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 163 records · Page 9Linked to original sources
PubMed2003

Quasi-independence, homology and the unity of type: a topological theory of characters.

In this paper Lewontin's notion of "quasi-independence" of characters is formalized as the assumption that a region of the phenotype space can be represented by a product space of orthogonal factors. In this picture each character corresponds to a factor of a region of the phenotype space. We consider any region of the phenotype space that has a given factorization as a "type", i.e. as a set of phenotypes that share the same set of phenotypic characters. Using the notion of local factorizations we develop a theory of character identity based on the continuation of common factors among different regions of the phenotype space. We also consider the topological constraints on evolutionary transitions among regions with different regional factorizations, i.e. for the evolution of new types or body plans. It is shown that direct transition between different "types" is only possible if the transitional forms have all the characters that the ancestral and the derived types have and are thus compatible with the factorization of both types. Transitional forms thus have to go over a "complexity hump" where they have more quasi-independent characters than either the ancestral as well as the derived type. The only logical, but biologically unlikely, alternative is a "hopeful monster" that transforms in a single step from the ancestral type to the derived type. Topological considerations also suggest a new factor that may contribute to the evolutionary stability of "types". It is shown that if the type is decomposable into factors which are vertex irregular (i.e. have states that are more or less preferred in a random walk), the region of phenotypes representing the type contains islands of strongly preferred states. In other words types have a statistical tendency of retaining evolutionary trajectories within their interior and thus add to the evolutionary persistence of types.

Animals↗
PubMed1998

Parsimony analysis as a specific kind of homology estimation and the implications for character weighting.

"Remane-Hennigian systematists" still reject parsimony analysis for phylogenetics, because homology or apomorphy analyses are not included. In contrast, "pattern cladists" regard homology as a deductive concept after applying a parsimony test of character congruence. However, as in molecular phylogeny, selection of "good" characters is always done on the basis of an a priori homology analysis. The distribution criterion of homology-"homologous characters have identical or hierarchical distribution"-is the basis of parsimony analysis. Because this criterion also might fail in cases of genealogical reticulation or concerted homoplasy, character congruence is not a strict test but another probabilistic criterion of homology. A synthetic approach is proposed for phenotypic analysis with application of a priori criteria of homology. The resulting a priori probabilities of homology serve as criteria for selection and weighting of characters (very low = not selected/poor/mediocre/good/Dollo characters). After application of a parsimony algorithm the final cladogram decides homology estimations.

Algorithms↗
PubMed2000

The information content of a character under a Markov model of evolution.

The rate of evolutionary change associated with a character determines its utility for the reconstruction of phylogenetic history. For a given age of lineage splits, we examine the information content of a character to assess the magnitude and range of an optimal rate of substitution. On the one hand an optimal transition rate must provide sufficiently many character changes to distinguish subclades, whereas on the other hand changes must be sufficiently rare that reversals on a single branch (and hence homoplasy) are uncommon. In this study, we evolve binary characters over three tree topologies with fixed branch lengths, while varying transition rate as a parameter. We use the character state distribution obtained to measure the "information content" of a character given a transition rate. This is done with respect to several criteria-the probability of obtaining the correct tree using parsimony, the probability of infering the correct ancestral state, and Shannon-Weaver and Fisher information measures on the configuration of probability distributions. All of the information measures suggest the intuitive result of the existence of optimal rates for phylogeny reconstruction. This nonzero optimum is less pronounced if one conditions on there having been a change, in which case the parsimony-based results of minimum change being the most informative tends to hold.

Animals↗
PubMed2006

A TMS examination of semantic radical combinability effects in Chinese character recognition.

The proposal of human foveal splitting assumes a vertical meridian split in the foveal representation and the consequent contralateral projection of information in the two hemifields to the two hemispheres and has been shown to have important implications for visual word recognition. According to this assumption, in Chinese character recognition, the two halves of a centrally fixated character may be initially projected to and processed in different hemispheres. Here, we describe a repetitive transcranial magnetic stimulation (rTMS) investigation of hemispheric processing in Chinese character recognition, through examining semantic radical combinability effects in a character semantic judgment task. The materials used were a dominant type of Chinese character which consists of a semantic radical on the left and a phonetic radical on the right. Thus, according to the split fovea assumption, the semantic and phonetic radicals are initially projected to and processed in the right hemisphere and the left hemisphere, respectively. We show that rTMS over the left occipital cortex impaired the facilitation of semantic radicals with large combinability, whereas right occipital rTMS did not. This interaction between stimulation site and radical combinability reveals a flexible division of labor between the hemispheres in Chinese character recognition, with each hemisphere responding optimally to the information in the contralateral visual hemifield to which it has direct access. The results are also consistent with the split fovea claim, suggesting functional foveal splitting as a universal processing constraint in reading.

