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PubMedDate not supplied

Heterogeneity of long-distance migration in studies of genetic structure.

One of the assumptions of migration matrix methods of population structure is that long-distance migrants are all sampled from a genetically homogeneous 'outside world'. This assumption has not often been tested. This paper examines migration and surname data from four towns in historical Massachusetts in order to examine this assumption and potential genetic effects of heterogeneous long-distance migration. Analysis of migration data shows that the rate of long-distance migration is significantly different for the four towns. The distributions of source populations for long-distance migrants into each town are significantly different. Surname analysis shows that in spite of the violation of the assumption of long-distance migrant homogeneity, there is little effect on the degree and pattern of within-group and among-group variation for these towns. This lack of effect seems related to genetic homogeneity of the long distance migrants.

Emigration and Immigration↗
PubMed2006

Complex genetic structures with repeated elements, a sul-type class 1 integron, and the blaVEB extended-spectrum beta-lactamase gene.

Two clinical isolates of Pseudomonas aeruginosa, TL-1 and TL-2, were isolated from a patient transferred from Bangladesh and hospitalized for osteomyelitis in Paris, France. P. aeruginosa TL-1 expressed the extended-spectrum beta-lactamase VEB-1a and was susceptible only to imipenem and colistin, while P. aeruginosa TL-2 expressed only the naturally occurring bla(AmpC) gene at a basal level and exhibited a wild-type beta-lactam resistance phenotype. In TL-1, the typical 5'-end conserved sequence (5'-CS) region of class 1 integrons usually present upstream of the bla(VEB-1a) gene was replaced by a truncated 3'-CS and a 135-bp repeated element (Re). Downstream of the bla(VEB-1a) gene, an insertion sequence, ISPa31 disrupted by ISPa30, and an orf513 sequence, belonging to a common region (conserved region 1 [CR1]) immediately upstream of the aphA-6 gene, were present. Further downstream, a second truncated 3'-CS region in direct repeat belonged to In51, an integron containing two gene cassettes (aadA6 and the OrfD cassette). Thus, the overall structure corresponded to a sul-type class 1 integron termed In121. Genetic analyses revealed that both isolates were clonally related and differed by a ca. 100-kb fragment that contained In121. Both isolates contained another integron, In122, that carried three gene cassettes: aadB, dfrA1, and the OrfX cassette. This work identifies for the first time the spread of Re-associated bla(VEB) genes located on a sul-type integron. It also reports for the first time a CR1 element in P. aeruginosa that is associated with an aminoglycoside resistance aphA-6 gene that is expressed from a composite promoter.

Alleles↗
PubMed1987

The genetic structure of natural populations of Drosophila melanogaster. XX. Comparison of genotype-environment interaction in viability between a northern and a southern population.

In order to examine the operation of diversifying selection as the maintenance mechanism of excessive additive genetic variance for viability in southern populations in comparison with northern populations of Drosophila melanogaster, two sets of experiments were conducted using second chromosomes extracted from the Ogasawara population (a southern population in Japan) and from the Aomori population (a northern population in Japan). Chromosomal homozygote and heterozygote viabilities were estimated in eight kinds of artificially produced breeding environments. The main findings in the present investigation are as follows: (1) Significant genotype-environment interaction was observed using chromosomes extracted from the Ogasawara population. Indeed, the estimate of the genotype-environment interaction variance for heterozygotes was significantly larger than that of the genotypic variance. On the other hand, when chromosomes sampled from the Aomori population were examined, that interaction variance was significant only for homozygotes and its value was no more than one quarter of that for the chromosomes from the Ogasawara population. (2) The average genetic correlation between any two viabilities of the same lines estimated in the eight kinds of breeding environments for the chromosomes sampled from the Ogasawara population was smaller than that for the chromosomes from the Aomori population both in homozygotes and in heterozygotes, especially in the latter. (3) The stability of heterozygotes over homozygotes against fluctuations of environmental conditions was seen in the chromosomes from the Ogasawara population, but not from the Aomori population. (4) From the excessive genotype-environment interaction variance compared with the genotypic variance in heterozygotes, it was suggested for the chromosomes from the Ogasawara population that the reversal of viability order between homozygotes took place in some environments at the locus level. On the basis of these findings, it is strongly suggested that diversifying selection is operating in a southern population of D. melanogaster on some of the viability polygenes which are probably located outside the structural loci, and the excessive additive genetic variance of viability in southern populations is maintained by this type of selection.

