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At least 991 records · Page 55Linked to original sources
PubMed1993

Genetic structure of Trypanosoma cruzi populations from Argentina estimated from enzyme polymorphism.

Isolates of Trypanosoma cruzi from human patients, domestic and sylvatic animals and vector insects were obtained in different areas of Argentina. Electrophoretic patterns of enzymes from extracts of 95 isolates were analysed. On the basis of zymograms providing information on 10 loci, 12 zymodemes are described according to their genotypes. Data presented show fixed heterozygosity, absence of segregation of genotypes, significant departures from Hardy-Weinberg equilibrium, and over-represented genotypes. This evidence supports the hypothesis that sexual reproduction is very restricted or absent in this parasite. The proportion of polymorphic loci is 80%. The expected mean heterozygosity per locus (He) is 0.43, while the observed value (Ho) is 0.24. Differences between these values may be explained by accepting a basically clonal structure for T. cruzi. The data matrix of 12 zymodemes using 28 characters was analysed using a Wagner parsimony algorithm. Two equally most parsimonious unrooted trees were generated; both have 39 steps. The results show clusters clearly separated according to the geographical origin of the stocks. There are some indications of some correlations between genetic composition of the parasite and the clinical picture of the infection in human patients.

Animals↗
PubMedDate not supplied

[Ecology and the genetic structure of sympatric leishmania species circulating in the intra-continental deserts of the south Palaearctic region].

A PCR fingerprinting approach with single non-specific primers--(GTG)5 and T3B--was apply to investigate variations in the genotyping of three species of Leishmania species within the Rhombomys opimus area. Forty-three strains of Leishmania major, L. turanica, and L. gerbilli circulating among great gerbils in Turkmenistan, Uzbekistan, Kazakhstan, and Mongolia were examined. PCR fingerprint revealed a high genetic intraspecific heterogeneity among L. turanica strains. Three groups of strains were clearly identified. The strains from Mongolia greatly differed from other L. turanica ones. The second group was formed by strains from Kazakhstan, they also demonstrated rather different patterns. L. turanica strains from Turkmenistan and Uzbekistan showed only minor differences, but greatly different from those from Kazakhstan and Mongolia. The groups identified by the PCR fingerprint correlate with the conditions of circulation: the duration of a transmission season and as the result of different periods of retention of Leishmania in the skin of great gerbils, as well as the presence or absence of L. major as coexisting species. There were no differences between L. turanica strains isolated from different hosts in the same geographical region, as well as between L. turanica strains isolated in the hyper- or meso and hypoendemic foci. There was no correlation between the genotypic and phenotypic characteristics of L. turanica. No intraspecific polymorphism was found among L. major and L. gerbilli strains from different geographical regions within the great gerbil area.

Animals↗
PubMed1999

Population structure and genetic divergence in Anopheles nuneztovari (Diptera: Culicidae) from Brazil and Colombia.

Anopheles nuneztovari is considered an important vector of human malaria in several localities in Venezuela and Colombia. Its status as a vector of human malaria is still unresolved in areas of the Brazilian Amazon, in spite of have been found infected with Plasmodium sp.. For a better understanding of the genetic differentiation of populations of A. nuneztovari, electrophoretic analysis using 11 enzymes was performed on four populations from Brazil and two from Colombia. The results showed a strong differentiation for two loci: alpha-glycerophosphate dehydrogenase (alpha-Gpd) and malate dehydrogenase (Mdh) from 16 loci analyzed. Diagnostic loci were not detected. The populations of A. nuneztovari from the Brazilian Amazon showed little genetic structure and low geographic differentiation, based on the F(IS) (0.029), F(ST) (0.070), and genetic distance (0.001-0.032) values. The results of the isozyme analysis do not coincide with the indication of two lineages in the Amazon Basin by analysis of mitochondrial DNA, suggesting that this evolutionary event is recent. The mean F(ST) value (0.324) suggests that there is considerable genetic divergence among populations from the Brazilian Amazon and Colombia. The genetic distance among populations from the Brazilian Amazon and Colombia is ranges from 0.047 to 0.148, with the highest values between the Brazilian Amazon and Sitronela (SIT) (0.125-0.148). These results are consistent with those observed among members of anopheline species complexes. It is suggested that geographic isolation has reduced the gene flow, resulting in the genetic divergence of the SIT population. Dendrogram analysis showed three large groups: one Amazonian and two Colombia, indicating some genetic structuring. The present study is important because it attempted to clarify the taxonomic status of A. nuneztovari and provide a better understanding of the role of this mosquito in transmission of human malaria in northern South America.

