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At least 145 records · Page 8Linked to original sources
PubMed2001

Molecular diversity of the plasmid genotypes among Rhizobium gene pools of sesbanias from different habitats of a semi-arid region (Delhi).

Plasmid genotypes of root nodulating rhizobial isolates of Sesbania, sampled from six ecologically distinct habitats, were characterized. Plasmid profile analysis revealed nine different plasmid types having molecular masses ranging from 30 to 300 MDa, distributed among six profile types that grouped the isolates into six plasmid classes. The six plasmid profiles were diverged from each other and lack many common plasmid types among them. Variation in number and types of symbiotic (Sym) plasmid was assessed by hybridization of plasmid profiles with sym gene probes. Relatedness among different plasmid types was assessed by hybridization of total DNAs as well as plasmid profiles of different isolates with labelled intact plasmid. Plasticity of plasmid genotype and possible recombination between different plasmid types is suggested from the results obtained. Structural diversity among sym plasmids was assessed by PCR amplified product profiles using primer corresponding to the reiterated nif promoter consensus element (NPC-PCR). A total of 26 NPC-PCR profile types were recognized. Genetic diversity among sym plasmids of isolates belonging to the same plasmid class and having similar sym plasmid suggested recombinations and rearrangements of sequences within the sym plasmids. Cluster analysis based upon similarity among profile types sorted the isolates across the ecological gradient. We suggest that habitat heterogeneity and plasticity of plasmid genotype together contribute for the generation of genetic diversity leading to strainal differentiation in rhizobia.

Fabaceae↗
PubMedDate not supplied

[Comparative analysis of the gene pool of the Ascanian polycarpous and purebred Karakul' sheep populations].

The Ascanian multi-foetus and pure-bred Karakul sheep reared in the steppe region of the Ukraine are characterized by five-allelic status of transferrin and by diallelic serum arylesterase and alkaline phosphatase. Besides the basic HbA and HbB alleles the rare HbC type has been revealed in the multi-foetus Karakul. Reliable differences in concentrations of the transferrin and haemoglobin alleles between the multi-foetus Karakul population and that of the pure-bred Karakul have been found.

Alleles↗
PubMed2001

Selection effects of air pollution on gene pools of Norway spruce, European silver fir and European beech.

The effects of industrial pollution on allelic and genotypic structures of Norway spruce. European silver fir and European beech were investigated by means of isozyme analysis. In a mixed Norway spruce-silver fir forest stand in an area heavily polluted by sulphur dioxide and heavy metals in the region of Spis (eastern Slovakia), pairs of neighbouring damaged and apparently healthy trees were selected in two replicates (44 and 69 pairs in a heavily and moderately damaged stand, respectively). Pairwise sampling of trees with contrasting vitality was applied to reduce potential effects of site heterogeneity on the vitality of sampled trees. No significant differences in allelic and genotypic frequencies were found between sets of healthy and declining trees. There were differences in the single-locus heterozygosities, but these were not consistent between the replicates. However, the set of damaged trees exhibited higher levels of genetic multiplicity and diversity, possibly due to the deleterious effect of rare alleles under the conditions of air pollution. Consequently. following the decline of pollutant-sensitive trees, the remaining stand will be depleted of a part of alleles with unknown adaptive value to future selection pressures.

Abies↗
PubMed1981

The still elusive T cell receptor: on the possibility of a common V-gene pool for B- and T-cell-antigen receptor molecules.

The contention that VH constitutes a part of T-cell receptors for antigens was probed by purifying rabbit T cells and analysing these cells for non-immunoglobulin VH, i.e. VH not associated with L chain. A number of anti-VH antisera were employed for this purpose, the most important being goat antiserum, reacting with common a1 allotype determinants (allotype determinants expressed on free VH and H chain as well as on intact immunoglobulins), rat antibody against common non-allotype VH determinants (VH framework determinants expressed on VH and H chain as well as on intact immunoglobulins) and chicken antibody against unmasked non-allotype determinants (VH determinants accessible only in the absence of L chain). VH and L chain was quantified by radioimmunoassays on extracts and supernatants from unstimulated T cells as well as from T cells stimulated by concanavalin A and by allogeneic cells. Absolute depletion of Ig-containing and -producing cells was not achieved but in no case was an excess of VH over L chain observed. This indicated that all detected VH originated from cells of the B lineage. The cells were also cultured in the presence of labelled amino acids followed by analysis of detergent extracts and supernatants by immunoadsorption and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) fluorography. Again, no evidence for T-cell VH could be found. Affinity purified anit-VH antibody was used to label viable rabbit T cells through the use of secondary fluorescence-labelled anti-immunoglobulin antibody. No VH-specific labelling of T cells could be observed. Mixed lymphocyte cultures were carried out in the presence of affinity-purified anti-VH antibodies. No inhibition of the reaction could be discerned. The failure to detect T-cell VH is in agreement with the recent finding that the VH-genome in T cells is not rearranged in a functional manner similar to that in B cells.

