9,069 research outputs found
Phylogenies and the forces of evolution
The construction of phylogenetic trees from gene frequency data assumes that a history of binary fissioning of populations has been the major cause of genetic variation. However, in many areas of the world human populations have been relatively stable with local gene flow. This population history is closer to an isolation by distance model. It was modelled by a simulation of gene frequency changes in a linear sequence of 50 stable populations with gene flow among neighboring populations. Phylogenetic trees were constructed from the gene frequencies after the simulation was run for 500 generations. Using only a few loci there is little correlation between genetic and geographic distance, but with 40 or more loci, there was a perfect correlation with geographic distance. A different population model can thus result in a phylogenetic tree comparable to those assumed to be produced by binary fission.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38549/1/1310030202_ftp.pd
Genetic drift at expanding frontiers promotes gene segregation
Competition between random genetic drift and natural selection plays a
central role in evolution: Whereas non-beneficial mutations often prevail in
small populations by chance, mutations that sweep through large populations
typically confer a selective advantage. Here, however, we observe chance
effects during range expansions that dramatically alter the gene pool even in
large microbial populations. Initially well-mixed populations of two
fluorescently labeled strains of Escherichia coli develop well-defined,
sector-like regions with fractal boundaries in expanding colonies. The
formation of these regions is driven by random fluctuations that originate in a
thin band of pioneers at the expanding frontier. A comparison of bacterial and
yeast colonies (Saccharomyces cerevisiae) suggests that this large-scale
genetic sectoring is a generic phenomenon that may provide a detectable
footprint of past range expansions.Comment: Please visit http://www.pnas.org/content/104/50/19926.abstract for
published articl
How to make experimental economics research more reproducible: lessons from other disciplines and a new proposal
Efforts in the spirit of this special issue aim at improving the reproducibility of experimental economics, in response to the recent discussions regarding the “research reproducibility crisis.” We put this endeavour in perspective by summarizing the main ways (to our knowledge) that have been proposed – by researchers from several disciplines – to alleviate the problem. We discuss the scope for economic theory to contribute to evaluating the proposals. We argue that a potential key impediment to replication is the expectation of negative reactions by the authors of the individual study, and suggest that incentives for having one’s work replicated should increase
A Technique of Direct Tension Measurement of a Strung Fine Wire
We present a new technique of direct measurement of wire tensions in wire
chambers. A specially designed circuit plucks the wire using the Lorentz force
and measures the frequency of damped transverse oscillations of the wire. The
technique avoids the usual time-consuming necessity of tuning circuit parameter
to a resonance. It allows a fast and convenient determination of tensions and
is straightforward to implement.Comment: 15 pages with 9 figure
On the within-sibship variance
An approximate formula for the expected within-sibship genotypic variance of a polygenic, diallelic, additive character is obtained for arbitrary recombination between the loci affecting the character. The formula is exact, when there is no recombination, or when the recombination is free. It is also shown that, if the value of (one-half of the parental genotypic variance) is assigned to the within-sibship genotypic variance, as in the model of Cavalli-Sforza and Feldman (1976, Proc. Natl. Acad. Sci. USA 73, 1689-1692), it implies the assumptions of random mating and of the perfect linkage. If, on the other hand, the value of (one-half of the linkage equilibrium genotypic variance) is assigned to the within-sibship variance, as in the model of Rice, Cloninger, and Reich (1978, Amer. J. Hum. Genet. 30, 618-643), it implies the assumptions of random mating and either of the free recombination, or of the linkage equilibrium, if the recombination is not free.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25254/1/0000697.pd
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