Genes on B chromosomes of vertebrates Makunin, Alexey I; Dementyeva, Polina V; Graphodatsky, Alexander S ...
Molecular cytogenetics,
12/2014, Letnik:
7, Številka:
1
Journal Article
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There is a growing body of evidence that B chromosomes, once regarded as totally heterochromatic and genetically inert, harbor multiple segmental duplications containing clusters of ribosomal RNA ...genes, processed pseudogenes and protein-coding genes. Application of novel molecular approaches further supports complex composition and possible phenotypic effects of B chromosomes.
Here we review recent findings of gene-carrying genomic segments on B chromosomes from different vertebrate groups. We demonstrate that the genetic content of B chromosomes is highly heterogeneous and some B chromosomes contain multiple large duplications derived from various chromosomes of the standard karyotype. Although B chromosomes seem to be mostly homologous to each other within a species, their genetic content differs between species. There are indications that some genomic regions are more likely to be located on B chromosomes.
The discovery of multiple autosomal genes on B chromosomes opens a new discussion about their possible effects ranging from sex determination to fitness and adaptation, their complex interactions with host genome and role in evolution.
Conventional cytogenetic studies of Sicista subtilis and S. severtzovi (Dipodidae, Sicistinae), both attributable to the subtilis group of birch mice, revealed extensive karyotype diversity with 2n = ...16-26 and NFa values of 26-46 indicating the overwhelming non-Robertsonian nature of chromosomal reorganization in these species. The numerical and structural chromosome variability was principally found in specimens located within a confined region of the East European (Russian) Plain. The approximately 135,000-km(2) area occurs in the vicinity of the Don River bend between 49°13'N/43°46'E and 51°32'N/36°16'E. The detection of cytotypes sharing similar 2n and NF values, but having morphologically distinct chromosomes, suggests that these may result from polymorphisms present both within recognized species and in cryptic taxa not hitherto described. We conducted a comprehensive, comparative chromosome banding analysis of 52 birch mice (21 localities) referable to the subtilis group and report the presence of 5 distinct karyotypes, each characterized by a combination of stable, variable, and partly overlapping 2n/NFa values. These karyotypes differed from each other by 10-29 structural chromosomal rearrangements (18.1 ± 6.3) that comprised Rb fusions/fissions (42.2%), pericentric inversions (31.1%), and tandem translocations (22.2%). The composition, and the high numbers of these chromosomal changes, is likely to provide an effective means of post-mating isolation, suggesting that taxonomic diversity within the subtilis group is larger than currently accepted. Additionally, we report the frequent fixation of tandem translocations in sample populations, one of which was found in a polymorphic state representing, as far as we are aware, the first case of an in statu nascendi tandem fusion in wild populations. Moreover, our data revealed that bi-armed chromosomes were involved in fusions detected in some of the subtilis taxa. In each instance, however, fusions were preceded by pericentric inversions that transform one or both bi-armed chromosomes into acrocentrics resulting in either centromere-telomere or Robertsonian translocations. Finally, a phylogenetic scenario inferred from a cladistic analysis of the chromosomal data suggests that the extensive karyotypic diversification within the subtilis group in the south-east region of the Russian Plain most likely results from fragmentation of a continuously distributed, ancestral population. It is thought that this occurred at the last glacial maximum (18,000-14,000 years B.P.), and that the process of isolation has been exacerbated by increasing human activity in the region in modern times.
The karyotypes of most birds consist of a small number of macrochromosomes and numerous microchromosomes. Intriguingly, most accipitrids which include hawks, eagles, kites, and Old World vultures ...(Falconiformes) show a sharp contrast to this basic avian karyotype. They exhibit strikingly few microchromosomes and appear to have been drastically restructured during evolution. Chromosome paints specific to the chicken (GGA) macrochromosomes 1-10 were hybridized to metaphase spreads of three species of Old World vultures (Gyps rueppelli, Gyps fulvus, Gypaetus barbatus). Paints of GGA chromosomes 6-10 hybridize only to single chromosomes or large chromosome segments, illustrating the existence of high chromosome homology. In contrast, paints of the large macrochromosomes 1-5 show split hybridization signals on the chromosomes of the accipitrids, disclosing excessive chromosome rearrangements which is in clear contrast to the high degree of chromosome conservation substantiated from comparative chromosome painting in other birds. Furthermore, the GGA chromosome paint hybridization patterns reveal remarkable interchromosomal conservation among the two species of the genus Gyps.
