Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “CHARACTER”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources
PubMed1994

Geographical variation in a quantitative character.

A model for the evolution of the local averages of a quantitative character under migration, selection, and random genetic drift in a subdivided population is formulated and investigated. Generations are discrete and nonoverlapping; the monoecious, diploid population mates at random in each deme. All three evolutionary forces are weak, but the migration pattern and the local population numbers are otherwise arbitrary. The character is determined by purely additive gene action and a stochastically independent environment; its distribution is Gaussian with a constant variance; and it is under Gaussian stabilizing selection with the same parameters in every deme. Linkage disequilibrium is neglected. Most of the results concern the covariances of the local averages. For a finite number of demes, explicit formulas are derived for (i) the asymptotic rate and pattern of convergence to equilibrium, (ii) the variance of a suitably weighted average of the local averages, and (iii) the equilibrium covariances when selection and random drift are much weaker than migration. Essentially complete analyses of equilibrium and convergence are presented for random outbreeding and site homing, the Levene and island models, the circular habitat and the unbounded linear stepping-stone model in the diffusion approximation, and the exact unbounded stepping-stone model in one and two dimensions.

Biological Evolution↗
PubMed1977

Simulation of quantitative characters by genes with biochemically definable action. VI. Modifications of a simple model.

Investigations on metric characters of defined genotypes of Matthiola incana, and application of different linear models for the estimation of genetic parameters, indicate that the use of midparental value as a reference point results in parameter estimates that do not correspond to the actual biological situation. Use of the most recessive genotype as a reference point causes all of the contributions of single loci to be undirectional and positive, and all the allelic and nonallelic interactions to be unidirectional and negative, in accord with our Model 2.2. The results indicate that the phenotypic response to allelic substitutions follows the characteristics of a saturation curve. The possibility is discussed that the saturation character results from regulating processes, whereas deviations of single measurements from the response curve, or response surface, reflect real interactions between allelic and nonallelic genes.

Genes, Recessive↗
PubMed2000

Classification of 3D structural character of RNA by hydrogen bond and base stacking.

We are developing a computational system to classify RNA structures by its structural character. Here, an improved grouping algorithm was introduced to the system and the base-stacking pattern (BSP) is used as a criterion for the classification in addition to hydrogen-bond pattern (HBP). 279 conformers of 15 mer RNA hairpin were classified into 89 and 36 groups by HBP and BSP, respectively, suggesting that HBP represents conformational character better than BSP.

Algorithms↗
PubMed1983

Classification of proteins into groups based on amino acid composition and other characters. I. Angular distribution.

Data on amino acid composition were collected in order to classify proteins into groups. The composition of a protein is expressed as a point in an orthogonal coordinate system, taking fractions of amino acids along 18 axes, which represent 18 amino acids (we use Asx and Glx for the sum of Asp and Asn and that of Glu and Gln, respectively). Thus, proteins of known amino acid compositions (356 single polypeptides chains) are distributed as points in this composition space. Since the radial distribution of the points from the origin (the average composition) did not show any distinct separation into groups, we checked the angular distribution of points in the space. Thirteen groups were found by a computer method based on the density. Analysis of the groups in terms of various characters of proteins, such as source (eukaryote or prokaryote), location in an organism, biological function, etc. revealed that the groups have strong correlations to the location (inside or outside the cell) and functional character (enzyme or nonenzyme). Also, the presence of disulfide bond(s) seems to be characteristic of extracellular proteins. Protein source, molecular size and ability to form an oligomer had little correlation to the grouping. Therefore, proteins may be classified into four types as follows: BI, intracellular enzymes; BII, intracellular nonenzymes; BIII, extracellular enzymes; and BIV, extracellular nonenzymes.

Amino Acids↗
PubMed1983

Classification of proteins into groups based on amino acid composition and other characters. II. Grouping into four types.

