Pair Of Large Metacentric Chromosomes Research Articles

Regions enriched for DNA repeats in chromosomes of Macrostomum mirumnovem, a species with a recent Whole Genome Duplication.

The free-living flatworm Macrostomum mirumnovem is a neopolyploid species whose genome underwent a recent Whole Genome Duplication (WGD). In the result of chromosome fusions of the ancient haploid chromosome set, large metacentric chromosomes were formed. In addition to three pairs of small metacentrics, the current karyotype of M. mirumnovem contains two pairs of large metacentric chromosomes, MMI1 and MMI2. The generation of microdissected DNA libraries enriched for DNA repeats followed by DNA probe preparation and fluorescent in situ hybridization (FISH) were performed. The DNA probes obtained marked chromosome regions enriched for different DNA repeats in the M. mirumnovem chromosomes. The size and localization of these regions varied in different copies of large chromosomes. They varied even in homologous chromosomes, suggesting their divergence due to genome re-diploidization after a WGD. Besides the newly formed chromosome regions enriched for DNA repeats, B chromosomes were found in the karyotypes of the studied specimens of M. mirumnovem. These B chromosomes varied in size and morphology. FISH with microdissected DNA probes revealed that some Bs had a distinct DNA content. FISH could paint differently B chromosomes in different worms and even in the same sample. B chromosomes could carry a bright specific fluorescent signal or could show no fluorescent signal at all. In latter cases, the specific FISH signal could be absent even in the pericentromeric region of the B chromosome. Possible mechanisms of B chromosome formation and their further evolution are discussed. The results obtained indicate an important role that repetitive DNAs play in genome re-diploidization initiating a rapid differentiation of large chromosome copies. Taking together, karyotype peculiarities (a high level of intraspecific karyotypic diversity associated with chromosome number variation, structural chromosomal rearrangements, and the formation of new regions enriched for DNA repeats) and some phenotypic features of M. mirumnovem (small body size, short lifecycle, easy maintenance in the laboratory) make this species a perspective model in the studies of genomic and karyotypic evolution in species passed through a recent WGD event.

Molecular cytogenetic differentiation of paralogs of Hox paralogs in duplicated and re-diploidized genome of the North American paddlefish (Polyodon spathula)

BackgroundAcipenseriformes is a basal lineage of ray-finned fishes and comprise 27 extant species of sturgeons and paddlefishes. They are characterized by several specific genomic features as broad ploidy variation, high chromosome numbers, presence of numerous microchromosomes and propensity to interspecific hybridization. The presumed palaeotetraploidy of the American paddlefish was recently validated by molecular phylogeny and Hox genes analyses. A whole genome duplication in the paddlefish lineage was estimated at approximately 42 Mya and was found to be independent from several genome duplications evidenced in its sister lineage, i.e. sturgeons. We tested the ploidy status of available chromosomal markers after the expected rediploidization. Further we tested, whether paralogs of Hox gene clusters originated from this paddlefish specific genome duplication are cytogenetically distinguishable.ResultsWe found that both paralogs HoxA alpha and beta were distinguishable without any overlapping of the hybridization signal - each on one pair of large metacentric chromosomes. Of the HoxD, only the beta paralog was unequivocally identified, whereas the alpha paralog did not work and yielded only an inconclusive diffuse signal. Chromosomal markers on three diverse ploidy levels reflecting different stages of rediploidization were identified: quadruplets retaining their ancestral tetraploid condition, semi-quadruplets still reflecting the ancestral tetraploidy with clear signs of advanced rediploidization, doublets were diploidized with ancestral tetraploidy already blurred. Also some of the available microsatellite data exhibited diploid allelic band patterns at their loci whereas another locus showed more than two alleles.ConclusionsOur exhaustive staining of paddlefish chromosomes combined with cytogenetic mapping of ribosomal genes and Hox paralogs and with microsatellite data, brings a closer look at results of the process of rediploidization in the course of paddlefish genome evolution. We show a partial rediploidization represented by a complex mosaic structure comparable with segmental paleotetraploidy revealed in sturgeons (Acipenseridae). Sturgeons and paddlefishes with their high propensity for whole genome duplication thus offer suitable animal model systems to further explore evolutionary processes that were shaping the early evolution of all vertebrates.

