Submetacentric Elements Research Articles

Multiple Chromosomal Polymorphism of “Evoron” Chromosomal Race of the Evoron Vole (Rodentia, Arvicolinae)

On the basis of a study of our own and published data on voles from the shores of Lake Evoron (n = 8) and the Amgun River (n = 8) in the Evoron-Chukchagir lowland, as well as individuals from laboratory breeding, new data on karyotypic variation (2n = 38–41, NF = 54–59), chromosomal transformations, and their combinations in the karyotype are presented. The numbering of chromosomes in the Evoron vole karyotype using differential (GTG) staining methods made it possible to identify pairs of chromosomes involved in various chromosomal rearrangements and to number the original pairs for the pairs formed from them by chromosome fusion. The tandem telomere-telomere (TTel) fusions of biarmed chromosomes form a large submetacentric element Mev1/4M; telomere-centromere fusion (TCen) as a result of inactivation of the centromere in one of the acrocentric pairs forms either an acrocentric (Mev17/18A) or metacentric element (Mev17/18M), and the Robertsonian translocation of the same pairs forms a metacentric element (Mev17/18M). The variability of the centromere position in two pairs of autosomes (Mev8 and Mev14) is also shown. The revealed rearrangements made it possible to describe twelve variants of the karyotype: two with 2n = 41, six with 2n = 40, three with 2n = 39, and one with 2n = 38. It is proposed that the voles of the Evoron-Chukchagir lowland be assigned to the “еvoron” chromosome race, and the other voles be assigned to the “argi” race. Prolific offspring from the individuals with TTel fusion in the karyotype and a high percentage of this rearrangement in individuals from natural sample sets indicates the absence of a harmful effect on the viability of voles.

Demonstration of 5-Methylcytosine-Rich DNA Sequences in Chiroptera

5-Methylcytosine-rich heterochromatic regions were demonstrated in metaphase chromosomes of 5 species of Chiroptera by indirect immunofluorescence using a monoclonal anti-5-methylcytosine antibody. These species belong to 4 genera and 2 families and are characterized by divergent karyotypes. One species (Glauconycteris beatrix) has an extremely low diploid chromosome number of 2n = 22 with only meta- to submetacentric elements and remarkably large amounts of constitutive heterochromatin located in the centromeric and pericentromeric regions of all chromosome pairs. Two species (G. beatrix and Neoromicia cf. guineensis) possess X-autosome translocations. In all species, the hypermethylated chromosome segments correspond to constitutive heterochromatin, and the numbers and positions of hypermethylated chromosome segments in the karyotypes are constant and species-specific. In some species (Pipistrellus hesperidus, Neoromicia cf. somalicus), there are several smaller chromosome pairs in which the bright anti-5-methylcytosine antibody labeling is not restricted to constitutively heterochromatic regions but is observed along the whole lengths of these chromosomes. The nature of these additional hypermethylated regions is discussed. The analysis of 5-methylcytosine-rich chromosome regions elucidates valuable data for chiropteran cytogenetics and reflects the high pace of evolution of the repetitive DNA fraction in their genomes.

Comparative cytogenetics of two endangered leuciscine fish, Squalius aradensis and S. torgalensis (Teleostei, Cyprinidae), from the Iberian Peninsula

In this study, the description of the karyotypes of the endangered chubs Squalius aradensis (Coelho, Bogutskaya, Rodrigues and Collares-Pereira, 1998) and Squalius torgalensis (Coelho, Bogutskaya, Rodrigues and Collares-Pereira, 1998) is presented by means of conventional (Giemsa-staining, Chromomycin A3 (CMA3)-fluorescence, Silver-impregnation (Ag-NORs)) and molecular (fluorescence in situ hybridization (FISH) with 18S rDNA probe) protocols. These endemic sister-species have an allopatric but adjacent distribution in the most southwestern part of the Iberian Peninsula. Diploid chromosome number was invariably 2n = 50 and karyotypes of both species were grossly similar, composed of metacentric and submetacentric elements with a reduced number of acrocentric pairs. Sequential staining using FISH with an 18S rDNA probe, CMA3 and Ag-NORs treatments revealed consistent positive signals located at the end of the short arms of a submetacentric chromosome pair, likely homologous in both species. While providing useful cytogenetic comparative data against other members of the genus Squalius Bonaparte, 1837, the work aimed to draw attention towards the conservation of two narrow-range and highly confined fish species.

