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At least 829 records · Page 46Linked to original sources
PubMed2001

Consequences of polluted environments on population structure: the bank vole (Clethrionomys glareolus) at Chornobyl.

The accident at the Chornobyl Nuclear Power Plant in April 1986, released 100-200 million Curies of radioactive material into the surrounding environment. To investigate the possible genetic and population effects resulting from chronic exposure to this environmental radiation, we have examined mitochondrial DNA (control region) sequences from bank voles, Clethrionomys glareolus, inhabiting contaminated sites. Our analysis indicates genetic diversity is elevated in the contaminated sites when compared to relatively uncontaminated reference sites. This may be attributed to either an increased mutation rate in the mtDNA control region or immigration of individuals from surrounding areas into the contaminated environment. Although our observations do indicate that the contaminated areas represent sink populations, we cannot statistically discriminate between these two alternatives at this time. In addition, we have been unable to attribute any significant detrimental effects to bank vole populations inhabiting the contaminated Chornobyl environment based on these data. This is particularly paradoxical considering bank voles in the contaminated areas harbor the highest radiocesium (137Cs) body burdens and external dose rates of any mammal ever measured. Our long-term research on the bank vole indicates that several factors, including contaminants, may affect haplotype dynamics both spatially and temporally. These multifarious influences subsequently affect population genetic estimates typically used to address the effects of environmental pollution on animal populations. Finally, we provide a general framework for designing experiments investigating the role contaminants play in altering the genetic characteristics of exposed populations.

Animals↗
PubMed2005

Macrogeographic population structure of the tsetse fly, Glossina pallidipes (Diptera: Glossinidae).

Tsetse flies are confined to sub-Saharan Africa where they occupy discontinuous habitats. In anticipation of area-wide control programmes, estimates of gene flow among tsetse populations are necessary. Genetic diversities were partitioned at eight microsatellite loci and five mitochondrial loci in 21 Glossina pallidipes Austin populations. At microsatellite loci, Nei's unbiased gene diversity averaged over loci was 0.659 and the total number of alleles was 214, only four of which were shared among all populations. The mean number of alleles per locus was 26.8. Random mating was observed within but not among populations (fixation index FST=0.18) and 81% of the genetic variance was within populations. Thirty-nine mitochondrial variants were detected. Mitochondrial diversities in populations varied from 0 to 0.85 and averaged 0.42, and FST=0.51. High levels of genetic differentiation were characteristic, extending even to subpopulations separated by tens and hundreds of kilometres, and indicating low rates of gene flow.

Africa South of the Sahara↗
PubMed1999

Microsatellite DNA analysis of population structure in Atlantic herring (Clupea harengus), with direct comparison to allozyme and mtDNA RFLP analyses.

Previous attempts to test for small-scale stock structuring within Atlantic herring (Clupea harengus L.) with molecular markers have been hampered by uninformative levels of genetic variation. Here we report the first application of microsatellite DNA markers to investigate population subdivision in Atlantic herring from Norwegian waters and the Barents Sea, and also examine microsatellite differentiation between C. harengus and Pacific herring (C. pallasi). Results from four microsatellite loci indicate high, and informative, variation compared to molecular markers used previously: number of alleles per locus=18-41; mean expected heterozygosity within samples=0.90-0.93. Significant genetic differences were detected between almost all samples representing postulated Icelandic summer-spawner, Norwegian spring-spawner and Norwegian fjord stocks, using Fisher's exact test, FST and RST values. Levels of allele frequency differentiation between Atlantic and Pacific herring overlapped the range seen among Atlantic herring samples, indicating that microsatellites are poor indicators of the degree of species differentiation. Comparison with allozyme and mitochondrial DNA restriction fragment length polymorphism (RFLP) datasets from the same samples suggests that microsatellites may detect structuring at a finer scale, but are less informative at larger scales of divergence.

Animals↗
PubMed1996

Molecular markers reveal that population structure of the human pathogen Candida albicans exhibits both clonality and recombination.

The life history of Candida albicans presents an enigma: this species is thought to be exclusively asexual, yet strains show extensive phenotypic variation. To address the population genetics of C. albicans, we developed a genetic typing method for codominant single-locus markers by screening randomly amplified DNA for single-strand conformation polymorphisms. DNA fragments amplified by arbitrary primers were initially screened for single-strand conformation polymorphisms and later sequenced using locus-specific primers. A total of 12 single base mutations and insertions were detected from six out of eight PCR fragments. Patterns of sequence-level polymorphism observed for individual strains detected considerable heterozygosity at the DNA sequence level, supporting the view that most C. albicans strains are diploid. Population genetic analyses of 52 natural isolates from Duke University Medical Center provide evidence for both clonality and recombination in C. albicans. Evidence for clonality is supported by the presence of several overrepresented genotypes, as well as by deviation of genotypic frequencies from random (Hardy-Weinberg) expectations. However, tests for nonrandom association of alleles across loci reveal less evidence for linkage disequilibrium than expected for strictly clonal populations. Although C. albicans populations are primarily clonal, evidence for recombination suggests that sexual reproduction or some other form of genetic exchange occurs in this species.

Candida albicans↗
PubMed2003

Multiple attractors in stage-structured population models with birth pulses.

