpanzees have identical breakpoints in Pan troglodytes and Pan paniscus

Seven of nine pericentric inversions that distinguish human (HSA) and chimpanzee karyotypes are chimpanzee-specific. In this study we investigated whether the two extant chimpanzee species, Pan troglodytes (common chimpanzee) and Pan paniscus (bonobo), share exactly the same pericentric inversions. The methods applied were FISH with breakpoint-spanning BAC/PAC clones and PCR analyses of the breakpoint junction sequences. Our findings for the homologues to HSA 4, 5, 9, 12, 16, and 17 confirm for the first time at the sequence level that these pericentric inversions have identical breakpoints in the common chimpanzee and the bonobo. Therefore, these inversions predate the separation of the two chimpanzee species 0.86-2 Mya. Further, the inversions distinguishing human and chimpanzee karyotypes may be regarded as early acquisitions, such that they are likely to have been present at the time of human/chimpanzee divergence. According to the chromosomal speciation theory the inversions themselves could have promoted human speciation.     

Subfertile couple with inv(2),inv(9) and 16qh+

This case report presents two chromosomal inversions in one of partners from a subfertile couple. The woman was referred due to a spontaneous abortion in the 5th week of pregnancy. Cytogenetic examination showed that the proband's karyotype was normal: 46,XX,16qh+, as centromeric heterochromatin is thought to be clinically insignificant. However, the proband's partner occurred to be a carrier of two pericentric inversions. His karyotype was 46,XY,inv(2)(p11q13),inv(9)(p11q13). The abnormal karyotype is recognised as a possible reason of fertility problems in the investigated couple. The risk of further miscarriages is considered high, but the risk of progeny with abnormal karyotypes is rather low, as small inversions may lead to lethal recombinants.     

Speciation and chromosomal evolution of the Baikalian endemic chironomids of the genus Sergentia Kief. (Diptera, Chironomidae): karyotype divergence and chromosomal polymorphism in the populations of eurybathic species Sergentia flavodentata Tshern. and littoral species Sergentia baicalensis Tshern

Specific karyotype structure and chromosomal polymorphism was investigated in the populations of the Baikalian endemic chironomid species, eurybathic Sergentia flavodentata Tshernovskij, 1949 and littoral Sergentia baicalensis Tshernovskij, 1949. In addition to two fluctuating homozygous inversions in arms A and E, both species were characterized by species-specific karyotype features, namely, nucleolar organizer in the region 1 of chromosome IV in S. flavodentata, and inversion in arm F in S. baicalensis. Moreover, S. baicalensis demonstrated the presence of intraspecific population polymorphism. The populations differing in the presence of secondary overlapping inversion in arm A were found. The highest number of chromosomal rearrangements (7) was detected in S. flavodentata. Most of these rearrangements (six) were found in the population from the underwater thermal spring at a depth of 420 to 430 m (Northern Baikal, Frolikha Bay). In the populations from Middle and Southern Baikal, a rare pericentric inversion in chromosome I was described. In S. baicalensis, in addition to two common heterozygous inversions in arms C and F, disturbance of homologous pairing in different regions of the remaining arms were often detected. Stable chromosomal polymorphism preserved during 13 years in the population of S. flavodentata from the region of hydrothermal venting, serves as an evidence of high genetic plasticity of the species, which favors successful colonization of different Baikal depths and biotopes.     

Chromosomal restructuring of three species of chiromonads from the Chernobyl region (Diptera, Chironomidae)

Chromosomal polymorphism of three species--Chironomus plumosus, Ch. balatonicus and Glyptotendipes glaucus collected from the Chernobyl Zone demonstrated following characteristics: lack of standard karyotype, the presence of hetero- and homozygotic inversions (seven para- and one pericentric), increase in centromeric heterochromatin (55% larvae in homo- and heterozygotic state), the presence of B chromosomes (21%)--in Ch. plumosus; only two larvae had a standard karyotype, the rest demonstrating hetero- and homozygotic inversions (eleven paracentrics), reciprocal translocations of the IVF and IA arms, B chromosomes (5.4%), increase in telomeric (43.6%) and centromeric (1.8%) heterochromatin--in Ch. balatonicus; two types of hetero- and homozygotic inversions, replacement of standard sequences in C and D for inversional homozygotic ones--in Gl. glaucus.     

Cytogenetics of the genus Arvicanthis (Rodentia,Muridae). 3. Comparative cytogenetics of A. neumanni and A. nairobae from Tanzania

The African rats of the genus Arvicanthis have been widely studied during recent years to clarify species boundaries and phylogenetic relationships. The wide chromosomal variability of the genus has been highlighted in several studies, with each accepted species characterised by its individual karyotypes and others being revealed as cryptic species. In the present paper we report the karyotype and the C- and G-banding patterns of the two species A. nairobae and A. neumanni from seven localities of Tanzania, an area of the range poorly studied. The two karyotypes were compared to that of A. niloticus, which is considered to be primitive. The karyotype of A. neumanni is characterised by 2n = 53–54 and NFa = 62. This karyotypic variability depends on a widespread Robertsonian polymorphism. The karyotype of A. nairobae shows 2n = 62 and NFa = 78; it diverges from that of A. niloticus through one reciprocal translocation, five inversions and three heterochromatic additions. The comparison with the karyotypes of other species of the genus showed that A. neumanni belongs to the east African lineage (with A. abyssinicus, A. blicki, A. niloticus), while A. nairobae is closer to the central and the west African representatives which were all previously under the name of A. niloticus (ANI-2, ANI-3, ANI-4). The distribution of A. nairobae in east Africa opens new scenarios in the biogeographical pattern of evolution of the genus.     

Cytogenetics and karyosystematics of South American oryzomyine rodents (Cricetidae: Sigmodontinae). IV. Karyotypes of Venezuelan, Trinidadian, and Argentinian water rats of the genus Nectomys.

Bone marrow chromosomes were studied in South American water rats of the genus Nectomys from Venezuela, Trinidad, and Argentina. Specimens of N. squamipes from western and southern Venezuela showed a 2n = 52-53 karyotype, whereas a 2n = 56-57 karyotype was found in specimens from northeastern Argentina. In both cases, odd karyotypes can be explained by the presence of a supernumerary chromosome. In contrast, water rats from northeastern Venezuela and Trinidad showed a strikingly reduced 2n = 16-17 polymorphic chromosome complement. Six different karyomorphs were found among the latter, which may have resulted from a combination of pericentric inversions in two pairs of autosomes and a centromeric fusion in another autosomal pair. It is proposed that the new 2n = 16-17 cytotypes belong to a species of its own, for which the name N. palmipes is suggested.     

Phylogenetic interpretation of chromosomal and nuclear-DNA-content data in the genus Blennius (Blenniidae: Perciformes)

The haploid DNA content and karyotypes of eight species of Blennius are studied. Six species had 2n=48, two had 2n=46.The karyotypes of these species have been compared with those of related species of the genus and it was suggested that pericentric inversions played an important role in the evolution of their karyotypes. No sex chromosomes were morphologically identifiable in these gonochorist species. The data are discussed in connection with possible lines of evolution within the genus.