SEARCH · PubMed Health

Results for “balancing selection”

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 667 records · Page 37Linked to original sources

PubMed2006

Fitness effects of X chromosome drive in the stalk-eyed fly, Cyrtodiopsis dalmanni.

Sex-ratio (SR) males produce predominantly female progeny because most Y chromosome sperm are rendered nonfunctional. The resulting transmission advantage of XSR chromosomes should eventually cause population extinction unless segregation distortion is masked by suppressors or balanced by selection. By screening male stalk-eyed flies, Cyrtodiopsis dalmanni, for brood sex ratio we found unique SR alleles at three X-linked microsatellite loci and used them to determine if SR persists as a balanced polymorphism. We found that XSR/XST females produced more offspring than other genotypes and that SR males had lower sperm precedence and exhibited lower fertility when mating eight females in 24 h. Adult survival was independent of SR genotype but positively correlated with eye span. We infer that the SR polymorphism is likely maintained by a combination of weak overdominance for female fecundity and frequency dependent selection acting on male fertility. Our discovery of two SR haplotypes in the same population in a 10-year period further suggests that this SR polymorphism may be evolving rapidly.

Animals↗

PubMed2003

Positive selection on a human-specific transcription factor binding site regulating IL4 expression.

A single nucleotide polymorphism in the promoter of the multifunctional cytokine Interleukin 4 (IL4) affects the binding of NFAT, a key transcriptional activator of IL4 in T cells. This regulatory polymorphism influences the balance of cytokine signaling in the immune system, with important consequences-positive and negative-for human health. We determined that the NFAT binding site is unique to humans; it arose by point mutation along the lineage separating humans from other great apes. We show that its frequency distribution among human subpopulations has been shaped by the balance of selective forces on IL4's diverse roles. New statistical approaches, based on parametric and nonparametric comparisons to neutral variants typed in the same individuals, indicate that differentiation among subpopulations at the IL4 promoter polymorphism is too great to be attributed to neutral drift. The allele frequencies of this binding site represent local adaptation to diverse pathogenic challenges; disease states associated with the common derived allele are side-effects of positive selection on other IL4 functions.

Animals↗

PubMed2002

Towards a global historical emission inventory for selected PCB congeners--a mass balance approach. 1. Global production and consumption.

Information on the historical global production and consumption of polychlorinated biphenyls (PCBs) is urgently needed for estimating PCB fluxes to the environment and for interpreting global contamination patterns by these pollutants. This study presents the methodology, principal uncertainties and selected results from an inventory, aiming to quantify the global production and consumption of total PCBs as well as 22 PCB congeners. The available data on the historical production of PCBs and the chemical composition of various technical mixtures have been compiled from the literature. For some producers with less detailed information, the production of individual PCB constituents has been estimated to derive a global estimate for individual homologues and selected congeners. Information on imports, exports and consumption, as well as restrictions on production and imports, has further been compiled for individual countries. These data, along with assumptions on the trade between countries and regions, have been utilised to derive an estimate of the global historical consumption pattern. Although there are substantial uncertainties involved in these estimates, important aspects governing the large scale temporal and spatial patterns are most likely captured in these estimates. In particular, the information on imports and exports for the principal users of PCBs around the time of peak production is considered to be fairly reliable. The estimates account for a reported historical global production of approximately 1.3 million t PCBs, more than 70% of which are tri-, tetra- and pentachlorinated biphenyls. The results further suggest that almost 97% of the global historical use of PCBs have occurred in the Northern Hemisphere.

Environmental Pollutants↗

PubMed1980

Evolution of recombination in a constant environment.

The theory of evolution at a selectively neutral locus that controls the recombination between two major loci that are under selection is studied. If the major loci are at a stable equilibrium in linkage disequilibrium under selection and recombination, then a mutation at the modifier locus will increase in frequency when rare if and only if it decreases the recombination fraction. If the major loci are in disequilibrium at a balance between selection against deleterious alleles and mutation towards them, then two new phenomena are observed. First, a recombination increasing mutation will succeed if the disequilibrium is negative and the modifier is sufficiently tightly linked to the major loci. Second, depending on the strength of selection, even if the disequilibrium is negative, recombination reduction may occur for looser linkage between the major and modifier loci.