The Chromosomes and the Sex Determining Mechanism ofScaphura nigra(Orthoptera, Ensifera, Tettigoniidae, Phaneropterinae)

Scaphura nigra has a unique chromosome complement among approximately 100 species studied so far belonging to the subfamily Phaneropterinae. It is formed by 2n (♂) = 26 and a FN = 29 and derived from the ancestral karyotype of the group 2n (♂) = 31, FN = 31, by means of two centric fusions and one tandem fusion. The first between the X chromosome and a medium-sized autosome giving rise to a neo-XY sex chromosome mechanism of recent origin, and the second between two acrocentric ones, the bigger and a medium size, that gave rise to a large submetacentric element whose length is very uncommon in the subfamily This process has created a bimodal karyotype that contrasts with the majority in this group, whose chromosomes usually can be arranged in a decreasing order of size. A third rearrangement incorporating the chromatin of a medium-sized autosome to the bigger one, explains the reduction observed in the number of chromosomes and the enlarged size of the submetacentric elements. These features demonstrate the effectiveness of chromosome number, their morphology and the change of the sex mechanism as useful tools for taxonomy.

Polyploidy in the evolution of the glacial relict Pontoporeia spp. (Amphipoda, Crustacea)

Salemaa, H. 1984. Polyploidy in the evolution of the glacial relict Pontoporeia spp. (Amphipoda, Crustacea). —Hereditas 100:53–60. Lund, Sweden. ISSN 0018–0661. Received April 19, 1983 The chromosome numbers and karyological features were investigated in two benthic amphipods, Pontoporeia femorata Kroyer, and Pontoporeia affinis Lindstrom, from the northern Baltic Sea. A considerable difference was observed between the chromosome numbers of the species. The diploid karyotype of P. femorata consists of six acrocentric and twenty-two metacentric and submetacentric elements, the fundamental number of chromosome arms being 50 (n = 14). P. affinis has evolved from P. femorata in the Ice Age through polyploidy and further chromosome fusions, the number of acrocentric elements being eight and that of metacentric and submetacentric chromosomes forty-four. There are 96 arms in the karyotype of P. affinis (n=26). No chromosomal mechanism for sex-determination was observed. Because polyploidy is a rare event in bisexual animals, being demonstrated for the first time in Amphipoda, an attempt has been made to elucidate polyploidy as an evolutionary strategy. Compared to its ancestor, P. femorata, P. affinis is characterized by ecological flexibility, high but fluctuating productivity and increased reproductive effort. These features, together with the zoogeographical history of glacial relicts in northern Eurasia, support the theory that polyploid animals are often generalistic pioneers, easily invading new habitats in peripheral or changing environmental conditions.

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.

Leuciscus (Pisces, Cyprinidae) karyotypes: Transect of Portuguese populations

The presently described Iberian chubs - Leuciscus carolitertii and L. pyrenaicus - sampled throughout their distribution ranges in Portugal were cytogenetically analyzed. Their chromosome numbers were consistently 2n = 50, except for two specimens of L. carolitertii, which exhibited a supernumerary chromosome in some of the metaphases. The karyotypes were found to be highly typical for other Leuciscus taxa, as well as for European leuciscine cyprinids: the chromosome sets are dominated by metacentric and submetacentric elements with a reduced number of acrocentric pairs (three to four); the largest pair of the complements belongs typically to this latter category. The chubs from northern drainages, assignable to L. carolitertii, have apparently a more stable karyotype structure (12M:30S:8A) than the chubs from L. pyrenaicus, which have 12M:32S:6A, but may exhibit in the most southern river basins (Guadiana, Mira, Aljezur, Bordeira and Arade) more variable karyotypes. Besides, these data support the very recent discovery of two genetically distinct Leuciscus taxa in this region of the Iberian Peninsula, suggesting the stochastic fixation of structural chromosome rearrangements in these small and isolated drainages, which may be affected by bottlenecks due to significant variations in hydrological regimes. The NORs were apparently located in one small submetacentric pair of chromosomes and the presence of a heteromorphic sex chromosome system of the ZW/ZZ type was also evidenced for the Iberian endemic chubs.

