Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Genetic Structures”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
PubMed2006

Population genetic structuring of the king weakfish, Macrodon ancylodon (Sciaenidae), in Atlantic coastal waters of South America: deep genetic divergence without morphological change.

Phylogeographic patterns in Macrodon ancylodon sampled from 12 locations across all its range were investigated using mitochondrial DNA cytochrome b sequences, and analysed together with patterns of morphometric differentiation. Populations of the North Brazil and the Brazil currents, with warmer waters, form a clade (tropical clade) separated by 23 fixed mutations from the populations that inhabit regions of colder waters influenced by the Brazil and Malvinas currents (subtropical clade). No gene flow exists between the tropical and subtropical clades, and most likely also between the two groups of the tropical clade. Distribution of these clades and groups is correlated with flow of currents and their temperatures, and is facilitated by larval retention and low adult migration. Despite differentiation at the molecular level, fishes analysed from all these current-influenced regions are morphometrically homogeneous. Throughout its range M. ancylodon inhabits the same, or very similar niche; thus, stabilizing selection probably promotes the retention of highly conserved morphology despite deep genetic divergence at the mitochondrial DNA cytochrome b.

Animals↗
PubMed2025

Genomic-based revelation of genetic structure and adaptive characterization of Schizopygopsis malacanthus in the Jinsha River and Yalong River.

BACKGROUND: As a highly specialized class of schizothoracine fishes, Schizopygopsis malacanthus has attracted much attention due to its widespread distribution. To investigate the impact of the Qinghai‒Tibet movement on S. malacanthus, we analyzed the genetic evolutionary history of this species. RESULTS: These results showed that there was a high level of genetic differentiation between Jinsha River (JSR) populations and Yalong River (YLR) populations. The genetic diversity of intra-YLR populations was higher than that of the intra-JSR populations. There was gene exchange of the Suwalong population to the Huoqu and Ganzi populations. Furthermore, both of the JSR and YLR populations exhibited a gradual increase in the genetic differentiation index from low to high altitudes, and the effective population of high-elevation populations has gradually expanded. In high-altitude populations, the selected genes were enriched in DNA repair, light transduction, and energy metabolism, reflecting the genetic basis for their migration to higher altitudes. CONCLUSIONS: S. malacanthus populations had the higher genetic differentiation and genetic diversity in the JSR and its main tributary YLR. Therefore, we should preserve high-elevation natural river sections as much as possible and reserve habitats for their migration and diffusion.

Animals↗
PubMed2000

The genetic structure of female life history in D. melanogaster: comparisons among populations.

Two questions were addressed: (1) What is the genetic variance-covariance structure of a suite of four female life history traits in D. melanogaster? and (2) Does the genetic architecture of these traits differ among populations? Three populations of D. melanogaster were studied. Genetic variances and covariances were estimated by sib analysis three times for each population: immediately upon establishment of populations in the laboratory, and subsequently after approximately 6 months and 2 years of laboratory culture. Entire genetic variance-covariance matrices, as well as their individual components, were compared between populations by means of likelihood ratio tests. All traits studied were significantly heritable in at least one-half of estimates. Despite large sample sizes, additive genetic covariances were for the most part not statistically significant, and only two significant negative covariance estimates were obtained throughout the experiments. Therefore, these experiments provide little support for evolutionary life history theories that are based on negative genetic correlations among life history components. Neither do they support the idea that genetic variance for fitness components is maintained by trade-offs. Evidence suggests that the G matrix of one population was initially different from those of the other two populations. Those differences disappeared after 2 years of laboratory culture. At the level of individual (co)variance components, there were relatively few differences among populations, and the overall impression was that the three populations had generally similar genetic architectures for the traits studied.

Animals↗
PubMed1999

Genetic multilocus studies of different strains of Cryptococcus neoformans: taxonomy and genetic structure.

The genotypes of 107 strains of Cryptococcus isolated from the environment or from patients from various geographical areas were determined by multilocus enzyme electrophoresis (MLEE). We analyzed the relationships between genotype structure and serotype and between genotype structure and strain origin. Twelve of the 14 enzyme-encoding loci studied were polymorphic, giving rise to 48 electrophoretic types. The genotypes of C. neoformans and C. laurentii were very similar. MLEE could not distinguish between these two pathogenic species. A correlation between the genetic multilocus structure and the origin of the sample (from the environment or patients) existed. A second analysis detected a correlation between genotype distribution and serotype. The second analysis considered three serotype groups (B, C, and A plus D plus A/D), proving that serotypes A, D, and A/D are closely related. MLEE is a useful epidemiological tool for improving our understanding of the biology of this fungus.