Journal Article↗

PubMed2001

Simulation of 'hitch-hiking' genealogies.

An ancestral influence graph is derived, an analogue of the coalescent and a composite of Griffiths' (1991) two-locus ancestral graph and Krone and Neuhauser's (1997) ancestral selection graph. This generalizes their use of branching-coalescing random graphs so as to incorporate both selection and recombination into gene genealogies. Qualitative understanding of a 'hitch-hiking' effect on genealogies is pursued via diagrammatic representation of the genealogical process in a two-locus, two-allele haploid model. Extending the simulation technique of Griffiths and Tavare (1996), computational estimation of expected times to the most recent common ancestor of samples of n genes under recombination and selection in two-locus, two-allele haploid and diploid models are presented. Such times are conditional on sample configuration. Monte Carlo simulations show that 'hitch-hiking' is a subtle effect that alters the conditional expected depth of the genealogy at the linked neutral locus depending on a mutation-selection-recombination balance.

Algorithms↗

PubMed2003

[The influence of hyperthyroidism on selected parameters of oxidant-antioxidant balance on animal model].

The aim of the experiment was to examine the influence of increased concentration of thyroid hormones on selected parameters of oxidant-antioxidant balance through the analysis of the antioxidant enzymes activity, the content of antioxidant vitamins, and the concentration of the unsaturated fatty acids peroxidation (TBARS). Administration of levothyroxine of the dose 100 micrograms/kg of body mass to rabbits for 21 days caused the increase of TBARS concentration, the decrease of concentration of vitamins C and E, and the increase of SOD activity.

Animals↗

PubMedDate not supplied

[Volumetric analysis of gray matter, white matter and cerebrospinal fluid space in schizophrenia].

Schizophrenia is characterized by diffuse brain abnormalities, some of them involving volumes of three intracranial compartments: gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF). Novel methods, such as Statistical Parametrical Mapping, provide an automated means of comparing structural features across high quality MRI scans and the measurement based on the principles of voxel based morphometry. For the purposes of the present study, we selected sex balanced group of young adults with recent onset illness to assess the effects of the illness on the volumes of compartments and also to minimize the effects of chronicity, medication, sex and aging. Sixty-four subjects were selected from a larger sample (inclusion criteria: age range 18-31). Thirty-one had DSM IV diagnosis of schizophrenia or schizoaffective disorder, 33 were controls. T1 weighted MRI images were acquired on two scanners (1.5T both): a) fast gradient echo sequence, FLASH, 40 msec repetition time, 5 ms echo time, 40 degree flip angle and b) turbo gradient echo, 12 msec repetition time, 4 msec echo time, 20 degree flip angle, 1 excitation). The resulting data set consisted of: a) 128 consecutive slices with 1.17 mm thickness and 256 x 256 pixels per slice and b) 160 consecutive slices of 1 mm thickness and 256 x 256 pixels per slice. All 64 images were processed by ANALZYE, and normalized and segmented by SPM99. Following the automatic segmentation of the images into the three intracranial compartments, volumetry was performed based on the principles of voxel analysis. Results were expressed relative to whole brain volume, and MANOVA analyses were performed to correct the confounding effects of MRI acquisition center differences and age difference between diagnostic groups. Young adults with recent onset schizophrenia had 6% reduction in GM volume and 14% increase in the volume of CSF, after all confounders were included into analyses (MANCOVA: p = 0.006 and 0.0002, respectively). No significant changes in WM volume were evident. In comparison to a few similar studies published recently, all results yielded similar scores regarding effects of recent onset illness and young adult population, thus confirming the reliability of the procedure. In conclusion, global neuropil reduction was discussed as a consequence of the cortical neurodevelopmental disgenesis. It was suggested that neuropil reduction i.e. synaptic and dendritic changes were to induce functional abnormalities and the expression of schizophrenia.