Adult↗
PubMed2005

The role of phonological activation in the visual semantic retrieval of Chinese characters.

The Stroop paradigm was used to examine the role of phonological activation in semantic access and its development in reading Chinese characters. Subjects (age 7-23 years) of different reading ability were asked to name the display color of Chinese characters. The characters were displayed in four different colors: red, yellow, blue and green. There were five types of relationships between a character and its display color: semantically congruent, phonologically congruent, semantically incongruent, phonologically incongruent and neutral. In addition to the classical Stroop effects, interference and facilitation effects from the homophones of color characters were also observed. The younger children and those with lower reading ability exhibited stronger Stroop effects. These findings suggest that phonological codes are activated automatically in Chinese character recognition. Furthermore, there is more phonological activation in the semantic retrieval of children in lower grades and those with lower reading ability.

Adult↗
PubMed2006

Systematics and morphological evolution within the moss family Bryaceae: a comparison between parsimony and Bayesian methods for reconstruction of ancestral character states.

The Bryaceae are a large cosmopolitan moss family including genera of significant morphological and taxonomic complexity. Phylogenetic relationships within the Bryaceae were reconstructed based on DNA sequence data from all three genomic compartments. In addition, maximum parsimony and Bayesian inference were employed to reconstruct ancestral character states of 38 morphological plus four habitat characters and eight insertion/deletion events. The recovered phylogenetic patterns are generally in accord with previous phylogenies based on chloroplast DNA sequence data and three major clades are identified. The first clade comprises Bryum bornholmense, B. rubens, B. caespiticium, and Plagiobryum. This corroborates the hypothesis suggested by previous studies that several Bryum species are more closely related to Plagiobryum than to the core Bryum species. The second clade includes Acidodontium, Anomobryum, and Haplodontium, while the third clade contains the core Bryum species plus Imbribryum. Within the latter clade, B. subapiculatum and B. tenuisetum form the sister clade to Imbribryum. Reconstructions of ancestral character states under maximum parsimony and Bayesian inference suggest fourteen morphological synapomorphies for the ingroup and synapomorphies are detected for most clades within the ingroup. Maximum parsimony and Bayesian reconstructions of ancestral character states are mostly congruent although Bayesian inference shows that the posterior probability of ancestral character states may decrease dramatically when node support is taken into account. Bayesian inference also indicates that reconstructions may be ambiguous at internal nodes for highly polymorphic characters.

Bayes Theorem↗
PubMed2005

Second hyperpolarizability (gamma) of singlet diradical system: dependence of gamma on the diradical character.

The dependence of the second hyperpolarizability (gamma) on the diradical character (y) for singlet diradical systems is investigated using a model compound, the p-quinodimethane (PQM) molecule with different both-end carbon-carbon (C-C) bond lengths, by several ab initio molecular orbital and density functional theory methods. The diradical character based on UHF calculations indicates that at equilibrium geometry PQM is in a singlet ground state and primarily exhibits a quinoid structure, whereas the diradical character increases when increasing both-end C-C bond lengths. At the highest level of approximation, that is, using the UCCSD(T) method with the 6-31G+diffuse p (zeta = 0.0523) basis set, the longitudinal static gamma of PQM presents a maximum value for intermediate diradical character (y approximately 0.5) while the gamma values are larger for intermediate and large diradical character (y approximately 0.5-0.7) than for small diradical character (y < 0.2). This feature suggests that the gamma values of singlet diradical systems in the intermediate and somewhat strong correlation regimes are significantly enhanced as compared to those in the weak correlation regime. These results are substantiated by a complementary study of the variation in gamma upon twisted ethylene.

Journal Article↗
PubMed1998

Quantitative trait loci for fluctuating asymmetry of discrete skeletal characters in mice.

Levels of fluctuating asymmetry (FA) are often taken as indicators of the degree to which genotypes differ in their ability to buffer genetic and environmental sources of variation. Interval mapping techniques were used to search for quantitative trait loci (QTLs) affecting directional asymmetry (DA) and fluctuating asymmetry (FA) in six bilateral discrete skeletal traits in house mice. These six characters as well as 76 microsatellite markers were scored in over 500 mice that resulted from crosses of F1 mice originally produced from matings of the Large (LG/J) and Small (SM/J) inbred strains. The number of QTLs affecting DA in each of the characters was no more than expected by chance alone so it was concluded that there was little evidence for individual genes affecting DA. There appeared to be a genetical basis for FA in these characters, however, because the number of QTLs significantly affecting FA (10 at the 5% level, three at the 1% level) was greater than expected by chance alone. The 10 QTLs significantly affecting FA in any given character were located on eight different chromosomes, mostly at locations for QTLs affecting other characters or DA in other characters. Their cumulative contribution to the total phenotypic variance was small, averaging only 3.9% per locus. Dominance genotypic values for these QTLs were more extreme than additive genotypic values, suggesting that heterozygotes at many loci are better buffered than homozygotes and that allelic interactions (dominance) may play an important role in the production of FA.

