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Results for “systematic evolution”

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At least 379 records · Page 21Linked to original sources

PubMed2003

Structural changes of hexamethylenetetramine and undecanedioic acid co-crystal (HMT-C11) as a function of the temperature.

HMT-C11 belongs to the family of adducts formed by the co-crystallization of N(4)(CH(2))(6) molecules (hexamethylenetetramine or HMT) and aliphatic dicarboxylic acids HOOC(CH(2))(n - 2)COOH with 5 </= n </= 13 (Cn). The adducts exhibit a layered structure in which the packing between HMT and Cn is determined by strong hydrogen bonds. The compounds in this family studied so far present thermotropic structural phase transitions and, depending on the chain length, disordered, twinned and modulated phases. The structure refinement of HMT-C11 based on X-ray diffraction experiments indicates three distinct phases from the melting point down to liquid nitrogen temperature: phase I is not crystalline; phase II is disordered (stacking fault) and its average structure is described in space group Bmmb; phase III is partially disordered and its symmetry is P2(1)/c. The systematic study of the structure evolution of phase III upon cooling revealed that the disorder has a dynamic character (anharmonicity). The main structural change observed from 293 K down to 93 K is the increase of the tilting angle of the C11 chains relative to the layer plane and the rotation of the HMT molecules. Both HMT and C11 behave like rigid bodies in the temperature range investigated. The quality of the refinements leads to a conclusive model for the O-H.N hydrogen bonds linking HMT and C11.

Journal Article↗

PubMedDate not supplied

[Instrument for the evaluation of the adult patients' ability for self-care--CADEM].

This study develops a tool to facilitate the determination of adult patients selfcare ability aiming at promoting clear and objective communication. The tool developed, called CADEM, establishes levels to determine patient's categorization according to their need of nursing care. It has been-considered that CADEM is a valid tool and can help in planning nursing care, and also to register the patients' evolution through its continued and systematic use, therefore helping to justify necessary changes in Nursing care planning.

Activities of Daily Living↗

PubMed2000

Emerging distance degree programs.

The variation in program focus and style is examined in this column, which also identifies resources for evaluation. The integration of Web-based or other distance modality materials to conventional courses, and the expansion of traditional universities to include a virtual campus, should proceed with caution and systematic evaluation. It is an evolution that offers both rewards and pitfalls, but requires more rigorous examination. This article provides information about pedagogical issues and additional distance-education master's degree programs. Some are new, while others are established.

Education, Distance↗

PubMed1992

[Gene pool and gene geography of the USSR population].

Gene pool and gene geography are discussed from the point of view of their conceptual history beginning from the original concept of A.S. Serebrovskiĭ (1928). Difference between the present-day gene geography and gene geography of gene pool is accentuated: the former only represents a portion of the latter. Historical and territorial integrity of the USSR population gene pool, in conjunction with its huge diversity, is the main problem being analysed by various means of computerized genetic cartography. Coupled with the gene frequency mapping, following methods were also used: mapping of average heterozygosity, of interpopulation differentiation, of principal component scores and mapping of geographical trend for each mapped genetic parameter. The work is based on 100 allelic genes and haplotypes from 30 independent loci studied on the average in 225 local populations. Statistical analysis of gene geographical maps is based on 3975 nodes of regular cartographic net for the USSR territory. The wind rose of systematic changes in the USSR gene pool has three main geographic orientations: W-E, SW-NE and S-N. At the same time, there are only two main systematic forces of gene pool evolution: the force of social history with predominant W-E orientation and the force of natural history with predominant S-N orientation of their actions. The heterozygosity level of gene pool declines strictly in accordance with the resultant in the SW-NE direction.

Alleles↗

PubMedDate not supplied

[Role of oxygen in the vital activity of aerobic organisms].