Chromosome Study of Yulong Vole (Eothenomys proditor).

A first description of the karyotype of Yulong vole (Eothenomys proditor) is presented. Karyotype studies were carried out using conventional staining, G-banding, C-banding and silverstaining. Yulong vole was sharp different from other allied voles on karyotype. The diploid number is 2n=32, with the fundamental number of 56. The autosomes consist of 13 pairs of meta-/submetacentric elements and two pairs of arcrocentric elements. The X chromosome is medium sized and submetacentric, whereas the Y chromosome is small and subacrocentric. The G-banding allows to identify chromosome pairing and to detect the chromosome rearrangements intervening in karyotypic differentiation. In the C-banded karyotype, the centromeric heterochromatin is observed in Nos. 2, 4 and 12 chromosomes, the terminal C-band is found in No. 13 and X chromosomes. Y chromosome is completely C-band-positive, moreover, the interstial distribution of C-bands has been demonstrated on the biarm of No. 2 chromosome pair and the long arm of Nos. 2, 9 and 10 chromosomes respectively. Nucleolus organizer regions (NORs) appeared in the long arm of Nos. 1, 2 and 4 chromosomes and short arm of No. 11 chromosome.

Karyotype morphology in Hyperiella dilatata Stebbing 1888 (Amphipoda: Hyperiidae) from the Ross Sea (Antarctica)

The chromosome complement and some karyological features were investigated in the pelagic amphipod Hyperiella dilatata Stebbing 1888 from the Ross Sea (Antarctica). The diploid karyotype consists of 48 metacentric and 10 submetacentric elements (2n = 58). The presence of secondary constrictions and supernumerary chromosomes is described. Available chromosome numbers of Hyperiidea exhibit a wide range of distribution, among which Hyperiella dilatata is the closest to the modal number of other amphipods.

The Crocidura fuliginosa species complex (Mammalia: Insectivora) in peninsular Malaysia: Biological, karyological and genetical evidence

Four West Malaysian shrew populations of the genus Crocidura were investigated through their karyotype and allozyme variations, and, in part, by interfertility experiments. Two different karyotypes characterize these shrews. The first, restricted to the Cameron Highlands (Peninsular Malaysia), invariably has 2 n=40 chromosomes but a varying fundamental number (FN-54–58). The second karyotype shows a fundamental number of 62–68 and a polymorphic chromosomal number of 2 n=38, 39 or 40, a rare event in the genus Crocidura. Thus both can be distinguished by either a low or a higher number of meta- and submetacentric elements. In heterospecific breeding experiments, mutual avoidance was observed suggesting prezygotic barriers, whereas intraspecific pairs produced 13 litters (mean 2.1 young). Furthermore, our biochemical results indicate that both karyotypes correspond to a relatively ancient separation (Nei's D=0.354), an amount of genetic differentiation comparable to the distance separating them from the West Palearctic C. russula ( D=0.429–0.583). In contrast, conspecific island and mainland Malaysian shrews possessing the second karyotype had only one fixed allelic difference over the 35 Loci surveyed. The problem of naming the two biological species remains unsolved and requires further comparative investigations

Karyotypes of two species of genus Euhadra, Euhadra callizona and Euhadra peliomphala simodae (Bradybaenidae, Gastropoda).

Somatic chromosomes of two species in the genus Enhadra are studied using air-drying methods. The diploid numbers of both E. callizona and E. p. simodae are 2n=56, and are the same as other Euhadra species described in Inaba's report (1959) and in our previous papers (1984, 1987). From the karyotype analysis of the two species E. callizona is found to have 19 pairs of metacentric and 9 pairs of submetacentric chromosomes, E. p. simodae bears 18 pairs of metacentric and 10 pairs of submetacentric elements. The differences in the karyotypes of these two species suggest that they differ from each other cytogenetically. E. callizona is found to bear a karyotype resembling that of E. dixoni and E. amaliae (1984, 1987); the similarity of form suggests that it is closer to those two species cytogenetically. The karyotype of E. p. simodae is found to have some different elements to that of E. c. hickonis in the medium- sized and the small-sized chromosomes, and is therefore shown to be distinct from E. c. hickonis cytogenetically.

