1,721,467 research outputs found
CpG islands in human X-inactivation
No full textSequence comparison analyses have been carried out for 19 genes escaping X-inactivation versus 73 genes subject to X-inactivation, and 100 randomly chosen X chromosome genes versus 100 randomly chosen autosomal genes. The coding sequence of the genes and their upstream and downstream flanking sequences were investigated using a series of windows (1 kb, 2 kb, 5 kb, 10 kb and 100 kb). No significant difference in number of LINE-L1 elements was observed in genes escaping X-inactivation compared to genes subject to X-inactivation. This result, therefore, does not support the suggestion that lack of LINE repeat elements is a key factor for genes escaping X-inactivation. However, significantly reduced numbers of CpG islands and SINE MIR elements were found to be associated with genes escaping X-inactivation. Compared to genes known to be inactivated, genes escaping X-inactivation were observed to have fewer CpG islands, particularly within the 2 kb upstream flanking sequence close to the coding region. The results suggest that CpG islands may play a role in the process of X-inactivation by providing sufficient DNA methylation targets for the maintenance of X-inactivation. Lack of CpG islands may be a major reason for genes escaping X-inactivation regulation
LDB2000: sequence-based integrated maps of the human genome
No full textMOTIVATION:
Integrated maps are useful for gene mapping and establishing the relationship between recombination and sequence. In this paper we describe algorithms and their implementation for constructing sequence-based integrated maps of the human chromosomes, which are presented in LDB2000, a web based resource. Gene mapping efforts are now focussing on linkage disequilibrium mapping and extension of the integrated map to represent the extent of linkage disequilibrium in different genomic regions would further increase the utility of these maps.
RESULTS:
Sequence-based integrated maps have been completed for chromosomes 21 and 22. These maps provide locations for genes and polymorphic markers in sequence and on genetic linkage, radiation hybrid and cytogenetic scales. Single nucleotide polymorphisms associated with genes in the maps are also included and their sequence locations indicated. Related locus information, such as aliases and expression information, can be searched on the WWW site
Tidally-induced flow structure over intertidal flats
No full textPrevious investigations have assumed that a significant linear relationship between uz-lnZis sufficient to define a logarithmic velocity profile given by the von Kármán–Prandtl equation. However, it is demonstrated here that such a criterion alone is insufficient.An internal consistency analysis is developed to establish realistic logarithmic velocity profiles, in the estimation of boundary layer parameters associated with intertidal flat environments. The analytical procedure includes: (i) onward linear regression, to establish the relationship between apparent u*values and near-bed current speeds, uz (here, the observed u50 is used); (ii) an assessment of the constant and correlation coefficient within the u*–uz relationship; (iii) calculation of z0 and C50 values, on the basis of the slope of the regression line; and (iv) undertaking a comparison between the derived z0 and C50 and those obtained using the instantaneous velocity profiles. The internal consistency is shown to be enhanced if the data are filtered, before a more detailed analysis.This approach is applied to the analysis of 192 current velocity (gradient rig) data sets collected from the intertidal flats of the Loughor Estuary and Swansea Bay (South Wales), and The Wash (eastern England). Overall, less than 40% of the data sets are logarithmic in character, with variations between the various stations. Nevertheless, boundary layer parameters were determined for most locations. Non-logarithmic profiles on intertidal flats are considered to be caused by: (i) rotary tidal currents; (ii) wind effects; (iii) wave action and other short-period oscillations; and (iv) topographically-induced secondary flows. Measurement errors can lead also to deviations from an ‘idealized’ logarithmic profile
Fluvial/wave interaction controls on delta formation for ephemeral rivers discharging into microtidal
No full text.Interaction between freshwater supply and wave activity is described in relation to delta formation associated with ephemeral Greek rivers, discharging into tideless ambient waters. The controlling variables are investigated using the discharge effectiveness index (E f), as applied elsewhere to worldwide large river systems.E f values differ in magnitude for large- and small-scale river/delta systems, characterized by analogous shoreline configurations (i.e., fluvially or wave-dominated). Seasonal fluctuations in river input and wave energy control the evolution of the small systems. High sediment fluxes, related to flood events, are also of fundamental importance to delta evolution.<br/
- …