New experimental data that underlie construction of an adaptive-metabolic conception as to curative effect of hyperbaric oxygenation are systematized in the aspect of evolution. Oxygen under high pressure (300 kPa, 60 min) exerts a specific effect on functions of redox and antiredox systems and nonspecific effect determining adaptation mechanisms of functional (regulatory, effector), metabolic (bioenergy, detoxication, biosynthetic) and morphogenetic (cellular and intracellular regeneration) types at different (hyper-, normo- and hypobiotic) levels of vital activity as dependent on the metabolic activity of the functional structures under pathology conditions.

Adaptation, Physiological↗

PubMed1976

[Historical origin and evolution of the agents of infectious diseases].

Data on the establishment and further evolution of the causative agents of human infectious diseases were systematized. Saprophytes proved to be the initial stage of this evolution for all the parasitic species. It was demonstrated by concrete examples that evolution of parasitism was the result of an interaction of many factors (the mechanism of transmission of the causative agents, the immunity formation in the population, hereditary resistance, etc.) and not only the sequence of a unilateral action of the transmission mechanism. The author considers that some properties of the causative agents of the infecticus diseases of man (spore formation, the capacity to reproduction on the objects of the external environment) were not newly acquired in the process of the parasitic species formation, but atavistic signs which persisted from saprophytic ancestors. The dialectics of progressive and regressive processes in the acqisition of the parasitic properties by saprophytes is considered.

Biological Evolution↗

PubMed2005

Trends in the evolution of the proopiomelanocortin gene.

The POMC gene is perhaps the most extensively studied member of the opioid/orphanin gene family. In Phylum Chordata this gene has been characterized in representatives of every class within the Gnathostomata, as well as in one representative agnathan vertebrate, the marine lamprey. This review provides a systematic overview of trends in the evolution of the melanocortins (ACTH/alpha-MSH, beta-MSH, gamma-MSH, and delta-MSH) and beta-endorphin in gnathostomes, and advances the hypothesis that the appearance of gamma-MSH occurred early in the radiation of the gnathostomes. A summary of the extensive work on POMC genes in the marine lamprey is also provided, as well as a reevaluation of the conserved regions in the sequence of CLIP (corticotropin-like-intermediate lobe peptide) in the POMC sequences of the various groups of gnathostomes.

Amino Acid Sequence↗

PubMed1998

Evolution of thyroid hormone distribution.

1. Appropriate distribution of thyroxine between the lipid-soluble compartments of cells and tissues and the extracellular aqueous space is established by binding to extracellular proteins. Among these proteins, transthyretin is of particular interest because it is the only one synthesized in the brain. 2. The evolutionary onset of transthyretin synthesis in cells of the blood-brain barrier precedes that in the liver, with the exception of a very short period of transthyretin synthesis in the liver of tadpoles, just prior to the climax of metamorphosis. In adult liver, transthyretin is only synthesized in endothermic vertebrates. 3. The affinity of transthyretin for thyroxine increases and that for 3,5,3'-triiodothyronine decreases during the evolution of eutherians from reptile/bird-like common ancestors. 4. A systematic change of the N-terminal region of transthyretin occurred during evolution, leading to shorter and more hydrophilic transthyretin N termini in eutherians compared with those in reptiles and birds. 5. The molecular mechanism of the evolution of the transthyretin N termini is a stepwise shift of the splice site at the intron 1/exon 2 border in the 3' direction. The most probable cause for this shift is a series of single base mutations. 6. As the N termini are located on the surface of transthyretin near the entrance to its central channel leading to the thyroxine binding sites, it is possible that a change in the structure of this region could influence the access of thyroxine to the binding sites. The increase in affinity for thyroxine could then be a driving force in the natural selection during evolution of transthyretins with shorter and more hydrophilic N termini.

Amino Acid Sequence↗

PubMed2003

Genic mutation rates in mammals: local similarity, chromosomal heterogeneity, and X-versus-autosome disparity.

