6,225 research outputs found
A MOSAIC of methods: Improving ortholog detection through integration of algorithmic diversity
Ortholog detection (OD) is a critical step for comparative genomic analysis
of protein-coding sequences. In this paper, we begin with a comprehensive
comparison of four popular, methodologically diverse OD methods: MultiParanoid,
Blat, Multiz, and OMA. In head-to-head comparisons, these methods are shown to
significantly outperform one another 12-30% of the time. This high
complementarity motivates the presentation of the first tool for integrating
methodologically diverse OD methods. We term this program MOSAIC, or Multiple
Orthologous Sequence Analysis and Integration by Cluster optimization. Relative
to component and competing methods, we demonstrate that MOSAIC more than
quintuples the number of alignments for which all species are present, while
simultaneously maintaining or improving functional-, phylogenetic-, and
sequence identity-based measures of ortholog quality. Further, we demonstrate
that this improvement in alignment quality yields 40-280% more confidently
aligned sites. Combined, these factors translate to higher estimated levels of
overall conservation, while at the same time allowing for the detection of up
to 180% more positively selected sites. MOSAIC is available as python package.
MOSAIC alignments, source code, and full documentation are available at
http://pythonhosted.org/bio-MOSAIC
Robust forward simulations of recurrent hitchhiking
Evolutionary forces shape patterns of genetic diversity within populations
and contribute to phenotypic variation. In particular, recurrent positive
selection has attracted significant interest in both theoretical and empirical
studies. However, most existing theoretical models of recurrent positive
selection cannot easily incorporate realistic confounding effects such as
interference between selected sites, arbitrary selection schemes, and
complicated demographic processes. It is possible to quantify the effects of
arbitrarily complex evolutionary models by performing forward population
genetic simulations, but forward simulations can be computationally prohibitive
for large population sizes (). A common approach for overcoming these
computational limitations is rescaling of the most computationally expensive
parameters, especially population size. Here, we show that ad hoc approaches to
parameter rescaling under the recurrent hitchhiking model do not always provide
sufficiently accurate dynamics, potentially skewing patterns of diversity in
simulated DNA sequences. We derive an extension of the recurrent hitchhiking
model that is appropriate for strong selection in small population sizes, and
use it to develop a method for parameter rescaling that provides the best
possible computational performance for a given error tolerance. We perform a
detailed theoretical analysis of the robustness of rescaling across the
parameter space. Finally, we apply our rescaling algorithms to parameters that
were previously inferred for Drosophila, and discuss practical considerations
such as interference between selected sites
Diffusion Approximations for Demographic Inference: DaDi
Models of demographic history (population sizes, migration rates, and divergence times) inferred from genetic data complement archeology and serve as null models in genome scans for selection. Most current inference methods are computationally limited to considering simple models or non-recombining data. We introduce a method based on a diffusion approximation to the joint frequency spectrum of genetic variation between populations. Our implementation, DaDi, can model up to three interacting populations and scales well to genome-wide data. We have applied DaDi to human data from Africa, Europe, and East Asia, building the most complex statistically well-characterized model of human migration out of Africa to date
Continuous Theta Rhythm During Spatial Working Memory Task in Rodent Models of Streptozotocin-induced Type 2 Diabetes
Alzheimer’s disease is a neurodegenerative disorder altering memory loss thought to be due to neuropathological symptoms such as the buildup of beta amyloid plaques (Ab) and neurofibrillary tangles (NFT). The etiology of Alzheimer’s is still unknown; however, potential risk factors such as diabetes may lead to its development. The most common form of diabetes is type 2 diabetes known for persistent insulin resistance leading to a state of hyperglycemia. Insulin resistance has been shown to affect cognitive abilities such as learning, memory and also alters synaptic plasticity. Neural connections between the hippocampus (HC) and anterior cingulate cortex (ACC) are known to be very important for learning and memory and are highly plastic, making them an intriguing target that could be altered by hyperglycemia. We hypothesize that hyperglycemic rodents will exhibit spatial memory deficits that may be associated with cognitively linked interactions between the HC and ACC. Minimal doses of streptozotocin (STZ), which is toxic to insulin producing beta cells, were given for 9-10 weeks. Using a spatial working memory task known as delayed alternation we found significant differences between control and experimental rats in working memory accuracy. This task places strong working memory demands on subjects which may be compromised by a hyperglycemic state. We measured EEG recordings from the HC and ACC during task performance and found that hyperglycemic rats had nearly continuous theta rhythm during the 30-minute session. Control rats however, displayed normal transitions between theta and lower frequency delta. Neural connectivity may be altered due to a change in frequency activity between the HC and ACC due to diabetes which is a risk factor in the development of AD impairments. These results show that hyperglycemia leads to changes along the circuit critical for learning and memory
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Reorganization of a government's engineering division to model civilian organization for success
textThe Directorate Public of Works Engineering Service Branch is responsible new designs, renovations of existing construction, and general supervision of new construction. Over the years (especially in the last two or three years), the Design Branch has been perceived as providing a low quality product. The quality can be directly related to personnel issues within the organization such as heavy workloads, low morale, lack of respect for management, and lack of leadership which is required to improve the quality of work. As a result of the evaluation of the current organizational structure and how it contributes to the personnel aspects of its staff I have recommended that the organization transitions from an operational structure to a matrix structure.
