scholarly journals Direct evidence of bi-directional sex change in natural populations of the oysters Saccostrea kegaki and S. mordax

2017 ◽  
Vol 12 (1) ◽  
pp. 78-81 ◽  
Author(s):  
Noriko Yasuoka ◽  
Yoichi Yusa
Keyword(s):  
Direct Evidence ◽  
Natural Populations ◽  
Sex Change

scholarly journals Evidence for a force favoring GC over AT at short intronic sites in Drosophila simulans and D. melanogaster

2021 ◽  
Author(s):  
Ben Jackson ◽  
Brian Charlesworth
Keyword(s):  
Gene Conversion ◽  
Direct Evidence ◽  
Natural Populations ◽  
Gc Content ◽  
Spontaneous Mutations ◽  
Selective Pressures ◽  
Use Of Data ◽  
Large Numbers ◽  
Biased Gene Conversion ◽  
Long Timescales

Abstract Population genetics studies often make use of a class of nucleotide site free from selective pressures, in order to make inferences about population size changes or natural selection at other sites. If such neutral sites can be identified, they offer the opportunity to avoid any confounding effects of selection. Here we investigate evolution at putatively neutrally evolving short intronic sites in natural populations of Drosophila melanogaster and D. simulans, in order to understand the properties of spontaneous mutations and the extent of GC-biased gene conversion in these species. Use of data on the genetics of natural populations is advantageous because it integrates information from large numbers of individuals over long timescales. In agreement with direct evidence from observations of spontaneous mutations in Drosophila, we find a bias in the spectrum of mutations towards AT basepairs. In addition, we find that this bias is stronger in the D. melanogaster lineage than in the D. simulans lineage. The evidence for GC-biased gene conversion in Drosophila has been equivocal. Here we provide evidence for a weak force favoring GC in both species, which is correlated with the GC content of introns and is stronger in D. simulans than in D. melanogaster.

scholarly journals Evidence for a force favouring GC over AT at short intronic sites in Drosophila simulans and D. melanogaster

2021 ◽  
Author(s):  
Ben Jackson ◽  
Brian Charlesworth
Keyword(s):  
Gene Conversion ◽  
Direct Evidence ◽  
Natural Populations ◽  
Gc Content ◽  
Spontaneous Mutations ◽  
Selective Pressures ◽  
Use Of Data ◽  
Large Numbers ◽  
Biased Gene Conversion ◽  
Long Timescales

AbstractPopulation genetics studies often make use of a class of nucleotide site free from selective pressures in order to make inferences about population size changes or natural selection at other sites. If such neutral sites can be identified, they offer the opportunity to avoid any confounding effects of selection. Here we investigate evolution at putatively neutrally evolving short intronic sites in natural populations of Drosophila melanogaster and D. simulans, in order to understand the properties of spontaneous mutations and the extent of GC-biased gene conversion in these species. Use of data on the genetics of natural populations is advantageous because it integrates information from large numbers of individuals over long timescales. In agreement with direct evidence from observations of spontaneous mutations in Drosophila, we find a bias in the spectrum of mutations towards AT basepairs. In addition, we find that this bias is stronger in the D. melanogaster lineage than the D. simulans lineage. The evidence for GC-biased gene conversion in Drosophila has been equivocal. Here we provide evidence for a weak force favouring GC in both species, which is stronger in D. simulans. Some homologous short intronic sites have diverged in GC content between the two species, which may have been caused by lineage-specific changes in the extent to which different regions of the genome are subject to a GC (or AT)-favouring force.

Introduction

1956 ◽  
Vol 145 (920) ◽  
pp. 291-293 ◽  
Keyword(s):  
Direct Evidence ◽  
Charles Darwin ◽  
Natural Populations ◽  
Wild Populations ◽  
Natural Conditions ◽  
Genetical Theory ◽  
To Come ◽  
Many Sources ◽  
Made In

It has seemed appropriate to hold a Discussion Meeting on this subject owing to the remarkable advances made in it during recent years. These are due principally to a realization that, in certain conditions evolution takes place in natural populations much more rapidly than had previously been suspected. Thus Major Leonard Darwin told me that he once discussed with his father the possibility of observing what we now call ‘evolution'* occurring in natural conditions. Charles Darwin said that if data were properly collected, they might reveal 'perhaps in no more than fifty years' the progress of evolutionary change. His son expressed himself as somewhat appalled at collecting data for the use only of posterity. Darwin replied that he could see no objection to this for, since astronomers often make observations which are only of value in generations to come, why should not biologists do the same? Further, the greatest work of evolutionary theory to appear this century, Sir Ronald Fisher’s Genetical theory of natural selection , published in 1930, is principally concerned with selective advantages of 1 % or less. For even a quarter of a century ago little evidence of evolution had been obtained by direct observation, while to Darwin the attempt to amass such, except as a long-term policy, seemingly appeared vain. The situation is now changed and direct evidence of evolution from the study of wild populations is beginning to accumulate from many sources. It is worth while to consider briefly to what this is due.