The reduction of mutation rates on the mammalian X chromosome relative to autosomes is most often explained in the literature as evidence of male-driven evolution. This hypothesis attributes lowered mutation rates on the X chromosome to the fact that this chromosome spends less time in the germline of males than in the germline of females. In contrast to this majority view, two articles argued that the patterns of mutation rates across chromosomes are inconsistent with male-driven evolution. One article reported a 40% reduction in synonymous substitution rates (Ks) for X-linked genes relative to autosomes in the mouse-rat lineage. The authors argued that this reduction is too dramatic to be explained by male-driven evolution and concluded that selection has systematically reduced mutation rate on the X chromosome to a level optimal for this male-hemizygous chromosome. More recently, a second article found that chromosomal mutation rates in both the human-mouse and mouse-rat lineages were so heterogeneous that the X chromosome was not an outlier. Here again, the authors argued that this is at odds with male-driven evolution and suggested that selection has modulated chromosomal mutation rates to locally optimal levels, thus extending the argument of the first mentioned article to include autosomes. Here, we reexamine these conclusions using mouse-rat and human-mouse coding-region data. We find a more modest reduction of Ks on the X chromosome, but our results contradict the finding that the X chromosome is not distinct from autosomes. Multiple statistical tests show that Ks rates on the X chromosome differ systematically from the autosomes in both lineages. We conclude that the moderate reduction of mutation rate on the X chromosome of both lineages is consistent with male-driven evolution; however, the large variance in mutation rates across chromosomes suggests that mutation rates are affected by additional factors besides male-driven evolution. Investigation of mutation rates by synteny reveals that synteny blocks, rather than entire chromosomes, might represent the unit of mutation rate variation.

Animals↗

PubMed2000

Molecular systematics of the African electric fishes (Mormyroidea: teleostei) and a model for the evolution of their electric organs.

We present a new molecular phylogeny for 41 species of African mormyroid electric fishes derived from the 12S, 16S and cytochrome b genes and the nuclear RAG2 gene. From this, we reconstruct the evolution of the complex electric organs of these fishes. Phylogenetic results are generally concordant with earlier preliminary molecular studies of a smaller group of species and with the osteology-based classification of Taverne, which divides the group into the Gymnarchidae and the Mormyridae, with the latter including the subfamilies Petrocephalinae (Petrocephalus) and Mormyrinae (all remaining taxa). However, we find that several genera previously recognized by Taverne are non-monophyletic. Within the Mormyrinae, the genus Myomyrus is the sister group to all the remaining taxa. Other well-supported clades within this group are recovered. A reconstruction of electrocyte evolution on the basis of our best-supported topology suggests that electrocytes with penetrating stalks evolved once early in the history of the mormyrids followed by multiple paedomorphic reversals to electrocytes with non-penetrating stalks.

Animals↗

PubMed2006

Long-term evolution of EEG in Unverricht-Lundborg disease.

PURPOSE: Unverricht-Lundborg disease (ULD) is a progressive myoclonus epilepsy characterized by myoclonus, epilepsy, and ataxia, without major cognitive decline. There is no systematic study on the long-term evolution of EEG in this condition. PATIENTS AND METHODS: Twenty-five patients with ULD who came to our observation before 1995 and periodically followed in our Epilepsy Centres were included. All waking EEG traces were visually reviewed for the characterization background activity, with particular regard to the frequency of the posterior dominant rhythm (PR), and for the occurrence of spontaneous generalized spike or polyspike and wave discharges (GSWD) and photoparoxysmal response (PPR). Sleep recordings were analyzed with particular regard to the preservation of the physiological sleep patterns and the occurrence of GSWD and other epileptic abnormalities. RESULTS: PR was normal in 68% of patients at the beginning of the disease and kept stable over the years. GSWD were present in 92% of patients at the onset of the disease and gradually disappeared during the follow-up with a significant difference (p<0.001) after the 15th year of disease. PPR was present in 88% of patients at the disease onset and gradually disappeared with a significant difference (p<0.001) after the 10th year of disease. A gradual reduction of GSWD and a progressive disappearance of physiological sleep patterns were observed in sleep EEGs. CONCLUSION: In patients with ULD followed for an extended period of time, EEG shows no relevant deterioration of BA while a gradual reduction of GSWD and PPR is observed over time, well correlating with the good seizure outcome in this condition.

