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At least 235 records · Page 13Linked to original sources
PubMed1996

Sexual reproduction plays a major role in the genetic structure of populations of the fungus Mycosphaerella graminicola.

The relative contributions of sexual and asexual reproduction to the genetic structure of populations can be difficult to determine for fungi that use a mixture of both types of propagation. Nuclear RFLPs and DNA fingerprints were used to make indirect and direct measures of departures from random mating in a population of the plant pathogenic fungus Mycosphaerella graminicola during the course of an epidemic cycle. DNA fingerprints resolved 617 different genotypes among 673 isolates sampled from a single field over a 3-month period. Only 7% of the isolates represented asexual clones that were found more than once in the sample. The most common clone was found four times. Genotypic diversity averaged 85% of its maximum possible value during the course of the epidemic. Analyses of multilocus structure showed that allelic distributions among RFLP loci were independent. Pairwise comparisons between individual RFLP loci showed that the majority of alleles at these loci were in gametic equilibrium. Though this fungus has the capacity for a significant level of asexual reproduction, each analysis suggested that M. graminicola populations maintain a genetic structure more consistent with random-mating over the course of an epidemic cycle.

Ascomycota↗
PubMed2006

Analysis of spatial genetic structure in an expanding Pinus halepensis population reveals development of fine-scale genetic clustering over time.

We analysed the change of spatial genetic structure (SGS) of reproductive individuals over time in an expanding Pinus halepensis population. To our knowledge, this is the first empirical study to analyse the temporal component of SGS by following the dynamics of successive cohorts of the same population over time, rather than analysing different age cohorts at a single time. SGS is influenced by various factors including restricted gene dispersal, microenvironmental selection, mating patterns and the spatial pattern of reproductive individuals. Several factors that affect SGS are expected to vary over time and as adult density increases. Using air photo analysis, tree-ring dating and molecular marker analysis we reconstructed the spread of reproductive individuals over 30 years beginning from five initial individuals. In the early stages, genotypes were distributed randomly in space. Over time and with increasing density, fine-scale (< 20 m) SGS developed and the magnitude of genetic clustering increased. The SGS was strongly affected by the initial spatial distribution and genetic variation of the founding individuals. The development of SGS may be explained by fine-scale environmental heterogeneity and possibly microenvironmental selection. Inbreeding and variation in reproductive success may have enhanced SGS magnitude over time.

Biomarkers↗
PubMed2004

Different matrilineal contributions to genetic structure of ethnic groups in the silk road region in china.

Previous studies have shown that there were extensive genetic admixtures in the Silk Road region. In the present study, we analyzed 252 mtDNAs of five ethnic groups (Uygur, Uzbek, Kazak, Mongolian, and Hui) from Xinjiang Province, China (through which the Silk Road once ran) together with some reported data from the adjacent regions in Central Asia. In a simple way, we classified the mtDNAs into different haplogroups (monophyletic clades in the rooted mtDNA tree) according to the available phylogenetic information and compared their frequencies to show the differences among the matrilineal genetic structures of these populations with different demographic histories. With the exception of eight unassigned M*, N*, and R* mtDNAs, all the mtDNA types identified here belonged to defined subhaplogroups of haplogroups M and N (including R) and consisted of subsets of both the eastern and western Eurasian pools, thus providing direct evidence supporting the suggestion that Central Asia is the location of genetic admixture of the East and the West. Although our samples were from the same geographic location, a decreasing tendency of the western Eurasian-specific haplogroup frequency was observed, with the highest frequency present in Uygur (42.6%) and Uzbek (41.4%) samples, followed by Kazak (30.2%), Mongolian (14.3%), and Hui (6.7%). No western Eurasian type was found in Han Chinese samples from the same place. The frequencies of the eastern Eurasian-specific haplogroups also varied in these samples. Combined with the historical records, ethno-origin, migratory history, and marriage customs might play different roles in shaping the matrilineal genetic structure of different ethnic populations residing in this region.

