1,720,995 research outputs found
Causes and Consequences of Recombination Rate Variation
Get PDFRecombination, the shuffling of alleles during meiosis, is a fundamental evolutionary process that is nearly ubiquitous across eukaryotes. By uncoupling linkage disequilibrium between harmful and beneficial mutations, recombination promotes more effective selection. However, recombination rate varies at multiple scales across nature, which has important implications for genome evolution at large. Here, I report four chapters that investigate recombination and genome evolution using the unicellular and facultatively sexual chlorophyte Chlamydomonas reinhardtii. I examine recombination rate variation at the level of populations, individuals, and across the genome itself. I show that recombination rates are consistent between populations and individuals, demonstrate evidence that recombination plays a role in reducing the effects of selection at linked sites, and estimate the rate of sexual reproduction in a wild population of C. reinhardtii. I also investigate recombination in a crossover-suppressed sex-determining region of the genome, and show how noncrossover recombination can still maintain effective selection, thus preventing long-term degeneration of these loci. Finally, I close off with a study pertaining to mutational biases introduced by environmental stressors in C. reinhardtii and demonstrate the effects of the former on adaptation. Altogether, my thesis addresses fundamental questions regarding recombination rate variation and adaptation in C. reinhardtii, and alongside existing detailed work on spontaneous mutation in the system, provides an empirical framework for understanding how these processes affect genome evolution over evolutionary time.Ph.D
The Genetic Basis of Natural Variation in Algal Neutral Lipid Accumulation
No full textNeutral lipids are known to be involved in an algal adaptation to cold, light, and nutrient stress, but the extent of intraspecific variation and the mechanisms maintaining the variation in this economically important trait are unclear. I predict algal strains from different latitudes will vary in neutral lipid accumulation because many of the stressor associate with climate. Inducing neutral lipid accumulation using nitrogen (N) starvation in 26 natural isolates of Chlamydomonas reinhardtii revealed genetic variation but no latitudinal pattern in neutral lipid accumulation. A further experiment demonstrated latitudinal variation in neutral lipid accumulation induced by cold shock and light deprivation. By analyzing molecular evolution of 473 lipid-candidate genes, I inferred stronger purifying selection and higher rates of positive selection driving genetic divergence in the lipid-associated genes. From this, I suggest the possibility that neutral lipid accumulation is an adaptive trait in C. reinhardtii under positive selection.M.Sc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Downregulation of Chloroplast Glycolysis Protects the Shikimate Pathway from Phosphoenolpyruvate Depletion
No full textChloroplasts harmonize seemingly incompatible metabolic processes during photosynthesis. The Calvin-Benson-Bassham cycle (CBC), glycolysis, the shikimate pathway and the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway, all potentially compete for the same C3 metabolic precursors yet avoid detrimental interference. I show that productive co-existence of these metabolic pathways in photosynthetic tissue depends on the developmental downregulation of the enzymatic steps linking the CBC to glycolysis. As a result, chloroplasts lack the ability to produce phosphoenolpyruvate (PEP) and pyruvate via endogenous glycolysis. Instead, PEP is re-routed through the cytosol, which ensures its exclusive provisioning to the shikimate pathway, while the MEP pathway and fatty acid synthesis obtain pyruvate directly from rubisco. Using quantitative 13C labeling of Arabidopsis plants and mutants with altered C3 transport, I demonstrate that this unique metabolic arrangement is crucial for preventing the futile consumption of PEP, accommodating simultaneous flux through the shikimate pathway, CBC, and all pyruvate-dependent biosynthetic routes.M.Sc.2025-11-12 00:00:0
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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