Adult↗

PubMedDate not supplied

[Genosystematics: from E. Chargaff and A. N. Belozersky up to date].

A review of history of genosystematics (macromolecular systematics) from E. Chargaff and A. N. Belozersky up to date. The role of A.N. Belozersky and his collaborators in the development of this new branch of systematics is analyzed. Genosystematics was the source of valuable information clarifying some aspects of biological evolution. Its methods were successfully employed in microorganisms--(e.g., discovery of archaebacteria) and in eucaryote systematics (origin of plastids, falcification of "molecular clock" hypothesis, substantial changes in higher plants phylogenetics, etc.). However, attempts to employ some fragmentary and unreliable data obtained by genosystematics for modifying the existing phylogenetic schemes and systems of organisms failed. Nowadays genosystematics is like a newborn child suffering from children's diseases well-known to "classical" systematics. It is rather far from final conclusions describing the evolution of genotypes. Some of its recent achievments, e.g., elaboration of the concept of PhyloCode, allow to believe that this science is able to suggest revolutionary changes in Linnean systematics.

Evolution, Molecular↗

PubMed1995

The maximum information principle and the evolution of nucleotide sequences.

The probability distributions of bases in nucleotide sequences are deduced from the maximum information principle by maximizing the entropy (due to random mutation of bases) under certain constraints (Markovian entropy, G + C content, etc, due to selection). Two formulations are given with respect to different selective constraints. The deviations of theoretical distributions from experimental data are lower than 10% for most sequences. It is shown that the Lagrange multipliers change from species to species systematically--i.e. selective constraints correlate with evolution.

Animals↗

PubMed2000

The evolution of the atpbeta-rbcL intergenic spacer in the epacrids (Ericales) and its systematic and evolutionary implications.

Sequence data from the noncoding region separating the plastid genes atpbeta and rbcL were gathered for 27 epacrid taxa, representing all previously recognized infrafamilial groups, and four outgroup taxa (Ericaceae), to address several persistent phylogenetic questions in the group. Parsimony analyses were conducted on these data, as well as on a complementary rbcL sequence dataset assembled from the literature and the combined dataset. The atpbeta-rbcL spacer was notable for the high frequency of insertion-deletion mutations (indels); their distributions were coded as binary characters and included as a adjunct matrix in some of the analyses. The phylogenetic patterns derived from the spacer and rbcL data and the combined analyses, both including and excluding the indel data, concur in resolving seven major lineages corresponding to the tribes of Crayn et al. (1998, Aust. J. Bot. 46, 187-200), viz. Prionoteae, Archerieae, Oligarrheneae, Cosmelieae, Richeeae, Epacrideae, and Styphelieae. The relationships of the tribes and within Styphelieae, however, are not convincingly resolved. Minor conflicts in the positions of some taxa between the spacer and the rbcL trees are poorly supported. Among epacrids, the spacer region provided more cladistically informative characters than rbcL and resulted in trees with lower homoplasy. Further, the spacer data, when analyzed alone and when combined with rbcL, resolved several clades that could not be retrieved on rbcL data alone and provided increased support for many other relationships. The evolution of a putative three-base inversion associated with a hairpin secondary structure in the spacer region is discussed in the light of the inferred phylogeny.

Classification↗

PubMed1999

Evolution of thyroid hormone binding by transthyretins in birds and mammals.

Transthyretin, a protein synthesized and secreted by the choroid plexus and liver, binds thyroid hormones in extracellular compartments. This binding prevents accumulation of thyroid hormones in the lipids of membranes, establishing extracellular thyroid hormone pools for the distribution of the hormones throughout the body and brain. The N-termini of the transthyretin subunits are longer and more hydrophobic in chicken than in eutherian transthyretins. Here, we show that this is a general structural feature of avian transthyretins. Systematic changes of protein structure during evolution result from selection pressure leading to changes in function. The evolution of transthyretin function, namely, the binding of thyroid hormones, was studied in nine vertebrate species. The affinity of thyroxine binding to transthyretin is lowest in avians (mean Kd of about 30 nm), intermediate in metatherians (mean Kd of about 17 nm) and highest in eutherians (mean Kd of about 11 nm). The affinity for 3,5,3'-triiodothyronine shows an opposite trend, being four times higher for avian transthyretins than for mammalian transthyretins.