Aconitate Hydratase↗
PubMed2004

Conservation and divergence of the genetic structure of larval foraging behaviour in two species of the Drosophila simulans clade.

Larvae of the sibling species Drosophila simulans and D. mauritiana have rates of locomotor and feeding activity that are closely similar. Comparisons of the trait means for intra- and interspecific hybrids show that significant epistatic interactions affect both characters when the genomes of the two species are combined. The phenotypic variances of progenies obtained by backcrossing the interspecific hybrids to their respective parent species show that appreciable genetic turnover affecting foraging behaviour has occurred since their two phylogenetic lines diverged.

Analysis of Variance↗
PubMed2000

Schistosome population genetic structure: when clumping worms is not just splitting hairs.

Schistosomiasis is a major public health problem, affecting over 200 million people worldwide. Although Schistosoma mansoni has been studied rigorously in an attempt to provide a vaccine based on a number of candidate antigens, there has been a lack of complementary effort to determine the range and distribution of variation in representative molecules throughout natural populations. Here, Jason Curtis and Dennis Minchella highlight current (and suggest future) research efforts aimed at assessing genetic variation in schistosome populations, and call for a more robust consideration of schistosome population genetics.

Animals↗
PubMed2000

[Genetic structure of geographically different populations of candida albicans].

Codominant single-locus markers were developed by amplifying genomic DNA of C. albicans with pairs of random primers. Monomorphic PCR products were screened for polymorphisms by the SSCP technique. Sequencing confirmed that SSCP's were mostly due to single nucleotide substitutions in the polymorphic fragments. A total of 85 polymorphic loci were observed within 13 PCR fragments. Populations from Africa displayed less genotype variation than the populations from Europe and USA. Two genetically similar African C. albicans populations exhibiting an atypical biotype were strictly clonal and perhaps represent a geographically distributed clone. Analyses of "typical" C. albicans populations of different geographical origin provided however evidence for both clonality and recombination. Evidence for clonality was supported by the absence of segregation genotypes, and by deviation of genotypic frequencies from Hardy-Weinberg expectations. Tests for nonrandom association of alleles across loci revealed less evidence for linkage disequilibrium than expected for strictly clonal populations. Although all C. albicans populations tested were primarily clonal, evidence for recombination suggests that sexual reproduction or some other form of genetic exchange occurs in this species.

Africa↗
PubMed1991

[Genealogical files and the analysis of the genetic structure of non-isolated populations. An application to an agricultural population of the Limousin region].

"This article shows the methodological problems appearing in the production of genealogical files for non-endogamous or 'open' populations. [The authors conclude that] the study area must be extended to a geographic space larger than the one where the [designated] population resides." The authors reconstitute family structures using data from the eighteenth, nineteenth, and twentieth centuries for an agricultural community in Limousin, France. (SUMMARY IN ENG AND SPA)

Biology↗
PubMed1990

The angiotensin I-converting enzyme (kininase II): progress in molecular and genetic structure.

The complete amino acid sequence of the human angiotensin I-converting enzyme (ACE) has been determined by protein sequencing of the purified kidney enzyme and cDNA cloning in endothelial cell libraries. The ACE molecule comprises 1,306 amino acids. It possesses a signal peptide of 29 residues cleaved off during maturation. The enzyme is most likely anchored to the plasma membrane by a short transmembrane domain situated near the carboxy-terminal extremity. Interestingly, the molecule presents a high degree of internal homology between two large peptidic domains. Each of these domains contains short sequences identical to zinc binding and active site sequences of other zinc metallopeptidases and therefore bears a putative active site. However, earlier experiments indicate only one zinc atom bound per molecule of ACE. Competitive inhibitors seem to interact with a unique class of high-affinity binding site. These observations may suggest that, despite the duplicated structure of the enzyme, there is only one functional active site per molecule of ACE. The respective role of the two homologous domains in this active site remains to be determined. A single gene coding for ACE is present in humans, transcribed as a 4.3-kilobase mRNA species in endothelial cells. In other studies, evidence for a genetic polymorphism in plasma ACE levels has been obtained by analyzing a large group of "healthy" nuclear families. A familial association of plasma ACE levels was observed. A major gene effect can possibly explain part of the interindividual variability observed in this enzyme.

