Chromosome analysis in cattle and horses

Foram analisados os cromossomos de 117 bovinos de diferentes raças para identificação de fusão cêntrica e os cromossomos de 100 éguas jovens da raça Brasileiro de Hipismo para identificação de linhagens 63,X, utilizando a técnica de identificação do X baseada na heterocromatina intersticial do braço longo.

Molecular cytogenetic analysis of heterochromatin in the chromosomes of tilapia, Oreochromis niloticus (Teleostei : Cichlidae)

The structure of the heterochromatic bands in mitotic chromosomes of the important tropical aquaculture species of tilapia, Oreochromis niloticus, was investigated by the combination of the C-banding technique, chromosomal digestion with two restriction endonucleases and fluorescence in situ hybridization (FISH) of two satellite DNAs (SATA and SATB). The tilapia chromosomes presented heterochromatic bands in the centromeres and in the short arms of almost all chromosomes that were differentially digested by the restriction endonucleases HaeIII and EcoRI. FISH of SATA showed that the satellite sequence is distributed in the centromeric region of all chromosomes of tilapia. FISH also revealed an intense hybridization signal for SATB in only one chromosome pair, but less intense signals were also present in several other pairs. The digestion of tilapia chromosomes by HaeIII and EcoRI was positively correlated with the position of SATA and SATB in chromosomes as revealed by FISH. The results obtained may be useful in future molecular and genetic studies of tilapias.

Chromosome evolution in fish: sex chromosome variability in Eigenmannia virescens (Gymnotiformes : Sternopygidae)

New data are presented on the sex chromosomes of the fish species Eigenmannia virescens (Gymnotiformes, Sternopygidae). A new finding, involving the occurrence of ZZ/ ZW sex chromosomes, is described in specimens sampled from the Sao Francisco and Amazon river basins in Brazil. All individuals had a chromosome number of 2n = 38. The homologs of the sex chromosome pair from the Sao Francisco river basin sample differed only in their morphology, while those from the Amazonian sample differed both in morphology and heterochromatin pattern. A possible model for the evolution of the sex chromosomes in E virescens is proposed, including data from populations from the Parana (Brazil) river basin, in which male heterogamety has already been described. The occurrence of different sex chromosome systems in species and populations of the neotropical freshwater fish fauna is discussed. Copyright (C) 2002 S. Karger AG, Basel.

Chromosome banding and 18S rDNA in situ hybridization analysis of seven species of the family Achiridae (Teleostei : Pleuronectiformes)

Achiridae is an important family of the order Pleuronectiformes widely distributed in North, Central, and South America with freshwater and marine species. In the present study cytogenetic analyses comprising conventional and molecular techniques were carried out in seven species of this family. The following diploid numbers (2n) and fundamental numbers (FN) were obtained: Achirus declivis 2n = 34, FN = 52; Achirus lineatus 2n = 40, FN = 66; Catathyridium jenynsi 2n = 40 and FN = 50; Gymnachirus nudus 2n = 36 and FN = 50; Hypoclinemus mentalis 2n = 38 and FN = 54; Trinectes paulistanus 2n = 42 and FN = 52; and Trinectes sp. 2n = 38 and FN = 54. All species presented a single nucleolar organizer region (NOR) bearing chromosome pair and C-band positive segments mainly distributed at the pericentromeric position. The wide variation observed in chromosome number and FN suggests the occurrence of larger chromosome rearrangements in the family Achiridae if compared with other families of the same order.

Cytogenetic studies of Mastacembelus armatus (Pisces, Mastacembelidae)

The mitotic chromosomes, nucleolus organizer regions (NORs), C-banding pattern and nuclear DNA content of Mastacembelus armatus were studied. The karyotype (2n = 48; 10m + 6sm + 4st + 28a) was characterized by the presence of one chromosome pair with NORs and a small quantity of heterochromatin. The DNA content observed in erythrocyte nuclei of M. armatus was 1.39 +/- 0.08 pg. Comparison of this karyotype with those of other Synbranchiformes revealed a strong similarity, suggesting that small chromosome rearrangements may have been maintained during its evolutionary history.

