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At least 991 records · Page 55Linked to original sources
PubMed2002

Multilocus population structure of Tapesia yallundae in Washington State.

Population genetic structure of the fungal wheat pathogen Tapesia yallundae in Washington State was determined using genetically characterized amplified fragment length polymorphic (AFLP) markers and mating-type (MAT1-1 or MAT1-2). Segregation and linkage relationships among 164 AFLP markers and MAT were analysed using 59 progeny derived from an in vitro cross. Alleles at 158 AFLP loci and the mating-type locus segregated in a 1:1 ratio. Ten unlinked markers were chosen to determine genetic and genotypic diversity and to test the hypothesis of random mating and population differentiation among five subpopulations of T. yallundae representative of the geographical distribution of wheat production in eastern Washington. Among 228 isolates collected, overall gene diversity was high (h = 0.425) and a total of 91 unique multilocus genotypes (MLG) were identified, with 32 MLG occurring at least twice. The overall population genetic structure was consistent with random mating based on the segregation of mating-type, index of association (IA), parsimony tree length permutation test (PTLPT) and genotypic diversity analyses. However, clonal genotypes were found within each subpopulation and were also distributed among the five subpopulations. No significant differences in allele frequencies were found among the five subpopulations for all 10 loci based on contingency table analysis (G2) and Wier & Cockerham's population differentiation statistic theta (theta = -0.008, P = 0.722). T. yallundae appears to consist of a large homogeneous population throughout eastern Washington with both sexual and asexual reproduction contributing to the observed population genetic structure despite no report of sexual fruiting bodies of T. yallundae occurring under natural field conditions.

Ascomycota↗
PubMedDate not supplied

[Immunologic and epidemiologic characterization of non-responders/low-responders to hepatitis B vaccine].

UNLABELLED: An important reduction in morbidity and mortality due to hepatitis B was achieved with the discovery of an effective vaccine. However, 2 to 10% of healthy adults do not respond to vaccination with the production of protective levels of antibody anti-HBs (assumed as protective, concentrations of ab. anti-HBs > 10 UI/L). Therefore, the aim of the present work was to study epidemiological (sex, age, obesity, alcoholic and smoking habits, previous diseases) and immunological factors (white cell count, immunoglobulins and sub-classes of IgG, lymphocytic populations and sub-populations) in a group of 20 healthcare workers with a low response (anti-HBs < 50 UI/L) to a genetically-engineered vaccine (Engerix B). The results were compared to the ones found in an identical sample of responders (anti-HBs > 100 UI/L) from the same population. No statistically significant differences regarding the epidemiological data, differential white cell counts and immunoglobulin quantification (IgG, IgA, IgM, IgG1, IgG2, IgG3) were detected. The mean value of IgG4 (mean = 54.53 +/- 59.8 mg/dl) in non/hyporesponders was significantly higher (p = 0.038) when compared to the same result in responders (mean = 33.76 +/- 31.30 mg/dl). A statistically significant difference (p < 0.05) in the quantification of double negative lymphocytic T sub-populations was also found, the mean value being higher in the responders (mean = 6.5 +/- 4.1% versus 4.6 +/- 2.3%). CONCLUSIONS: The effectiveness of recombinant hepatitis B vaccines is well known. However, a number of apparently healthy people are unable to achieve protective titres of anti-HBs after vaccination. As our study groups did not have a considerable number of cases, we can not establish definitive conclusions based on differences found in the quantification of IgG4 and double negative lymphocytic T sub-populations. It seems to us that an investment in future research into the eventual causes of nonprotective response and into new strategies of immunization of non/hyporesponders are appropriate. In the meantime, the occupational daily risk of exposure to infected body fluids makes adequate hepatitis B immunization of healthcare workers a priority.

Adult↗
PubMed1991

An empirical analysis of the effect of length of forecast horizon on population forecast errors.

Many studies have found that population forecast errors generally increase with the length of the forecast horizon, but none have examined this relationship in detail. Do errors grow linearly, exponentially, or in some other manner as the forecast horizon becomes longer? Does the error-horizon relationship differ by forecasting technique, launch year, size of place, or rate of growth? Do alternative measures of error make a difference? In this article we address these questions using two simple forecasting techniques and population data from 1900 to 1980 for states in the United States. We find that in most instances there is a linear or nearly linear relationship between forecast accuracy and the length of the forecast horizon, but no consistent relationship between bias and the length of the horizon. We believe that these results provide useful information regarding the nature of population forecast errors.

