Matching Items (4)

Selection of the AMA-1 Gene in Plasmodium falciparum and Plasmodium vivax

Description

Plasmodium falciparum and Plasmodium vivax are two of the main propagators of human malaria. Both species contain the protein, Apical Membrane Antigen 1 (AMA-1), which is involved in the process

Plasmodium falciparum and Plasmodium vivax are two of the main propagators of human malaria. Both species contain the protein, Apical Membrane Antigen 1 (AMA-1), which is involved in the process of host cell invasion. However, the high degree of polymorphisms and antigenic diversity in this protein has prevented consistent single-vaccine success. Furthermore, the three main domains within AMA-1 (Domains I, II, and III), possess variable polymorphic features and levels of diversity. Overcoming this issue may require an understanding of the type of selection acting on AMA-1 in P. falciparum and P. vivax. Therefore, this investigation aimed to determine the type of selection acting on the whole AMA-1 coding sequence and in each domain for P. falciparum and P. vivax. Population structure was investigated on a global scale and among individual countries. AMA-1 sequences were obtained from the National Center for Biotechnology. For P. falciparum, 649 complete and 382 partial sequences were obtained. For P. vivax, 395 sequences were obtained (370 partial). The AMA-1 gene in P. falciparum was found to possess high nonsynonymous polymorphisms and disproportionately low synonymous polymorphisms. Domain I was found to have the most diverse region with consistently high nonsynonymous substitutions across all countries. Large, positive, and significant Z-test scores indicated the presence of positive selection while FST and NST values showed low genetic differentiation across populations. Data trends for all analyses were relatively consistent for the global and country-based analyses. The only country to deviate was Venezuela, which was the only South American country analyzed. Network analyses did not show distinguishable groupings. For P. falciparum, it was concluded that positive diversifying selection was acting on the AMA-1 gene, particularly in Domain I. In AMA-1 of P. vivax, nonsynonymous and synonymous polymorphisms were relatively equal across all analyses. FST and NST values were high, indicating that countries were genetically distinct populations. Network analyses did not show distinguishable grouping; however, the data was limited to small sample sizes. From the data, it was concluded that AMA-1 in P. vivax was evolving neutrally, where selective pressures did not strongly encourage positive or purifying selection specifically. In addition, different AMA-1 P. vivax strains were genetically distinct and this genetic identity correlated with geographic region. Therefore, AMA-1 strains in P. falciparum and P. vivax not only evolve differently and undergo different form of selection, but they also require different vaccine development strategies. A combination of strain-specific vaccines along with preventative measures on an environmental level will likely be more effective than trying to achieve a single, comprehensive vaccine.

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Created

Date Created
  • 2015-05

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The Effects of Natural Selection, Drift, and Genetic Background on Phenotypic Variation and Correlation in E. coli

Description

Phenotypic evolution is an essential topic within the general field of evolution. Theoretically, the outcome of phenotypic evolution may be influenced by factors such as genetic background and the interaction

Phenotypic evolution is an essential topic within the general field of evolution. Theoretically, the outcome of phenotypic evolution may be influenced by factors such as genetic background and the interaction of natural selection and genetic drift. To gain empirical evidence for testing the effects of those factors, we used eight long-term evolved Escherichia coli populations as a model system. These populations differ in terms of genetic background (different mutation rates) as well as bottleneck size (small- and large-magnitude). Specifically, we used a plate reader to measure three growth-related traits: maximum growth rate (umax), carrying capacity (Kc), and lag time (Lt) for 40 clones within each population. For each trait we quantified the change in mean per generation, the change in variance per generation, and the correlation coefficient between pairs of traits. Interestingly, we found that the small and large bottleneck populations of one background displayed clear, distinguishing trends that were not present within the populations of the other background. This leads to the conclusion that the influence of selection and drift on a population’s phenotypic outcomes is itself influenced by the genetic background of that population. Additionally, we found a strong positive correlation between umax and Kc within each of the high-mutation populations that was not consistent with our neutral expectation. However, the other two pairs did not exhibit a similar pattern. Our results provide a novel understanding in the relationship between the evolution of E. coli growth-related phenotypes and the population-genetic environment.

