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At least 991 records · Page 55Linked to original sources
PubMed2002

Molecular analysis of the Pleistocene history of Saxifraga oppositifolia in the Alps.

A recent circumpolar survey of chloroplast DNA (cpDNA) haplotypes identified Pleistocene glacial refugia for the Arctic-Alpine Saxifraga oppositifolia in the Arctic and, potentially, at more southern latitudes. However, evidence for glacial refugia within the ice sheet covering northern Europe during the last glacial period was not detected either with cpDNA or in another study of S. oppositifolia that surveyed random amplified polymorphic DNA (RAPD) variation. If any genotypes survived in such refugia, they must have been swamped by massive postglacial immigration of periglacial genotypes. The present study tested whether it is possible to reconstruct the Pleistocene history of S. oppositifolia in the European Alps using molecular methods. Restriction fragment length polymorphism (RFLP) analysis of cpDNA of S. oppositifolia, partly sampled from potential nunatak areas, detected two common European haplotypes throughout the Alps, while three populations harboured two additional, rare haplotypes. RAPD analysis confirmed the results of former studies on S. oppositifolia; high within, but low among population genetic variation and no particular geographical patterning. Some Alpine populations were not perfectly nested in this common gene pool and contained private RAPD markers, high molecular variance or rare cpDNA haplotypes, indicating that the species could possibly have survived on ice-free mountain tops (nunataks) in some parts of the Alps during the last glaciation. However, the overall lack of a geographical genetic pattern suggests that there was massive immigration of cpDNA and RAPD genotypes by seed and pollen flow during postglacial times. Thus, the glacial history of S. oppositifolia in the Alps appears to resemble closely that suggested previously for the species in northern Europe.

Austria↗
PubMed2002

The Baltic Sea as a model system for studying postglacial colonization and ecological differentiation, exemplified by the red alga Ceramium tenuicorne.

The Baltic Sea provides a unique model system for studying genetic effects of postglacial colonization and ecological differentiation, because all marine organisms must have immigrated after the opening of the Danish Straits 8000 years ago and responded to the development of the steep Skagerrak-Baltic salinity gradient. The red alga Ceramium tenuicorne shows conspicuous variation in growth and reproduction along this gradient. Herein we obtained reproductive data coupled with two types of molecular markers, one organellar (cox2-3 spacer sequences of mitochondrial DNA; mtDNA) and one mainly nuclear (random amplified polymorphic DNAs; RAPDs). Nine main populations were sampled in a nested spatial hierarchy including three salinity regions (Oslofjorden, Kattegat, and the Baltic Sea), and nine additional populations were sampled for the mtDNA analysis. Asexuality was frequent at low (Baltic) and medium (Kattegat) salinities but virtually absent at the highest salinity (Oslofjorden). Five mtDNA haplotypes were observed, of which two highly divergent ones were common. One was restricted to and fixed in Oslofjorden, and the other, which was closely related to the three rare haplotypes, was found from southernmost Norway via Kattegat into the Baltic. The RAPD data revealed, on the other hand, a continuous cline corresponding to the salinity gradient, with 27.4% divergence among salinity regions and most of the variation stored at the smallest spatial scale analysed (64.2%; within 1 m2 subpopulations). The combined data suggest colonization from a diverse Atlantic glacial gene pool followed by (1) lineage sorting of ancestral mtDNA polymorphisms and (2) strong differential selection among nuclear genotypes along the salinity gradient, including selection for nonrecombinant multiplication of those best fit to the marginal low-salinity habitats.

Adaptation, Physiological↗
PubMed2000

Frequent interspecific genetic exchange between commensal Neisseriae and Neisseria meningitidis.

Natural sequence variation was investigated among serogroup A subgroup IV-1 Neisseria meningitidis isolated from diseased patients and healthy carriers in The Gambia, West Africa. The frequencies of DNA import were analysed by sequencing fragments of four linked genes encoding the immunogenic outer membrane proteins TbpB (transferrin binding protein B) and OpaA (an adhesin) plus two housekeeping enzymes. Seventeen foreign tbpB alleles were independently imported into the 98 strains tested, apparently due to immune selection. The median size of the imported DNA fragments was 5 kb, resulting in the occasional concurrent import of linked housekeeping genes by hitchhiking. Sequences of tbpB from other strains of N. meningitidis as well as commensal Neisseria lactamica and Neisseria spp. isolated from the same geographical area revealed that these species share a common tbpB gene pool and identified several examples of interspecific genetic exchange. These observations indicate that recombination can be more frequent between related species than within a species and indicate that effective vaccination against serogroup B meningococcal disease may be difficult to achieve.

Amino Acid Sequence↗
PubMed2003

Prophages and bacterial genomics: what have we learned so far?