We explore clustering stability of sequential recombination jet reconstruction algorithms. Events are reconstructed many times, using random variations of kinematic properties of the jet ...fragmentation process. Sensitivity of different algorithms to initial conditions are quantified by introducing probabilistic assignment of initial particles to jets (fuzzy clustering). A criterion detecting unstable configurations (bifurcation points) is proposed, based on the overall fuzziness of the event.
The CLEO RICH detector Artuso, M.; Ayad, R.; Bukin, K. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2005, Letnik:
554, Številka:
1
Journal Article
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We describe the design, construction and performance of a Ring Imaging Cherenkov Detector (RICH) constructed to identify charged particles in the CLEO experiment. Cherenkov radiation occurs in LiF ...crystals, both planar and ones with a novel “sawtooth”-shaped exit surface. Photons in the wavelength interval 135–165
nm are detected using multi-wire chambers filled with a mixture of methane gas and triethylamine vapor. Excellent
π
/
K
separation is demonstrated.
The stone curlew, also known as thick-knee (Burhinus oedicnemus, BOE), represents a phylogenetically young species of the shorebirds (Charadriiformes) that exhibits one of the most atypical genome ...organizations known within the class of Aves, due to an extremely low diploid number (2n = 42) and only 6 pairs of microchromosomes in its complement. This distinct deviation from the 'typical' avian karyotype is attributed to repeated fusions of ancestral microchromosomes. In order to compare different species with this atypical avian karyotype and to investigate the chromosome rearrangement patterns, chromosome-specific painting probes representing the whole genome of the stone curlew were used to delineate chromosome homology between BOE and 5 species belonging to 5 different avian orders: herring gull (Charadriiformes), cockatiel (Psittaciformes), rock pigeon (Columbiformes), great gray owl (Strigiformes) and Eurasian coot (Gruiformes). Paints derived from the 20 BOE autosomes delimited 28 to 33 evolutionarily conserved segments in the karyotypes of the 5 species, similar to the number recognized by BOE paints in such a basal lineage as the chicken (28 conserved segments). This suggests a high degree of conservation in genome organization in birds. BOE paints also revealed some species-specific rearrangements. In particular, chromosomes BOE1-4 and 14, as well as to a large extent BOE5 and 6, showed conserved synteny with macrochromosomes, whereas homologous regions for BOE7-13 are found to be largely distributed on microchromosomes in the species investigated. Interestingly, the 6 pairs of BOE microchromosomes 15-20 appear to have undergone very few rearrangements in the 5 lineages investigated. Although the arrangements of BOE homologous segments on some chromosomes can be explained by complex fusions and inversions, the occurrence of homologous regions at multiple sites may point to fission of ancestral chromosomes in the karyotypes of the species investigated. However, the present results demonstrate that the ancestral microchromosomes most likely experienced fusion in the stone curlew lineage forming the medium-sized BOE chromosomes, while they have been conserved as microchromosomes in the other neoavian lineages.
Separation of crystal signals into scintillation and Cherenkov components Akchurin, N.; Astwood, A.; Cardini, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/2008, Letnik:
595, Številka:
2
Journal Article
Recenzirano
The signals from high-
Z scintillating crystals such as PbWO
4 and BGO contain a significant Cherenkov component. We investigate methods to determine the contribution of Cherenkov light to the ...signals generated by high-energy electrons and pions (mips), both statistically and event-by-event. These methods are based on differences in the spectra, the time structure and/or the directionality of the two types of light. The electron signals, and their composition, are also analyzed as a function of the age (or depth) of the shower.
New crystals for dual-readout calorimetry Akchurin, N.; Bedeschi, F.; Cardini, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
06/2009, Letnik:
604, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Lead tungstate crystals doped with small fractions of praesodynium or molybdenum have been tested in beams of high-energy electrons. The goal of these tests was to study the effects of such dopants ...on the capability to separate the signal components deriving from the Cherenkov and scintillation light generated by the beam particles. These studies were carried out in view of the possible application of such crystals in dual-readout calorimeters.
Optimization of crystals for applications in dual-readout calorimetry Akchurin, N.; Bedeschi, F.; Cardini, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2010, Letnik:
621, Številka:
1
Journal Article
Recenzirano
We present a systematic study of lead tungstate crystals doped with a small fraction of molybdenum, varying between 0.1% and 5%. These crystals were exposed to a beam of 50
GeV electrons and the ...signals were unraveled into scintillation and Cherenkov contributions, using the time structure of the signals and/or different types of transmission filters. These studies were carried out in view of the possible application of such crystals in dual-readout calorimeters.
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