The origin of the large metacentric chromosome pair in Chinese medaka (Oryzias sinensis)

Japanese medakas (Oryzias latipes and Oryzias sakaizumii) have 48 chromosomes, while the Chinese medaka (Oryzias sinensis) has 46 chromosomes, including one pair of large metacentric chromosomes. Linkage analysis using O. sakaizumii and O. sinensis strains showed that DNA markers in linkage groups (LG) 11 and 13 were tightly linked. Centromeric genomic clones of LG 11 and 13 derived from an O. latipes strain hybridized across the centromeres of the pair of large metacentric chromosomes in an O. sinensis strain. These results demonstrate that the large metacentric chromosome pair was derived from two pairs of acrocentric chromosomes (LG 11 and 13) through Robertsonian fusion.

Karyotype of Araucaria angustifolia and the decondensation/activation mode of its nucleolus organiser region

The chromosomes of the gymnosperm Araucaria angustifolia (Bertol.) Kuntze were analysed with the fluorochromes chromomycin A3 (CMA) and 4′,6-diamidino-2-phenylindole (DAPI) and with C-banding. This species contains a diploid complement made of 26 chromosomes, with 18 larger metacentric, four smaller metacentric and four submetacentric chromosomes. The only CMA+/DAPI– region observed corresponded to the nucleolus organiser region (NOR) localised at the proximal portion of a large metacentric chromosome pair. C-banding marked the NOR as well as a terminal region of another chromosome pair. In addition, small C-bands were occasionally seen interspersed in many chromosomes. The NOR appeared to condense at approximately the same rate as the rest of the chromosome from prophase throughout metaphase. In interphase nuclei, NOR decondensation and activation was characterised by the formation of CMA+ blocks that resembled a string of beads inside the nucleolus. The number and size of beads was inversely proportional to the size of the nucleolus, suggesting that transcriptional activation of the nucleolar cistrons starts simultaneously at several points of the NOR. The mode of NOR activation in A. angustifolia differs from that observed in most species, providing a unique opportunity to study activation and transcriptional control of rRNA genes.

Karyotype characterization of Trigona fulviventris Guérin, 1835 (Hymenoptera, Meliponini) by C banding and fluorochrome staining: report of a new chromosome number in the genus

Although many species of the genus Trigona have been taxonomically described, cytogenetic studies of these species are still rare. The aim of the present study was to obtain cytogenetic data by conventional staining, C banding and fluorochrome staining for the karyotype characterization of the species Trigona fulviventris. Cytogenetic analysis revealed that this species possesses a diploid chromosome number of 2n = 32, different from most other species of this genus studied so far. This variation was probably due to the centric fusion in a higher numbered ancestral karyotype, this fusion producing the large metacentric chromosome pair and the lower chromosome number observed in Trigona fulviventris. Heterochromatin was detected in the pericentromeric region of the first chromosome pair and in one of the arms of the remaining pairs. Base-specific fluorochrome staining with 4'-6-diamidino-2-phenylindole (DAPI) showed that the heterochromatin was rich in AT base pairs (DAPI+) except for pair 13, which was chromomycin A3 (CMA3) positive indicating an excess of GC base pairs. Our data also suggests that there was variation in heterochromatin base composition.

Meiotic Chromosome Configurations of XY and "XO" Type Males from Four Species of the Genus Chymomyza(Diptera, Drosophilidae) with a Description of the Karyotype of C. rufithorax.

The karyotype of Chymomyza rufithorax, a species belonging to the procnemis species group of the genus Cymomyza (Diptera, Drosophilidae), is the fundamental one of Cymomyza species, consisting of a pair of rods with a proximal constriction (X chromosome), 2 pairs of large metacentric chromosomes, and a pair of dots. In males of this species, the X chromosome does not have a synaptic mate, and the chromosome number is 7. Therefore the male of this species belongs to the “XO” type, which has been reported for only 3 species in the genus Chymomyza. Meiotic chromosome configurations of the “XO” type males from C. rufithorax and C. obscuroides and the XY males from C. pararufithorax and C. costata were described. XY pairing was found in the XY males, but an X chromosome univalent was observed in the “XO” type males. Meiotic pairing configurations of other autosomes in the “XO” males were found to be similar to those in XY males. These data suggest that the Y chromosome or its pairing site might have degenerated or been eliminated from the genome during the course of speciation.