Correlations of the amino acid composition of a protein to its location in an organism, biological function, folding type, and disulfide bond(s) were examined for 356 proteins. In the present data set, 325 proteins of known location and biological characters were divided into 122 intracellular enzymes (BI), 73 intracellular non-enzymes (BII), 45 extracellular enzymes (BIII), and 85 extracellular nonenzymes (BIV). The composition of these proteins were expressed as points in the composition space of 18 orthogonal axes, each representing the content of an amino acid. The distributions of points of BI and BIII were narrow and approximately spherical but those of BII and BIV were distributed rather widely. The groups are separated from each other in the space. We divided the space into four regions (A1 to A4) corresponding to the groups BI to BIV. A protein could be assigned to one of the four groups (A1 to A4) from its amino acid composition: The proteins correctly assigned amounted to 177 out of 195 intracellular proteins, and 94 out of 130 extracellular proteins. The correspondence was about 80% for classification into intracellular and extracellular proteins and 66% for that into the four groups. The folding type also had a significant correlation to the above groups, i.e., intracellular enzymes are rich in alpha/beta, nonenzymes alpha, extracellular enzymes beta and alpha + beta, and nonenzymes beta. The differences in average composition between intra- and extracellular proteins, and between enzymes and nonenzymes were related to the structural characters, i.e., intracellular proteins contain more amino acids favoring alpha-helix than extracellular ones, and enzymes contain more hydrophobic amino acids than nonenzymes. The statistics on 213 Cys-containing proteins showed that disulfide bond(s) are found mostly (90%) in the extracellular proteins. The results indicate that amino acid composition is well correlated to location in an organism, biological function, folding type, and disulfide bonding. The implications of the new findings are discussed from the protein-taxonomical point of view, and the validity of the present method is assessed.

Amino Acids↗
PubMed2002

Molecular phylogeny of living xenarthrans and the impact of character and taxon sampling on the placental tree rooting.

Extant xenarthrans (armadillos, anteaters and sloths) are among the most derived placental mammals ever evolved. South America was the cradle of their evolutionary history. During the Tertiary, xenarthrans experienced an extraordinary radiation, whereas South America remained isolated from other continents. The 13 living genera are relics of this earlier diversification and represent one of the four major clades of placental mammals. Sequences of the three independent protein-coding nuclear markers alpha2B adrenergic receptor (ADRA2B), breast cancer susceptibility (BRCA1), and von Willebrand Factor (VWF) were determined for 12 of the 13 living xenarthran genera. Comparative evolutionary dynamics of these nuclear exons using a likelihood framework revealed contrasting patterns of molecular evolution. All codon positions of BRCA1 were shown to evolve in a strikingly similar manner, and third codon positions appeared less saturated within placentals than those of ADRA2B and VWF. Maximum likelihood and Bayesian phylogenetic analyses of a 47 placental taxa data set rooted by three marsupial outgroups resolved the phylogeny of Xenarthra with some evidence for two radiation events in armadillos and provided a strongly supported picture of placental interordinal relationships. This topology was fully compatible with recent studies, dividing placentals into the Southern Hemisphere clades Afrotheria and Xenarthra and a monophyletic Northern Hemisphere clade (Boreoeutheria) composed of Laurasiatheria and Euarchontoglires. Partitioned likelihood statistical tests of the position of the root, under different character partition schemes, identified three almost equally likely hypotheses for early placental divergences: a basal Afrotheria, an Afrotheria + Xenarthra clade, or a basal Xenarthra (Epitheria hypothesis). We took advantage of the extensive sampling realized within Xenarthra to assess its impact on the location of the root on the placental tree. By resampling taxa within Xenarthra, the conservative Shimodaira-Hasegawa likelihood-based test of alternative topologies was shown to be sensitive to both character and taxon sampling.

Animals↗
PubMed1992

Phylogenetic position of phylum Nemertini, inferred from 18S rRNA sequences: molecular data as a test of morphological character homology.

