| 11. |
- Jallow, Muminatou, et al.
(author)
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Genome-wide and fine-resolution association analysis of malaria in West Africa.
- 2009
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In: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; , s. 657-665
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Journal article (peer-reviewed)abstract
- We report a genome-wide association (GWA) study of severe malaria in The Gambia. The initial GWA scan included 2,500 children genotyped on the Affymetrix 500K GeneChip, and a replication study included 3,400 children. We used this to examine the performance of GWA methods in Africa. We found considerable population stratification, and also that signals of association at known malaria resistance loci were greatly attenuated owing to weak linkage disequilibrium (LD). To investigate possible solutions to the problem of low LD, we focused on the HbS locus, sequencing this region of the genome in 62 Gambian individuals and then using these data to conduct multipoint imputation in the GWA samples. This increased the signal of association, from P = 4 x 10(-7) to P = 4 x 10(-14), with the peak of the signal located precisely at the HbS causal variant. Our findings provide proof of principle that fine-resolution multipoint imputation, based on population-specific sequencing data, can substantially boost authentic GWA signals and enable fine mapping of causal variants in African populations.
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| 12. |
- Jones, Owen R., et al.
(author)
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Senescence rates are determined by ranking on the fast-slow life-history continuum
- 2008
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In: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 11:7, s. 664-673
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Journal article (peer-reviewed)abstract
- Comparative analyses of survival senescence by using life tables have identified generalizations including the observation that mammals senesce faster than similar-sized birds. These generalizations have been challenged because of limitations of life-table approaches and the growing appreciation that senescence is more than an increasing probability of death. Without using life tables, we examine senescence rates in annual individual fitness using 20 individual-based data sets of terrestrial vertebrates with contrasting life histories and body size. We find that senescence is widespread in the wild and equally likely to occur in survival and reproduction. Additionally, mammals senesce faster than birds because they have a faster life history for a given body size. By allowing us to disentangle the effects of two major fitness components our methods allow an assessment of the robustness of the prevalent life-table approach. Focusing on one aspect of life history - survival or recruitment - can provide reliable information on overall senescence.
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| 13. |
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| 14. |
- Kumar, Ravhi S., et al.
(author)
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Pressure-induced valence change in YbAl3 : A combined high-pressure inelastic x-ray scattering and theoretical investigation
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:7, s. 075117-
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Journal article (peer-reviewed)abstract
- High-resolution x-ray-absorption (XAS) experiments in the partial fluorescence yield mode (PFY) and resonant inelastic x-ray emission (RXES) measurements were performed on the intermediate-valence compound YbAl3 under pressure of up to 38 GPa. The results of the YbAl3 PFY-XAS and RXES studies show that the valence of Yb increases smoothly from 2.75 at ambient pressure to 2.93 at 38 GPa. In situ angle-dispersive synchrotron high-pressure x-ray-diffraction experiments carried out using a diamond cell at room temperature show that the ambient pressure cubic phase is stable up to 40 GPa. The results obtained from self-interaction corrected local spin density-functional calculations to understand the pressure effect on the Yb valence and compressibility are in good agreement with the experimental results.
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| 15. |
- Poulton, Alex J., et al.
(author)
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Phytoplankton carbon fixation, chlorophyll-biomass and diagnostic pigments in the Atlantic Ocean
- 2006
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In: Deep-sea research. Part II, Topical studies in oceanography. - : Elsevier BV. - 0967-0645 .- 1879-0100. ; 53:14-16, s. 1593-1610
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Journal article (peer-reviewed)abstract
- We have made daily measurements of phytoplankton pigments, size-fractionated (< 2 and > 2-mu m) carbon fixation and chlorophyll-a concentration during four Atlantic Meridional Transect (AMT) cruises in 2003-04. Surface rates of carbon fixation ranged from < 0.2-mmol C m(-3) d(-1) in the subtropical gyres to 0.2-0.5-mmol C m(-3) d(-1) in the tropical equatorial Atlantic. Significant intercruise variability was restricted to the subtropical gyres, with higher chlorophyll-a concentrations and carbon fixation in the subsurface chlorophyll maximum during spring in either hemisphere. In surface waters, although picoplankton (<-mu m) represented the dominant fraction in terms of both carbon fixation (50-70%) and chlorophyll-alpha (80-90%), nanoplankton (> 2-mu m) contributions to total carbon fixation (30-50%) were higher than to total chlorophyll-alpha (10-20%). However, in the subsurface chlorophyll maximum picoplankton dominated both carbon fixation (70-90%) and chlorophyll-alpha (70-90%). Thus, in surface waters chlorophyll-normalised carbon fixation was 2-3 times higher for nanoplankton and differences in picoplankton and nanoplankton carbon to chlorophyll-alpha ratios may lead to either higher or similar growth rates. These low chlorophyll-normalised carbon fixation rates for picoplankton may also reflect losses of fixed carbon (cell leakage or respiration), decreases in photosynthetic efficiency, grazing losses during the incubations, or some combination of all these. Comparison of nitrate concentrations in the subsurface chlorophyll maximum with estimates of those required to support the observed rates of carbon fixation (assuming Redfield stoichiometry) indicate that primary production in the chlorophyll maximum may be light rather than nutrient limited.
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| 16. |
- Swarup, Ranjan, et al.
(author)
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Ethylene upregulates auxin biosynthesis in Arabidopsis seedlings to enhance inhibition of root cell elongation.
- 2007
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In: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 19:7, s. 2186-96
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Journal article (peer-reviewed)abstract
- Ethylene represents an important regulatory signal for root development. Genetic studies in Arabidopsis thaliana have demonstrated that ethylene inhibition of root growth involves another hormone signal, auxin. This study investigated why auxin was required by ethylene to regulate root growth. We initially observed that ethylene positively controls auxin biosynthesis in the root apex. We subsequently demonstrated that ethylene-regulated root growth is dependent on (1) the transport of auxin from the root apex via the lateral root cap and (2) auxin responses occurring in multiple elongation zone tissues. Detailed growth studies revealed that the ability of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid to inhibit root cell elongation was significantly enhanced in the presence of auxin. We conclude that by upregulating auxin biosynthesis, ethylene facilitates its ability to inhibit root cell expansion.
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