Chromosome analysis and FISH mapping of ribosomal DNA (rDNA), telomeric (TTAGGG)n and (GATA)n repeats in the leech Haemopis sanguisuga (L.) (Annelida: Hirudinea).

In the present paper the chromosome complement (n = 13; 2n = 26) of the common leech Haemopis sanguisuga (L.) (Annelida: Hirudinea: Hirudinidae) was analyzed using banding techniques and fluorescent in situ hybridization (FISH) with three repetitive DNA probes [ribosomal DNA (rDNA), (TTAGGG)n and (GATA)n]. FISH with the rDNA probe consistently mapped major ribosomal clusters (18S-28S rDNA) in the pericentromeric region of one large metacentric chromosome pair; this region, which consisted of heterochromatin rich in GC base pairs, was preferentially stained by silver nitrate (Ag-NOR). The (TTAGGG)n telomeric probe was hybridized with the termini of nearly all chromosomes, whereas the (GATA)n probe did not label any chromosome areas.

The species and chromosomal distribution of the centromeric α-satellite I sequence from sheep in the tribe Caprini and other Bovidae

The evolution of chromosomes in species in the family Bovidae includes fusion and fission of chromosome arms (giving different numbers of acrocentric and metacentric chromosomes with a relatively conserved total number of arms) and evolution in both DNA sequence and copy number of the pericentromeric α-satellite I repetitive DNA sequence. Here, a probe representing the sheep α-satellite I sequence was isolated and hybridized to genomic DNA digests and metaphase chromosomes from various Bovidae species. The probe was highly homologous to the centromeric sequence in all species in the tribe Caprini, including sheep (Ovis aries), goat (Capra hircus) and the aoudad or Barbary sheep (Amnotragus lervia), but showed no detectable hybridization to the α-satellite I sequence present in the tribe Bovini and at most very weak to species in the tribes Hippotragini, Alcelaphini or Aepycerotini. The sex chromosomes of sheep, goat and aoudad did not contain detectable α-satellite I sequence; in sheep, one of the three metacentric autosomal chromosomes does not carry the sequence, while in aoudad, it is essentially absent in three large autosomal pairs as well as the large metacentric chromosome pair. The satellite probes can be used as robust chromosome and karyotype markers of evolution among tribes and increase the resolution of the evolutionary tree at the base of the Artiodactyla.

Physical mapping and characterization of 5S rRNA genes in Douglas-fir.

Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] is one of the world's most valuable timber species and is widely used in reforestation. Therefore there is considerable interest in understanding its genetic structure. In conifers approximately 75% of the genome is composed of repetitive DNA. Thus for conifers characterization of repetitive DNA is a significant part of genome analysis. We have characterized the organization of 5S rRNA genes in Douglas-fir at both the molecular and chromosome levels. 5S DNA repeat units containing the coding sequence for 5S rRNA and the nontranscribed spacer (NTS) were cloned using PCR. Sequencing and Southern hybridization revealed repeat units of 888 and 871 bp in length, the latter with a 17 bp deletion in the NTS. The coding region showed high homology with other eukaryotic 5S rRNA genes. A 35 bp region of the NTS immediately upstream of the 5' end of the coding region showed high similarity to other conifers but not to other published plant 5S rDNA sequences. Physical mapping of 5S rDNA by fluorescent in situ hybridization using a biotinilated homologous probe revealed a single subtelomeric site on one pair of large metacentric chromosomes.

Evidence for an unusual ZW/ZW'/ZZ sex-chromosome system in Scardinius erythrophthalmus (Pisces, Cyprinidae), as detected by cytogenetic and H-Y antigen analyses.