Partial 18S rRNA sequence of the nemertine Cerebratulus lacteus was obtained and compared with those of coelomate metazoans and acoelomate platyhelminths to test whether nemertines share a most recent common ancestor with the platyhelminths, as traditionally has been implied, or whether nemertines lie within a protostome coelomate clade, as suggested by more recent morphological analyses. Maximum-parsimony analysis supports the inclusion of the nemertine within a protostome-coelomate clade that falls within a more inclusive coelomate clade. Bootstrap analysis indicates strong support for a monophyletic Coelomata composed of a deuterostome and protostome-coelomate clade. Support for a monophyletic protostome Coelomata is weak. Inference by distance analysis is consistent with that of maximum parsimony. Analysis of down-weighted paired sites by maximum parsimony reveals variation in topology only within the protostome-coelomate clade. The relationships among the protostome coelomates cannot be reliably inferred from the partial sequences, suggesting that coelomate protostomes diversified rapidly. Results with evolutionary parsimony are consistent with the inclusion of the nemertine in a coelomate clade. The molecular inference corroborates recent morphological character analyses that reveal no synapomorphies of nemertines and flatworms but instead suggest that the circulatory system and rhynchocoel of nemertines are homologous to coelomic cavities of protostome coelomates, thus supporting the corresponding hypothesis that nemertines belong within a protostome-coelomate clade. The sequence data provide an independent test of morphological character homology.

Animals↗
PubMed2004

Realizability of optical systems of given linear optical character.

The linear optical character of an optical system is represented by a particular type of 5 x 5 matrix. This article shows that the converse is also true, namely, that an optical system can be constructed in principle with linear optical character represented by any matrix of this type. In other words, every matrix of this type is realizable as an optical system. The system may have astigmatic and decentered elements.

Linear Models↗
PubMed2006

Temperament and character personality dimensions in patients with nonspecific musculoskeletal disorders.

OBJECTIVE: The aim of this study was to investigate temperament and character dimensions in a group of patients with nonspecific musculoskeletal disorders and to show how personality is related to pain and psychologic distress in pain patients. METHOD: A total of 78 patients with musculoskeletal disorders were compared with a matched control group of 118 nonpatients. The Temperament and Character Inventory, the Symptom Check List, and the Multidimensional Pain Inventory were used. RESULTS: The pain patients differed significantly from the controls and exhibited a personality profile with high harm avoidance and low self-directness, which indicate that patients with nonspecific musculoskeletal pain disorders can be characterized as being cautious, insecure, and pessimistic. In addition, they can be described as having difficulties in accepting responsibility, lack of long-term goals, chronically low self-esteem, and struggle with identity. This is probably a salient characteristic of patients with chronic pain. The results also showed that personality dimensions had a stronger correlation to psychologic distress than to pain. The result indicated that harm avoidance probably is an important personality trait in anxiety states. CONCLUSIONS: The results underline the importance of using instruments assessing personality and psychologic symptoms in patients with nonspecific musculoskeletal disorders both as diagnostic tools and in treatment planning.

Adult↗
PubMed2001

Geographical variation in reproductive character displacement in mate choice by male sailfin mollies.

Female Amazon mollies, Poecilia formosa, are a unisexual species that reproduce by gynogenesis. They must coexist and mate with males of other species (usually the mollies Poecilia latipinna or Poecilia mexicana) to induce embryogenesis, but inheritance is strictly maternal. We examined the mating preference of the male sailfin molly, P. latipinna, for female sailfin mollies versus Amazon mollies, P. formosa. We compared the mating preferences of sympatric and allopatric populations collected throughout the Gulf Coast of North America. Male P. latipinna from six populations sympatric with Amazon mollies showed a significantly greater strength of preference for conspecific sailfin females than males from five populations that were allopatric with Amazon mollies. These results provide strong evidence for reproductive character displacement of male mate choice in sympatry. Furthermore, the large geographical range of populations that we tested revealed variation among populations within sympatry and allopatry, indicating that it is important to evaluate a large number of populations when examining reproductive character displacement.

Animals↗
PubMed2006

Reproductive character displacement generates reproductive isolation among conspecific populations: an artificial neural network study.