I have furthermore, identifying the strengths of the recommended structure and how it will contribute to the improvement in the quality of the design. I have also identified weaknesses of the recommended structure and sought to identify solutions to minimize negative impacts on the organization. The roles and responsibilities are also identified in the recommended matrix organizational structure.Engineering Managemen
Population Genetics of Rare Variants and Complex Diseases
Identifying drivers of complex traits from the noisy signals of genetic
variation obtained from high throughput genome sequencing technologies is a
central challenge faced by human geneticists today. We hypothesize that the
variants involved in complex diseases are likely to exhibit non-neutral
evolutionary signatures. Uncovering the evolutionary history of all variants is
therefore of intrinsic interest for complex disease research. However, doing so
necessitates the simultaneous elucidation of the targets of natural selection
and population-specific demographic history. Here we characterize the action of
natural selection operating across complex disease categories, and use
population genetic simulations to evaluate the expected patterns of genetic
variation in large samples. We focus on populations that have experienced
historical bottlenecks followed by explosive growth (consistent with most human
populations), and describe the differences between evolutionarily deleterious
mutations and those that are neutral. Genes associated with several complex
disease categories exhibit stronger signatures of purifying selection than
non-disease genes. In addition, loci identified through genome-wide association
studies of complex traits also exhibit signatures consistent with being in
regions recurrently targeted by purifying selection. Through simulations, we
show that population bottlenecks and rapid growth enables deleterious rare
variants to persist at low frequencies just as long as neutral variants, but
low frequency and common variants tend to be much younger than neutral
variants. This has resulted in a large proportion of modern-day rare alleles
that have a deleterious effect on function, and that potentially contribute to
disease susceptibility.Comment: 36 pages, 7 figure
Coping with climate change in the tourism industry: a review and agenda for future research
The two-way relationship between tourism and Climate Change has important economic and developmental implications for numerous regions worldwide. Purpose: The purpose of this paper is to present an overview of the existing literature on the relationship between tourism and climate change in order to establish the current state of corporate and institutional responses in the tourism industry and to set out an agenda for research. Methodology: As this is a literature review paper, a comprehensive review was undertaken of the management journals and related topics. Findings: The global or overall impact of tourism on climate has received little attention by researchers. In general, the majority of companies are still in a preliminary phase in terms of
implementing adaptation and mitigation measures. There is a requirement to examine the determinants of these strategies in organisations, as well as their associated outcomes. There is a
need to examine tourist preferences in terms of activities and destinations, the impacts of climate change, and whether and how this affects tourist-consumer decision making. Academic research
has focused mostly on specific and individual solutions to address the impact of climate change on tourism. The analysis of the interplay of these measures and their possible synergies constitute an important topic for future research. Originality: The timeliness of the review is evident given the recent surge in popular debate on climate change, its effects on tourism and the appearance of a broad and disparate array of studies on this topic
Heavy and Light Quarks with Lattice Chiral Fermions
The feasibility of using lattice chiral fermions which are free of
errors for both the heavy and light quarks is examined. The fact that the
effective quark propagators in these fermions have the same form as that in the
continuum with the quark mass being only an additive parameter to a chirally
symmetric antihermitian Dirac operator is highlighted. This implies that there
is no distinction between the heavy and light quarks and no mass dependent
tuning of the action or operators as long as the discretization error is negligible. Using the overlap fermion, we find that the
(and ) errors in the dispersion relations of the pseudoscalar and
vector mesons and the renormalization of the axial-vector current and scalar
density are small. This suggests that the applicable range of may be
extended to with only 5% error, which is a factor of
larger than that of the improved Wilson action. We show that the generalized
Gell-Mann-Oakes-Renner relation with unequal masses can be utilized to
determine the finite errors in the renormalization of the matrix elements
for the heavy-light decay constants and semileptonic decay constants of the B/D
meson.Comment: final version to appear in Int. Jou. Mod. Phys.
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