Fifty-seven individuals of the European cyprinid fish species Scardinius erythrophthalmus were sexed by gonad histology, and their karyotypes were analyzed by Giemsa staining and C-banding. The chromosome number in somatic metaphase plates was 2n = 50. Karyotypes of all gonadal male animals were identical, consisting of 48 small meta- or submetacentric chromosomes and a pair of large metacentric chromosomes (ZZ males). Of the 33 gonadal females, 16 had a karyotype similar to the males' (ZW' females) and 17 had a heteromorphic pair of chromosomes, including a large metacentric Z chromosome and a small acrocentric W chromosome (ZW females). H-Y antigen typing with cells obtained from a variety of tissues revealed that the homogametic ZZ males were H-Y negative and the heterogametic ZW females were H-Y positive in all tissues tested. In contrast, ZW' females showed no expression of the H-Y antigen in somatic cells but were H-Y positive in ovarian cells. These results suggest that the ZW/ZW'/ZZ sex chromosomes of S. erythrophthalmus represent an unusual system of sex determination and that H-Y antigen expression is coupled with the heterogametic sex. Whether the ZW' individuals are indeed heterogametic females or actually sex-reversed ZZ males, in which chromosomal sex determination is overruled by external factors, is discussed.

Intra-individual variations of chromosomes and DNA content in meristems of adventitious roots ofOrnithogalum umbellatumL.

SUMMARYThe 92 bulbs from a population of Ornithogalum umbellatum which is stable at 2n = 2x = 18, are characterized by a karyotype containing one pair of large metacentric chromosomes, five pairs of large telocentric chromosomes and three pairs of small submetacentric chromosomes; only, two meristematic root cells of one bulb show aneuploidy (2n = 19 and 2n = 25). Although the mean DNA content measured in metaphase plates of meristematic cells of adventitious roots from a single bulb is highly variable (up to 50% difference); in the two cases where aneuploidy was encountered very little or no increase in DNA content was observed.

'n Vergelykende studie van die kariotipes van <i>Tilapia rendalli<i/>, <i>Tilapia sparrmanii<i/> en <i>Oreochromis mossambicus<i/> (Cichlidae)

Optimal chromosome preparations were obtained from stimulated lymphocyte cultures with a new method based on a combination and modification of several techniques. Tilapia rendalli, T. sparrmanii and Oreochromis mossambicus have somatic chromosome numbers of 44, 42 and 44, respectively. Chromosome pairs L1 and L2 are easily identified in all the karyotypes and distinctive of the tilapias. Tilapia sparrmanii has one additional large metacentric chromosome pair(L3), which occurs concurrently with the reduction of two in the total chromosome number. The F chromosomes were divided into two groups, viz a submetacentric (sm) and a telocentric (t) group. T. rendalli has 8 sm chromosomes, while both T. sparrmanii and O. mossambicus have 6 chromosomes in the sm group. The rest of the F chromosomes were telocentric. The identification of the sex chromosomes in the karyotypes of tilapia has thus far not been possible using standard techniques.

The karyotype of Eubothrium rugosum (Cestoda: Pseudophyllidea)

The diploid chromosome set of Eubothrium rugosum contains 16 elements. The karyotype consists of three pairs of metacentric, three pairs of acrocentric and two pairs of submeta-metacentric chromosomes. Their mean absolute length ranges from 2.20 to 8.80 μm. The first two pairs of large metacentric chromosomes comprise over 45% of the total complement length.

Karyological Observations on Monocelididae (Turbellaria, Proseriata): Karyometrical Analysis of Four Species Pertaining to the Subfamily Minoninae

SUMMARYFour species of Minoninae (Turbellaria, Proseriata) have been examined (Minona n. sp., Duplominona paucispina, D. corsicana, Duploperaclistus circocirrus). All show n = 3, 2n = 6 and they have remarkably similar karyotypes. The basic diploid set is made up of one pair of large metacentric chromosomes, one pair of medium-sized chromosomes (metacentric in three species and submetacentric in the fourth) and a third pair of small acrocentric chromosomes. Absolute haploid genome length is similar in three of the species but differs significantly in Duplominona corsicana where it is much higher. The chromosome number n = 3, found not only in these species but also in others of the family Monocelididae, can be considered as the basic number of the family and a plesiomorphic condition for all the Proseriata.