Base Sequence↗
PubMedDate not supplied

The effect of differential reproductive success on population genetic structure: correlations of life history with matrilines in humpback whales of the gulf of maine.

To examine whether demographic and life-history traits are correlated with genetic structure, we contrasted mtDNA lineages of individual humpback whales (Megaptera novaeangliae) with sighting and reproductive histories of female humpback whales between 1979 and 1995. Maternal lineage haplotypes were obtained for 323 whales, either from direct sequencing of the mtDNA control region (n = 159) or inferred from known relationships along matrilines from the sequenced sample of individuals (n = 164). Sequence variation in the 550 bp of the control region defined a total of 19 maternal lineage haplotypes that formed two main clades. Fecundity increased significantly over the study period among females of several lineages among the two clades. Individual maternal lineages and other clades were characterized by significant variation in fecundity. The detected heterogeneity of reproductive success has the potential to substantially affect the frequency and distribution of maternal lineages found in this population over time. There were significant yearly effects on adult resighting rates and calf survivorship based on examination of sighting histories with varying capture-recapture probability models. These results indicate that population structure can be influenced by interactions or associations between reproductive success, genetic structure, and environmental factors in a natural population of long-lived mammals.

Animals↗
PubMedDate not supplied

[Dynamics of the genetic structure in experimental Drosophila populations for the Adh locus as affected by ethanol].

Electrophoresis method was used to analyze the genetic structure of four experimental Drosophila populations (the control one and those with 5, 10 and 15% of ethanol in the nutrient medium) with initial frequency of AdhF = 0.5 for 50 monitoring generations. It was established that F and S alleles had different selective values. Natural selection favoured the F-allele. Addition of ethanol to the nutrient medium increased the selection intensity in the first 15 generations but did not change the relative adaptability of three genotypes. This caused a similarity of genetic structure in experimental populations during 50 generations.

Alcohol Oxidoreductases↗
PubMed2006

[Genetic structure, subdivision, and population differentiation in Stankewiczii pine Pinus stankewiczii (Sukacz.) Fomin from Mountain Crimea].

In order to analyze the genetic structure, subdivision and differentiation within and between two small isolated populations of the Crimea relict endemic, Pinus stankewiczii (Sukacz.) Fomin, electrophoretic analysis of the isozyme variation at nine enzymatic systems was carried out using 183 oldest trees. It was demonstrated that in populations of P. stankewiczii, 80% of the genes were in polymorphic state. Each tree was heterozygous at 19.1% loci, and at 21.6% loci in artificial 50-year-old plantation. The genetic structure of two populations was less differentiated (DN = 0.006), compared to their individual localities (DN = 0.008-0.009). Within-population subdivision of the diffusely dispersed populations was higher (FST-GST = 1.8-2.0%) than that of the populations themselves (0.8%).

Alleles↗
PubMed2000

Genetic structure of the Iberian pig breed using microsatellites.

An analysis of 25 microsatellite loci in 210 animals has been used to define the genetic structure of the Iberian pig, traditionally classified into several varieties. In addition, a sample of 20 Duroc pigs was used as an outgroup for topology trees. Inter-variety genetic variation was estimated by unbiased average heterozygosity and the number of alleles observed. Significant deviations from the Hardy-Weinberg equilibrium (HWE) were shown for 19 loci across the whole population. By contrast, equilibrium deviation within varieties was much lower. Genetic variation measures, genetic distance values and a neighbour-joining tree were used to estimate subdivision. In addition, an individual tree was constructed to contrast the assignation of animals into varieties. Despite the low bootstrap values obtained in the varieties neighbour-joining tree, the degree of genetic variation found was sufficient to support the division of the Iberian pig into varieties, although in some cases the traditional classification cannot be accepted. These results have shown the value of this marker panel in the study of intra-breed genetic structures.

Alleles↗
PubMed1987

[Biochemical polymorphic systems in the migrant population of northeastern USSR. VI. Genetic structure of patients in separate nosological groups].