When interactions with heterospecifics prevent females from identifying conspecific mates, natural selection can promote the evolution of mating behaviours that minimize such interactions. Consequently, mating behaviours may diverge among conspecific populations in sympatry and in allopatry with heterospecifics. This divergence in conspecific mating behaviours-reproductive character displacement-can initiate speciation if mating behaviours become so divergent as to generate reproductive isolation between sympatric and allopatric conspecifics. We tested these ideas by using artificial neural networks to simulate the evolution of conspecific mate recognition in populations sympatric and allopatric with different heterospecifics. We found that advertisement calls diverged among the different conspecific populations. Consequently, networks strongly preferred calls from their own population to those from foreign conspecific populations. Thus, reproductive character displacement may promote reproductive isolation and, ultimately, speciation among conspecific populations.

Animal Communication↗
PubMed2006

Evolutionary patterns in early tetrapods. I. Rapid initial diversification followed by decrease in rates of character change.

Although numerous studies have examined morphological diversification during major radiations of marine taxa, much less attention has been paid to terrestrial radiations. Here, we examine rates of character change over phylogeny and over time for Palaeozoic limbed tetrapods. Palaeozoic tetrapods show significant decreases in rates of character change whether the rate is measured per sampled cladistic branch or per million years along phylogeny. Given changes per branch, rates decrease significantly from the Devonian through the Pennsylvanian, but not from the Pennsylvanian through the Permian. Given changes per million years, rates decrease significantly over each boundary, although the decrease is least significant over the Pennsylvanian-Permian boundary. Decreasing rates per million years through the Permian might be an artefact of the method being able to ascribe longer durations to Permian branches than to Carboniferous ones; however, it is difficult to ascribe the general pattern of decreasing rates of change over time to sampling biases or methodological biases. Thus, the results implicate biological explanations for this pattern.

Amphibians↗
PubMed1988

Frequency-dependent selection, metrical characters and molecular evolution.

Computer models of selection acting on a quantitative character show that a combination of frequency-dependent and stabilizing selection can maintain many polymorphisms among the genes that determine the character. The models also show that the random order of mutations can give rise to selectively driven stochastic effects that are sometimes more important than random genetic drift. They suggest simple explanations for patterns of divergence between populations and species, and for apparent discrepancies between the rates of morphological and molecular evolution. They point towards a selective theory of 'molecular clocks'.

Animals↗
PubMed1978

Lipopolysaccharide core defects in Salmonella typhimurium mutants which are resistant to Felix O phage but retain smooth character.

FOR mutants of Salmonella typhimurium are resistant to Felix O phage, whose receptor includes the N-acetylglucosamine branch of the lipopolysaccharide (LPS) core, but smooth in cultural properties, antigenic character and phage sensitivity pattern (MacPhee et al., 1975). The rfa(FOR) genes determining the FOR character of nine mutants were transduced into a smooth cysE pyrE recipient: the nine FOR transductants (and a tenth FOR mutant) were then made rfb (i.e. unable to make O chains) by transduction or Hfr crosses. The rfb FOR strains were sensitive to FO phage but nearly all of them showed a somewhat reduced efficiency of plating and diminished rate of adsorption of the phage. This observation and the Ra (complete core) serological activity of their LPS (tested by haemagglutination inhibition) indicate the presence of some, but less than the normal number of, completed core chains in FOR rfb LPS. On the basis of the sensitivities of the FOR transductants and their rfb derivatives to various 'rough-specific' phages, their increased sensitivities to some antibiotics and to deoxycholate and the serological activity of the rfb FOR LPS in various incomplete core systems, the mutants were divided into three groups: (i) five mutants with probable defects in previously undetected rfa gene(s) concerned with formation of both the galactose I and the galactose II units of the LPS core; (ii) two mutants with defects inferred to affect the structure of the inner part of the core and also interfere with addition of the N-acetylglucosamine branch; (iii) three mutants in which no type of incomplete core could be detected, probably affected in formation of the inner part of the core chain. The mutation of one mutant of the last class, unlike those of the other nine mutants tested, lay outside the cysE-pyrE segment, in the 90 to 116 min region of the linkage map.