Comparative chromosome mapping of 5S rDNA and 5SHindIII repetitive sequences in Erythrinidae fishes (Characiformes) with emphasis on the Hoplias malabaricus 'species complex'

Chromosomal localization of 5S rDNA and 5SHindIII repetitive sequences was carried out in several representatives of the Erythrinidae family, namely in karyomorphs A, D, and F of Hoplias malabaricus, and in H. lacerdae, Hoplerythrinusunitaeniatus and Erythrinus erythrinus. The 5S rDNA mapped interstitially in two chromosome pairs in karyomorph A and in one chromosome pair in karyomorphs D and F and in H. lacerdae. The 5SHindIII repetitive DNA mapped to the centromeric region of several chromosomes (18 to 22 chromosomes) with variations related to the different karyomorphs of H. malabaricus. on the other hand, no signal was detected in the chromosomes of H. lacerdae, H. unitaeniatus and E. erythrinus, suggesting that the 5SHindIII-DNA sequences have originated or were lost after the divergence of H. malabaricus from the other erythrinid species. The chromosome distribution of 5S rDNA and 5SHindIII-DNA sequences contributes to a better understanding of the mechanisms of karyotype differentiation among the Erythrinidae members.Copyright (c) 2007 S. Karger AG, Basel.

Cytogenetic characterization of a supernumerary chromosome segment and of B-chromosomes in Astyanax scabripinnis (Teleostei, Characidae)

The chromosome complement of a local population of Astyanax scabripinnis in Brazil was investigated with emphasis on the study of the heterochromatin attached to the A-chromosomes and present in the macro B-chromosome. Analysis after C-banding, silver and CMA(3) staining, incorporation of 5-bromo-2'-deoxyuridine and chromosome digestion with nine restriction endonucleases revealed that the heterochromatin in the B-chromosomes was different from that found in the A-chromosomes. A polymorphism due to the presence of a supernumerary heterochromatic chromosome segment was observed in the population investigated. Some aspects related to the origin of the heterochromatin polymorphism in Astyanax scabripinnis are discussed.

Dynamics of 5S rDNA in the tilapia (Oreochromis niloticus) genome: repeat units, inverted sequences, pseudogenes and chromosome loci

In higher eukaryotes, the 5S ribosomal DNA (5S rDNA) is organized in tandem arrays with repeat units composed of a coding region and a non-transcribed spacer sequence (NTS). These tandem arrays can be found on either one or more chromosome pairs. 5S rDNA copies from the tilapia fish. Oreochromis niloticus, were cloned and the nucleotide sequences of the coding region and of the non-transcribed spacer were deter-mined. Moreover, the genomic organization of the 5S rDNA tandem repeats was investigated by fluorescence in situ hybridization (FISH) and Southern blot hybridization. Two 5S rDNA classes, one consisting of 1.4-kb repeats and another one with 0.5-kb repeats were identified and designated 5S rDNA type I and type II, respectively, An inverted 5S rRNA gene and a 5S rRNA putative pseudogene were also identified inside the tandem repeats of 5S rDNA type I. FISH permitted the visualization of the 5S rRNA genes at three chromosome loci, one of them consisting of arrays of the 5S rDNA type I, and the two others corresponding to arrays of the 5S rDNA type II. The two classes of the 5S rDNA. The presence of pseudogenes, and the inverted genes observed in the O. niloticus genome might be a consequence of the intense dynamics of the evolution of these tandem repeat elements. Copyright (C) 2002 S. Karger AG, Basel.