Genotype frequency distribution for a number of polymorphic loci in patients differs significantly in different nosologic groups, in relation to each other and to a sample of healthy individuals. Genetic structure specificity of each nosologic group and different trends of genetic frequency variations, in relation to the sample of healthy individuals, leads to considerable decrease in genetic differences between the united group of pathology and healthy individuals' sample. Spatial differentiation of genetic structure of separate nosologic groups and healthy individuals' sample also confirms genetic isolation of each of these groups and, at the same time, reveals clearly nonspecific biological resistance of human organism.

Disease Susceptibility↗
PubMed2001

Population genetic structure of variable drug response.

Geographic patterns of genetic variation, including variation at drug metabolizing enzyme (DME) loci and drug targets, indicate that geographic structuring of inter-individual variation in drug response may occur frequently. This raises two questions: how to represent human population genetic structure in the evaluation of drug safety and efficacy, and how to relate this structure to drug response. We address these by (i) inferring the genetic structure present in a heterogeneous sample and (ii) comparing the distribution of DME variants across the inferred genetic clusters of individuals. We find that commonly used ethnic labels are both insufficient and inaccurate representations of the inferred genetic clusters, and that drug-metabolizing profiles, defined by the distribution of DME variants, differ significantly among the clusters. We note, however, that the complexity of human demographic history means that there is no obvious natural clustering scheme, nor an obvious appropriate degree of resolution. Our comparison of drug-metabolizing profiles across the inferred clusters establishes a framework for assessing the appropriate level of resolution in relating genetic structure to drug response.

Chi-Square Distribution↗
PubMed2000

Genetic structure of a 2,500-year-old human population in China and its spatiotemporal changes.

To examine temporal changes in population genetic structure, we compared the mitochondrial DNA (mtDNA) sequences of three populations that lived in the same location, Linzi, China, in different periods: 2,500 years ago (the Spring-Autumn era), 2,000 years ago (the Han era), and the present day. Two indices were used to compare the genetic differences: the frequency distributions of the radiating haplotype groups and the genetic distances among the populations. The results indicate that the genetic backgrounds of the three populations are distinct from each other. Inconsistent with the geographical distribution, the 2,500-year-old Linzi population showed greater genetic similarity to present-day European populations than to present-day east Asian populations. The 2, 000-year-old Linzi population had features that were intermediate between the present-day European/2,500-year-old Linzi populations and the present-day east Asian populations. These relationships suggest the occurrence of drastic spatiotemporal changes in the genetic structure of Chinese people during the past 2,500 years.

China↗
PubMed2005

Genetic diversity and genetic structure of an endangered species, Trillium tschonoskii.

The genetic diversity and genetic structure of Trillium tschonoskii (Maxim) were investigated using amplified fragment length polymorphism markers. Eight primer combinations were carried out on 105 different individuals sampled from seven populations. Of the 619 discernible DNA fragments generated, 169 (27.3%) were polymorphic. The percentage of polymorphic bands within populations ranged from 4.52 to 10.50. Genetic diversity (H(E)) within populations ranged from 0.0130 to 0.0379, averaging 0.0536 at the species level. Genetic differentiation among populations was detected based on Nei's genetic diversity analysis (53.03%) and analysis of molecular variance (AMOVA) (52.43%). AMOVA indicated significant genetic differentiation among populations (52.43% of the variance) and within populations (47.57% of the variance) (p < 0.0002). Gene flow was low (0.4429) among populations. Species breeding system and limited gene flow among populations are plausible reasons for the high genetic differentiation observed for this species. We propose an appropriate strategy for conserving the genetic resources of T. tschonoskii in China.

China↗
PubMed2003

Genetic structure and diversity among maize inbred lines as inferred from DNA microsatellites.