Animals↗
PubMed2003

Genetic variation of polygenic characters and the evolution of genetic degeneracy.

The classical model of mutation-selection balance for quantitative characters sums the effects of individual sites to determine overall character value. I develop an alternative version of this classical model in which character value depends on the averaging of the effects of the individual sites. In this new averaging model, the equilibrium patterns of variance in allelic effects and character values change with the number of sites that affect a character in a different way from the classical model of summing effects. Besides changing the patterns of variance, the averaging model favours the addition of loci to the control of character values, perhaps explaining in part the recent observation of widespread genetic degeneracy.

Biological Evolution↗
PubMed2006

Origin of the enhancement of the second hyperpolarizability of singlet diradical systems with intermediate diradical character.

The origin of the diradical character dependence of the second hyperpolarizability (gamma) of neutral singlet diradical systems is clarified based on the perturbation formula of gamma using the simplest diradical molecular model with different diradical characters, i.e., H2 under bond dissociation. The enhancement of gamma in the intermediate diradical character region turns out to originate from the increasing magnitude of the transition moment between the first and second excited states and the decrease of that between the ground and first excited states, respectively, with the increase in diradical character. This feature confirms that open-shell singlet conjugated molecules with intermediate diradical characters constitute a new class of third-order nonlinear optical systems, whose gamma values can be controlled by the diradical character in addition to the conjugation length.

Journal Article↗
PubMed1971

The characters of the symmetric group.

A short and simple derivation of the formula of Frobenius, which gives the dimensions of the irreducible representations of S(n), the symmetric group on any number, n, of symbols, is given. These dimensions are the characters of the identity element of the group, i.e., of the element all of whose cycles are unary. It is shown how a slight modification of Frobenius' formula yields, when n = 2p is even, the characters of an element of S(n) all of whose cycles are binary and, when n = 3p is a multiple of 3, the characters of an element of S(n) all of whose cycles are ternary and, generally, when n = kp is a multiple of any positive integer k, the characters of an element of S(n) all of whose cycles are of length k. It is noteworthy that the calculations become simpler, rather than more complicated, as k increases. Finally, this paper shows how to derive from Frobenius' formula the characters of an element of S(n) which has at least one unary cycle and, from the present modifications of Frobenius' formula, the characters of an element of S(n) which has at least one cycle of length k, k = 2, 3,..., n.

Journal Article↗
PubMed1992

Rate of evolution of a quantitative character.

The rate of change of the mean of a quantitative character is evaluated exactly and also under the hypothesis of linear biparental regression. Generations are discrete and nonoverlapping; the monoecious population mates at random. The genotypic and environmental contributions to the character are additive and stochastically independent. The character is influenced by arbitrarily many multiallelic loci and has constant genotypic values; dominance, epistasis, and the linkage map are also arbitrary. The population is initially in linkage equilibrium, and there is no position effect. If the biparental regression is linear, then the regression coefficient is simply Vgam/V, and hence the single-generation change in the mean is deltaZ = (Vgam/V)S, where Vgam and V denote the gametic and total variances in the character and S designates the selection differential. The corresponding exact result is DeltaZ = (C/W) + (B/W2), where C, W and B represent the gametic covariance of the character and fitness, the mean fitness, and a correction term, respectively. If selection is weak, then DeltaZ approximately C/W. Furthermore, deltaZ = C/W if either there is no environmental contribution and the gametic effects are additive or the character is fitness itself. In the latter case, C is the gametic variance in fitness. Thus, even in linkage equilibrium, weakness of selection generally does not suffice to validate the linear-regression result. This conclusion holds even for additive loci.

Journal Article↗
PubMed1995

Assessment of visual memory: a comparison of Chinese characters and geometric figures as stimulus materials.

The study compared the suitability of geometric figures and Chinese characters for assessing visual memory. In Study 1, 40 Chinese characters were found to be significantly less verbalisable than were 40 geometric figures from the Biber Figure Learning Test. In Study 2, memory for Chinese characters, for Biber figures, and for items on the Rey Auditory Verbal Learning Test were compared using 14 subjects with left cerebrovascular accident, 15 subjects with right cerebrovascular accident, and 29 matched controls. Subjects in the left hemisphere group showed impairment on the Rey Auditory Verbal Learning Test but not on Chinese characters, whereas subjects in the right hemisphere group showed impairment on Chinese characters but not on the Rey Auditory Verbal Learning Test. This double dissociation was not evident when comparisons involved the Biber Figure Learning Test. The Chinese character set used in this study was thus judged to be more suitable than were geometric figures in the Biber Figure Learning Test for assessing visual memory.