Humans↗
PubMedDate not supplied

Sex-linked strategies of human reproductive behavior.

We present data on fertility characteristics in the Venezuelan population for each sex separately, allowing a detailed comparative analysis of the variance in fertility between males and females. We show that the fertility distribution for both sexes is discontinuous, that the average female has a larger number of offspring per individual than the average male, and that highly fertile males outnumber highly fertile females so that the total number of offspring produced by males and females is balanced. Results indicate that a few males are responsible for a relative higher fertility of the average female and that interactions between polyandric females with monogamic and polygynic males are common. Among the Yanomami, a relatively unacculturated hunter-gatherer-horticulturist tribe, similar differences in fertility distribution of both sexes are apparent. The data suggest that human populations contain statistically distinct subpopulations, with different reproductive strategies, suggesting the existence of complex interactions among human populations which are not evident from the study of individuals or groups.

Adolescent↗
PubMed1998

Arthroscopic removal of palmar/plantar osteochondral fragments (POF) in the metacarpo- and metatarso-phalangeal joints of standardbred trotters--outcome and possible genetic background to POF.

A clinical material of 133 Standardbred horses with palmar/plantar osteochondral fragments (POF) in the metacarpo- and metatarsophalangeal joints were studied. All horses had their fragments removed with arthroscopic surgery. 102 of the horses were 3 years old or younger when surgery was performed. Anatomical localisations of the fragments were in agreement with earlier reports. There was no statistical significant difference in month of birth in the POF--group compared to the total population. Eighty % of the horses that had raced before surgery came back to racing. The racing performance relative to their contemporaries remained the same after the POF operation. 65% of the horses that had not raced before surgery raced after the operation. The breeding index BLUP (Best Linear Unbiased Prediction) was used to evaluate if the POF-horses differed genetically in racing ability from the total population. The average BLUP value of the POF group was 103.4 (+/- 0.65), while the mean BLUP value of the total population was 98.9. This difference was highly significant and indicated that these POF horses belonged to a selected group. A homogeneity test of allele frequencies in blood type systems was performed to evaluate if any genetic difference was persistent between POF horses compared to the total population. The statistical analysis of gene frequencies for alleles in blood type systems indicated a genetic discrimination in blood type systems D and Tf.

Age Factors↗
PubMed2005

Power laws of complex systems from extreme physical information.

Many complex systems obey allometric, or power, laws y=Y x(a) . Here y > or = 0 is the measured value of some system attribute a , Y> or =0 is a constant, and x is a stochastic variable. Remarkably, for many living systems the exponent a is limited to values n/4 , n=0, +/-1, +/-2.... Here x is the mass of a randomly selected creature in the population. These quarter-power laws hold for many attributes, such as pulse rate (n=-1) . Allometry has, in the past, been theoretically justified on a case-by-case basis. An ultimate goal is to find a common cause for allometry of all types and for both living and nonliving systems. The principle I-J=extremum of extreme physical information is found to provide such a cause. It describes the flow of Fisher information J-->I from an attribute value a on the cell level to its exterior observation y . Data y are formed via a system channel function y identical to f (x,a) , with f (x,a) to be found. Extremizing the difference I-J through variation of f (x,a) results in a general allometric law f (x,a) identical to y=Y x(a) . Darwinian evolution is presumed to cause a second extremization of I-J , now with respect to the choice of a . The solution is a=n/4 , n=0,+/-1,+/-2..., defining the particular powers of biological allometry. Under special circumstances, the model predicts that such biological systems are controlled by only two distinct intracellular information sources. These sources are conjectured to be cellular DNA and cellular transmembrane ion gradients.

Algorithms↗
PubMed1997

Identifying comparison groups for evaluating occupational hearing loss: a statistical assessment of 22 industrial populations.

