Drift Shape Research Articles

Intercontinental population structure of the chestnut blight fungus,Cryphonectria parasitica

The population structure of the chestnut blight fungus, Cryphonectria parasitica was analyzed using restriction fragment length polymorphisms (RFLPs). A total of 791 isolates were sampled from four regions, China, Japan, North America and Europe, and assayed for alleles at eight RFLP loci. Alleles at all eight loci segregated in simple Mendelian ratios, and most loci were unlinked. Gene diversity was decomposed hierarchically: 56% of gene diversity was attributable to diversity within subpopulations, compared to 7% among subpopulations within regions, and 37% among regions. Subpopulations of C. parasitica in China have distinctly different allele frequencies from subpopulations in other regions, including Japan. DNA fingerprint genotypes in China were also significandy different from those in the other regions. There was an average of 3.2 restriction fragments hybridizing to a DNA fingerprinting probe in Chinese isolates from 11 subpopulations compared to 8.6 in isolates from Japan; the exception was in one subpopulation in northeastern China where there was an average of 11.1 fragments per isolate. North American and European subpopulations were similar to each other, and more similar to Japan than to China, for both RFLP allele frequencies and DNA fingerprints. The results suggest that C. parasitica was introduced into North America from Japan, not China. The origin of C. parasitica for European subpopulations cannot be determined from these results, but eastern China was not a likely source. Analysis of population structure within China showed moderate differentiation, with 11% of gene diversity attributable to differences among subpopulations (ĜST = 0.11). Pairwise estimates of gene flow between sub-populations were negatively correlated to geographic distances between subpopulations in China. This result suggests that Chinese populations are in equilibrium, and that restricted gene flow and genetic drift shape these populations.

Intercontinental Population Structure of the Chestnut Blight Fungus, Cryphonectria parasitica

The population structure of the chestnut blight fungus, Cryphonectria parasitica was analyzed using restriction fragment length polymorphisms (RFLPs). A total of 791 isolates were sampled from four regions, China, Japan, North America and Europe, and assayed for alleles at eight RFLP loci. Alleles at all eight loci segregated in simple Mendelian ratios, and most loci were unlinked. Gene diversity was decomposed hierarchically: 56% of gene diversity was attributable to diversity within subpopulations, compared to 7% among subpopulations within regions, and 37% among regions. Subpopulations of C. parasitica in China have distinctly different allele frequencies from subpopulations in other regions, including Japan. DNA fingerprint genotypes in China were also significandy different from those in the other regions. There was an average of 3.2 restriction fragments hybridizing to a DNA fingerprinting probe in Chinese isolates from 11 subpopulations compared to 8.6 in isolates from Japan; the exception was in one subpopulation in northeastern China where there was an average of 11.1 fragments per isolate. North American and European subpopulations were similar to each other, and more similar to Japan than to China, for both RFLP allele frequencies and DNA fingerprints. The results suggest that C. parasitica was introduced into North America from Japan, not China. The origin of C. parasitica for European subpopulations cannot be determined from these results, but eastern China was not a likely source. Analysis of population structure within China showed moderate differentiation, with 11% of gene diversity attributable to differences among subpopulations (ĜST = 0.11). Pairwise estimates of gene flow between sub-populations were negatively correlated to geographic distances between subpopulations in China. This result suggests that Chinese populations are in equilibrium, and that restricted gene flow and genetic drift shape these populations.

Scaling snowdrift development rate

AbstractFor successful snowdrift modelling, measured drift shapes should be geometrically similar to full‐scale shapes and develop at rates that scale in a known manner. Consensus exists on most modelling methods and the similitude requirements needed to meet these objectives. A notable exception is the manner to scale drift development rates. A rationale is presented for rate scaling based on an independent model and prototype mass transport measurements. This approach is validated by comparing the rate of drift development for a model Wyoming snow fence with corresponding field data. This method yields excellent agreement, whereas the alternatives differ substantially.

An estimated shape function for drift in a platelet-transport model

Prior work has shown that concentration profiles of platelets in flowing whole blood and of platelet-sized beads in flowing blood suspensions can include near-wall excesses. A model to describe this phenomenon was built about a single-component convective diffusion equation. To incorporate redistribution to preferred sites by shear flows of red cell suspensions, the model used a drift shape function (in addition to the commonly used augmented diffusion coefficient). This paper reports experiments that provide an average concentration profile from which the shape function for that model is calculated; the experiments and shape function are for the particular conditions of 40% hematocrit, platelet-sized latex beads (2.5 microns diameter), tube ID of 217 microns, and a wall shear rate of 555 s-1. Less precise estimates of the shape function obtained from data of previous studies indicate that the shape function is similar for the hematocrit of 15%.