Amino Acid Sequence↗

PubMed2005

Phylogenetic reconstruction of ancestral character states for gene expression and mRNA splicing data.

BACKGROUND: As genomes evolve after speciation, gene content, coding sequence, gene expression, and splicing all diverge with time from ancestors with close relatives. A minimum evolution general method for continuous character analysis in a phylogenetic perspective is presented that allows for reconstruction of ancestral character states and for measuring along branch evolution. RESULTS: A software package for reconstruction of continuous character traits, like relative gene expression levels or alternative splice site usage data is presented and is available for download at http://www.rossnes.org/phyrex. This program was applied to a primate gene expression dataset to detect transcription factor binding sites that have undergone substitution, potentially having driven lineage-specific differences in gene expression. CONCLUSION: Systematic analysis of lineage-specific evolution is becoming the cornerstone of comparative genomics. New methods, like phyrex, extend the capabilities of comparative genomics by tracing the evolution of additional biomolecular processes.

Alternative Splicing↗

PubMed1996

Mitochondrial gene sequences and the molecular systematics of the artiodactyl subfamily bovinae.

Nucleotide sequence evolution of the mitochondrial cytochrome c oxidase subunit II (COII) gene was used to examine the molecular phylogenetics and evolution of the Bovinae, a subfamily within the mammalian order Artiodactyla. The COII gene was sequenced in representatives of three bovine tribes (Bovini, Boselaphini, and Tragelaphini) and the outgroup taxon Capra (subfamily Caprinae). Although the phylogenetic analyses grouped Bison as sister to Bos, the genus Bison was paraphyletic, with the American bison being most closely related to species of Bos rather than to the European bison. COII data also supported a close relationship between African (Syncerus) and Asian (bubalus) buffaloes, the monophyly of the tribe Bovini, and a sister-group relationship between the tribes Bovini and Boselaphini. Analysis of nucleotide substitutions in the COII gene prompted a system of differential weighting of nucleotide substitutions for inferring phylogenetic relationships across the range of divergence times examined here (2-20 million years). Rates of evolution in the COII gene are examined and compared to evolutionary rates in mtDNA tRNA/rRNA genes and the D-loop among other artiodactyl taxa.

Animals↗

PubMed2001

Evolution of the FAD2-1 fatty acid desaturase 5' UTR intron and the molecular systematics of Gossypium (Malvaceae).

The FAD2-1 microsomal omega-6 desaturase gene contains a large intron ( approximately 1133 bp [base pairs]) in the 5' untranslated region that may participate in gene regulation and, in GOSSYPIUM:, is evolving at an evolutionary rate useful for elucidating recently diverged lineages. FAD2-1 is single copy in diploid GOSSYPIUM: species, and two orthologs are present in the allotetraploid species. Among the diploid species, the D-genome FAD2-1 introns have accumulated substitutions 1.4-1.8 times faster than the A-genome introns. In the tetraploids, the difference between the D-subgenome introns and their A-subgenome orthologs is even greater. The substitution rate of the intron in the D-genome diploid G. gossypioides more closely approximates that of the A genome than other D genome species, highlighting its unique evolutionary history. However, phylogenetic analyses support G. raimondii as the closest living relative of the D-subgenome donor. The Australian K-genome species diverged 8-16 million years ago into two clades. One clade comprises the sporadically distributed, erect to suberect coastal species; a second clade comprises the more widely spread, prostrate, inland species. A comparison of published gene trees to the FAD2-1 intron topology suggests that G. bickii arose from an early divergence, but that it carries a G. australe-like rDNA captured via a previously undetected hybridization event.

Journal Article↗