SEARCH · PubMed Health

Results for “VARIATION”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 91 records · Page 5Linked to original sources

PubMed2006

Investigating the relationship between variations in students' perceptions of their academic environment and variations in study behaviour in distance education.

BACKGROUND: Recent research on student learning in higher education has identified clear associations between variations in students' perceptions of their academic environment and variations in their study behaviour. AIMS: This research investigated a general theoretical model linking students' demographic characteristics, perceptions and study behaviour with measures of outcome and in particular compared four accounts of the casual relationship between perceptions and study behaviour. SAMPLES: Study 1 employed data from 1,123 students taking six courses by distance learning; Study 2 employed data from 2,049 students taking seven courses by distance learning. METHODS: Path analysis was used to assess the causal relationships among the students' age, gender and prior qualifications, their scores on the Course Experience Questionnaire, their scores on a short version of the Approaches to Studying Inventory or the Revised Approaches to Studying Inventory, their overall marks and their ratings of general satisfaction. RESULTS: Both studies yielded evidence for the causal efficacy of all the paths identified in the general theoretical model. CONCLUSIONS: There exists a bi-directional causal relationship between variations in students' perceptions of their academic environment and variations in their study behaviour.

Achievement↗

PubMed1999

Unilateral variation of the arterial pattern of the human upper extremity with a muscle variation of the hand.

A unilateral variation in the origin and distribution of the arterial pattern of the human upper extremity on the right side is reported on. Apart from its usual branches, the third part of the right axillary artery gave origin to a common branch, the profunda brachii artery and the superior ulnar collateral artery. The right brachial artery, at a point 5.0 cm distal to its origin, bifurcated into the radial and ulnar arteries; their origin was in a position opposite the usual location. The radial artery continued on the medial side of the arm for 2.5 cm and crossed the ulnar artery anteriorly to gain a lateral position in the arm. The inferior ulnar collateral artery arose not from the brachial artery, but from the ulnar artery. A muscle variation was also observed in the right hand, which is compatible with the notion variations within one system of a limb will frequently be accompanied by variations in other systems of the same limb.

Aged↗

PubMed2003

Explaining variations in reported diabetes prevalence in general practice: how much variation is explained by differences between practice populations?

There are large variations in reported diabetes prevalence within United Kingdom (UK) populations. Linear regression was used to investigate whether population characteristics could explain the variation in prevalence between 19 practices with relatively complete diagnostic recording. Population obesity and South Asian ethnicity largely explained observed variation in prevalence (adjusted R2 = 0.80). When adjusted for obesity and ethnicity, the deprivation score was no longer a predictor of diabetes prevalence. If true variation in prevalence between practices is largely predicted by population ethnicity and obesity, these population characteristics could be used to predict expected prevalence and to assess the completeness of practice registers.

Aged↗

PubMed2004

[One-week variation of cotton dust and endotoxin levels in a cotton mill. Relation with the daily variation of the expiratory flow rates].

UNLABELLED: The prevalence of respiratory occupational diseases in the textile industry depends on environmental factors such cotton dust (CTD) levels and gram negative bacteria endotoxin (EDX) contamination. OBJECTIVE: To assess the environmental conditions (CTD and EDX) during one week in a cotton mill with respect to FEV1 variation throughout the work shift. POPULATION AND METHODS: 47 cotton mill workers (24F, 23M); average age: 42 +/- 11 years; average exposure to cotton dust: 22.5 +/- 9.4 years; Asthma: 15 (32%), Byssinosis: 11 (23%) and Asymptomatics: 21 (45%); a past history of respiratory symptoms: 13.1 +/- 11.7 years. Clinical evaluation, skin prick tests, a metacholine challenge, lung function tests and a work-place evaluation were performed. FEV1 Shift-variation (Delta-Shift) = end-shift FEV1 - start-shift FEV1, was calculated during one week. CTD and EDX levels were measured daily for each work place throughout this week and everyday during different operation tasks (work, cleaning, maintenance). The average values of CTD and EDX were calculated according to the time spent on each of these tasks for every worker who was exposed. RESULTS: Great variability of the environment conditions was observed throughout the week with the highest levels of CTD and EDX on Friday, even in comparison with Monday (CTD = 1.01 +/- 0.31 mg/m3 vs 0.68 +/- 0.65 mg/m3; p < 0.0005 e EDX = 33.1 +/- 8.9 ng/m3 vs 20.8 +/- 9.4 ng/m3; p < 0.0001). The shift variation was -129 +/- 97 ml for all the workers. The workers with asthma had the greatest reduction in expiratory flow rates, highest BHR and Delta-Shift but there were no differences in the levels of CTD and EDX among the three groups. Delta-Shift showed an association with the levels of EDX, specially in individuals with BHR but not with CTD levels. CONCLUSION: The environmental conditions that textile workers are exposed to, varies throughout the week and are associated with variations in flow rates and so lung function tests should be performed in a serial manner for the evaluation of respiratory occupational disease. The highest levels of EDX were recorded on Friday and this confirms the low reliability of the diagnostic criteria of byssinosis and points to the necessity of more objective measures.