Differentiation in uniform width microphotometric trace of Bufo melanostictus chromosomes.

Broad based differential regions were detected in microphotometric tracings of Giemsa stained but unbanded Bufo melanostictus chromosomes. This was facilitated by the combination of (1) a very small photometric step size of 0.05μ, (2) scanning at “minimum effective aperture” with the magnification of the chromatid width adjusted to fall within it, and (3) direct multidirectional tracing along the exact pathway of the chromatid arms. It seems possible that Giemsa stained bandings could be superimposed phenomena since they are consequent upon various treatments to the chromosome, including some which produce gross structural alterations.B. melanostictus is the common toad found in gardens of the South East Asian region, whose karyotype has not been previously documented because of the dif-ficulty in culturing its cells in vitro. We succeeded by using medium enriched with 10, 000 mol. wt. ultrafiltrate of unfertilized eggs of the female. The karyotype (2n=22) consisted of all metacentric chromosomes except for a single submetacentric ele-ment. By size, the chromosomes were divisible into 2 groupings, a bigger and a smaller, easily discernible by simple inspection.

Comparative karyotypes of two land snails, Euhadra subnimbosa and Euhadra dixoni (Bradybaenidae, gastropoda).

Somatic chromosomes of two species in the genus Euhadra were observed using the air-drying methods supplying abundance of mitotic cells. The diploid numbers of E. dixoni and E. subnimbosa are confirmed to have 56 in each case. E. subnimbosa bears 21 pairs of metacentric and 7 pairs of submetacentric elements, while E. dixoni has 19 pairs of metacentric and 9 pairs of submetacentric chromosomes. They not only show the same fundamental number NF=112, but also have a secondary constriction in the approximal chromosomal position and in the same sized metacentric pairs. Consequently, the minor karyotypical difference found in the two suggests a close similarity cytologically, though they bear morphological differences.

Karyological and serological studies in Rana lessonae, R. ridibunda and in their hybrid R. ‘esculenta’ (Amphibia, Anura)

The karyotypes of the three water frog forms: Rana lessonae, R. ridibunda and R. ‘esculenta’ were analysed from bone marrow cell preparations of animals captured in several localities of the GDR. In the three forms chromosome morphology was similar (5 large and 8 small pairs), although differences in the relative length of most elements were found; R. ‘esculenta’ chromosomes were always intermediate. One of the small pairs (Chr. 12) was found to be metacentric in R. lessonae and submetacentric in R. ridibunda. Most R. ‘esculenta’ individuals examined had one meta-and one submetacentric 12th element, indicating the hybrid nature of this form. However 16.6% ‘esculenta’ proved to be homozygous for either the metacentric or the submetacentric chromosome 12, while 13% lessonae individuals and 7.7% ridibunda were heterozygous for this element. By starch gel electrophoresis an analysis was undertaken of serum proteins from water frogs coming from regions in which the forms occur together (sympatric populations) and from zones in which only one of them lives (allopatric populations). In Rana lessonae, where only one allele had been previously described, two different alleles were found in animals coming from the GDR. If genetic polymorphism is excluded, between 6.1% and 9.1% individuals from sympatric lessonae and ridibunda populations showed introgression of an albumin allele. No gene introgression was found in allopatric lessonae populations from the Leningrad region or in ridibunda from Alma Ata and southern Bulgaria.