Adolescent↗

PubMed1993

Differentiation of balance deficits through examination of selected components of static stabilometry.

Stabilometry, which measures the body's center of pressure (COP) movements, during relaxed standing, has been used to distinguish individuals with vestibular and neurologic dysfunctions from normal subjects. The purpose of this study was to determine whether mathematical differences in the magnitudes of the COP obtained from six somatosensory testing conditions could be used to discriminate between different types of balance deficits. Stabilometry measures, using a fixed force platform, were obtained from normal (N = 52) and dizzy (N = 149), peripheral vestibular dysfunction (PVD), post-concussion syndrome (PCS), psychogenic (PSG), and unknown/undetermined etiology (UNK). The data significantly differentiated CVD, PVD and PSG patients from normals and between some of the dizzy groups: CVD versus PVD, PCS; and PSG versus CVD, PVD, PCS and UNK. The measures of anterior-posterior COP movements provided the greatest discrimination.

Adolescent↗

PubMed2002

Perceptual-motor contributions to static and dynamic balance control in children.

The authors addressed balance control in children from the perspective of skill development and examined the relationship between specific perceptual and motor skills and static and dynamic balance performance. Fifty 11- to 13-year-old children performed a series of 1-legged balance tasks while standing on a force platform. Postural control was reflected in the maximum displacement of the center of mass in anterior-posterior and mediolateral directions. Simple visual, discrimination, and choice reaction times; sustained attention; visuomotor coordination; kinesthesis; and depth perception were also assessed in a series of perceptual and motor tests. The correlation analysis revealed that balancing under static conditions was strongly associated with the ability to perceive and process visual information, which is important for feedback-based control of balance. On the other hand, when greater task demands were imposed on the system under dynamic balancing conditions, the ability to respond to the destabilizing hip abductions-adductions in order to maintain equilibrium was associated with motor response speed, suggesting the use of a descending, feedforward control strategy. Therefore, like adults, 11- to 13-year-old children have the ability to select varying balance strategies (feedback, feedforward, or both), depending on the constraints of a particular task.

Child↗

PubMed2006

Distinct phenotypes of obesity-prone AKR/J, DBA2J and C57BL/6J mice compared to control strains.

OBJECTIVE: To characterize and compare three obesity-prone inbred strains, AKR/J, DBA/2J and C57BL/6J, to three control strains, C3H/HeJ, BALB/cByJ and C57L/J, selected based on their normal eating patterns and moderate weight gain on high-calorie diets. METHODS AND PROCEDURES: These six strains were examined at 5 weeks of age while still of normal body weight, and they were maintained for 1 day or 3 weeks on different feeding paradigms with macronutrient diets. Measurements were taken of macronutrient intake, body weight and body fat accrual, circulating hormones and metabolites, and the hypothalamic peptide, galanin. RESULTS: The three control strains each selected a balanced diet with 50% carbohydrate and 15-25% fat when given a choice of macronutrients, and they had similar, normal range of scores for the measures of body weight, adiposity, the hormones, insulin and leptin, and the metabolites, glucose and triglycerides. When compared to this control baseline, the obesity-prone strains with similar total caloric intake to controls selected a diet with significantly more fat (30-40%) and less carbohydrate (<40%). They also had greater adiposity, with the largest differences detected for the AKR/J and DBA/2J strains. These two obesity-prone strains compared to control strains had elevated levels of insulin and leptin. They also had higher triglyceride levels and increased expression and levels of galanin in the hypothalamic paraventricular nucleus. A very different pattern was detected in the obesity-prone C57BL/6J strain, which exhibited a stronger preference for protein as well as fat, normal levels of insulin, leptin and triglycerides, hyperglycemia relative to all other strains, and a small increase in galanin. CONCLUSION: These comparisons to control strains revealed a distinct phenotype in the two obesity-prone strains, AKR/J and DBA/2J, which is very similar to that described in obesity-prone, outbred rats. They also identified a clearly different phenotype in the obesity-prone C57BL/6J strain.