Karyotype differentiation and its consequences in Mediterranean « Limonium »

Summary Within the genus Limonium (Plumbaginaceae) the following chromosome numbers occur in the Old World 2n = 12, 14, 16, 18, 25, 26, 27, 32, 34, 35, 36, 42, 43, 54. Many of the species are apomictic. It can be shown that all species with chromosome numbers higher than 18 (perhaps with the exception of 2n = 32, 36 and 54) are hybrids basing on x = 8 or x = 9 or of the combination of both numbers. X = 8 could have its origin by fusion of two chromosomes of x = 9. Since one pair of large metacentric chromosomes appears in all x = 8 chromosome sets (with exception of the species L. sinuatum, L. diffusum and L. ferulaceum, which form rather isolated groups within the genus). The pollen grains and the stigmas of the amphimictic species are dimorphous. Cross pollination there is necessary. Within one population of the other species normally only one type occurs. Nevertheless these plants too show a high degree of fertility—another hint for its apomictic status.

Cytogenetic studies of the somatic and germ-line cells in sand rats (Psammomys obesus).

The chromosomes in both somatic and germ-line cells of the sand rat (Psammomys obesus) were studied. The diploid number of chromosomes was 48. The autosomes consisted of 4 pairs of large metacentric chromosomes, 10 pairs of medium to small metacentric and submetacentric chromosomes and 9 pairs of telocentric chromosomes. The X chromosomes in both sexes were the largest of the entire complement. The Y chromosome was a mediumsized metacentric chromosome. The two X chromosomes in the female cells were similar in size and morphology but differed in the DNA replication pattern. Studies of the meiotic chromosomes in the male germ-line cells revealed 23 autosome bivalents and the sex chromosomes either as an XY bivalent or X and Y univalents.

The idiogram of the sheep with particular reference to secondary constrictions.

Current improved techniques for making human and other mammalian mitotic chromosornc preparations have been used to show that the diploid chromosome number of the domestic sheep is 54 (Gimenez-Martin and LopezSaez, 1962; Borland, 1964; McFee, Banner and Murphree, 1965). This confirms the finding of a number of earlier worlters who used embryo and testicular material for thcir studies (Shivngo, 1930; Berry, 1938, 1941; Ahmed, 1940; Maltino, 1943; Melsnder, 1959). Latterly the X Chromosome has been identified as the largcst of the ncrocentric group of cl~romosomes by ~McFee et al. (1965), who also confirmed the Y to be the smallest chromosome and suggested that it was probably submetacentric. None of these workers has suggested, however, any means of identifying individual chromosomes of either the 3 pairs of large metacentric chromosomes or the 23 pairs of smaller acrocentric chromosomes. Nor have they described the modal chromosome number of counted metaphases from a number of narmal sheep of a similar age group. In man the presence of secondary constrictions on certain chromosomes of the human karyotype is now an accepted aid to identification The London conference on the normal Human Karyotype, 1963). There are, however, varying reports on the incidence of these and their value in cl~romosome recognition. The most constant constrictions in the human karyotype are the terminal satellites which occur on the short arms of all acrocentic chromosomes (Ferguson-Smith and Handmalter, 1961, 1963). These latter chromosomes are now known to be associated with nucleolus formation (FergusonSmith, 1964). Secondary constrictions have been described, however, on a number of the other chromoson~es at various positions on either the short or long arms (Muldal and Ockey, 1961; De la Chapelle, 1961; Ferguson-Smith, Ellis and Dicltson, 1962). The incidence of these secondary constrictions does show, however, considerable variations between different workers (Palmer and Funderburlt. 1965). This has been shown to be associated with various fdctors, including concentration of colchicine (Palmer and Funderburk, 1965), the use of calcium free medium (Sasalti and Maltino, 1963) or B.U.d.R. (5 Bromo deoxyuridine) (Kabaclt, Saksela and Mellman, 1964). None of these workers has discussed the effect of type of hypotonic solution used during Chromosome ~ r e ~ a r a t i o n . 1 1 Interest in disease of domestic animals associated with chromosomal abnormality has already been summarised by Pakes and Griesemer (1965) and Hare, Weber, McFeely and Tsu-Ju Yang (1966). Among the various reports there is only passing reference to secondary constrictions on the chromosomes of the domestic animals except in the cat in which one pair of the small group E chromosomes is satellited (Chu, Thuline and Norby, 1961; Jones 1965).