Genetic polymorphism of buffalo Bubalus bubalis bubalis by cytogenetic and molecular markers

Aim. To estimate genetic polymorphism of buffaloes Bubalus bubalis bubalis by the characteristics of karyotype and microsatellite loci of DNA. Methods. The method of preparing chromosome preparations using blood lymphocytes of 30 animals and the analysis of 9 microsatellite loci of DNA, recommended by the International Society for Animal Genetics (ISAG) for cattle genotyping, were used in the investigation. Results. Based on the results of the analysis of GTG–stained preparations of metaphase chromosomes, it was determined that the karyotype of the investigated animals consisted of 25 pairs of chromosomes, which identifi ed them as river (murrah) buffaloes (Bubalus bubalis bubalis). The average frequency of detected quantitative and structural chromosome aberrations in the buffalo population under investigation was 13.58±3.18 % for males and 14.8±2.88 % for females. Active centers of nucleolus organizers were found on six pairs of chromosomes: 3p, 4p, 6q, 21q, 23q and 24q. In nine investigated microsatellite loci of DNA, 61 allele variants were identifi ed with the variation from four alleles (ILST 006) to 11 (TGLA) with the average number of alleles per locus being 6.77. The expected heterozygosity (He) exceeded the average value of the observed heterozygosity (Ho) which demonstrated the use of inbreeding in the breeding of the investigated group of animals. Conclusions. The application of quantitative and morphological characteristics of the karyotype and microsatellite DNA– markers (ILST005 (ILSTS005), ILST006 (D7S8), BM1818 (D23S21), BM2113 (D2S26), ETH10 (D5S3), ETH225 (D9S1), SPS115(D15), TGLA126 (D20S1), TGLA122 (D21S6) demonstrated their informative value and reasonability of their use for genetic monitoring of buffaloes in Ukraine with the purpose of developing selection programs of keeping and breeding this species.

Structure and molecular evolution of the ribosomal DNA external transcribed spacer in the cockroach genus Blattella

The ribosomal DNA (rDNA) cluster of insects contains several hundred repeating structural–functional units and, therefore, is a typical example of a multigene family. Eukaryotic ribosomal RNA (rRNA) genes (18S, 5.8S, and 28S like) are arranged in tandemly repeated clusters in the nucleolus organizers, separated by several spacers, namely the nontranscribed spacer, the external transcribed spacer (ETS), and the internal transcribed spacers. The nucleotide sequences of the ETS of the three closely related Blattella cockroach species, Blattella germanica (Linnaeus, 1767), Blattella asahinai (Mizukubo, 1981), and Blattella lituricollis (Walker, 1868), were determined and compared. The three species had relatively similar ETS lengths, and sequence differences among them could be explained by two types of rearrangements, namely deletions of subrepeats and nucleotide substitutions. Minor ETS variants in B. germanica differed from the major variant in the same way that the major ETS variants of the three Blattella species differed from each other. Concerted evolution and the birth-and-death models, which are often invoked to explain the diversity and evolution of the multigene families of rDNA clusters, are discussed in the light of our data. A new model is proposed to explain the evolutionary reorganization of the ETS region: evolution of rDNA by “magnification-and-fixation” is characterized by magnification of minor subrepeats, which become adaptive in a new rapidly changed environment, and subsequent fixation of this variant type as a major component of the multigene family of a new species.

Chromosomal nucleolar organizer regions in four sturgeon species as markers of karyotype evolution in Acipenseriformes (Pisces)

Nucleolar organizer regions in Acipenser ruthenus (2n = 118 ± 4) are localized on the telomeric regions of two morphologically different pairs of chromosomes. In A. baeri (2n = 250 ± 8), A. transmontanus (2n = 248 ± 8), and A. naccarii (2n = 246 ± 8) they are localized on eight chromosomes arranged in two quadruplets. Contrary to what is commonly accepted, such distribution suggests that species with 120 chromosomes should be considered diploids and species with 240–250 chromosomes should be considered tetraploid.Key words: Acipenseridae, karyotype, nucleolus organizers, polyploidy.

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.Key words: Sparidae, karyotype, heterochromatin, nucleolus organizers, chromosome polymorphism.

Karyotype divergence in Symphodus melops and Symphodus roissali (Labridae, Perciforms): C-banded and Ag-NOR karyotypes

A comparative analysis of conventional C-banded and Ag-NOR karyotypes involving the closely related labrid species Symphodus melops and Symphodus roissali showed conspicuous differences between them, reflected mainly in their 2n and fundamental number values. The chromosome rearrangements apparently involved consisted of three centric fusions, pericentric inversions, and (or) translocations, as well as small heterochromatic additions. In spite of this clear divergence, the two species seem to have one larger metacentric pair, the nucleolar organizer region (NOR) carrier chromosomes, and some smaller unidentified pairs in common. Both karyotypes are fully representative of the described tendency in the labrids towards symmetric morphology. The NOR regions were shown to have C-banding and a heteromorphism between homologous regions was detected by conventional and silver staining, but not by the C-banding technique, which leads us to suggest that the NOR regions' heteromorphism is functional rather than structural in nature.Key words: Labridae, heterochromatin, nucleolus organizers.

Rex-induced recombination implies bipolar organization of the ribosomal RNA genes of Drosophila melanogaster.

Rex-induced mitotic recombination was used to determine whether nucleolus organizers can pair in both inverted and noninverted orientations. Two target chromosomes, each duplicated for the rDNA region, were exposed to maternal Rex activity. Recombination in one orientation should yield deletion of the material between the two nucleolus organizers, recombination in the other orientation should yield inversion of the same material. Both products were recovered from both target chromosomes. The generality of using Rex-mediated recombination for analysis of the rDNA is considered.

X-Y Exchange and the Coevolution of the X and Y rDNA Arrays in Drosophila melanogaster

ABSTRACT The nucleolus organizers on the X and Y chromosomes of Drosophila melanogaster are the sites of 200-250 tandemly repeated genes for ribosomal RNA. As there is no meiotic crossing over in male Drosophila, the X and Y chromosomal rDNA arrays should be evolutionarily independent, and therefore divergent. The rRNAs produced by X and Y are, however, very similar, if not identical. Molecular, genetic and cytological analyses of a series of X chromosome rDNA deletions (bb alleles) showed that they arose by unequal exchange through the nucleolus organizers of the X and Y chromosomes. Three separate exchange events generated compound X·YL chromosomes carrying mainly Y-specific rDNA. This led to the hypothesis that X-Y exchange is responsible for the coevolution of X and Y chromosomal rDNA. We have tested and confirmed several of the predictions of this hypothesis: First, X·YL chromosomes must be found in wild populations. We have found such a chromosome. Second, the X·YL chromosome must lose the YL arm, and/or be at a selective disadvantage to normal X+ chromosomes, to retain the normal morphology of the X chromosome. Six of seventeen sublines founded from homozygous X·YLbb stocks have become fixed for chromosomes with spontaneous loss of part or all of the appended YL. Third, rDNA variants on the X chromosome are expected to be clustered within the X+ nucleolus organizer, recently donated ("Y") forms being proximal, and X-specific forms distal. We present evidence for clustering of rRNA genes containing Type 1 insertions. Consequently, X-Y exchange is probably responsible for the coevolution of X and Y rDNA arrays.