Animals↗
PubMed2002

Unequal contributions of male and female gene pools from parental populations in the African descendants of the city of Melo, Uruguay.

In admixed populations, genetic contributions from males and females of specific parental populations can be of different proportions due to past directional mating during the process of genetic admixture. In this research paper, we provide evidence of such male- and female-specific differential admixture components of African, European, and American Indian origin in an admixed population from the city of Melo, in the northeastern region of Uruguay. From data on 11 autosomal markers from a sample of 41 individuals of mixed African descent, we estimated 47% African, 38% European, and 15% Amerindian contributions. In contrast, 6 mtDNA site-specific polymorphic markers showed that the mtDNA genome of these individuals was 52% African, 19% European, and 29% Amerindian, while from 3 Y-specific polymorphic sites, we estimated 30% African, 64% European, and 6% Amerindian contributions. We argue that this heterogeneity of admixture estimates results from disproportionate unions of European males with African and American Indian females from which this mixed African population was formed. Also, we argue that the asymmetry of the admixture estimates from the three sets of markers (autosomal, mtDNA, and Y-linked) is a result of the changes in the direction of mating during the history of the population. Implications of such evidence of directional mating are discussed, indicating the need of further demographic data for a quantitative assessment of the impact of directional mating on genetic structure of admixed populations.

Africa↗
PubMed2006

Distorting gene pools by conservation: Assessing the case of doomed turtle eggs.

Sea turtles have a high reproductive output and high mortality at early stages of the life cycle. In particular, many nests are laid below or close to high tide lines, and subsequently large numbers of eggs may be inundated and destroyed. A common conservation procedure is to relocate such doomed eggs to higher ground. This article examines this practice in the light of recent data revealing that some individual turtles tend to nest relatively near the water and others relatively higher up the beach. Discussion is focused on the question of why apparently poor placement of nests has not been selected against. Comparison between the ecology of leatherback and hawksbill turtle nesting beaches suggests that predictability of environmental conditions on the nesting beaches has an important influence on patterns of nest-site selection. Options are outlined for the management of nesting beaches where a high proportion of turtle eggs is subject to destruction by flooding.

Animals↗
PubMed2000

The gene pool

Explore the source record for details and available documents.

Journal Article↗
PubMed2001

Transmission genetics of chromatin from a synthetic amphidiploid to cultivated peanut (Arachis hypogaea L.). broadening the gene pool of a monophyletic polyploid species.

Polyploidy creates severe genetic bottlenecks, contributing to the genetic vulnerability of leading crops. Cultivated peanut is thought to be of monophyletic origin, harboring relatively little genetic diversity. To introduce variability from diploid wild species into tetraploid cultivated Arachis hypogaea, a synthetic amphidiploid [[A. batizocoi K9484 x (A. cardenasii GKP10017 x A. diogoi GKP10602)](4x)] was used as donor parent to generate a backcross population of 78 progeny. Three hundred seventy RFLP loci were mapped onto 23 linkage groups, spanning 2210 cM. Chromatin derived from the two A-genome diploid ancestors (A. cardenasii and A. diogoi) comprised mosaic chromosomes, reflecting crossing over in the diploid A-genome interspecific F(1) hybrid. Recombination between chromosomes in the tetraploid progeny was similar to chromosome pairing reported for A. hypogaea, with recombination generally between chromosomes of the same subgenomic affinity. Segregation distortion was observed for 25% of the markers, distributed over 20 linkage groups. Unexpectedly, 68% of the markers deviating from expected segregation showed an excess of the synthetic parent allele. Genetic consequences, relationship to species origins, and significance for comparative genetics are discussed.

Arachis↗
PubMed1998

Gene-pool variation in caledonian and European Scots pine (Pinus sylvestris L.) revealed by chloroplast simple-sequence repeats.

We have used polymorphic chloroplast simple-sequence repeats to analyse levels of genetic variation within and between seven native Scottish and eight mainland European populations of Scots pine (Pinus sylvestris L.). Diversity levels for the Scottish populations based on haplotype frequency were far in excess of those previously obtained using monoterpenes and isozymes and confirmed lower levels of genetic variation within the derelict population at Glen Falloch. The diversity levels were higher than those reported in similar studies in other Pinus species. An analysis of molecular variance (AMOVA) showed that small (3.24-8.81%) but significant (p < or = 0.001) portions of the variation existed between the populations and that there was no significant difference between the Scottish and the mainland European populations. Evidence of population substructure was found in the Rannoch population, which exhibited two subgroups. Finally, one of the loci studied exhibited an allele distribution uncharacteristic of the stepwise mutation model of evolution of simple-sequence repeats, and sequencing of the PCR products revealed that this was due to a duplication rather than slippage in the repeat region. An examination of the distribution of this mutation suggests that it may have occurred fairly recently in the Wester Ross region or that it may be evidence of a refugial population.