Two hundred and sixty maize inbred lines, representative of the genetic diversity among essentially all public lines of importance to temperate breeding and many important tropical and subtropical lines, were assayed for polymorphism at 94 microsatellite loci. The 2039 alleles identified served as raw data for estimating genetic structure and diversity. A model-based clustering analysis placed the inbred lines in five clusters that correspond to major breeding groups plus a set of lines showing evidence of mixed origins. A "phylogenetic" tree was constructed to further assess the genetic structure of maize inbreds, showing good agreement with the pedigree information and the cluster analysis. Tropical and subtropical inbreds possess a greater number of alleles and greater gene diversity than their temperate counterparts. The temperate Stiff Stalk lines are on average the most divergent from all other inbred groups. Comparison of diversity in equivalent samples of inbreds and open-pollinated landraces revealed that maize inbreds capture <80% of the alleles in the landraces, suggesting that landraces can provide additional genetic diversity for maize breeding. The contributions of four different segments of the landrace gene pool to each inbred group's gene pool were estimated using a novel likelihood-based model. The estimates are largely consistent with known histories of the inbreds and indicate that tropical highland germplasm is poorly represented in maize inbreds. Core sets of inbreds that capture maximal allelic richness were defined. These or similar core sets can be used for a variety of genetic applications in maize.

Alleles↗
PubMed2005

Optimal sampling strategy for estimation of spatial genetic structure in tree populations.

Fine-scale spatial genetic structure (SGS) in natural tree populations is largely a result of restricted pollen and seed dispersal. Understanding the link between limitations to dispersal in gene vectors and SGS is of key interest to biologists and the availability of highly variable molecular markers has facilitated fine-scale analysis of populations. However, estimation of SGS may depend strongly on the type of genetic marker and sampling strategy (of both loci and individuals). To explore sampling limits, we created a model population with simulated distributions of dominant and codominant alleles, resulting from natural regeneration with restricted gene flow. SGS estimates from subsamples (simulating collection and analysis with amplified fragment length polymorphism (AFLP) and microsatellite markers) were correlated with the 'real' estimate (from the full model population). For both marker types, sampling ranges were evident, with lower limits below which estimation was poorly correlated and upper limits above which sampling became inefficient. Lower limits (correlation of 0.9) were 100 individuals, 10 loci for microsatellites and 150 individuals, 100 loci for AFLPs. Upper limits were 200 individuals, five loci for microsatellites and 200 individuals, 100 loci for AFLPs. The limits indicated by simulation were compared with data sets from real species. Instances where sampling effort had been either insufficient or inefficient were identified. The model results should form practical boundaries for studies aiming to detect SGS. However, greater sample sizes will be required in cases where SGS is weaker than for our simulated population, for example, in species with effective pollen/seed dispersal mechanisms.

Computer Simulation↗
PubMed1986

[Genetic and ecological study of aboriginal populations of northeastern Siberia. II. Polymorphic blood systems, immunoglobulin allotypes and other genetic markers in asian eskimos. Genetic structure of Bering sea eskimos].

Blood groups, immunoglobulin allotypes, serum proteins and red cell enzymes were tested in four populations of Asiatic Eskimos. 12 of 16 gene loci studied were found to be polymorphic. Analysis of covariance and variance matrices for gene frequencies of 8 Bering Sea populations revealed major aspects of regional genetic structure. Regression of average heterozygosity on genetic distance from centroid permitted us to interpret it in the light of counterbalancing action of systematic and non-systematic pressure. Analysis of R matrix containing gene frequencies for both Eskimo and Chukchi populations revealed two different clusters - more heterogeneous Eskimo cluster and less heterogeneous Chukchi cluster. Good fit was observed between regional genetic structure, history and geography.

Blood Group Antigens↗
PubMedDate not supplied

Use of short tandem repeats loci to study the genetic structure of several populations from Zulia State, Venezuela.