Alleles↗
PubMed1998

Population genetic structure, phylogeography and spawning philopatry in walleye (Stizostedion vitreum) from mitochondrial DNA control region sequences.

Mitochondrial (mt) DNA control region sequences were used to test the genetic and phylogeographic structure of walleye Stizostedion vitreum populations at different geographical scales: among spawning sites, lake basins, lakes, and putative glacial refugia in the Great Lakes region. Sequencing 199 walleye revealed nucleotide substitutions and tandemly repeated sequences that varied in copy number, as well as in sequence composition, in approximately 1200 bp of the mtDNA control region. Variable numbers of copies of an 11-bp tandem repeat showed no geographical patterning and were not used in further analyses. Substitutions in the other areas of the control region yielded 19 haplotypes, revealing phylogeographic structure and significant differences among glacial refugia, lakes, basins and some spawning sites. Differences among spawning populations were consistent with reduced gene flow, philopatry and possible natal homing. Analysis of spawning populations showed consistency of genotypic frequencies among years and between males and females, supporting philopatry in both sexes. The unglaciated plateau in southern Ohio, USA housed a very different haplotype that diverged prior to the Missouri, Mississippi and Atlantic glacial refugia types. Haplotypes from the three refugia colonized the Great Lakes after retreat of the Wisconsin glaciers, and their present distribution reflects the geography of their prior isolation and differential colonization. Populations that became associated with spawning localities appear to have diverged further due to philopatry, resulting in fine-scale phylogeographic structuring.

Animals↗
PubMed2001

Effect of race, genetic population structure, and genetic models in two-locus association studies: clustering of functional renin-angiotensin system gene variants in hypertension association studies.

Previous genetic association studies have overlooked the potential for biased results when analyzing different population structures in ethnically diverse populations. The purpose of the present study was to quantify this bias in two-locus association studies conducted on an admixtured urban population. We studied the genetic structure distribution of angiotensin-converting enzyme insertion/deletion (ACE I/D) and angiotensinogen methionine/threonine (M/T) polymorphisms in 382 subjects from three subgroups in a highly admixtured urban population. Group I included 150 white subjects; group II, 142 mulatto subjects, and group III, 90 black subjects. We conducted sample size simulation studies using these data in different genetic models of gene action and interaction and used genetic distance calculation algorithms to help determine the population structure for the studied loci. Our results showed a statistically different population structure distribution of both ACE I/D (P = 0.02, OR = 1.56, 95% CI = 1.05-2.33 for the D allele, white versus black subgroup) and angiotensinogen M/T polymorphism (P = 0.007, OR = 1.71, 95% CI = 1.14-2.58 for the T allele, white versus black subgroup). Different sample sizes are predicted to be determinant of the power to detect a given genotypic association with a particular phenotype when conducting two-locus association studies in admixtured populations. In addition, the postulated genetic model is also a major determinant of the power to detect any association in a given sample size. The present simulation study helped to demonstrate the complex interrelation among ethnicity, power of the association, and the postulated genetic model of action of a particular allele in the context of clustering studies. This information is essential for the correct planning and interpretation of future association studies conducted on this population.

Alleles↗
PubMed2000

Minisatellite marker analysis of Trypanosoma brucei: reconciliation of clonal, panmictic, and epidemic population genetic structures.

The African trypanosome, Trypanosoma brucei, has been shown to undergo genetic exchange in the laboratory, but controversy exists as to the role of genetic exchange in natural populations. Much of the analysis to date has been derived from isoenzyme or randomly amplified polymorphic DNA data with parasite material from a range of hosts and geographical locations. These markers fail to distinguish between the human infective (T. b. rhodesiense) and nonhuman infective (T. b. brucei) "subspecies" so that parasites derived from hosts other than humans potentially contain both subspecies. To overcome some of the inherent problems with the use of such markers and diverse populations, we have analyzed a well-defined population from a discrete geographical location (Busoga, Uganda) using three recently described minisatellite markers. The parasites were primarily isolated from humans and cattle with the latter isolates further characterized by their ability to resist lysis by human serum (equivalent to human infectivity). The minisatellite markers show high levels of polymorphism, and from the data obtained we conclude that T. b. rhodesiense is genetically isolated from T. b. brucei and can be unambiguously identified by its multilocus genotype. Analysis of the genotype frequencies in the separated T. b. brucei and T. b. rhodesiense populations shows the former has an epidemic population structure whereas the latter is clonal. This finding suggests that the strong linkage disequilibrium observed in previous analyses, where human and nonhuman infective trypanosomes were not distinguished, results from the treatment of two genetically isolated populations as a single population.