Alleles↗
PubMed1999

Genetic structure and dynamics of Plasmodium falciparum infections in the Kilombero region of Tanzania.

Plasmodium falciparum parasites exist as genetically distinct haploid clones in infected people. In the Kilombero valley in south-east Tanzania, at least 85% of the inhabitants of Michenga village harbour more than one clone. Using 2 highly polymorphic unlinked markers, it has been estimated that each infected person harbours between one and 6 P. falciparum clones at any one time, with a mean of 3.5 clones. When mosquitoes acquire gametocytes of 2 different clones in a blood meal, crossing generates recombinant clones differing from their parental genotypes. The inbreeding coefficient of the parasite population has been estimated as 0.33.

Animals↗
PubMedDate not supplied

Genetic structure of human populations in the British Isles.

Spatial patterns were studied for 36 allele frequencies representing 14 genetic systems (blood antigens, enzymes and serum proteins) in the United Kingdom and Irish Republic. The total number of data points over all systems and localities is 331. Patterns of genetic variation in space are graphically represented by one-dimensional and directional correlograms, and by interpolated allele-frequency surfaces. The data surfaces were examined by the various techniques of spatial autocorrelation analysis. Zones of rapid change across allele surfaces were discovered by the wombling method. Six allele frequency surfaces from four genetic systems exhibit significant spatial patterns. Only one pattern (IO; in the ABO system) may be described as purely clinal in an east-west direction; another (IB; in ABO) approximates a cline or at least north-south differentiation. A method was developed for testing the direction of maximal genetic autocorrelation. Two previously unrecorded patterns for the British Isles, north-south gradients for Rhesus and P, were detected. Twelve zones of rapid genetic change were discovered; some of these seem to reflect maritime and montane physical barriers as well as long-held cultural and linguistic differences, particularly between early Germanic and Celtic speakers. Moreover, some appear to reflect past historic events such as the invasions of Anglo-Saxons and Anglo-Normans.

ABO Blood-Group System↗
PubMed1984

Stability distribution in the phage lambda-DNA double helix: a correlation between physical and genetic structure.

Statistical analyses on the positional correlation of physical-stability and base-sequence distribution maps with genetic map are made for the whole DNA (48502 bases) of lambda-phage. The susceptibility to a double-helix unfolding perturbation and the fraction of the transient opening of a particular region of the double helix are adopted to define this physical stability. The principal features obtained are: A) The DNA double strand of protein coding regions is found to have homostabilizing propensity around a defined stability which is characteristic to each individual gene. B) The stability of the double helix in non-protein coding region fluctuates, on average over the whole region, more than that in protein coding region. C) Boundary regions of protein coding and non-protein coding regions are regions of high stability-fluctuation. Stability especially fluctuates at the protein-coding-region side of the boundary. Contrary to the quiet feature of the interior part of protein coding region rather noisy part exists at its edge. D) One frequently opening region coincides with the attaching site for the site specific recombination between phage and bacterial DNA. There are two possible ways to explain the noisy feature in the stability distribution in non-protein coding regions: 1) The region has been used as the locus of recombination as evolution took place. Thus DNAs which were homostabilized around a different value characteristic to each individual DNA, have been joined there many times, so that the noise has accumulated as a remnant of evolutional history; and/or 2) the base-composition homogenizing or double-helix homostabilizing mechanism does not work in unneeded region such as non-protein coding region or introns. Since corresponding characteristics have been found in our previous analyses on other viral and globin-gene DNAs, the rules mentioned above may be comprehensively extended to other DNAs.

Bacteriophage lambda↗
PubMed2005

Contemporary gene flow and the spatio-temporal genetic structure of subdivided newt populations (Triturus cristatus, T. marmoratus).