Amino Acid Sequence↗
PubMed2005

Postglacial colonization of the Tibetan plateau inferred from the matrilineal genetic structure of the endemic red-necked snow finch, Pyrgilauda ruficollis.

Most phylogeographical studies of postglacial colonization focus on high latitude locations in the Northern Hemisphere. Here, we studied the phylogeographical structure of the red-necked snow finch Pyrgilauda ruficollis, an endemic species of the Tibetan plateau. We analysed 879 base pairs (bp) of the mitochondrial cytochrome b gene and 529 bp of the control region in 41 birds from four regional groups separated by mountain ranges. We detected 34 haplotypes, 31 of which occurred in a single individual and only three of which were shared among sampling sites within regional groups or among regional groups. Haplotype diversity was high (h = 0.94); nucleotide diversity was low (eth = 0.00415) and genetic differentiation was virtually non-existent. Analyses of mismatch distributions and geographically nested clades yielded results consistent with contiguous range expansion, and the expansion times were estimated as 0.07-0.19 million years ago (Ma). Our results suggest that P. ruficollis colonized the Tibetan plateau after the extensive glacial period (0.5-0.175 Ma), expanding from the eastern margin towards the inner plateau. Thus, in contrast to many of the post-glacial phylogeographical structures known at high latitudes, this colonization occurred without matrilineal population structuring. This might be due to the short glacial cycles typical of the Tibetan plateau, adaptation of P. ruficollis to cold conditions, or refugia and colonized habitat being semicontinuous and thus promoting population mixing.

Animals↗
PubMed2005

Genetic structure of populations of Alternaria brassicicola suggests the occurrence of sexual recombination.

Substantial polymorphism was detected between isolates from five populations of Alternaria brassicicola attacking Cakile maritima along the New South Wales coast of Australia, with a maximum of two genotypes being shared between population pairs. Of ten pair-wise population comparisons, six had no pathogen genotypes in common; only one genotype occurred five times, and most (93 %) were found only once. Although an UPGMA based on Nei's measure of genetic distance separated the five populations, a cluster analysis using individual isolates failed to group them according to population, indicating significant gene flow. An analysis of molecular variance indicated ca 14% of the variation occurred between populations, representing moderate population differentiation over the spatial scale of the study. Tests of the relative contribution of clonality and sexual recombination indicated low, albeit significant levels of linkage disequilibrium in all populations. The level of linkage disequilibrium, and the high genotype diversity, provides support for the contention that a hitherto unidentified sexual stage might be a significant factor in the life-cycle of A. brassicicola.

Alternaria↗
PubMed1997

Genetic structure of an aphid studied using microsatellites: cyclic parthenogenesis, differentiated lineages and host specialization.

In a previous study, samples of the grain aphid Sitobion avenae (F.) were collected from wheat and adjacent cocksfoot hosts in a population thought to be primarily parthenogenetic, and DNA from individual aphids was analysed with a multilocus technique. Here we have applied single-locus microsatellites and a mitochondrial DNA marker to a subset of the same DNA extracts, and have made several additional inferences about important genetic and population processes in S. avenae. Microsatellite analysis indicated very high levels of genic and genotypic variation. S. avenae fell into three genotypic groups inferred to be almost noninterbreeding, while analysis of linkage and Hardy-Weinberg equilibria suggested high levels of sexual recombination within each genotypic group. Host specialization was evident: one lineage was found only on wheat, and one (bearing many alleles inferred to be introgressed from the blackberry-grass aphid S. fragariae (Walker)) was found only on cocksfoot. The third group of interrelated genotypes was found commonly on both hosts. Although most genotypes were found only once, some were much more numerous in the sample than expected from the frequency of the alleles they contained. This, and rapid temporal changes in genotypic composition of samples, indicates strong selective differences between genotypes and lineages. In the major genotypic group, the commonest genotypes were significantly more homozygous than were rare ones: thus these data may help to explain the frequent observation of homozygous excess in aphid allozymes. The genotype group showing S. avenae-like as well as S. fragariae-like alleles also carried S. fragariae-like mitochondrial DNA in at least 25/31 cases, indicating gender-asymmetrical hybridization.