Adipose Tissue↗

PubMed1997

The effect of strength and endurance training on gait, balance, fall risk, and health services use in community-living older adults.

BACKGROUND: The study tested the effect of strength and endurance training on gait, balance, physical health status, fall risk, and health services use in older adults. METHODS: The study was a single-blinded, randomized controlled trial with intention-to-treat analysis. Adults (n = 105) age 68-85 with at least mild deficits in strength and balance were selected from a random sample of enrollees in a health maintenance organization. The intervention was supervised exercise (1-h sessions, three per week, for 24-26 weeks), followed by self-supervised exercise. Exercise groups included strength training using weight machines (n = 25), endurance training using bicycles (n = 25), and strength and endurance training (n = 25). Study outcomes included gait tests, balance tests, physical health status measures, self-reported falls (up to 25 months of follow-up), and inpatient and outpatient use and costs. RESULTS: There were no effects of exercise on gait, balance, or physical health status. Exercise had a protective effect on risk of falling (relative hazard = .53, 95% CI = .30-.91). Between 7 and 18 months after randomization, control subjects had more outpatient clinic visits (p < .06) and were more likely to sustain hospital costs over $5000 (p < .05). CONCLUSIONS: Exercise may have beneficial effects on fall rates and health care use in some subgroups of older adults. In community-living adults with mainly mild impairments in gait, balance, and physical health status, short-term exercise may not have a restorative effect on these impairments.

Accidental Falls↗

PubMed1984

Calcium and phosphorus intakes, balances, and blood levels of adults consuming self-selected diets.

Metabolic calcium and phosphorus balances, blood calcium and phosphorus levels, and alkaline phosphatase activity of 34 men and women, 20 to 53 yr of age, were determined each season during 1 yr while consuming customary diets. Dietary records were maintained 365 days. Analysis of variance indicated that serum Ca, P, and alkaline phosphatase levels were affected by season (p less than 0.0001), whereas calcium or phosphorus intakes were not. Calcium and phosphorus intakes of the men (1075 and 1533 mg, respectively) were higher (p less than 0.01) than of the women (695 and 1095 mg, respectively), but balances were not statistically different between them. Daily calcium balances for the men and women for the year were -81 and -85 mg, respectively; daily phosphorus balances were -239 and -130 mg, respectively. Stepwise regression analysis indicated that dietary calcium and protein were significantly associated with calcium and phosphorus balances, but in opposite directions, and only in women over 35 yr of age.

Adult↗

PubMed2006

Space, selection, and surveillance: setting boundaries with BLyS.

The BLyS family of ligands and receptors governs B cell homeostasis by controlling survival, differentiation, and lifespan. This family consists of multiple receptors and ligands, allowing independent regulation of different B cell subsets by varying the combination and levels of receptors expressed. Multiple downstream signaling pathways are implicated in these activities, reflecting this receptor complexity as well as cross-talk with other B cell signaling systems. BLyS levels are associated with multiple forms of humoral autoimmunity and can modulate tolerogenic elimination at the transitional checkpoint. BLyS responsiveness thus balances peripheral selection against cell numbers, providing an elastic system that varies selective stringency based on homeostatic demands.

Animals↗

PubMed2006

Nutrient regulation in relation to diet breadth: a comparison of Heliothis sister species and a hybrid.