Gene flow and drift shape the distribution of neutral genetic diversity in metapopulations, but their local rates are difficult to quantify. To identify gene flow between demes as distinct from individual migration, we present a modified Bayesian method to genetically test for descendants between an immigrant and a resident in a nonmigratory life stage. Applied to a metapopulation of pond-breeding European newts (Triturus cristatus, T. marmoratus) in western France, the evidence for gene flow was usually asymmetric and, for demes of known census size (N), translated into maximally seven reproducing immigrants. Temporal sampling also enabled the joint estimation of the effective demic population size (Ne) and the immigration rate m (including nonreproductive individuals). Ne ranged between 4.1 and 19.3 individuals, Ne/N ranged between 0.05 and 0.65 and always decreased with N; m was estimated as 0.19-0.63, and was possibly biased upwards. We discuss how genotypic data can reveal fine-scale demographic processes with important microevolutionary implications.

Animals↗
PubMedDate not supplied

[Genetic structure of the Voltaic population of the Mossi plateau (Upper Volta)].

This study is about the placement of genetic markers of the "erythrocytaire ABO system". The area of study is the people of the central region of Upper Volta that is to say the following ethnic groups: Mossi, Bissa, Gourounsi, Samo, Peulh. The analysis of results permits us to conclude that the population of the central region is divided into two distinct groups: one group made up of the Bissa, Mossi, Gourounsi, Samo ethnic groups, constituting with respect to the "system ABO" a uniform population. And secondly a group constituted by the Peulh ethnic group which is different from the first group. The calculation of the inter-ethnic "genetic-distances" permits to see the similarities and the differences that one can conclude and discover between the diverse groups. Some studies to take place in the future in the east and west will permit us to further complete the map of "genetic distances" between ethnic groups of Upper-volta.

ABO Blood-Group System↗
PubMed1996

[Genetic structure and the load of hereditary diseases in five populations of Arkhangel'skaia region].

A population and medical genetic investigation was performed in a number of raions in the Arkhangel' skaya oblast. Random inbreeding coefficients were 0.000358 and 0.000361 in the Vinogradovskii and Krasnoborskii raions. Malecot's local inbreeding coefficients were 0.000565 and 0.000472, respectively. The endogamy indices were 0.37 and 0.54, respectively. In the urban population, the loads of autosomal dominant, autosomal recessive, and X-linked pathology were 1.01 and 0.98 per 1000 individuals, and 0.29 per 1000 men; in the rural population, they were 1.22, 1.55, and 1.08, respectively. In the populations studied, the hereditary pathology spectrum is described.

Consanguinity↗
PubMed2003

Host-dependent genetic structure of parasite populations: differential dispersal of seabird tick host races.

Despite the fact that parasite dispersal is likely to be one of the most important processes influencing the dynamics and coevolution of host-parasite interactions, little information is available on the factors that affect it. In most cases, opportunities for parasite dispersal should be closely linked to host biology. Here we use microsatellite genetic markers to compare the population structure and dispersal of two host races of the seabird tick Ixodes uriae at the scale of the North Atlantic. Interestingly, tick populations showed high within-population genetic variation and relatively low population differentiation. However, gene flow at different spatial scales seemed to depend on the host species exploited. The black-legged kittiwake (Rissa tridactyla) had structured tick populations showing patterns of isolation by distance, whereas tick populations of the Atlantic puffin (Fratercula arctica) were only weakly structured at the largest scale considered. Host-dependent rates of tick dispersal between colonies will alter infestation probabilities and local dynamics and may thus modify the adaptation potential of ticks to local hosts. Moreover, as I. uriae is a vector of the Lyme disease agent Borrelia burgdorferi sensu lato in both hemispheres, the large-scale movements of birds and the subsequent dispersal of ticks will have important consequences for the dynamics and coevolutionary interactions of this microparasite with its different vertebrate and invertebrate hosts.

Alleles↗
PubMed1996

Cytonuclear genetic structure of a hybrid zone in lizards of the Sceloporus grammicus complex (Sauria, Phrynosomatidae).