Finding appropriate comparison groups to study occupational hearing loss has been difficult. Recently, however, the National Institute for Occupational Safety and Health sponsored the complication of potentially useful data from 22 diverse industrial companies in the U.S.A. and Canada. We conducted a statistical evaluation to determine which of the 22 populations might be suited as comparison groups in future studies of workers exposed to hazardous noise. In a Cox Proportional Hazards model that included age and sex, the relative risk of developing hearing loss in each company was estimated at two, five, and ten years of follow-up. We ranked the companies based on their relative risks, and rated them on a five-point scale from "excellent" to "poor" to indicate their suitability as comparison groups. The risk profiles developed and other variables described in this study will assist researchers in selecting appropriate comparison groups for evaluating occupational hearing loss.

Age Distribution↗
PubMed2003

Biochemical genetic variability in brown hares (Lepus europaeus) from Greece.

Allozyme variability of 91 brown hares (Lepus europaeus) from seven regions in Greece was compared to existing data of Bulgarian populations to test the hypothesis of the occurrence ofspecific alleles in Greece, likely stemming from an isolated Late Pleistocene refugial population in the southern Balkans. This hypothesis is particularly suggested by some subfossil Late Pleistocene hare remains in Greece and the reported high mtDNA diversity in Greek hares. Allozymic diversity could be higher in Greek hares than in hares from neighboring regions as a result of the accumulation of variants in a long-lasting Pleistocene refugium. Conversely, Greek hares could exhibit reduced genetic diversity because of long-lasting low effective population sizes during the Late Glacial Maximum and a lower chance of postglacial gene flow from other populations into this rather marginal part in the southern Balkans. Horizontal starch gel electrophoresis of proteins from 35 loci revealed three alleles (Es-1(-162), Pep-2(114), Mpi(88)) at low frequencies, which were not found in Bulgarian or any other brown hare population. In contrast, some alleles from the populations from Bulgaria and other regions of Europe were absent in the Greek samples. Population genetic statistics indicated only a slight tendency of increased gene pool diversity in Greek hares, little substructuring in Greek and Bulgarian populations, respectively, as well as an only slightly lower level of gene flow between the two neighboring regions, as compared to the gene flow within each region. The results conform to the hypothesis of a Late Pleistocene refugial population in the southern Balkans, with some few specific nuclear gene pool characteristics, but little effect on the overall genetic differentiation between Greek and Bulgarian hares.

Alleles↗
PubMed1992

[Forecast intervals of population size].

"This article describes a method for assessing a statistical confidence interval of future population size. The method is based on an autoregressive model of forecast errors of the population growth rate. An English-language version of this article is available upon request (address: Netherlands Central Bureau of Statistics, Department of Population Statistics, P.O. Box 959, 2270 AZ Voorburg)." (SUMMARY IN ENG)

Demography↗
PubMed1989

The role of chlamydial serology in fertile and subfertile men.

The incidence of serum antibodies to Chlamydia trachomatis and the possible association of a positive serology on semen parameters in 120 subfertile men were studied. The findings were compared with those of 120 fertile volunteers fathering two or more children. The two groups were divided into those without and those with a history of genito-urinary infection. There was no significant difference (p greater than 0.1) in the prevalence of antibody testing between the subgroups of fertile population. A statistically significant difference in the incidence of antibodies was found between the two subgroups of subfertile population. No significant difference was noted in the semen parameters between Chlamydia-positive and Chlamydia-negative fertile and subfertile patients.

Adult↗
PubMed1991

Breast cancer risk and oral contraceptive use: results from a large case-control study.

The association between oral contraceptive use and breast cancer risk was examined using data from a case-control study of breast cancer in Long Island, New York. Cases were defined as female residents of Nassau and Suffolk Counties between the ages of 20 and 79, diagnosed with breast cancer between January 1, 1984 and December 31, 1986. Age- and county-matched controls were selected from driver's license files. Among all women under age 70 at diagnosis, there was no association between oral contraceptive use and breast cancer; there was, however, a positive association in the subgroup ages 20-49 (adjusted odds ratio = 1.68, 95% CI: 1.16-2.42). Risk increased with increasing duration of use, but did not differ between women who first used oral contraceptives before the first pregnancy and those who first used them later, or between women who first used oral contraceptives before age 25 and those who first used them at a later age. Risk also appeared to increase with number of years of use before the first pregnancy or before age 25, although numbers were small. History of benign breast disease did not influence risk. The association of breast cancer risk with oral contraceptive use appeared stronger in women from Suffolk County than Nassau County.