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Created

Date Created
  • 2020-05

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Improving the Saudi Arabia Procurement System: Perception and Development of the Construction Industry

Description

ABSTRACT

The current Saudi Arabian (SA) procurement system leads to many losses in money and benefits in projects. Also, the use of the traditional procurement system in SA has been identified

ABSTRACT

The current Saudi Arabian (SA) procurement system leads to many losses in money and benefits in projects. Also, the use of the traditional procurement system in SA has been identified as one of the causes for poor performance in the delivery of construction and the major risk to the SA government. A questionnaire has been developed and carefully designed based on literature review. The purpose of the survey was to identify the validity of the recent claims that the procurement system in SA is broken and to improve the current SA procurement system. The questionnaire was sent out to 1,396 participants including included 867 engineers, 256 consultants, 93 contractors, 35 owners and 132 architects and 13 academics.

All participants have been registered and licensed professionals at the SA Council for professional engineers, who work in both private and public sectors. The participants are interested in the SA procurement and contracts system with experience ranging from one to more than twenty-five years with the majority of twenty-five years of experience in common construction sectors such as; residential and commercial buildings, healthcare buildings, industrial building and heavy civil construction.

Most of the participants from both private and public sectors agreed with the survey questions subject matter regarding: zone price proposals, contractors' evaluation, risks, planning, projects' scope, owners concern and weekly risks reports (WRR). The survey results showed that the procurement system is the major risk to projects, affects construction projects negatively and is in need of improvement.

Based on the survey and literature review, a model, called Saudi government performance procurement model (SGPPM), has been developed in which the most expert contractor is chosen through four phases: submittals& education, vendors selection, illustration and execution. The resulting model is easy to implement by SA government and does not require special skills or backgrounds.

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Created

Date Created
  • 2017

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Differences in Fruit and Vegetable Consumption Among Children Related to Serving Container Color

Description

Background: Children’s fruit and vegetable consumption in the United States is lower than recommended. School lunch is an opportunity for students to be exposed to fruits and vegetables and potentially

Background: Children’s fruit and vegetable consumption in the United States is lower than recommended. School lunch is an opportunity for students to be exposed to fruits and vegetables and potentially increase their daily intake. The purpose of this study is to examine the relationship between tray color and fruit and vegetable selection, consumption, and waste at lunch.

Methods: Study participants (n=1469) were elementary and middle school students who ate school lunch on the day of data collection. Photographs and weights (to nearest 2 g) were taken of fruits and vegetables on students’ trays before and after lunch. Trained research assistants viewed photographs and sorted trays into variable categories: color of main tray, presence/absence of secondary fruit/vegetable container, and color of secondary fruit/vegetable container. Fruit and vegetable selection, consumption, and waste were calculated using tray weights. Negative binomial regression models adjusted for gender, grade level, race/ethnicity, free/reduced price lunch status, and within-school similarities were used to examine relationships between tray color and fruit and vegetable selection, consumption, and waste.

Results: Findings indicated that students with a light tray selected (IRR= 0.44), consumed (IRR=0.73) and wasted (IRR=0.81) less fruit and vegetables. Students without a secondary fruit/vegetable container selected (IRR=0.66) and consumed (IRR=0.49) less fruit and vegetables compared to those with a secondary container. Light or clear secondary fruit and vegetable containers were related to increased selection (IRR=2.06 light, 2.30 clear) and consumption (IRR=1.95 light, 2.78 clear) compared to dark secondary containers, while light secondary containers were related to decreased waste (IRR= 0.57).

Conclusion: Tray color may influence fruit and vegetable selection, consumption, and waste among students eating school lunch. Further research is needed to determine if there is a cause and effect relationship. If so, adjusting container colors may be a practical intervention for schools hoping to increase fruit and vegetable intake among students.

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Created

Date Created
  • 2020