Adolescent↗
PubMed2004

Complex data produce better characters.

Two studies were conducted to explore the use of complex data in character description and hybrid identification. In order to determine if complex data allow the production of better characters, eight groups of plant systematists were given two classes of drawings of plant parts, and asked to divide them into character states (clusters) in two separate experiments. The first class of drawings consisted only of cotyledons. The second class consisted of triplets of drawings: a cotyledon, seedling leaf, and inflorescence bract. The triplets were used to simulate complex data such as might be garnered by looking at a plant. Each experiment resulted in four characters (groups of clusters), one for each group of systematists. Visual and statistical analysis of the data showed that the systematists were able to produce smaller, more precisely defined character states using the more complex drawings. The character states created with the complex drawings also were more consistent across systematists, and agreed more closely with an independent assessment of phylogeny. To investigate the utility of complex data in an applied task, four observers rated 250 hybrids of Dubautia ciliolata X arborea based on the overall form (Gestalt) of the plants, and took measurements of a number of features of the same plants. A composite score of the measurements was created using principal components analysis. The correlation between the scores on the first principal component and the Gestalt ratings was computed. The Gestalt ratings and PC scores were significantly correlated, demonstrating that assessments of overall similarity can be as useful as more conventional approaches in determining the hybrid status of plants.

Asteraceae↗
PubMedDate not supplied

Contribution of finger tracing to the recognition of Chinese characters.

Finger tracing is a simulation of the act of writing without the use of pen and paper. It is claimed to help in the processing of Chinese characters, possibly by providing additional motor coding. In this study, blindfolded subjects were equally good at identifying Chinese characters and novel visual stimuli through passive movements made with the index finger of the preferred hand and those made with the last finger of that hand. This suggests that finger tracing provides a relatively high level of coding specific to individual characters, but non-specific to motor effectors. Beginning each stroke from the same location, i.e. removing spatial information, impaired recognition of the familiar characters and the novel nonsense figures. Passively tracing the strokes in a random sequence also impaired recognition of the characters. These results therefore suggest that the beneficial effect of finger tracing on writing or recall of Chinese characters is mediated by sequence and spatial information embedded in the motor movements, and that proprioceptive channel may play a part in mediating visuo-spatial information. Finger tracing may be a useful strategy for remediation of Chinese language impairments.

Adult↗
PubMed1996

Hunting for trees in binary character sets: efficient algorithms for extraction, enumeration, and optimization.

We describe a useful and efficient tree building technique that is closely related to the maximum compatible subset method. Given a set of binary characters C and a degree bound d, the algorithm we describe counts the number of trees T that satisfy (1) the edges of T correspond to characters contained in C, and (2) the vertices of T have degree bounded by d. If the characters are weighted then we can efficiently determine which of these trees have maximum summed edge weight, where the weight of an edge equals the weight of the corresponding binary character in C. The complexity of the algorithms equals O(nk + ndK(d-1), where n is the number of taxa, k is the number of characters, and K is the number of distinct characters. A number of new tree consensus methods based on the algorithm are introduced, including one that uses edge weighted trees. As well, we illustrate the applicability of the algorithm for large sequence data sets by analyzing sequences from the "Out of Africa" mtDNA data set.

Algorithms↗
PubMed1986

Additive variation maintained under stabilizing selection: a two-locus model of pleiotropy for two quantitative characters.

A model with two diallelic loci controlling two additive quantitative characters is suggested. One of the loci has a similar effect on both characters, whereas the second locus has an antagonistic effect on two characters. Both characters experience direct stabilizing selection. The model yields a stable polymorphic state, with both characters maintaining genetic variation. The genetic correlation between the characters at the equilibrium is zero, in spite of the pleiotropic effects of the loci controlling them.

Alleles↗
PubMed2000

Wings and bristles: character specificity of the asymmetry phenotype in insecticide-resistant strains of Lucilia cuprina.

We investigated the hypothesis that observed higher levels of asymmetry displayed by insecticide-resistance genotypes of Lucilia cuprina are restricted to bristle characters, due to the action of resistance genes in bristle cell development, rather than through the disruption of genomic coadaptation. We compared the level of asymmetry of three bristle characters and three wing characters in non-modified and modified-resistance genotypes. Consistent with previous studies, resistance genotypes displayed greater levels of bristle asymmetry than either susceptible or modified genotypes. However, there were no differences among genotypes for any of the wing characters. To confirm that this result is attributable to the action of the resistance and modifier genes themselves, we also examined the responses of both bristle and wing characters to the more general developmental stress of extreme temperature. Sub-optimal temperature was shown to increase both bristle and wing asymmetry, suggesting that there are no underlying differences between the two character types which could, of themselves, explain the differential response observed in the resistance genotypes.

Animals↗