Adult↗

PubMed2005

Abdominal pigmentation variation in drosophila polymorpha: geographic variation in the trait, and underlying phylogeography.

Drosophila polymorpha is a widespread species that exhibits abdominal pigmentation variation throughout its range. To gain insight into this variation we combined phenotypic and genotypic data to test a series of nested hypotheses. First, we tested the null hypothesis that geographic variation in pigmentation is due to neutral factors. We used nested clade analysis to examine the distribution of haplotypes from a nuclear and a mitochrondrial locus. Restricted gene flow via isolation by distance, the primary inference of this phylogeographic analysis, was then used to generate and test the hypothesis of increasing average abdominal pigmentation difference with increasing geographic distance. We found no correlation between geographic distance and phenotypic distance. We then tested the hypothesis that pigmentation is affected by environmental differences among localities. We found a significant effect of habitat type on the average abdominal pigmentation phenotype of different localities. Finally, we tested the hypothesis that pigmentation in D. polymorpha is associated with desiccation resistance. We found that dark individuals of both sexes survived significantly longer in a desiccating environment than light individuals. These patterns combined lead us to hypothesize that abdominal pigmentation variation in D. polymorpha is important in mediating the organism's interactions with local ecological factors.

Abdomen↗

PubMed1993

Effect of circadian variation in energy expenditure, within-subject variation and weight reduction on thermic effect of food.

Thermic effect of food (TEF) studies give conflicting answers to research questions and in many cases data from one laboratory to another is not comparable because of the utilization of different experimental methods. Likewise, how weight reduction affects measurement of TEF is controversial. Two studies were conducted on how TEF affects energy expenditure. The first study examined how resting energy expenditure (REE) measurements can affect TEF studies and how much within-subject variation is found in TEF studies. The TEF of a standard meal was measured in six subjects for 6.5 h on three different occasions by indirect calorimetry. REE was measured on each subject for 1 h before the meal was given on each measurement occasion. On a separate day, the energy expenditure was measured on each subject during the same time period as the TEF measurement, but without any food given to determine if a circadian increase in REE over the time period of the measurement was observed. We found no circadian increase in energy expenditure during the 6.5 h of the REE study. While the within-subject variation in REE (four measurements) had an average coefficient of variation of 5.2% (range 2.4-8.5%), the coefficient of variation of the TEF measured (three measurements) was 26.4% (range 13.6-50.9). In the second study, REF and the TEF were measured before and after weight reduction in moderately overweight adult women. Nine women weighing between 62.1 and 84.7 kg lost an average of 7.3 kg while on a reduced calorie, low fat diet for between 12 and 14 weeks. After weight reduction, the average REE of these subjects decreased by 8.8% or 515 kJ (123 kcal)/24 h. The TEF of these nine women was measured for 6.5 h before and after weight reduction using 16 oz of Sustacal, 2008 kJ (480 kcal). Before weight reduction the thermic effect of Sustacal was 264 kJ (63 kcal) or 13% of calories consumed, and after weight reduction it was 251 kJ (60 kcal) or 12.5% of calories consumed. We did not find the TEF to be lower than expected in these subjects before weight reduction, since TEF is often reported to be around 10% of energy consumed, and it was not changed after weight reduction.

Adult↗

PubMed2002

Population variation in linkage disequilibrium across the COMT gene considering promoter region and coding region variation.