The Immuno-Electron Microscopic Localization of the Mo-Fe Protein Component of Nitrogenase in Cells of Azotobacter Vinelandii

1973 ◽  
Vol 31 ◽  
pp. 574-575
Author(s):  
J. T. Stasny ◽  
R. C. Burns ◽  
R. W. F. Hardy
Keyword(s):  
Cellular Localization ◽  
Direct Evidence ◽  
Azotobacter Vinelandii ◽  
Intracellular Localization ◽  
Protein Component ◽  
Electron Microscopic ◽  
Thin Sections ◽  
Fe Protein ◽  
Intracytoplasmic Membranes

Structure-functlon studies of biological N2-fixation have correlated the presence of the enzyme nitrogenase with increased numbers of intracytoplasmic membranes in Azotobacter. However no direct evidence has been provided for the internal cellular localization of any nitrogenase. Recent advances concerned with the crystallizatiorTand the electron microscopic characterization of the Mo-Fe protein component of Azotobacter nitrogenase, prompted the use of this purified protein to obtain antibodies (Ab) to be conjugated to electron dense markers for the intracellular localization of the protein by electron microscopy. The present study describes the use of ferritin conjugated to goat antitMo-Fe protein immunoglobulin (IgG) and the observations following its topical application to thin sections of N2-grown Azotobacter.

Structural similarity of ribosomes from E. coli and A. salina

1978 ◽  
Vol 36 (2) ◽  
pp. 242-243
Author(s):  
M. Boublik ◽  
R.M. Wydro ◽  
W. Hellmann ◽  
F. Jenkins
Keyword(s):  
Ribosomal Proteins ◽  
Direct Evidence ◽  
Structural Similarity ◽  
Carbon Support ◽  
Artemia Salina ◽  
Uranyl Acetate ◽  
Biological Assays ◽  
E Coli ◽  
And Function ◽  
Fine Carbon

Ribosomes are ribonucleoprotein particles necessary for processing the genetic information of mRNA into proteins. Analogy in composition and function of ribosomes from diverse species, established by biochemical and biological assays, implies their structural similarity. Direct evidence obtained by electron microscopy seems to be of increasing relevance in understanding the structure of ribosomes and the mechanism of their role in protein synthesis.The extent of the structural homology between prokaryotic and eukaryotic ribosomes has been studied on ribosomes of Escherichia coli (E.c.) and Artemia salina (A.s.). Despite the established differences in size and in the amount and proportion of ribosomal proteins and RNAs both types of ribosomes show an overall similarity. The monosomes (stained with 0.5% aqueous uranyl acetate and deposited on a fine carbon support) appear in the electron micrographs as round particles with a diameter of approximately 225Å for the 70S E.c. (Fig. 1) and 260Å for the 80S A.s. monosome (Fig. 2).

High-voltage electron microscopy of maxillary gland of spirochete-infected brine shrimp: lesion of efferent tubule

1988 ◽  
Vol 46 ◽  
pp. 362-363
Author(s):  
G. E. Tyson ◽  
M. J. Song
Keyword(s):  
Electron Microscopy ◽  
High Voltage ◽  
Brine Shrimp ◽  
Natural Populations ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
High Voltage Electron ◽  
Infected Adult

Natural populations of the brine shrimp, Artemia, may possess spirochete- infected animals in low numbers. The ultrastructure of Artemia's spirochete has been described by conventional transmission electron microscopy. In infected shrimp, spirochetal cells were abundant in the blood and also occurred intra- and extracellularly in the three organs examined, i.e. the maxillary gland (segmental excretory organ), the integument, and certain muscles The efferent-tubule region of the maxillary gland possessed a distinctive lesion comprised of a group of spirochetes, together with numerous small vesicles, situated in a cave-like indentation of the base of the tubule epithelium. in some instances the basal lamina at a lesion site was clearly discontinuous. High-voltage electron microscopy has now been used to study lesions of the efferent tubule, with the aim of understanding better their three-dimensional structure.Tissue from one maxillary gland of an infected, adult, female brine shrimp was used for HVEM study.

Stress Relaxation and the Formation of Silicides in the Process of the Crystallization of NI-NB Films on SI

1991 ◽  
Vol 49 ◽  
pp. 898-899
Author(s):  
N. Rozhanski ◽  
V. Lifshitz
Keyword(s):  
Thin Films ◽  
Stress Relaxation ◽  
Integrated Circuits ◽  
Direct Evidence ◽  
Alloy Film ◽  
Diffusion Barriers ◽  
Effective Barrier

Thin films of amorphous Ni-Nb alloys are of interest since they can be used as diffusion barriers for integrated circuits on Si. A native SiO2 layer is an effective barrier for Ni diffusion but it deformation during the crystallization of the alloy film lead to the appearence of diffusion fluxes through it and the following formation of silicides. This study concerns the direct evidence of the action of stresses in the process of the crystallization of Ni-Nb films on Si and the structure of forming NiSi2 islands.

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