Animals↗
PubMed2003

Population genetic structure of Taenia solium from Madagascar and Mexico: implications for clinical profile diversity and immunological technology.

Taenia solium is a cestode parasitic of humans and pigs that strongly impacts on public health in developing countries. Its larvae (cysticercus) lodge in the brain, causing neurocysticercosis, and in other tissues, like skeletal muscle and subcutaneous space, causing extraneuronal cysticercosis. Prevalences of these two clinical manifestations vary greatly among continents. Also, neurocysticercosis may be clinically heterogeneous, ranging from asymptomatic forms to severely incapacitating and even fatal presentation. Further, vaccine design and diagnosis technology have met with difficulties in sensitivity, specificity and reproducibility. Parasite diversity underlying clinical heterogeneity and technological difficulties is little explored. Here, T. solium genetic population structure and diversity was studied by way of random amplified polymorphic DNA in individual cysticerci collected from pigs in Madagascar and two regions in Mexico. The amplification profiles of T. solium were also compared with those of the murine cysticercus Taenia crassiceps (ORF strain). We show significant genetic differentiation between Madagascar and Mexico and between regions in Mexico, but less so between cysticerci from different localities in Mexico and none between cysticerci from different tissues from the same pig. We also found restricted genetic variability within populations and gene flow was estimated to be low between populations. Thus, genetic differentiation of T. solium suggests that different evolutionary paths have been taken and provides support for its involvement in the differential tissue distribution of cysticerci and varying degrees of severity of the disease. It may also explain difficulties in the development of vaccines and tools for immunodiagnosis.

Animals↗
PubMed2002

Genetic structure of Oestrus ovis populations in sheep and goats.

A genetic analysis using RAPD markers was performed on 12 natural populations of Oestrus ovis (Linné, 1761). Three-hundred and six O. ovis larvae (first, second and third instars) were randomly recovered in nasal cavities of sheep and goats naturally infected in Algeria, Ethiopia, France, Mauritania, Rumania and Tunisia and were analysed by 56 RAPD fragments. The results showed a high diversity within all samples. A significant genetic divergence was showed by discriminant analyses among the 12 populations sampled (p<0.0001). Moreover, discriminant analyses showed significant differentiation (p<0.0001) between O. ovis larva populations of sheep and goats and also among samples collected in the same region.

Animals↗
PubMed2005

Genetic structure of the Pleurotus eryngii species-complex.

Assessment of genetic and phenotypic diversity is necessary to confidently distinguish genotypes of Pleurotus eryngii when seeking traits of interest and to identify strains with high yield potential. We studied 154 strains from Italy for quantitative (shape, size and yield), qualitative (colour, malformations and growing behaviour), and molecular (RAPD and minisatellite) traits. This population consisted of isolates mostly belonging to P. eryngii var. eryngii, var. ferulae or var. nebrodensis, from different regions of Italy. A replicated cultivation trial, with three blocks and three replicates for each strain within the block, was used as an experimental design to calculate trait estimates. Significant differences were observed between strains for basidiome number and weight, while no significant differentiation for quantitative morphological traits was observed between geographical origins and taxonomic groups. Qualitative morphological traits were efficient in differentiating isolates of P. eryngii var. nebrodensis. On average, yield per strain (basidiome weight) was correlated more with basidiome number than with size. The most stable yield traits were basidiome number and weight per strain. An average heritability of 0.31 was estimated for yield related traits. A significant difference between var. ferulae and var. eryngii populations was detected for basidiome production measured as 'average harvest time'. Molecular markers showed a high level of heterogeneity within populations and a low, but significant, degree of differentiation among populations defined a priori. No population-specific marker was detected and the differential pattern of variation between vars. ferulae and eryngii was due to frequency-dependent alleles. The nebrodensis type was more differentiated from var. eryngii than from var. ferulae using either molecular or qualitative morphological traits.