Catechol-O-methyl transferase (COMT) catalyzes the first step in one of the major pathways in the degradation of catecholamines. The COMT gene on chromosome 22 has been considered a candidate gene for many neuropsychiatric disorders, in part because an exon 4 single nucleotide polymorphism (SNP) in COMT causes an amino acid substitution associated with significantly altered enzyme activity. This functional variant, detected as an NlaIII restriction site polymorphism (RSP), is polymorphic in populations from around the world. A four-site haplotype spanning 28 kb effectively encompasses COMT. This haplotype is comprised of two novel polymorphisms [a tetranucleotide short tandem repeat polymorphism (STRP) in intron 1 and a HindIII RSP at the 5' end of COMT], the NlaIII site, and another previously published site - a BglI RSP at the 3' end of the gene. Overall linkage disequilibrium (LD) for this haplotype is strong and significant in 32 population samples from around the world. Conditional probabilities indicate that, in spite of moderate to strong disequilibrium in most non-African populations, the NlaIII site, although often used for prediction, would not always be a reliable predictor of allelic variation at the other sites. Because other functional variation might exist, especially regulatory variation, these findings indicate that haplotypes would be more effective indicators of possible involvement of COMT in disease etiology.

Base Sequence↗

PubMed2005

Studying genetics of adaptive variation in model organisms: flowering time variation in Arabidopsis lyrata.

Arabidopsis thaliana has emerged as a model organism for plant developmental genetics, but it is also now being widely used for population genetic studies. Outcrossing relatives of A. thaliana are likely to provide suitable additional or alternative species for studies of evolutionary and population genetics. We have examined patterns of adaptive flowering time variation in the outcrossing, perennial A. lyrata. In addition, we examine the distribution of variation at marker genes in populations form North America and Europe. The probability of flowering in this species differs between southern and northern populations. Northern populations are much less likely to flower in short than in long days. A significant daylength by region interaction shows that the northern and southern populations respond differently to the daylength. The timing of flowering also differs between populations, and is made shorter by long days, and in some populations, by vernalization. North American and European populations show consistent genetic differentiation over microsatellite and isozyme loci and alcohol dehydrogenase sequences. Thus, the patterns of variation are quite different from those in A. thaliana, where flowering time differences show little relationship to latitude of origin and the genealogical trees of accessions vary depending on the genomic region studied. The genetic architecture of adaptation can be compared in these species with different life histories.

Adaptation, Physiological↗

PubMed2000

Allozyme variation patterns and multiple hybridization origins: clonal variation among four sibling parthenogenetic Caucasian rock lizards.

Allozyme electrophoresis of four sibling parthenogenetic Caucasian rock lizards Darevskia unisexualis, D. uzzelli, D. sapphirina, and D. bendimahiensis found seven clones and five variable loci. The data supported the hypothesis that D. raddei and D. valentini are the parental species of all four parthenogens. Variation patterns in Darevskia were summarized. Species that originated from a single F1 typically consisted of one widespread clone with a few rare clones. Species with multiple origins displayed variation only slightly higher than species with a single origin. This is contrary to other genera of parthenogenetic lizards, in which cases massive clonal variations were observed.

Animals↗

PubMed2004

Chloroplast DNA variation in the Quercus affinis-Q. laurina complex in Mexico: geographical structure and associations with nuclear and morphological variation.

The geographical distribution of chloroplast DNA (cpDNA) variation in 39 populations of two hybridizing Mexican red oaks, Quercus affinis and Q. laurina, was investigated using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Six haplotypes were identified. Of these, two (H1 and H4), separated by four mutations, had high frequencies (58 and 23% of the individuals, respectively) and were present across the whole geographical range of both species, often co occurring in the same populations. The other four haplotypes were rare, geographically restricted, and are probably derived from the two frequent haplotypes. Latitudinal or other clinal patterns in diversity levels or haplotype composition of populations were not apparent. The pattern of haplotype distribution was characterized by some mosaicism, with contrasting populations often situated in proximity. Average within-population diversity (hS=0.299) and population differentiation (GST=0.499) were, respectively, higher and lower than values reported in previous studies of oak species. There was evidence for phylogeographical structure, as indicated by NST (0.566) being significantly higher than GST. Haplotypic variation was largely species-independent, although some very weak associations were detected between haplotypes H1 and H4 and morphological and nuclear molecular variation correspondingly characterizing Q. affinis and Q. laurina. These oaks probably did not experience a marked restriction to one or a few particular subregions of their present range during the last glacial cycle. It is more likely that substantial populations persisted throughout several episodes of climatic change, but experienced recurrent latitudinal and altitudinal migrations which may have caused the widespread distribution of haplotypes H1 and H4 and frequent intermixing of populations.