Bacterial genome nucleotide sequences are being completed at a rapid and increasing rate. Integrated virus genomes (prophages) are common in such genomes. Fifty-one of the 82 such genomes published to date carry prophages, and these contain 230 recognizable putative prophages. Prophages can constitute as much as 10-20% of a bacterium's genome and are major contributors to differences between individuals within species. Many of these prophages appear to be defective and are in a state of mutational decay. Prophages, including defective ones, can contribute important biological properties to their bacterial hosts. Therefore, if we are to comprehend bacterial genomes fully, it is essential that we are able to recognize accurately and understand their prophages from nucleotide sequence analysis. Analysis of the evolution of prophages can shed light on the evolution of both bacteriophages and their hosts. Comparison of the Rac prophages in the sequenced genomes of three Escherichia coli strains and the Pnm prophages in two Neisseria meningitidis strains suggests that some prophages can lie in residence for very long times, perhaps millions of years, and that recombination events have occurred between related prophages that reside at different locations in a bacterium's genome. In addition, many genes in defective prophages remain functional, so a significant portion of the temperate bacteriophage gene pool resides in prophages.

Base Sequence↗
PubMed2000

Predictors of weight gain: the biological-behavioural debate.

The rapidly increasing prevalence of obesity, in spite of an unchanged gene pool, makes it interesting to search for biological factors which increase the susceptibility at the individual level as well as searching for the responsible environmental factors. Among the identified metabolic factors is a low resting metabolic rate for given body size and composition, a high respiratory quotient (RQ) indicating a low fat oxidation and a low spontaneous physical activity, all factors which are regarded as being under substantial genetic influence. Among the environmental factors, it is low levels of physical activity, increasing inactivity and a high fat diet that are probably the most important ones. In this review we have focused on controversies in this area. Understanding the interaction between the constitutional biological factors and the environmentally determined lifestyle factors it is important to produce better options for both the prevention and treatment of obesity.

Animals↗
PubMed2003

A reassessment of genetic diversity in Icelanders: strong evidence from multiple loci for relative homogeneity caused by genetic drift.

There has been some controversy in the literature concerning whether Icelanders are genetically homogenous or heterogeneous relative to other European populations. We reassess this question in the light of large data sets spanning 83 autosomal SNP loci, 14 serogenetic loci, 6622 Y-chromosomes and 3214 sequences from mtDNA hypervariable segments 1 and 2 (HVS1 and HVS2). Our results strongly support the hypothesis that genetic drift, with a consequent loss of variation, has had a greater impact on Icelanders than most other Europeans. We also analyse 7245 HVS1 sequences from 25 European populations. In line with other studies, we observe a deficit of rare HVS1 haplotypes and an excess of intermediate frequency haplotypes in Icelanders compared to most European populations, with some measures of genetic diversity indicating relative heterogeneity and others indicating relative homogeneity of Icelanders. Simulations indicate that genetic drift, and not admixture (as proposed by Arnason, 2003) is the most likely cause of the atypical Icelandic HVS1 frequency spectrum. These simulations reveal that gene diversity (heterozygosity) and mean pairwise differences are largely insensitive to events in recent population history, while statistics based on the number of haplotypes or segregating sites are much more sensitive. Overall, our analyses strongly indicate that the Icelandic gene pool is less heterogeneous than those of most other European populations.

Chromosomes, Human, Y↗
PubMed1998

Spectrum of congenital heart disease in Malta. An excess of lesions causing right ventricular outflow tract obstruction in a population-base study.

AIMS: To quantify birth prevalence and spectrum of congenital heart disease in the Island population of Malta, and compare these rates with previous studies. METHODS: All patients diagnosed as having congenital heart disease by echocardiography, cardiac catheterization, surgery or post-mortem by 1 year of age between 1990-1994 were included. There were 231 cases of live born congenital heart disease with a birth prevalence of 8.8/1000 live births. The commonest lesions were ventricular septal defect, pulmonary stenosis and tetralogy of Fallot. The rates of individual lesions were compared with two recent epidemiological studies with similar methodologies. RESULTS: Although the overall birth prevalence of congenital heart disease was similar in three studies, significantly higher rates of pulmonary stenosis, tetralogy of Fallot and double outlet right ventricle were found in Malta, all of which predispose to right ventricular outflow tract obstruction. In contrast, there were lower rates of lesions causing left ventricular outflow tract obstruction. A higher rate of ventricular septal defect was also found. The Maltese gene pool may contain an inherent predisposition towards lesions causing right ventricular outflow tract obstruction.

Double Outlet Right Ventricle↗
PubMed1997

The metabolic syndrome: from inherited survival trait to a health care problem.

A critical role is proposed for the quantity and quality of dietary carbohydrate in the pathogenesis of the insulin resistance and hyperinsulinaemia which characterise the Metabolic Syndrome. We propose that an insulin-resistant genotype evolved to provide survival and reproductive advantages for the cold-climate, large game hunters of the last Ice Age who consumed a low carbohydrate, high protein diet with periodic starvation. Insulin resistance would have minimised glucose utilisation by muscles thereby facilitating the preferential utilisation of glucose by the brain, foetus and mammary gland. But beginning about 10,000 years ago following the end of the last Ice Age and the development of agriculture, dietary carbohydrate increased and the selection pressure for insulin resistance decreased in some groups. Agriculture began in the Middle East and spread throughout Europe long before it was developed elsewhere. Hence the prevalence of the insulin-resistant genotype decreased in Europeans and other groups exposed to a high carbohydrate intake for sufficiently long. Some geographically isolated groups such as the Pima Indians and Nauruans experienced conditions which further diminished the gene pool diversity and resulted in particularly insulin resistant populations. Traditional carbohydrate foods have a low glycaemic index and produce only modest increases in plasma insulin. However, the constant supply of highly refined high glycaemic index carbohydrate in modern diets, results in postprandial hyperinsulinaemia. The insulin-resistant genotype is now disadvantageous and predisposes to the development of the Metabolic Syndrome.