In most models of population dynamics, increases in population due to birth are assumed to be time-independent, but many species reproduce only during a single period of the year. A single species stage-structured model with density-dependent maturation rate and birth pulse is formulated. Using the discrete dynamical system determined by its Poincaré map, we report a detailed study of the various dynamics, including (a) existence and stability of nonnegative equilibria, (b) nonunique dynamics, meaning that several attractors coexist, (c) basins of attraction (defined as the set of the initial conditions leading to a certain type of attractor), (d) supertransients, and (e) chaotic attractors. The occurrence of these complex dynamic behaviour is related to the fact that minor changes in parameter or initial values can strikingly change the dynamic behaviours of system. Further, it is shown that periodic birth pulse, in effect, provides a natural period or cyclicity that allows multiple oscillatory solutions in the continuous dynamical systems.

Animals↗
PubMed2005

ADH4 gene variation is associated with alcohol and drug dependence: results from family controlled and population-structured association studies.

We found strong associations between ADH4 gene variation and alcohol and drug dependence by the Hardy-Weinberg Disequilibrium (HWD) test and case-control association analysis in an initial study. The present study aimed to confirm these findings by controlling for population stratification and admixture effects to which the HWD test and case-control association methods may be vulnerable. In addition to 365 unrelated healthy controls and 560 unrelated cases in the initial study, we evaluated 104 small nuclear families with affected offspring who had diagnoses of alcohol and/or drug dependence. Seven single nucleotide polymorphisms (SNPs) at the ADH4 gene locus were genotyped in all subjects, and 38 unlinked ancestry-informative markers were also genotyped in unrelated cases and controls. Structured association analysis demonstrated that the genotypes of six ADH4 markers were associated with alcohol dependence, and all seven ADH4 markers were associated with drug dependence (P=10-0.047). Logistic regression analysis showed that: (i) the genotypes of SNP2 (rs1042363) were significantly associated with alcohol dependence and drug dependence (mainly cocaine dependence), and the genotypes of SNP3 (rs1126671) were also significantly associated with alcohol dependence and (ii) one seven-variant haplotype and one diplotype were significantly associated with alcohol dependence and other seven-variant diplotypes were significantly associated with drug dependence (including cocaine and opioid dependence). Transmission disequilibrium test, haplotype-based haplotype relative risk and genotype-based haplotype relative risk analyses all confirmed the association of the ADH4 markers with alcohol dependence and drug dependence. Using rigorous study designs that account for possible population stratification, these findings confirm and extend our original observations indicating that variation at ADH4 predisposes to alcohol and drug dependence.

Adult↗
PubMed2002

Population structure, history and gene flow in a group of closely related land snails: genetic variation in Partula from the Society Islands of the Pacific.

Previous studies of Partula land snails from the Society Islands, French Polynesia, have shown that populations within species are highly differentiated in terms of their morphology, behaviour, ecology and molecular genetic variation. Despite this level of variability, differences between species are sometimes small, possibly reflecting the fact that reproductive isolation is not always complete and there exists the opportunity for genetic exchange between taxa through hybridization. The present study uses sequence data from a mitochondrial gene to further investigate genetic variation in Society Island Partula. Most populations are found in this study to be highly differentiated, but within individual species there seems to be no simple relationship either between genetic distance and geographical proximity, or between variation in mitochondria and that in allozymes or morphological characteristics. Among species there appears to be no simple correlation between degrees of reproductive isolation and genetic relatedness according to mitochondrial DNA. The results suggest that past events as well as ongoing drift and selection may have been important in affecting patterns of variation. Similarities among species at specific localities suggest that there must have been some genetic exchange in the past, although this may not necessarily reflect ongoing rates of hybridization. The discrepancy between results for different markers probably reflects the differential effects of drift and selection on mitochondrial and nuclear genes.

Animals↗
PubMed1987

Study on a Brazilian isolate. I. Population structure and random genetic drift.

A number of parameters were evaluated in order to determine the level of isolation of a small Brazilian community existing in partial geographic isolation and thereby evaluate the random genetic drift potential in the population. On a theoretical basis, it is concluded that the probability of genetic drift is low but cannot be excluded. The relatively small proportion of migrants (26%), the limited individual mobility, as given by marital distance (29 +/- 7 km), the mean migrational distance (46 +/- 11 km), the small effective size (122), and the value of the product Neme (26) agree with the possibility of genetic drift in this population. The observed coefficient of inbreeding (0.00239) is lower than that expected (0.0066) for random mating, suggesting some pressures against consanguineous marriage.

Adolescent↗
PubMed2000

Population structure and recent evolution of Plasmodium falciparum.

Plasmodium falciparum is the agent of malignant malaria, one of mankind's most severe maladies. The parasite exhibits antigenic polymorphisms that have been postulated to be ancient. We have proposed that the extant world populations of P. falciparum have derived from one single parasite, a cenancestor, within the last 5, 000-50,000 years. This inference derives from the virtual or complete absence of synonymous nucleotide polymorphisms at genes not involved in immune or drug responses. Seeking to conciliate this claim with extensive antigenic polymorphism, we first note that allele substitutions or polymorphisms can arise very rapidly, even in a single generation, in large populations subject to strong natural selection. Second, new alleles can arise not only by single-nucleotide mutations, but also by duplication/deletion of short simple-repeat DNA sequences, a process several orders of magnitude faster than single-nucleotide mutation. We analyze three antigenic genes known to be extremely polymorphic: Csp, Msp-1, and Msp-2. We identify regions consisting of tandem or proximally repetitive short DNA sequences, including some previously unnoticed. We conclude that the antigenic polymorphisms are consistent with the recent origin of the world populations of P. falciparum inferred from the analysis of nonantigenic genes.

Amino Acid Sequence↗