Adult↗
PubMed1997

Genetic polymorphism of catechol-O-methyltransferase (COMT): correlation of genotype with individual variation of S-COMT activity and comparison of the allele frequencies in the normal population and parkinsonian patients in Finland.

The catechol-O-methyltransferase (COMT) gene occurs as two polymorphic alleles, which code for a high activity thermostable and low activity thermolabile form of the enzyme. We devised a fast solid-phase minisequencing assay for genotyping the COMT gene at nucleotide position 544 encoding amino acid residue 158. The method was applied to correlate the genotype of the COMT gene with the biological activity of the COMT enzyme. In red blood cells from individuals homozygous for G at nucleotide position 544 coding for Val-158, the activity of COMT ranged from 0.55-1.03 pmol min-1 mg-1 protein, and in individuals homozygous for A at position 544 coding for Met-158, the activity ranged from 0.21-0.43 pmol min-1 mg-1. Heterozygotes showed intermediate activities of 0.20-0.88 pmol min-1 mg-1. The thermostability (heated/unheated) at 48 degrees C of the high activity form was shown to be about two-fold compared to that of the low activity form of the enzyme. By analysing 76 individual samples and three pooled samples representing altogether 3140 individuals using the solid-phase minisequencing method, the two COMT alleles were shown to be equally distributed in the Finnish population. No statistically significant difference in the frequencies of the COMT alleles was found when comparing the normal population with a sample of 158 Finnish patients with Parkinson's disease.

Catechol O-Methyltransferase↗
PubMed2005

Patterns of male sterility in a grasshopper hybrid zone imply accumulation of hybrid incompatibilities without selection.

It is now widely accepted that post-zygotic reproductive isolation is the result of negative epistatic interactions between derived alleles fixed independently at different loci in diverging populations (the Dobzhansky-Muller model). What is less clear is the nature of the loci involved and whether the derived alleles increase in frequency through genetic drift, or as a result of natural or sexual selection. If incompatible alleles are fixed by selection, transient polymorphisms will be rare and clines for these alleles will be steep where divergent populations meet. If they evolve by drift, populations are expected to harbour substantial genetic variation in compatibility and alleles will introgress across hybrid zones once they recombine onto a genetic background with which they are compatible. Here we show that variation in male sterility in a naturally occurring Chorthippus parallelus grasshopper hybrid zone conforms to the neutral expectations. Asymmetrical clines for male sterility have long tails of introgression and populations distant from the zone centre show significant genetic variation for compatibility. Our data contrast with recent observations on 'speciation genes' that have diverged as a result of strong natural selection.

Animals↗
PubMed2006

Genetic structure among and within peripheral and central populations of three endangered floodplain violets.

Understanding the partitioning of genetic variance in peripheral and central populations may shed more light on the effects of genetic drift and gene flow on population genetic structure and, thereby, improve attempts to conserve genetic diversity. We analysed genetic structure of peripheral and central populations of three insect-pollinated violets (Viola elatior, Viola pumila, Viola stagnina) to evaluate to what extent these patterns can be explained by gene flow and genetic drift. Amplified fragment length polymorphism was used to analyse 930 individuals of 50 populations. Consistent with theoretical predictions, peripheral populations were smaller and more isolated, differentiation was stronger, and genetic diversity and gene flow lower in peripheral populations of V. pumila and V. stagnina. In V. elatior, probably historic fragmentation effects linked to its specific habitat type were superimposed on the plant geographic (peripheral-central) patterns, resulting in lower relative importance of gene flow in central populations. Genetic variation between regions (3-6%), among (30-37%) and within populations (60-64%) was significant. Peripheral populations lacked markers that were rare and localized in central populations. Loss of widespread markers in peripheral V. stagnina populations indicated genetic erosion. Autocorrelation within populations was statistically significant up to a distance of 10-20 m. Higher average genetic similarity in peripheral populations than in central ones indicated higher local gene flow, probably owing to management practices. Peripheral populations contributed significantly to genetic variation and contained unique markers, which made them valuable for the conservation of genetic diversity.

Biodiversity↗