Genetic relationships between populations can be studied by comparing genotypic and allelic similarities. This investigation aims to demonstrate that selected autosomal microsatellite markers could be used to study the genetic structures of different populations living in northwest Venezuela, in Zulia State. Seven autosomal systems (CSF1PO, TPOX, TH01, vWA, D7S820, D13S317, and D5S818) were tested by PCR in a multiplex format on 688 different chromosomes from unrelated individuals living in Maracaibo, "Isla de Toas," and "San José de Heras," and from two Amerindian populations from the "Sierra de Perijá," Barí' and Yukpa. Allele frequencies, Hardy-Weinberg equilibria, genetic distances, phylogenetic trees, and ethnic admixtures were estimated. The study shows the existence of a clear genetic difference among these populations in accordance with their historic evolution. The populations of Maracaibo and "Isla de Toas" showed a triracial origin, with a large European contribution, followed by an Amerindian component and a small African component. The indigenous groups, Barí' and Yukpa, showed exclusively an Amerindian component, and "San José de Heras" showed only an African component. These results indicate that microsatellite markers are useful for molecular anthropology in a regional and worldwide context and provide important genetic information about contemporary populations of Venezuela.

Alleles↗
PubMed2004

Impact of Ice Ages on the genetic structure of trees and shrubs.

Data on the genetic structure of tree and shrub populations on the continental scale have accumulated dramatically over the past decade. However, our ability to make inferences on the impact of the last ice age still depends crucially on the availability of informative palaeoecological data. This is well illustrated by the results from a recent project, during which new pollen fossil maps were established and the variation in chloroplast DNA was studied in 22 European species of trees and shrubs. Species exhibit very different levels of genetic variation between and within populations, and obviously went through very different histories after Ice Ages. However, when palaeoecological data are non-informative, inferences on past history are difficult to draw from entirely genetic data. On the other hand, as illustrated by a study in ponderosa pine, when we can infer the species' history with some certainty, coalescent simulations can be used and new hypotheses can be tested.

Climate↗
PubMed1999

The genetic structure of Drosophila subobscura populations from the Islands of Majorca and Minorca (Balearic Islands, Spain) based on allozymes and mitochondrial DNA.

The genetic structure of seven populations of Drosophila subobscura from different locations on Majorca and Minorca (Balearic Islands, Spain) was studied using two types of markers: allozyme and mitochondrial DNA restriction analyses. Both markers showed congruent results. In the allozyme data, when the Acph-1 locus was excluded from the joint FST statistics, only three out of 21 comparisons were statistically significant, lending support to the hypothesis of low genetic differentiation. The mtDNA restriction analyses showed two haplotypes at a high frequency (more than 40% each), irrespective of the location considered, and a number of endemic haplotypes at very low frequencies (not higher than 2% each). The analyses of the genetic structure yielded a pattern similar to the allozymes. The cytonuclear disequilibrium analyses showed the difficulty of detecting cytonuclear associations in natural populations because they are mainly transient.

Alleles↗
PubMed2006

Demographic spatial genetic structure of the Neotropical tree, Jacaranda copaia.

We used genotypes from six microsatellite loci and demographic data from a large mapped forest plot to study changes in spatial genetic structure across demographic stages, from seed rain to seedlings, juveniles, and adult diameter classes in the Neotropical tree, Jacaranda copaia. In pairwise comparisons of genetic differentiation among demographic classes, only seedlings were significantly differentiated from the other diameter classes; F(ST) values ranged from 0.006 to 0.009. Furthermore, only seedlings showed homozygote excess suggesting biparental inbreeding in the large diameter reproductive adults. We found very low levels of relatedness in the first distance class of trees, 1-26 cm diameter (F(ij) = 0.011). However, there was a 5- to 10-fold rise in relatedness in the smallest distance class, from the smallest to the largest tree diameter classes (F(ij) = 0.110 for individuals > 56 cm diameter). A variety of non-mutually exclusive mechanisms have been invoked perviously to explain such a pattern, including natural selection, history, or nonequilibrium population dynamics. The long-term demographic data available for this species allow us to evaluate these mechanisms. Jacaranda is a fast-growing, light-demanding species with low recruitment rates and high mortality rates in the smaller diameter classes. It successfully regenerates only in large light gaps, which occur infrequently and stochastically in space and time. These factors contribute to the nonequilibrium population dynamics and observed low genetic structure in the small size classes. We conclude that the pattern of spatial genetic transitions in Jacaranda is consistent with overlapping related generations and strong but infrequent periods of high recruitment, followed by long periods of population decline.

Bignoniaceae↗