Alleles↗
PubMed2004

The rare silver gum, Eucalyptus cordata, is leaving its trace in the organellar gene pool of Eucalyptus globulus.

The process of genetic assimilation of rare species by hybridizing congeners has been documented in a number of plant genera. This raises the possibility that some of the genetic diversity found in phylogeographical studies of widespread species has been acquired through hybridization with species that are now rare or extinct. In this fine-scale phylogeographical analysis, we show that a rare eucalypt species is leaving its trace in the chloroplast genome of a more abundant congener. The heart-leafed silver gum, Eucalyptus cordata, is a rare endemic of south-eastern Tasmania. Its populations are scattered amidst populations of more abundant related species, including the Tasmanian blue gum, Eucalyptus globulus. Using 339 samples from across the full range of both species, we compared chloroplast (cp) DNA haplotype phylogeography in E. globulus and E. cordata. The genealogy and distribution of chloroplast haplotypes suggest that E. globulus has acquired cpDNA from E. cordata in at least four different mixed populations. Shared haplotypes are highest in E. globulus sampled within 2 km of known E. cordata populations and drop to zero at a distance of 25 km from the nearest known E. cordata population. Localized haplotype sharing occurs in the absence of obvious hybrid zones or locally shared nuclear ribosomal DNA sequences. Given that the future loss of E. cordata from some mixed populations is likely, these findings indicate that phylogeographical analyses of organellar DNA should consider the possibility of introgression, even from species that have been eliminated from the sites of interest.

Base Sequence↗
PubMed1977

Survey of the extrachromosomal gene pool of Streptococcus mutans.

Fifty strains of Streptococcus mutans independently isolated from human dental plaque were examined for the presence of covalently closed circular plasmid deoxyribonucleic acid (DNA). Cesium chloride-ethidium bromide centrifugation of [3H]thymidine-labeled, Sarkosyl-lysed cells revealed that 2 of the 50 strains contained plasmid DNA. The plasmid DNA from these strains was characterized by velocity and equilibrium centrifugation and by electron microscopy. The plasmids in these strains were virtually identical in size, with molecular weights of 3.6 X 10(6) and 3.7 X 10(6), Both were present to the extent of approximately 20 molecules per genome equivalent. Interlocked catenated dimeric molecules of each plasmid were readily detected by velocity sedimentation and electron microscopy. These plasmid-containing strains were compared with representative plasmid-free S. mutans strains by using such criteria as bacteriocin production, antibiotic susceptibility, and hemolysis of mammalian erythrocytes. Although no correlation of phenotype to plasmid content could be made, production of bacteriocin-like activity differed significantly between the two plasmid-containing S. mutans isolates. Thus, although the plasmids in these two isolates appeared identical by the criteria of molecular weight, presence of dimers, and copy number, they appeared to be harbored by two distinct S. mutans strains.

Anti-Bacterial Agents↗
PubMed2001

Was the historic contribution of Spain to the Mexican gene pool partially responsible for the higher prevalence of type 2 diabetes in mexican-origin populations? The Spanish Insulin Resistance Study Group, the San Antonio Heart Study, and the Mexico City Diabetes Study.

OBJECTIVE: Mexican-American populations in San Antonio, Texas (SA-MA) and Mexico have a higher prevalence of type 2 diabetes than non-Hispanic whites in San Antonio (SA-NHW). However, the higher prevalence of type 2 diabetes in Mexican-origin populations might be related, in part, not to Native American genetic admixture but to Spanish genetic admixture. RESEARCH DESIGN AND METHODS: Four population-based epidemiological surveys conducted with Mexican-origin and European-origin samples provided data relevant to this question. In all four surveys, type 2 diabetes was defined as fasting plasma glucose > or =7.0 mmol/l or 2-h glucose > or =11.1 mmol/l or use of antidiabetic agents. RESULTS: A comparison of the two Mexican-origin populations showed that the age- and sex-adjusted prevalence of type 2 diabetes was lower in Mexico than in SA-MA (15.1 vs. 17.9%, P = 0.032). Between the two European-origin populations, the prevalence of type 2 diabetes was lower in SA-NHW than in Spain (6.2 vs. 9.1%, P < 0.0001), but differences were attenuated by adjustment for BMI or after stratification by education. In logistic regression analyses, type 2 diabetes was associated with Mexican ethnic origin after adjusting for age, education, BMI, and waist-to-hip ratio. CONCLUSIONS: The prevalence of type 2 diabetes in Spain was intermediate between that in Mexican-origin populations and SA-NHW. Although the higher degree of Native American admixture is a major contributor to the higher rates of type 2 diabetes, we cannot completely rule out a partial contribution of Spanish admixture to diabetes susceptibility among Mexican- origin populations.

Age Factors↗