Rate of adaptation in sexuals and asexuals: A solvable model of the Fisher-Muller effect

The adaptation of large asexual populations is hampered by the competition between independently arising beneficial mutations in different individuals, which is known as clonal interference. Fisher and Muller proposed that recombination provides an evolutionary advantage in large populations by alleviating this competition. Based on recent progress in quantifying the speed of adaptation in asexual populations undergoing clonal interference, we present a detailed analysis of the Fisher-Muller mechanism for a model genome consisting of two loci with an infinite number of beneficial alleles each and multiplicative fitness effects. We solve the infinite population dynamics exactly and show that, for a particular, natural mutation scheme, the speed of adaptation in sexuals is twice as large as in asexuals. Guided by the infinite population result and by previous work on asexual adaptation, we postulate an expression for the speed of adaptation in finite sexual populations that agrees with numerical simulations over a wide range of population sizes and recombination rates. The ratio of the sexual to asexual adaptation speed is a function of population size that increases in the clonal interference regime and approaches 2 for extremely large populations. The simulations also show that the imbalance between the numbers of accumulated mutations at the two loci is strongly suppressed even by a small amount of recombination. The generalization of the model to an arbitrary number $L$ of loci is briefly discussed. If each offspring samples the alleles at each locus from the gene pool of the whole population rather than from two parents, the ratio of the sexual to asexual adaptation speed is approximately equal to $L$ in large populations. A possible realization of this scenario is the reassortment of genetic material in RNA viruses with $L$ genomic segments.Comment: Title has been changed. Supporting Information (animation) can be found in the source file. 53 pages. 10 figures. To appear in Genetic

Large non-adiabatic hole polarons and matrix element effects in the angle-resolved photoemission spectroscopy of dielectric cuprates

It has been made an extention of the conventional theory based on the assumption of the well isolated Zhang-Rice singlet to be a first electron-removal state in dielectric copper oxide. One assumes the photohole has been localised on either small (pseudo)Jahn-Teller polaron or large non-adiabatic polaron enclosed one or four to five $CuO_4$ centers, respectively, with active one-center valent $(^{1}A_{1g}-{}^{1,3}E_{u})$ manifold. In the framework of the cluster model we have performed a model microscopic calculation of the ${\bf k}$-dependence of the matrix element effects and photon polarization effects for the angle-resolved photoemission in dielectric cuprate like $Sr_{2}CuO_{2}Cl_{2}$. We show that effects like the ''remnant Fermi surface'' detected in ARPES experiment for $Ca_{2}CuO_{2}Cl_{2}$ may be, in fact, a reflection of the matrix element effects, not a reflection of the original band-structure Fermi surface, or the strong antiferromagnetic correlations. The measured dispersion-like features in the low-energy part of the ARPES spectra may be a manifestation of the complex momentum-dependent spectral line-shape of the large PJT polaron response, not the dispersion of the well-isolated Zhang-Rice singlet in antiferromagnetic matrix.Comment: 16 pages, TeX, 9 eps figures adde

C–H activation through late transition metal cyclometallation. Addressing selectivity and reactivity problems.

The ligand-directed C—H activation relies on a coordinating donor atom being in proximity to the C—H bond activated. Cyclometallation of 2-(1-naphthyl)-pyridine – a substrate containing both γ- and δ-positions in proximity to the directing nitrogen atom – was studied. Cycloruthenation and cyclopalladation result in γ-substitution and formation of the corresponding 5-membered metallacycles, which is in agreement with published regioselectivities of the corresponding catalytic reactions. Simultaneously, cycloauration and cycloborylation result in δ-substitution and formation of the corresponding 6-membered metallacycles. X-ray structures of all the metallacycles are presented. Deuterium labelling studies show that the cyclopalladation and cycloauration are irreversible, while the cycloruthenation is reversible and happens in both γ- and δ-positions. Attempts to synthesise bimetallic palladium complexes, consisting of two (2-phenyl-pyridine) palladium fragments connected via bridging ligands, resulted predominantly in the formation of monometallic species. While 1,8-naphthyridine and 7-aza-indole bind to palladium in an L-fashion with only one of the two nitrogen atoms, N-piperidine dithiocarbamic acid binds with both sulfur atoms in a chelating, rather than a bridging fashion. 3,3-Dimethylglutaric acid acts as a bridging ligand. X-ray structures of naphthyridine and dithiocarbamate complexes are presented. No increase in the reactivity is observed, when 1,8-naphthyridine, 7-aza-indole and N-piperidine dithiocarbamic acid were used as additives in palladium-catalysed acetoxylation and bromination of 2-phenyl-pyridine. Oxidative anion metathesis was employed as a method of synthesis of organic salts. Trimethylsulfoxonium iodide salts can be converted to tetrafluoroborate, hexafluorophosphate, trifluoroacetate, tosylate and bis-triflimide salts in the presence of hydrogen peroxide and the corresponding acids. The scope of cations, suitable for this reaction also includes N-alkylpyridinium and quaternary phosphonium salts. N-acetoxypyridinium chloride was employed as an oxidant in the palladium-catalysed C—H functionalisation of 2-aryl-pyridine resulting in the formation of the corresponding chloro-derivative. Trimethylsulfoxonium tetrafluoroborate, hexafluorophosphate and tosylate are unreactive as oxidants towards 2-(phenyl)-pyridine palladium acetate. Cyclopalladation of PCP pincer ligands with aromatic and aliphatic backbones by (PhCN)2PdCl2 was shown to proceed at temperatures as low as -62⁰C. The initial interaction results in the formation of a mixture of coordinated species, only some of which react further to form metallacyclic pincer compounds. The formation of pre-cyclometallation intermediates is kinetically disfavoured. However, C—H activation is fast and not rate-limiting in case of neither sp2 nor sp3 C—H bonds

How Altering Gut Microbiota Affects Autism Spectrum Disorder (ASD) and its Associated Gastrointestinal (GI) Symptoms

If the abnormal gut flora and increased GI symptoms in ASD patients are indicative of a pathophysiologic process causing neurobehavioral disturbances, then perhaps altering the gut flora may improve both the GI and neurobehavioral symptoms. Recent research has explored this possibility and produced findings that are promising for treatment with a different approach, altering the gut microbiome

How Altering Gut Microbiota Affects Autism Spectrum Disorder (ASD) and its Associated Gastrointestinal (GI) Symptoms

If the abnormal gut flora and increased GI symptoms in ASD patients are indicative of a pathophysiologic process causing neurobehavioral disturbances, then perhaps altering the gut flora may improve both the GI and neurobehavioral symptoms. Recent research has explored this possibility and produced findings that are promising for treatment with a different approach, altering the gut microbiome