DNA, Chloroplast↗

PubMed2006

Patterns of genetic variation in the hypertension candidate gene GRK4: ethnic variation and haplotype structure.

Association studies using single nucleotide polymorphisms (SNPs) have the potential to help unravel the genetic basis of hypertension. Nevertheless, to date, association studies of hypertension have yielded ambiguous results. It is becoming clear that such association studies must be interpreted within the context of the genetic structure of the populations being studied, and patterns of variation within specific genomic regions. With this in mind we analyzed genetic variation in the G protein-coupled receptor kinase 4 (GRK4) gene, a gene whose product has recently been shown to inhibit the dopamine receptor D1 (DRD1) from increasing sodium excretion. We genotyped three previously identified GRK4 SNPs, as well as ten additional SNPs, over 71.6 kb of the GRK4 locus in four populations: African Americans, Asians, Hispanics and Caucasians. Haplotype structure varied among populations, with Hispanics and Caucasians having the most linkage disequilibrium (LD) among SNPs. African Americans had three shorter haplotype blocks, while patterns of markers in the Asian populations demonstrated less LD among markers, a pattern inconsistent with block structure. We observed limited haplotype diversity in each of the four populations, with differing haplotype frequencies among the ethnic groups. We also found substantial evidence for population differentiation, with the largest differences between the African-American and Asian samples with F(ST) values in the upper 90(th) percentile when compared to a genome-wide distribution. However, for all population comparisons, F(ST) values decreased sharply in the 3' region of the gene. This pattern of differentiation among populations is consistent with selection in this part of the gene maintaining similar patterns of variation among otherwise divergent populations. Our results document not only different allele frequencies between populations, but differences in haplotype structure that may be important in evaluating association studies between hypertension and GRK4.

Black or African American↗

PubMed1987

Genome size variation in North American minnows (Cyprinidae). II. Variation among 20 species.

Genome sizes (nuclear DNA contents) from 200 individuals representing 20 species of North American cyprinid fishes (minnows) were examined spectrophotometrically. The distributions of DNA values of individuals within populations of the 20 species were essentially continuous and normal; the distribution of DNA values among species was continuous and overlapping. These observations suggest that changes in DNA quantity in cyprinids are small in amount, involve both gains and losses of DNA, and are cumulative and independent in effect. Significant heterogeneity in mean genome size occurs both between individuals within populations of species and among species. The former averages maximally around 6% of the cyprinid genome and is nearly the same as the amount of DNA theoretically needed for the entire cyprinid structural gene component. The majority of the DNA content variation among the 20 species is distributed above the level of individuals within populations. Comparisons of average genome size difference or distance between individuals drawn from different levels of taxonomic organization indicate that considerably greater divergence in genome size has occurred in the extremely speciose cyprinid genus Notropis as compared with other North American cyprinid genera. This may suggest that genome size change is concentrated in speciation episodes. Finally, no associations were found between interspecific variation in genome size and five life-history characters. This suggests that much of the variation in genome size within and among the 20 species may be phenotypically inconsequential.

Animals↗

PubMed1993

Annual variations in hypothalamic serotonin and monoamine oxidase in the catfish Heteropneustes fossilis with a note on brain regional differences of day-night variations in gonadal preparatory phase.

In Heteropneustes fossilis, significant annual variations in serotonin (5-HT) and monoamine oxidase (MAO) were found in the hypothalamus both at 12 and 24 hr with high values of content and turnover index (TI) during gonadal recrudescence, and low values during gonadal quiescence. The 5-HT content reached high levels during April-July (late preparatory, prespawning, and spawning phases). The TI of 5-HT showed two peaks in its midday value; a major peak occurred in March (midpreparatory phase) and a minor one in June (prespawning phase). High MAO activity was seen in June (prespawning phase) and low values during February, March, and April (preparatory phase). Significant day-night variations in 5-HT content and TI, and MAO activity were observed in the hypothalamus and telencephalon in February and March (early and midpreparatory phase), but not at other times of the year. In the whole brain and separate regions such as the thalamus, midbrain, and hindbrain no day-night patterns were seen. A comparison of the data shows that the increase in 5-HT content and TI from February to March was significantly higher in the hypothalamus than in telencephalon and the opposite is true for MAO. The results suggest that the high hypothalamic activities of 5-HT and MAO during recrudescence is related to breeding activity; the day-night variations during the early and midpreparatory phase in these variables may be related to initiation of breeding in this species.