We examined the nutritional correlates of diet breadth in insect herbivores by comparing patterns of diet selection, nutrient balancing, post-ingestive utilization and development in two sister species of caterpillar and a hybrid between them. One species, Heliothis virescens (HV) has a broad host range, feeding on plants in at least 14 families. The other, Heliothis subflexa (HS), is a specialist on plants in the genus Physalis (Solanaceae). Experiments using synthetic foods showed that when the caterpillars were allowed to mix their diet, the generalist self-selected a higher-protein diet whereas the specialist ate almost equal amounts of protein and carbohydrate, which accords with differences between the two species in the nutrient content of their natural diets. When confined to nutritionally imbalanced diets, the generalist showed a propensity to over-eat high protein:carbohydrate (P:C) diets to a greater degree than did the specialist and maintained higher rates of development. The generalist did not, however, over-eat low P:C diets to the same degree as the specialist. The hybrid selected a diet composition that was indistinguishable to that of its generalist father (HV), while its response to imbalanced diets was closely similar to that of the specialist mother (HS). The generalist converted ingested nutrient to growth with lower efficiency than did the specialist and the hybrid. Our findings imply that different behavioural and physiological traits linked to nutrient regulation are under genetic control and are explicable in terms of the different life-histories, feeding ecologies and presumed levels of nutritional heterogeneity in the environments of the two insects.

Animals↗

PubMed1998

Codon usage in highly expressed genes of Haemophillus influenzae and Mycobacterium tuberculosis: translational selection versus mutational bias.

Biases in the codon usage and base compositions at three codon sites in different genes of A+T-rich Gram-negative bacterium Haemophillus influenzae and G+C-rich Gram-positive bacterium Mycobacterium tuberculosis have been examined to address the following questions: (1) whether the synonymous codon usage in organisms having highly skewed base compositions is totally dictated by the mutational bias as reported previously (Sharp, P.M., Devine, K.M., 1989. Codon usage and gene expression level in Dictyostelium discoideum: highly expressed genes do 'prefer' optimal codons. Nucleic Acids Res. 17, 5029-5039), or is also controlled by translational selection; (2) whether preference of G in the first codon positions by highly expressed genes, as reported in Escherichia coli (Gutierrez, G., Marquez, L., Marin, A., 1996. Preference for guanosine at first codon position in highly expressed Escherichia coli genes. A relationship with translational efficiency. Nucleic Acids Res. 24, 2525-2527), is true in other bacteria; and (3) whether the usage of bases in three codon positions is species-specific. Result presented here show that even in organisms with high mutational bias, translational selection plays an important role in dictating the synonymous codon usage, though the set of optimal codons is chosen in accordance with the mutational pressure. The frequencies of G-starting codons are positively correlated to the level of expression of genes, as estimated by their Codon Adaptation Index (CAI) values, in M. tuberculosis as well as in H. influenzae in spite of having an A+T-rich genome. The present study on the codon preferences of two organisms with oppositely skewed base compositions thus suggests that the preference of G-starting codons by highly expressed genes might be a general feature of bacteria, irrespective of their overall G+C contents. The ranges of variations in the frequencies of individual bases at the first and second codon positions of genes of both H. influenzae and M. tuberculosis are similar to those of E. coli, implying that though the composition of all three codon positions is governed by a selection-mutation balance, the mutational pressure has little influence in the choice of bases at the first two codon positions, even in organisms with highly biased base compositions.

Animals↗

PubMed2026

Genomic diversity, inbreeding, and selection signatures in duroc, landrace, and yorkshire pigs from a long-term closed breeding system.

