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At least 739 records · Page 41Linked to original sources
PubMed2000

Genetic diversity and population structure of the serpentine endemic Calystegia collina (Convolvulaceae) in northern California.

We used enzyme electrophoresis to evaluate genetic diversity in 32 populations of Calystegia collina, a clonal plant species endemic to serpentine outcrops in northern California (USA). Of 34 loci examined 56% were polymorphic, but on average only 17% were polymorphic within local populations. Neither the total number of alleles nor the number of multilocus genotypes differed significantly between populations in small vs. large serpentine outcrops. Genetic and geographic distances between populations were positively correlated, but this relationship was not significantly affected by the isolation of serpentine outcrops. Populations were highly differentiated (F(st) = 0.417) and little genetic variation was explained by geographic region or serpentine outcrop.Observed heterozygosity within populations almost always exceeded Hardy-Weinberg expectations. In many populations, all 30 sample ramets were uniformly heterozygous at one or more loci yet were genetically variable at other loci. These results imply that many C. collina populations originate from one or a few genetic founders, with little recruitment from seeds. Genetic variation within uniformly heterozygous populations must be the product of multiple, closely related founders or somatic mutations within the population. We conclude that vegetative reproduction, perhaps coupled with somatic mutation, helps maintain genetic diversity in these isolated but long-lived populations.

Journal Article↗
PubMed1975

Population structure and dynamics of the house dust mite Dermatophagoides farinae (Acarina: Pyroglyphidae) in Czechoslovakia.

The relationship between the room microclimate and population dynamics of the house dust mite Dermatophagoides farinae Hughes, 1961 was studied. A distinct increase of the mite population density in mattresses was observed only in the period, when the monthly means of relative air humidity in rooms were higher than 47-50%, denominated by the author as critical air humidity. This is a considerably lower value than that relevant to Dermatophagoides pteronyssinus (Trouessart, 1897) from the paper by Bronswijk et al. (1971) (critical air humidity 60-65%). The climatic humidity affecting the room microclimate is consequently the main reason why one species or another is predominant under different geographical conditions. From October till May the D. farinae population is primarily composed of protonymphs, in the period of maximum population density (May-October) the presence of adults is predominant. Protonymphs are considered to be least resistant to the humidity decrease in their environment.

Animals↗
PubMed1983

[Medical genetic study of the population or Turkmenia. II. The population structure of the inhabitants of the rural soviet Izgant, Geok-Tepe District, Ashkhabad Province].

This report is devoted to the populational description of the Ashkhabad district. Examination of one of the typical agricultural villages (Izgant of the Ashkhabad district) gave the main parameters of the population. The total number of the inhabitants studied is 1596, the proportion of the studied is 56%, the average family size for the parent with completed reproduction period being 5.47, the average generation time - 33 to 38, the gametic index - 0.67 and the inbreeding coefficient - 0.002267. The distribution of some markers (ABO, MN, Hp, Rh, Pp) have been studied. A rather low coefficient of inbreeding, as a result of the absence of geographical isolation, may account for incidence of autosomal recessive disorders.

Adolescent↗
PubMed1989

Population structure and evolutionary progress.

Wright's shifting-balance theory is discussed as an example of a process that can cause species to evolve combinations of characters that could not evolve under natural selection alone. A review of the existing theory of peak shifts indicates that the conditions of extreme isolation that are necessary to permit genetic drift to alter the outcome of natural selection in local populations would make gene flow too weak to spread a new combination of genes to other populations in a reasonable time. Instead, it seems likely that major demographic changes must occur in a species for the shifting-balance process to work. A discussion of direct and indirect studies of gene flow in natural populations suggests that the current genetic structure of many species is likely to reflect past demographic events rather than ongoing gene flow. It is possible then that demographic processes could be responsible for spreading new traits in a species, but that would be true whether those new traits evolved only owing to natural selection or owing in addition to genetic drift and other forces.

Animals↗
PubMed2006

Origin, genetic diversity, and population structure of Chinese domestic sheep.

