1,720,963 research outputs found
Evolution of beta satellite DNA sequences: Evidence for duplication-mediated repeat amplification and spreading RID E-6420-2011
No full textIn this article, we report studies on the evolutionary history of beta satellite repeats (BSR) in primates. In the orangutan genome, the bulk of BSR sequences was found organized as very short stretches of approximately 100 to 170 bp, embedded in a 60-kb to 80-kb duplicated DNA segment. The estimated copy number of the duplicon that carries BSR sequences ranges from 70 to 100 per orangutan haploid genome. In both macaque and gibbon, the duplicon mapped to a single chromosomal region at the boundary of the rDNA on the marker chromosome (chromosome 13 and 12, respectively). However, only in the gibbon, the duplicon comprised 100 by of beta satellite. Thus, the ancestral copy of the duplicon appeared in Old World monkeys (similar to25 to similar to35 MYA), whereas the prototype of beta satellite repeats took place in a gibbon ancestor, after apes/Old World monkeys divergence (similar to25 MYA). Subsequently, a burst in spreading of the duplicon that carries the beta satellite was observed in the orangutan, after lesser apes divergence from the great apes-humans lineage (similar to18 MYA). The analysis of the orangutan genome also indicated the existence of two variants of the duplication that differ for the length (100 or 170 bp) of beta satellite repeats. The latter organization was probably generated by nonhomologous recombination between two 100-bp repeated regions, and it likely led to the duplication of the single Sau3A site present in the 100-bp variant, which generated the prototype of Sau3A 68-bp beta satellite tandem organization. The two variants of the duplication, although with a different ratios, characterize the hominoid genomes from the orangutan to humans, preferentially involving acrocentric chromosomes. At variance to alpha satellite, which appeared before the divergence of New World and Old World monkeys, the beta satellite evolutionary history began in apes ancestor, where we have first documented a low-copy, nonduplicated BSR sequence. The first step of BSR amplification and spreading occurred, most likely, because the BSR was part of a large duplicon, which underwent a burst dispersal in great apes' ancestor after the lesser apes' branching. Then, after orangutan divergence, BSR acquired the clustered structural organization typical of satellite DNA
Growth hormone secretion among adult patients with Prader-Willi syndrome due to different genetic subtypes
No full textHuman genome dispersal and evolution of 4q35 duplications and interspersed LSau repeats
No full textWe have investigated the evolutionary history of the 4q35 paralogous region, and of a sub-family of interspersed LSau repeats. In HSA, 4q35 duplications were localized at 1q12, 3p12.3, 4q35, 10q26, 20cen, whereas duplicons and interspersed LSau repeats simultaneously labeled the p arm of acrocentric chromosomes. A multi-site localization of 4q35-like sequences was also observed in PTR, GGO, PPY, HLA (Hominoidea) and PAN (Old World monkey), thus indicating that duplications of this region have occurred extensively in the two clades, which diverged at least 25 million years ago. In HSA, PTR and PAN, 4q35-derived duplicons co-localized with rDNA, whereas in GGO and PPY this association was partially lacking. In PAN, the single- and multi-site distribution of rDNA and paralogous sequences, respectively, indicates a different timing of sequence dispersal. The sub-family of interspersed LSau repeats showed a lesser dispersal than 4q35 duplications both in man and great apes. This finding suggests that duplications and repeated sequences have undergone different expansion/contraction events during evolution. The mechanisms underlying the dispersal of paralogous regions may be further derived through studies comparing the detailed structural organization of these genomic regions in man and primates
The structure of duplications on human acrocentric chromosome short arms derived by the analysis of 15p
No full textWe report the molecular analysis of a 130-kb DNA region containing a junction between beta and non-beta satellite DNA from chromosome 15p. The genomic region is characterized by beta satellite blocks intermingled with variants of the D4Z4 repeat, and duplicons from 4q24 and 4q35. Besides the p-arm of acrocentric chromosomes, the duplicons showed a wide genomespread involving pericentromeric, sub-telomeric, and interstitial regions. In this regard, the paralogous sequences were characterized by a high similarity index (96%), thus indicating a recent transposition during the evolution. The acrocentrics differedwith regard to the location of the 4q24 paralogous region, since it mapped on the p-arm of chromosomes 13-15 and 21, but only on 22q11.2. Conversely, the 4q35 duplication marked the p-arm of all the acrocentrics. In different individuals, the short arm of acrocentric chromosomes revealed a great variability of sequence representation and location at p11 and/or p13 for both the 4q24 and 4q35 duplications. The studied genomic region from chromosome 15p, of which a contig of approximately 200 kb has been derived, could lead to more detailed investigations into the sequence organization and possible biological function of chromosome regions that are located close to the rDNA array
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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