Animals↗
PubMed1995

Biochemical systematics and population genetic structure of Anopheles pseudopunctipennis, vector of malaria in Central and South America.

An electrophoretic survey of 42 populations of Anopheles pseudopunctipennis collected throughout its known geographic distribution was performed to clarify the taxonomic status of this important malaria vector species. The results indicated strong differences in the allele frequencies of three enzyme loci (glycerol dehydrogenase, 6-phosphogluconate dehydrogenase, and phosphoglucomutase) of the 33 loci analyzed. No fixed electromorphic differences separate the populations of An. pseudopunctipennis. The populations of An. pseudopunctipennis showed little genetic divergence, with Nei distances ranging from 0 to 0.079. A comparison of An. pseudopunctipennis data with either one of three other Anopheles species showed a high genetic distance of 0.335 with a closely related species, An. franciscanus; 0.997 with An. crucians, and 2.355 with An. (Nyssorhynchus) albimanus. Geographic populations of An. pseudopunctipennis were classified into three clusters; one cluster included populations collected in North America (United States and Mexico) and Guatemala, one cluster included populations from Belize and South America (Colombia, Ecuador, Peru, Chile, and Argentina); and one cluster was represented by populations from the Island of Grenada (type-locality of An. pseudopunctipennis). Based on our isozyme analyses, we defined these clusters as three geographic populations of An. pseudopunctipennis. Of the two mainland populations, one extends from the southern United States south through Mexico and Guatemala, and the other extends north from southern South America through Central America to Belize. These two geographic populations converge in southern Mexico and northern Central America. One part of the convergence zone was identified in the area of eastern Guatemala and southern Belize.

Alleles↗
PubMed1988

[Medico-genetic study of the Kostroma Region population. VIII. Genetic structure of large subdivided populations and its relation with the incidence of autosomal-recessive pathology].

FST was estimated for 67 communities and 6 small towns of Kostroma province. The mean FST value for rural and urban populations was (0.83 +/- 0.08).10(-3) and (0.29 +/- 0.07).10(-3), respectively. The connection between FST values and the load of autosomal-recessive disorders was established; the coefficient of correlation (by Chuprov) was 0.34 (chi 2 = 8.45; P less than 0.05). The matrices of genetic distances for two groups of districts of Kostroma province, based on surnames frequencies, were calculated. Dendrogramms were constructed using genetic distances, which reflect the degree of genetical similarity of the populations. The conclusion drawn from the analysis of these dendrogramms is that there is distinct isolation by distance in populations of Kostroma province. It is shown that genetical subdivision of populations is dependent on geographical and some other factors and on the load of autosomal-recessive pathology in the population.

Genes, Recessive↗
PubMed1975

[New data on the genetic structure of dimorphic populations of the common hamster (Cricetus cricetus L.)].

Long-term (1965-1974) Mendelian crossbreedings of two coloured forms (black and red) of Cricetus cricetus, carried out by the author, have shown that dominant melanistic mutation exists in a homozygous state. Thus, it is proved experimentally that natural population of C. cricetus consisting of black and red individuals is a dimorphous one by the phenotype and a polymorphous one by the genotype. The structure of the population includes the black homozygotes (genotype AA), black heterozygotes (genotype Aa) and red recessive homozygotes (genotype aa). All three forms are fully fertile and give quite viable and fertile progeny.

Animals↗
PubMed1995

Genetic structure of the dnaA region of the cyanobacterium Synechocystis sp. strain PCC6803.

We have cloned and sequenced the dnaA region of Synechocystis sp. strain PCC6803, a bacterium with a light-dependent cell cycle. The dnaA gene product, DnaA, is the central factor for replication initiation in bacteria. The deduced amino acid sequence of the protein encoded by the cyanobacterial dnaA gene is 45% identical to DnaA of Bacillus subtilis and fits very well into the homology pattern of the known eubacterial DnaA proteins. The genetic environment of the Synechocystis sp. strain PCC6803 dnaA gene is completely different from the one in other eubacteria. An open reading frame of unknown function, orf134, was detected upstream of dnaA. The purT gene homolog encoding the glycinamide ribonucleotide transformylase T starts about 200 bp away from this open reading frame in the opposite direction. Downstream of the dnaA gene we detected the start of the psbDC operon, which codes for the photosystem II reaction center proteins D2 and CP43 that are involved in the positioning of chlorophyll a.

Acyltransferases↗