To characterize the origin, genetic diversity, and phylogeographic structure of Chinese domestic sheep, we here analyzed a 531-bp fragment of mtDNA control region of 449 Chinese autochthonous sheep from 19 breeds/populations from 13 geographic regions, together with previously reported 44 sequences from Chinese indigenous sheep. Phylogenetic analysis showed that all three previously defined lineages A, B, and C were found in all sampled Chinese sheep populations, except for the absence of lineage C in four populations. Network profiles revealed that the lineages B and C displayed a star-like phylogeny with the founder haplotype in the centre, and that two star-like subclades with two founder haplotypes were identified in lineage A. The pattern of genetic variation in lineage A, together with the divergence time between the two central founder haplotypes suggested that two independent domestication events have occurred in sheep lineage A. Considerable mitochondrial diversity was observed in Chinese sheep. Weak structuring was observed either among Chinese indigenous sheep populations or between Asian and European sheep and this can be attributable to long-term strong gene flow induced by historical human movements. The high levels of intra-population diversity in Chinese sheep and the weak phylogeographic structuring indicated three geographically independent domestication events have occurred and the domestication place was not only confined to the Near East, but also occurred in other regions.

Animal Migration↗
PubMed1992

Changes in the density, population structure, growth and reproduction of perch, Perca fluviatilis L. in two acidic forest lakes in southern Finland.

The density of the perch populations decreased rapidly during the 1980s in two acidified lakes in southern Finland. In an acid-humic lake the density of the perch population decreased from 240 to 60 ha(-1) and in an acid clearwater lake from 150 to 20 ha(-1). In both lakes the rapid decrease was mainly due to failures in reproduction, although post-spawning mortality of adult fish was also recorded. The perch spawned annually in both lakes but according to the field exposures of egg strands, most of the eggs died before hatching. Nevertheless, some new recruits appeared in both lakes. These perch, born in 1983-1986, grew faster than those of the more abundant year-classes of the late 1970s, indicating a clear density-dependent growth response. According to the mortality estimate and the age distribution of perch, the latest year-classes that produced more than 100 adult perch ha(-1) were born in 1978 or 1979 in both lakes. It was calculated that the density of both populations was >500 ha(-1) in the early 1980s.

Journal Article↗
PubMed2003

Mexican American ancestry-informative markers: examination of population structure and marker characteristics in European Americans, Mexican Americans, Amerindians and Asians.

Markers with large differences in allele frequencies between ethnicities provide ancestry information that can be applied to genetic studies. We identified over 100 biallelic ancestry informative markers (AIMs) with large allele frequency differences between European Americans (EA) and Pima Amerindians from laboratory and database screens. For 35 of these markers, Mayan, Yavapai and Quechuan Amerindians were genotyped and compared with EA and Pima allele frequencies. Markers with large allele frequency differences between EA and one Amerindian tribe showed only small differences between the Amerindian tribes. Examination of structure in individuals demonstrated a clear separation of subjects of European from those of Amerindian ancestry, and similarity between individuals from disparate Amerindian populations. The AIMs demonstrated the variation in ancestral composition of individual Mexican Americans, providing evidence of applicability in admixture mapping and in controlling for structure in association tests. In addition, a high percentage of single-nucleotide polymorphisms (SNPs) selected on the basis of large frequency differences between EA and Asian populations had large allele frequency differences between EA and Amerindians, suggesting an efficient method for greatly expanding AIMs for use in admixture mapping/structure analysis in Mexican Americans. Together, these data provide additional support for the practical application of admixture mapping in the Mexican American population.

Alleles↗
PubMed2026

Genetic Diversity and Population Structure of Zambian Indigenous Cattle.

A study was conducted to determine the genetic diversity of Zambian indigenous cattle using microsatellites. In Zambia, cattle provide draft power, food, manure and generate income. DNA extraction followed the Qiagen protocol, and Arlequin V3.0 was used for data analysis. 72 unrelated animals from three regions, Eastern (Angoni), Southern (Tonga) and Western (Barotse), were sampled. 315 alleles observed were higher in TGLA 263 (106 bp) with 0.861, 0.824 and 0.753, BMS650 (160 bp) with 0.710 and SPS 115 (248 bp) with 0.581, 0.710 and 0.794 for Angoni, Tonga and Barotse, respectively. Effective allele frequency was 4.521 ± 0.351, 4.246 ± 0.299 and 3.888 ± 0.289 for Angoni, Tonga and Barotse, respectively. Global deficit of heterozygotes across populations (Fit) amounted to 4.2%. Overall mean deficit of heterozygotes (Fis = 1%), genetic differentiation among breeds (Fst = 3.2%),, and genetic flow between populations (Nm = 11.3) ranged from RM 067 (40.564) to BLI (3.016). Analysis of molecular variance revealed 2.7% genetic variation among populations and 97.3% within the cattle population, with a mean genetic diversity of 0.753. Structure analysis (PCoA) demonstrated the presence of two subpopulations in which all three populations are represented and these two groups showed evidence of substructuring. In the Bayesian analysis, Tonga and Barotse populations were clustered together, while the Angoni were separated from the rest of the populations in K = 2. There was no evidence of panmixia and linkage equilibrium; the VD (9.153) value is greater than L (5.929), indicating that the population was in equilibrium. This study presents a comprehensive genetic characterisation of indigenous cattle in Zambia, which is important for further studies.