Unusual occurrence of a ZZ/ZW sex-chromosome system and supernumerary chromosomes in Characidium cf. fasciatum (Pisces, Characiformes, Characidiinae)

Individuals of two populations of the fish Characidium cf. fasciatum were cytogenetically studied and showed a basic diploid number of 50 chromosomes. Some fishes were found to have 51 to 54 chromosomes due to the presence of one to four small subtelocentric/acrocentric supernumerary chromosomes. When analyzed by conventional Giemsa staining, male and female specimens of C. cf. fasciatum from the Quinta stream and Pardo River presented the same basic karyotypic macro- and microstructure, consisting of 32 metacentric and 18 submetacentric chromosomes.Ag-NORs were terminally located on the long arms of two submetacentric chromosome pairs. Constitutive heterochromatin was identified by C-banding as small pericentromeric blocks in the majority of the chromosomes, and B-chromosomes were found to be heterochromatic. The occurrence of one totally heterochromatic submetacentric chromosome restricted to females and considered as an unusual feature in fish karyotypes led to the identification of a ZZ/ZW sex-chromosome system. The implications of chromosomic differentiation observed in the genus Characidium are discussed.

Karyotypic relationships among the tribes of Hypostominae (Siluriformes : Loricariidae) with description of XO sex chromosome system in a neotropical fish species

The family Loricariidae, with about 683 species, is one the largest fish families in the world. The subfamily Hypostominae was recently reviewed and is now divided in five tribes. With the main objective of contributing to a better understanding of the relationships of the members of the subfamily Hypostominae, cytogenetic analyses were conducted in seven species (three Hypostomini, three Pterygoplichthini and two Ancistrini) from Brazil and Venezuela. In Pterygoplichthini, all species show 2n = 52 chromosomes. In Hypostomini Hypostomus ancistroides has 2n = 68, H. regani 2n = 72 and Hypostomus goyazensis 2n = 72 chromosomes. In Ancistrini Ancistrus n. sp. 1 has 2n = 39/40 with a sex chromosome system of the type XX/X0, which is a novelty for neotropical fishes, and Ancistrus n. sp. 2 has 2n = 52 chromosomes. Six species have single Ag-NORs and two multiple Ag-NORs. The possible cytogenetic relationships among the species of Hypostominae are discussed.

Sex chromosome evolution in fish: the formation of the neo-Y chromosome in Eigenmannia (Gymnotiformes)

Chromosomes of a species of Eigenmannia presenting a X1X1X2X2:X1X2Y sex chromosome system, resulting from a Y-autosome Robertsonian translocation, were analyzed using the C-banding technique, chromomycin A(3) (CMA(3)) and mithramycin (MM) staining and in situ digestion by the restriction endonuclease AluI. A comparison of the metacentric Y chromosome of males with the corresponding acrocentrics in females indicated that a C-band-positive, CMA(3)/MM-fluorescent and AluI digestion-resistant region had been lost during the process of translocation, resulting in a diminution of heterochromatin in the males. It is hypothesized that the presence of a smaller amount of G+C-rich heterochromatin in the sex chromosomes of the heteromorphic sex when compared with the homomorphic sex may be associated with the sex determination mechanism in this species and may be a more widely occurring phenomenon in fish with differentiated sex chromosomes than was initially thought.

XX : XY sex chromosome system with X heterochromatinization: an early stage of sex chromosome differentiation in the Neotropic electric eel Eigenmannia virescens

An early stage of sex chromosome differentiation is reported to occur in the electric eel Eigenmannia virescens (Pisces, Sternopygidae) from populations of two tributaries of the Parana river system (Brazil). Cytogenetic studies carried out in the two populations showed that the Mogi-Guacu population is characterized by 2n = 38 chromosomes and undifferentiated sex chromosomes and the Tiete population presents 2n = 38 both for males and females and an XX:XY sex chromosome system. The X-chromosome is acrocentric, easily recognized by the presence of a conspicuous heterochromatin block in its distal portion; the Y-chromosome is probably one of the medium sized acrocentrics present in the male karyotype. BrdU induced R-bands of the two populations did not reveal any difference in the euchromatic regions of the chromosomes. AluI and HaeIII restriction enzyme digestion patterns and chromomycin A3 staining of the X-chromosome are presented. The possible role of heterochromatinization in the evolution of sex chromosomes in fish is discussed.