Lizards of the Sceloporus grammicus complex are comprised of multiple chromosome races that form several zones of parapatric hybridization in central Mexico. We scored diagnostic mitochondrial DNA (mtDNA) haplotypes and autosomal chromosome markers in a sample of 342 lizards from one well-defined zone between 2n = 34 and 2n = 46 races. A two-part analysis was performed on this data set in an attempt to infer the predominant evolutionary forces shaping the cytonuclear structure of this zone. The complications posed by its spatial structure were addressed by analysing a hierarchical series of smaller subsamples chosen to approximate single mating units. Two critical conclusions were drawn from this first-stage analysis. First and foremost, the three chromosomes have largely concordant cytonuclear disequilibrium patterns within each subsample with adequate numbers of individuals for detecting nonrandom cytonuclear associations. This suggests that the cytonuclear structure of this zone is predominantly a result of deterministic genome-wide forces rather than genetic drift of deterministic forces specific to individual chromosomes or loci. Second, the fit of a series of migration models to the data shows that the cytonuclear structure of the subsamples is well accounted for by continued gene flow from the two parental races alone, with random mating with respect to cytonuclear genotype and no other evolutionary forces. These results motivate several further empirical and theoretical investigations to refine our understanding of the relative roles of migration and other potentially important forces such as natural selection and genetic drift, in this and other hybrid zones.

Animals↗
PubMed2006

Gene polymorphisms for elucidating the genetic structure of the heavy-metal hyperaccumulating trait in Thlaspi caerulescens and their cross-genera amplification in Brassicaceae.

Genetic polymorphism was investigated in Thlaspi caerulescens J. & C. Presl at 15 gene regions, of which seven have been identified to putatively play a role in heavy-metal tolerance or hyperaccumulation. Single nucleotide and length polymorphisms were assessed at four cleaved amplified polymorphic sequences (CAPS) and 11 simple sequence repeat (microsatellite) loci, respectively. The utility of these loci for genetic studies in T. caerulescens was measured among seven natural populations (135 individuals). Fourteen loci rendered polymorphism, and the number of alleles per locus varied from 2 to 5 and 1 to 27 for CAPS and microsatellites, respectively. Up to 12 alleles per locus were detected in a population. The global observed heterozygosity per population varied between 0.01 and 0.31. Additionally, cross-species/genera amplification of loci was investigated on eight other Brassicaceae (five individuals per population). Overall, 70% of the cross-species/genera amplifications were successful, and among them, more than 40% provided intraspecific polymorphisms within a single population. This indicates that such markers may, as well, allow comparative population genetic or mapping studies between and within several Brassicaceae, particularly for genes involved in traits such as heavy-metal tolerance and/or hyperaccumulation.

Alleles↗
PubMed1994

Genetic structure is determined by stochastic factors in a natural population of Drosophila buzzatii in Argentina.

D. buzzatii is a cactophilic species associated with several cactaceae in Argentina. This particular ecological niche implies that this species is faced with a non-uniform environment constituted by discrete and ephemeral breeding sites, which are colonized by a finite number of inseminated females. The genetic consequences of this population structure upon the second chromosome polymorphism were investigated by means of F-statistics in a natural endemic population of Argentina. The present study suggests that differentiation of inversion frequencies in third instar larvae among breeding sites has taken place mainly at random and selection is not operating to determine the structure of this population. The average number of parents breeding on a single pad seems to be similar to the number colonizing Opuntia ficus indica rotting cladodes in Carboneras, a derived population from Spain. There is no significant excess of heterokaryotypes within pads or in the population as a whole. The results obtained in the present study suggest that the potential role of selective versus stochastic factors relative to the among pad heterogeneity in the population here studied is different from that of the Spanish population previously reported. Potential mechanisms responsible for these differences are discussed.

Animals↗
PubMed2004

Comparison of population genetic structures of common wild rice (Oryza rufipogon Griff.), as revealed by analyses of quantitative traits, allozymes, and RFLPs.

We investigated genetic diversity among and within natural populations of Asian common wild rice, Oryza rufipogon, from three different classes of data: quantitative traits, allozymes, and restriction fragment length polymorphisms (RFLPs). The seven populations examined showed polymorphism to varying degrees. The amount of intrapopulation variability appeared to be influenced not only by breeding system but also by the evolutionary history of each population. Interpopulation differentiation was clear, but different classes of data elucidated different patterns. Quantitative traits revealed ecotype differentiation into perennial and annual types of population, whereas allozyme and RFLP analyses revealed geographical differentiation among populations. These results suggest that the diversity patterns shown by quantitative trait analysis reflect mainly the occurrence of adaptive differentiation in response to habitat conditions and that those shown by allozyme and RFLP analyses reflect mainly the effect of isolation by distance. Population differentiation parameters (F(ST)) were highly variable among loci in allozymes as well as in RFLPs.

Alleles↗