Genetic Markers↗
PubMed1989

Fine-structure genetic mapping of human chromosomes using the polymerase chain reaction on single sperm: experimental design considerations.

The polymerase chain reaction (PCR) makes it possible to rapidly generate a very large number of copies of a specific region of DNA. Application of PCR to individual human sperm cells permits the typing of a large number of independent male meiotic events. If the donor male is heterozygous at three loci, sperm typing using PCR will permit ordering of loci in a manner analogous to classical methods of experimental genetics. Sequential analysis of trios of loci by sperm typing will provide a very accurate means of ordering any number of tightly linked loci. Here, we describe experimental design and sample-size issues raised by the application of sperm typing by PCR for mapping human chromosomes, and we demonstrate that sperm typing will be an efficient method for generating fine-structure human genetic maps.

Alleles↗
PubMed1991

[Genetic structure of the population of Ashkhabad City of the Turkmen SSR].

Some genetical demographic characteristics of population of Ashkhabad city were studied by direct interviewing of women aged over 18 years. The influence of urbanization on the basic genetical-demographic indices was found, the indices being essentially different from those of rural population studied elsewhere. Analysis of intensity and the structure of marriage migrations showed considerable ethnic subdivision in Ashkhabad population and stability of marriage policy in an every ethnic group. The level and structure of inbreeding as well as positive marriage assortativity are of the same order as in the Turkmen rural population.

Consanguinity↗
PubMed2001

Genetic structures and linguistic boundaries in Italy: a microregional approach.

The amount of genetic data (sequences, gene frequencies, and isonymy) available for the Province of Ferrara, Italy, makes this area one of the world's best known. In an effort to infer the underlying demographic processes, we studied the province's population structure by comparing geological, palaeoclimatic, archeological, historical, and linguistic data. This multilevel approach allowed us to date some characteristics of the population structure from prehistoric times to the Roman and Middle Ages, and to detect overlapping biological, cultural, and geographic boundaries. To detect linguistic boundaries within this area we turned pronunciation differences into phonetic notation. We then computed pairwise distances by using methods for multiple genetic sequence analysis, in order to obtain a distance matrix of the overall pronunciation variability. This approach enabled us to test the association among linguistic, geographical, and genetic distance matrices using the same statistical tests. Results indicate that demographic phenomena can be traced in an area as small as the Province of Ferrara and that, on a microregional scale, recent events may have influenced important aspects of the overall genetic variation.

Genetics, Population↗
PubMed1979

Genetic structure of the Greek gypsies.

Data are presented on several polymorphic genetic markers in 200 Greek gypsies. Polymorphic loci studied were: the ABO, MN, Rhesus, Kell and Duffy blood groups, hemoglobin, and ceruloplasmin. A survey for congenital malformations and hereditary diseases was also carried out on this group. The ABO, Rhesus, MN and Duffy system frequencies varied significantly from the figures obtained for the Greek population. However, there is a characteristic similarity between various gypsy groups studied in other nations and the distribution of polymorphic traits in the Punjab region of India. Cystic fibrosis, renal tubular acidosis, 21-hydroxylase deficiency, Hoty-Oram syndrome and homozygous beta-thalassemia were diagnosed within the gypsy group studied.

ABO Blood-Group System↗
PubMed2001

Diversity and genetic structure in populations of Pseudotsuga menziesii (Pinaceae) at chloroplast microsatellite loci.

Genetic variation was compared between uniparentally-inherited (chloroplast simple sequence repeats, cpSSRs) vs. biparentally-inherited (isozyme and random amplified polymorphic DNA, RAPD) genetic markers in Douglas-fir (Pseudotsuga mensiezii) from British Columbia. Three-hundred twenty-three individuals from 11 populations were assayed. In Douglas-fir, the cpSSR primer sites were well-conserved relative to Pinus thunbergii (11 of 17 loci clearly amplified), but only 3 loci were appreciably polymorphic. At these cpSSR loci, we found an unexpectedly low level of polymorphism within populations, and no genetic differentiation among populations. By contrast, the nuclear markers showed variation typical of conifers, with significant among-population differentiation. This difference is likely the outcome of both historical factors and high pollen dispersal.

Alleles↗