732 research outputs found
The Adaptive Significance of Natural Genetic Variation in the DNA Damage Response of Drosophila melanogaster.
Despite decades of work, our understanding of the distribution of fitness effects of segregating genetic variants in natural populations remains largely incomplete. One form of selection that can maintain genetic variation is spatially varying selection, such as that leading to latitudinal clines. While the introduction of population genomic approaches to understanding spatially varying selection has generated much excitement, little successful effort has been devoted to moving beyond genome scans for selection to experimental analysis of the relevant biology and the development of experimentally motivated hypotheses regarding the agents of selection; it remains an interesting question as to whether the vast majority of population genomic work will lead to satisfying biological insights. Here, motivated by population genomic results, we investigate how spatially varying selection in the genetic model system, Drosophila melanogaster, has led to genetic differences between populations in several components of the DNA damage response. UVB incidence, which is negatively correlated with latitude, is an important agent of DNA damage. We show that sensitivity of early embryos to UVB exposure is strongly correlated with latitude such that low latitude populations show much lower sensitivity to UVB. We then show that lines with lower embryo UVB sensitivity also exhibit increased capacity for repair of damaged sperm DNA by the oocyte. A comparison of the early embryo transcriptome in high and low latitude embryos provides evidence that one mechanism of adaptive DNA repair differences between populations is the greater abundance of DNA repair transcripts in the eggs of low latitude females. Finally, we use population genomic comparisons of high and low latitude samples to reveal evidence that multiple components of the DNA damage response and both coding and non-coding variation likely contribute to adaptive differences in DNA repair between populations
Multiplicity Distributions in Canonical and Microcanonical Statistical Ensembles
The aim of this paper is to introduce a new technique for calculation of
observables, in particular multiplicity distributions, in various statistical
ensembles at finite volume. The method is based on Fourier analysis of the
grand canonical partition function. Taylor expansion of the generating function
is used to separate contributions to the partition function in their power in
volume. We employ Laplace's asymptotic expansion to show that any equilibrium
distribution of multiplicity, charge, energy, etc. tends to a multivariate
normal distribution in the thermodynamic limit. Gram-Charlier expansion allows
additionally for calculation of finite volume corrections. Analytical formulas
are presented for inclusion of resonance decay and finite acceptance effects
directly into the system partition function. This paper consolidates and
extends previously published results of current investigation into properties
of statistical ensembles.Comment: 53 pages, 7 figure
Particle Number Fluctuations in Canonical Ensemble
Fluctuations of charged particle number are studied in the canonical
ensemble. In the infinite volume limit the fluctuations in the canonical
ensemble are different from the fluctuations in the grand canonical one. Thus,
the well-known equivalence of both ensembles for the average quantities does
not extend for the fluctuations. In view of a possible relevance of the results
for the analysis of fluctuations in nuclear collisions at high energies, a role
of the limited kinematical acceptance is studied.Comment: 13 pages, 9 figures, LaTe
Multiplicity fluctuations in relativistic nuclear collisions
Multiplicity distributions of hadrons produced in central nucleus-nucleus
collisions are studied within the hadron-resonance gas model in the large
volume limit. In the canonical ensemble conservation of three charges (baryon
number, electric charge, and strangeness) is enforced. In addition, in the
micro-canonical ensemble energy conservation is included. An analytical method
is used to account for resonance decays. Multiplicity distributions and scaled
variances for negatively charged hadrons are presented along the chemical
freeze-out line of central Pb+Pb (Au+Au) collisions from SIS to LHC energies.
Predictions obtained within different statistical ensembles are compared with
preliminary NA49 experimental results on central Pb+Pb collisions in the SPS
energy range. The measured fluctuations are significantly narrower than a
Poisson reference distribution, and clearly favor expectations for the
micro-canonical ensemble.Comment: 6 pages, 3 figure
Pion Number Fluctuations and Correlations in the Statistical System with Fixed Isospin
The statistical system of pions with zero total isospin is studied. The
suppression effects for the average yields due to isospin conservation are the
same for , and . However, a behavior of the corresponding
particle number fluctuations are different. For neutral pions there is the
enhancement of the fluctuations, whereas for charged pions the isospin
conservation suppresses fluctuations. The correlations between the numbers of
charged and neutral pions are observed for finite systems. This causes a
maximum of the total pion number fluctuations for small systems. The
thermodynamic limit values for the scaled variances of neutral and charged
pions are calculated. The enhancements of the fluctuations due to Bose
statistics are found and discussed
Particle Number Fluctuations in Statistical Model with Exact Charge Conservation Laws
Even though the first momenta i.e. the ensemble average quantities in
canonical ensemble (CE) give the grand canonical (GC) results in large
multiplicity limit, the fluctuations involving second moments do not respect
this asymptotic behaviour. Instead, the asymptotics are strikingly different,
giving a new handle in study of statistical particle number fluctuations in
relativistic nuclear reactions. Here we study the analytical large volume
asymptotics to general case of multispecies hadron gas carrying fixed baryon
number, strangeness and electric charge. By means of Monte Carlo simulations we
have also studied the general multiplicity probability distributions taking
into account the decay chains of resonance states.Comment: 4 pages, 2 figures. The report of the talk given in Strangeness in
Quark Matter 2004, Cape Town. Submitted to J. Phys. G: Nucl. Part. Phy
Multiplicity Fluctuations in the Pion-Fireball Gas
The pion number fluctuations are considered in the system of pions and large
mass fireballs decaying finally into pions. A formulation which gives an
extension of the model of independent sources is suggested. The grand canonical
and micro-canonical ensemble formulations of the pion-fireball gas are
considered as particular examples.Comment: 13 pages, 4 figure
Rampant Adaptive Evolution in Regions of Proteins with Unknown Function in Drosophila simulans
Adaptive protein evolution is pervasive in Drosophila. Genomic studies, thus far, have analyzed each protein as a single entity. However, the targets of adaptive events may be localized to particular parts of proteins, such as protein domains or regions involved in protein folding. We compared the population genetic mechanisms driving sequence polymorphism and divergence in defined protein domains and non-domain regions. Interestingly, we find that non-domain regions of proteins are more frequent targets of directional selection. Protein domains are also evolving under directional selection, but appear to be under stronger purifying selection than non-domain regions. Non-domain regions of proteins clearly play a major role in adaptive protein evolution on a genomic scale and merit future investigations of their functional properties
Strongly Intensive Measures for Multiplicity Fluctuations
The recently proposed two families of strongly intensive measures of
fluctuations and correlations are studied within Hadron-String-Dynamics (HSD)
transport approach to nucleus-nucleus collisions. We consider the measures
and for kaon and pion multiplicities in Au+Au
collisions in a wide range of collision energies and centralities. These
strongly intensive measures appear to cancel the participant number
fluctuations. This allows to enlarge the centrality window in the analysis of
event-by-event fluctuations up to at least of 10% most central collisions. We
also present a comparison of the HSD results with the data of NA49 and STAR
collaborations. The HSD describes reasonably well. However, the
HSD results depend monotonously on collision energy and do not reproduce the
bump-deep structure of observed from the NA49 data in the
region of the center of mass energy of nucleon pair
GeV. This fact deserves further studies. The origin of this `structure' is not
connected with simple geometrical or limited acceptance effects, as these
effects are taken into account in the HSD simulations
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