Animals↗

PubMed2006

Structural themes and variations in protein kinase A as seen by small-angle scattering and neutron contrast variation.

Using small-angle solution scattering and neutron contrast variation, we have studied the structure of the multi-subunit protein kinase A. We have gained insights into how nature can take a set of common structural domains (or themes) and modulate their interactions via sequence variations and second messenger mediated signaling to affect enzyme activity and receptor binding important for targeting this multi-function enzyme to specific sub-cellular locations. These studies demonstrate the power of neutron contrast variation to expand our knowledge of the dynamic supra-molecular structures that carry out biological function.

Binding Sites↗

PubMed2006

Complex patterns of copy number variation at sites of segmental duplications: an important category of structural variation in the human genome.

The structural diversity of the human genome is much higher than previously assumed although its full extent remains unknown. To investigate the association between segmental duplications that display constitutive copy number differences (CNDs) between humans and the great apes and those which exhibit polymorphic copy number variations (CNVs) between humans, we analysed a BAC array enriched with segmental duplications displaying such CNDs. This study documents for the first time that in addition to human-specific gains common to all humans, these duplication clusters (DCs) also exhibit polymorphic CNVs > 40 kb. Segmental duplication is known to have been a frequent event during human genome evolution. Importantly, among the CNV-associated genes identified here, those involved in transcriptional regulation were found to be significantly overrepresented. Complex patterns of variation were evident at sites of DCs, manifesting as inter-individual differentially sized copy number alterations at the same genomic loci. Thus, CNVs associated with segmental duplications do not simply represent insertion/deletion polymorphisms, but rather constitute a wide variety of rearrangements involving differential amplification and partial gains and losses with high inter-individual variability. Although the number of CNVs was not found to differ between Africans and Caucasians/Asians, the average number of variant patterns per locus was significantly lower in Africans. Thus, complex variation patterns characterizing segmental duplications result from relatively recent genomic rearrangements. The high number of these rearrangements, some of which are potentially recurrent, together with differences in population size and expansion dynamics, may account for the greater diversity of CNV in Caucasians/Asians as compared with Africans.

Animals↗

PubMed1980

Genetic studies of daily variations of first-step enzymes of monoamines metabolism in the brain of inbred strains of mice and hybrids. I. Daily variations of tryptophan hydroxylase activity in the nuclei raphe dorsalis, raphe centralis and in the striatum.

A daily variation of tryptophan hydroxylase (TrH) activity was observed in the raphe dorsalis (RD), raphe centralis (RC) and striatum (St) of 3 inbred strains of mice (BALB/c, C57BL/6, C57BR) and of the reciprocal hybrids obtained from Balb/c and C57BL6. Significant differences of the characteristics of these rhythms have been found in the same strain between different structures and for the same structure between different strains. In RD and RC hybridization led to less defined daily variations which, in the striatum, remained well synchronized and could be controlled by a dominant genetic mechanism part. These results help to discuss evidence for selective control mechanisms of regulation responsible for daily variation of TrH in the 5-HT cell bodies and terminals and their relative independence.

Animals↗

PubMed1980

Genetic studies of daily variations of first-step enzymes of monoamines metabolism in the brain of inbred strains of mice and hybrids. II. Daily variations of tyrosine hydroxylase activity in the locus coeruleus.

Daily variations of tyrosine hydroxylase (TH) activity in the locus coeruleus of 3 inbred strains of mice (BALB/c; C57BL6; C57Br) and the F1 hybrids obtained from BALB/c and C57BL/6 are discussed. Precise characteristics of the circadian rhythms were observed in each strain. They were found significantly different in two genetically pure parents (BALB/c and C57BL6). In their two F1 hybrids the daily variation of TH activity was similar to that observed in one of the parents (C57BL6). This strongly suggests selective and genetically controlled mechanisms of regulation responsible for the daily variation of TH activity in the locus coeruleus of mice.

Animals↗

PubMed1997

Variation in optic zone radii of a contact lens during manufacturing and the effects of temperature on this variation.

There is little information in the literature on the causes of variation in the optic zone radii of a contact lens and the effects of temperature on this variation. In this study, the lathe cutting method of producing contact lenses was reviewed. The cause of the variation in the back optic zone radius was then identified as change in the operating condition from that of the calibrating one. Also, using finite element and theoretical methods, it was found that the effect of an increase in lens blank temperature is to make the back optic zone radius obtained steeper than that required, and this effect was verified experimentally.

Journal Article↗