Karyotype and heterochromatin pattern of the field mouse,Apodemus argenteus Temminck

The field mouse,Apodemus argenteus Temminck, has 46 chromosomes. The autosomes comprise 20 pairs of acrocentrics and 2 pairs of metacentrics. The X chromosome is represented by an outstandingly large submetacentric element, while the Y is an acrocentric corresponding in size to the 5th or 6th pair of autosomes. All of the autosomes and gonosomes can be unequivocally identified by their characteristic Q-band or G-band patterns. The constitutive heterochromatin, as revealed by C-banding, is localized at the centromeric regions of all autosomes, the short arm and the proximal 1/3 of the long arm of the X chromosome, and the entire Y chromosome. The C-band-positive segments which constitute 33.5% of the genome exhibit dark fluorescence after Q-banding, late DNA replication, faint or positive staining reaction to G-banding, fast reassociation of DNA revealed by AO staining, and allocyclic behavior of the sex-bivalent in male meiosis. An exception to the above is the distal segment of the Y which is positive to both C- and Q-banding. The giant X chromosome occupies 13.1% of the genome, leaving 5.6% of euchromatic segments, the latter value being equivalent to that of the original type X.

Apparent convergence of karyotypes in two species of pocket gophers of the genus Thomomys (Mammalia, Rodentia).

Intraspecific variation in chromosome morphology is greater in two species of pocket gophers than within any other presently studied mammalian species. Diploid number varies only from 76 to 78. Therefore, the majority of the differences appear to be the results of pericentric inversions. These geographical chromosomal differences in <i>Thomomys bottae </i>and <i>T</i>. <i>umbrinus </i>are best explained as adaptations to habitat characteristics. Within both species, populations occurring in arid or shallow soil habitats have karyotypes characterized by a high number of acrocentrics, whereas populations in more favorable conditions have karyotypes composed entirely of metacentrics or submetacentric elements. These parallel trends suggest that the symmetry of the karyotype as a whole may have functional significance.

The somatic chromosomes of five crocodilian species.

The somatic karyotypes of five crocodilian species are described. These species include <i>Caiman sclerops</i> (spectacled caiman or South American alligator, 2N = 42), <i>Alligator mississippiensis</i> (North American alligator, 2N == 32), <i>Crocoa¦ylus porosus</i> (salt-water crocodile, 2N = 34), <i>Crocodylus niloticus</i> (Nile crocodile, 2N = 32), and <i>Tomistoma schlegeli</i> (false gavial, 2N = 32). Metacentric, submetacentric and telocentric chromosomes were observed in all species tested. Satellites were observed on a submetacentric element of <i>A</i>. <i>mississippiensis</i>, and the apparently identical chromosome with an obvious secondary constriction was found in both <i>C</i>. <i>porosus</i> and <i>C</i>. <i>niloticus</i>. No microchromosomes were found. Possible pathways of chromosomal evolution to explain the observed karyotypic relationships are suggested.

Sex Chromosomes in the Domestic Fowl (<i>Gallus domesticus</i>), Turkey (Meleagris gallopavo) and the Chinese Pheasant (<i>Phasianus colchicu</i><i>s</i>)

A small W-sex chromosome is described in the female karyotype of the domestic fowl (<i>Gallus domesticus</i>), turkey (<i>Meleagris gallopavo</i>) and pheasant (<i>Phasianus colchicus</i>). In the domestic fowl, the W-chromosome is a small unpaired, metacentric chromosome intermediate in size between the chromosomes of the ninth and the tenth pair. In the female turkey, the W is a sub-metacentric element with an arm ratio of about 1:2 and a size intermediate between that of the sixth and the seventh pairs. In the case of the female pheasant, the Wis an unpaired, sub-metacentric element with an arm ratio of approximately 1:2.4 and a size slightly larger than that of the seventh pair.

Un cas nouveau de polymorphisme chromosomique intraspécifique chez un Mammifère (Leggada minutoides Smith. Rodentia-Muridae)

The African mouse,Leggada minutoides Smith, shows a chromosomal polymorphism: a first male (Coast of Ivory) had 32 chromosomes; theX is a big metacentric, theY a big submetacentric and the autosomes are acrocentric, with the single exception of the biggest pair which associates two submetacentric elements. By a second male (Congo), 33 chromosomes are found, amongst them only one big submetacentric autosome. This statement and the odd diploid number shows clearly that we have to deal with an heterozygot, two acrocentric elements representing respectively one arm of the submetacentric autosome. Now, we may be sure that this male belongs to a population built of individuals having 32, 33 and 34 chromosomes. The origin of such a population must have arisen in a primitive population where 34 was the diploid number, through a centric fusion.