Duroc (DD), Landrace (LL), and Yorkshire (YY) are among the most widely used commercial pig breeds, having undergone intense long-term selection within closed breeding systems. This study presents a comprehensive genomic analysis of genetic diversity, inbreeding patterns, and selection signatures in DD, LL, and YY populations that have been subject to close breeding for over 15 years. Genomic and pedigree data were available for 1,088 animals (DD = 348, LL = 276, YY = 464), genotyped using the GenoBaits® Porcine 100 K SNP panel. Principal component analysis and genetic diversity metrics revealed distinct population structures among the three breeds. Pairwise genetic differentiation supported this pattern, with DD showing the greatest divergence from LL (0.34 ± 0.24) and YY (0.33 ± 0.24), while LL and YY were more closely related (FST = 0.22 ± 0.19). Linkage disequilibrium (LD) analysis further confirmed these differences, as DD exhibited the highest average r² (0.34), followed by LL (0.28) and YY (0.25). Within-breed genetic diversity metrics, including observed heterozygosity (HO: 0.37 in DD, 0.39 in LL, 0.38 in YY), expected heterozygosity (HE: 0.36 in DD, 0.37 in LL, 0.38 in YY), and minor allele frequency (MAF: 0.27 in DD, 0.28 in LL, 0.29 in YY), indicated greater genetic variability in LL and YY compared to DD. Runs of homozygosity (ROH) analyses revealed different patterns of autozygosity, with DD exhibiting more long ROH indicative of recent inbreeding, while YY harbored a higher number of short ROH, suggestive of more ancient demographic events. ROH-based inbreeding coefficients (FROH) consistently exceeded pedigree-based estimates (FPED) across all breeds, highlighting the presence of recent or unrecorded inbreeding that pedigree data may not fully capture. According to Generation Proxy Selection Mapping (GPSM), 17, 1, and 12 significant SNPs were detected in DD, LL, and YY, respectively. Functional annotation of ROH islands and GPSM-significant loci revealed both breed-specific and overlapping QTLs related to traits such as growth, reproduction, and carcass. In general, the findings of this study contribute to a deeper understanding of the genomic consequences of long-term closed breeding and provide reference information to support consideration of breeding strategies that balance continued selection for productivity with the maintenance of genetic diversity in modern commercial pig populations.

Animals↗

PubMed1982

The effect of burn wound size on ureagenesis and nitrogen balance.

Hypermetabolic burn patients are frequently in negative nitrogen balance despite provision of estimated caloric needs. We studied 18 thermally injured adult patients in order to evaluate the relationship of burn wound size to urea production and nitrogen balance. We selected data from 147 patient-days when the patients received 100 +/- 25% of their estimated caloric needs. Three significantly different burn size groups (by body surface area [BSA]) were identified by calculation of the catabolic index (CI): group 1, 0-10% BSA (CI = -0.1); group 2, 11-30% BSA (CI = 6.4); and group 3,31-60% BSA (CI = 10.5). The urine urea nitrogen (UUN) for groups 1,2, and 3 was 11.1, 18.9, and 25.3 gm/day, and nitrogen balance was 1.0, -3.9, and -5.8 gm/day, respectively. When nitrogen was given in a calorie:nitrogen ratio of 150:1, only those patients in group I were able to achieve positive balance. We conclude that large burn wounds are associated with increased ureagenesis and impaired nitrogen retention. The protein intake, at the customary calorie:nitrogen ratio of 150:1, may not provide adequate nitrogen to achieve equilibrium, even when energy demands have been met, in patients with burn wounds greater than 10% BSA.

Adult↗

PubMed1994

The evolution of virulence in parasites and pathogens: reconciliation between two competing hypotheses.

According to conventional wisdom, parasites and pathogens should evolve reduced virulence to their hosts, because more virulent parasites and pathogens are more likely to drive their hosts, and themselves, to extinction. But this view has been criticized for its reliance on group selection. According to an alternative perspective, selection will favor whatever level of virulence maximizes the rate of increase of the parasite or pathogen. This optimum virulence depends on the functional relationship between a parasite or pathogen's transmissibility and its effect on host mortality, with selection often favoring an intermediate degree of virulence. The thesis of this paper is that models in which intermediate levels of virulence are favored lead quite naturally to the further conclusion that parasites and pathogens should-up to a point-become less virulent over time, once the feedbacks between ecological and evolutionary processes are incorporated into the analysis. As a consequence of successive adaptations by the parasite or pathogen, the density of susceptible hosts is reduced, thereby altering the balance between selective forces so as to favor reduced virulence. However, the evolutionarily stable strategy that is achieved is bounded away from complete avirulence. We conclude that models in which intermediate virulence is favored do not necessarily contradict the conventional wisdom in the long run; in fact, these models provide a simple mechanistic explanation for the evolution of reduced virulence.

Animals↗