Animals↗
PubMed1993

Population structure in Daphnia obtusa: quantitative genetic and allozymic variation.

Quantitative genetic analyses for body size and for life history characters within and among populations of Daphnia obtusa reveal substantial genetic variance at both hierarchical levels for all traits measured. Simultaneous allozymic analysis on the same population samples indicate a moderate degree of differentiation: GST = 0.28. No associations between electrophoretic genotype and phenotypic characters were found, providing support for the null hypothesis that the allozymic variants are effectively neutral. Therefore, GST can be used as the null hypothesis that neutral phenotypic evolution within populations led to the observed differentiation for the quantitative traits, which I call QST. The results of this study provide evidence that natural selection has promoted diversification for body size among populations, and has impeded diversification for relative fitness. Analyses of population differentiation for clutch size, age at reproduction, and growth rate indicate that neutral phenotypic evolution cannot be excluded as the cause.

Analysis of Variance↗
PubMed1974

A model for analysis of population structure.

Arguments have been presented for the appropriateness of a multinomial Dirichlet distribution for describing single-locus genotypic frequencies in a subdivided population. This distribution is defined as a function of allele frequency, the average (over the entire population) inbreeding coefficient and the correlation between genotypes within a subdivision. Alternative parameterizations and their genetic interpretations are given.-We then show how information from a sample drawn from this subdivided population, in the absence of pedigrees, can be combined with the multinomial Dirichlet model to form a likelihood function. This likelihood function is then used as the basis for estimation and testing hypotheses concerning the genetic parameters of the model. Comparisons of this approach to the alternative procedure of Cockerham (1969) and (1973) are made using human data obtained from Tecumseh, Michigan and Monte Carlo simulations.-Finally, implications of these results to statistical inference and to mutation rates are presented.

Alleles↗
PubMed2005

Clines, clusters, and the effect of study design on the inference of human population structure.

Previously, we observed that without using prior information about individual sampling locations, a clustering algorithm applied to multilocus genotypes from worldwide human populations produced genetic clusters largely coincident with major geographic regions. It has been argued, however, that the degree of clustering is diminished by use of samples with greater uniformity in geographic distribution, and that the clusters we identified were a consequence of uneven sampling along genetic clines. Expanding our earlier dataset from 377 to 993 markers, we systematically examine the influence of several study design variables--sample size, number of loci, number of clusters, assumptions about correlations in allele frequencies across populations, and the geographic dispersion of the sample--on the "clusteredness" of individuals. With all other variables held constant, geographic dispersion is seen to have comparatively little effect on the degree of clustering. Examination of the relationship between genetic and geographic distance supports a view in which the clusters arise not as an artifact of the sampling scheme, but from small discontinuous jumps in genetic distance for most population pairs on opposite sides of geographic barriers, in comparison with genetic distance for pairs on the same side. Thus, analysis of the 993-locus dataset corroborates our earlier results: if enough markers are used with a sufficiently large worldwide sample, individuals can be partitioned into genetic clusters that match major geographic subdivisions of the globe, with some individuals from intermediate geographic locations having mixed membership in the clusters that correspond to neighboring regions.

Alleles↗
PubMed2006

Age and sex bias in the reconstruction of past population structures.

Palaeodemographical studies are founded on the assumption that the sex and age distribution of the skeletal sample reflects the constitution of the original population. It is becoming increasingly clear, however, that the type and amount of information that may be derived from osteoarchaeological collections are related to the state of preservation of remains. This work proposes a new method to evaluate bone preservation, to identify age and sex biases in the preservation of human skeletal remains, and to assess whether differences in preservation patterns are more dependent on factors intrinsic or extrinsic to anatomical features of human bones. Three osteological collections and over 600 skeletons were observed. The state of preservation of human bones was assessed using three preservation indexes: the anatomical preservation index (API), the bone representation index (BRI), and the qualitative bone index (QBI). The results suggest that subadult skeletons are generally more poorly preserved and with bones less well-represented than adult skeletons. Among subadults, female and male skeletons have different patterns of preservation according to their age. This pattern of preservation depends on intrinsic anatomical properties of bones themselves, while external factors can only increase these differences in the state of preservation and representation of osseous remains. It is concluded from this that failure to recognize these differences may lead to misleading interpretations of paleodemography of past human populations.

Adolescent↗