Anti-Bacterial Agents↗
PubMed2005

Intrinsic character of the (3 x 3) to (square root 3 x square root 3) phase transition in Pb/Si(111).

We have investigated the (3 x 3) to (square root 3 x square root 3) reversible phase transition in Pb/Si(111) by means of variable temperature scanning tunneling microscopy and density functional first-principles calculations. By tracking exactly the same regions of the surface with atomic resolution in a temperature range between 40 and 200 K, we have observed the phase transition in real time. The ability to prepare and track exceptionally large domains without defects has allowed us to detect the intrinsic character of the phase transition at temperatures around 86 K. This intrinsic character is in full agreement with our first-principles calculations. Moreover, our results show that the hypothesis that point defects play a fundamental role as the driving force, reported for similar systems, can be discarded for Pb/Si(111).

Journal Article↗
PubMed2004

Correlation filter: an accurate approach to detect and locate low contrast character strings in complex table environment.

Correlation has been used extensively in object detection field. In this paper, two kinds of correlation filters, Minimum Average Correlation Energy (MACE) and Extended Maximum Average Correlation Height (EMACH), are applied as adaptive shift locators to detect and locate smudgy character strings in complex tabular color flight coupon images. These strings in irregular tabular coupon are computer-printed characters but of low contrast and could be shifted out of the table so that we cannot detect and locate them using traditional algorithms. In our experiment, strings are extracted in the preprocessing phase by removing background and then based on geometric information, two correlation filters are applied to locate expected fields. We compare results from two correlation filters and demonstrate that this algorithm is a high accurate approach.

Journal Article↗
PubMed2001

Evolution of egg target size: an analysis of selection on correlated characters.

In broadcast-spawning marine organisms, chronic sperm limitation should select for traits that improve chances of sperm-egg contact. One mechanism may involve increasing the size of the physical or chemical target for sperm. However, models of fertilization kinetics predict that increasing egg size can reduce net zygote production due to an associated decline in fecundity. An alternate method for increasing physical target size is through addition of energetically inexpensive external structures, such as the jelly coats typical of eggs in species from several phyla. In selection experiments on eggs of the echinoid Dendraster excentricus, in which sperm was used as the agent of selection, eggs with larger overall targets were favored in fertilization. Actual shifts in target size following selection matched quantitative predictions of a model that assumed fertilization was proportional to target size. Jelly volume and ovum volume, two characters that contribute to target size, were correlated both within and among females. A cross-sectional analysis of selection partitioned the independent effects of these characters on fertilization success and showed that they experience similar direct selection pressures. Coupled with data on relative organic costs of the two materials, these results suggest that, under conditions where fertilization is limited by egg target size, selection should favor investment in low-cost accessory structures and may have a relatively weak effect on the evolution of ovum size.

Animals↗
PubMed2003

Reproductive character displacement in the acoustic communication system of green tree frogs (Hyla cinerea).

Interactions between species can affect the evolution of their sexual signals, receiver selectivity, or both. One commonly expected outcome is reproductive character displacement, whereby adverse consequences of mismating select for greater differentiation of communication systems in areas of sympatry than in areas of allopatry. We found evidence of reproductive character displacement in the acoustic communication system of green tree frogs (Hyla cinerea). The strength of female preferences for the spectral properties of calls that distinguish conspecific calls from those of a closely related congener, H. gratiosa, was greater in areas of sympatry with H. gratiosa than in areas of allopatry. We also found subtle differences in advertisement calls and in the heights of male calling perches when we restricted our comparisons to localities in which H. gratiosa was also breeding (syntopy) with localities where this species was absent. Hyla cinerea and H. gratiosa show only weak genetic incompatibility, but the calls representative of interspecific hybrids were unattractive to females of both parental species. Hybrids might also be at an ecological disadvantages because of different habitat preferences of the two taxa. Thus, selection against production of less fit or less attractive hybrid or backcross offspring are probably the main causes responsible for the differences documented in this paper.

Animals↗