Blood Glucose↗
PubMed2002

Genetics in autoimmune hepatitis.

Current hypotheses suggest that autoimmune hepatitis (AIH) is triggered by an environmental factor in a genetically susceptible host. Multiple genes may interact to produce a "permissive gene pool" that determines both disease risk and phenotype. Studies of type 1 AIH have focused on the major histocompatibility complex (MHC), mapping susceptibility to the DRB1 region. Three different molecular models have been proposed based on histidine at DRbeta13, lysine at DRbeta71, and valine at DRbeta86. Although the lysine-71 model has been adapted to explain data from several other studies, the DRbeta13 and DRbeta86 models are exclusive to their founder populations. It is possible that all three models apply and that the different associations reflect the "molecular footprint" of the common environmental triggers in the different study populations. Studies outside the MHC have identified the CTLA4 A+49G, G allele as a possible second risk allele. There are many neutral polymorphisms in the genome, and further studies are currently needed to identify other disease alleles in type 1 AIH.

Hepatitis, Autoimmune↗
PubMedDate not supplied

Sterility.

Whether or not you are still swimming in the gene pool, if you are a member of a flight crew, this article is intended to help you avoid that ultimate form of sterility known as death. Sterile cockpit is an aviation term meaning the absence of nonessential conversation, not silence. This concept is really important to flight crews for a number of very exciting reasons.

Air Ambulances↗
PubMed2005

A MAPK gene from Dead Sea fungus confers stress tolerance to lithium salt and freezing-thawing: Prospects for saline agriculture.

The Dead Sea is one of the most saline lakes on earth ( approximately 340 g/liter salinity) and is approximately 10 times saltier than the oceans. Eurotium herbariorum, a common fungal species, was isolated from its water. EhHOG gene, encoding a mitogen-activated protein kinase (MAPK) that plays an essential role in the osmoregulatory pathway in yeast and many other eukaryotes, was isolated from E. herbariorum. The deduced amino acid sequences of EhHOG indicated high similarity with homologous genes from Aspergillus nidulans, Saccharomyces cerevisiae, and Schizosaccharomyces pombe and contained a TGY motif for phosphorylation by MAPK kinase. When EhHOG was expressed in S. cerevisiae hog1Delta mutant, the growth and aberrant morphology of hog1Delta mutant was restored under high osmotic stress condition. Moreover, intracellular glycerol content in the transformant increased to a much higher level than that in the mutant during salt-stress situations. hog1Delta mutant complemented by EhHOG outperformed the wild type or had higher genetic fitness under high Li(+) and freezing-thawing conditions. The present study revealed the putative presence of a high-osmolarity glycerol response (HOG) pathway in E. herbariorum and the significance of EhHOG in osmotic regulation, heat stress, freeze stress, and oxidative stress. The Dead Sea is becoming increasingly more saline while the fungi living in it evolutionarily adapt to its high-saline environment, particularly with the extraordinarily high Li(+) concentration. The Dead Sea is potentially an excellent model for studies of evolution under extreme environments and is an important gene pool for future agricultural genetic engineering prospects.

Agriculture↗
PubMed2026

Ancient DNA reveals early use of melons in China's Song dynasty.

Melon (Cucumis melo L.) domestication is thought to have occurred independently once in Northeast Africa and twice in India, but archaeobotanical seed remains point to a possible additional domestication event in China. Because Cucumis seeds are difficult to diagnose morphologically, genomic data from archaeological material are needed to evaluate these scenarios and reconstruct ancient melon traits. We sequenced two Song Dynasty (960-1279 CE) melon seeds from Shuomen Gugang (China), recovering 5.5× and 2.1× nuclear genome coverage. Nuclear and chloroplast analyses place both seeds within cultivated C. melo from China, within the "agrestis" East Asian gene pool. To assess whether these seeds carried traits associated with sweet dessert melons, we examined loci underlying fruit phenotypes. Neither seed carried alleles for orange flesh; one harbored an allele linked to yellow/orange peel, the other possessed alleles associated with green flesh and reduced acidity. Since wild melons are monoecious, the presence of the derived andromonoecy allele in one seed, associated with rounder fruit shape, suggests early selection on fruit morphology. Together, these findings indicate that Song Dynasty melons were likely consumed as fresh or culinary fruits rather than sweet dessert melons. Their flesh coloration resonates with Song-period aesthetic sensibilities, exemplified by jade-green celadon ceramics frequently crafted in melon-shaped forms. By anchoring East Asian archaeobotanical remains within modern melon genomic variation, this study provides a temporal framework for melon cultivation in China and shows how ancient genomics can illuminate past crop use.

China↗
PubMed1970

Ecological consequences of island colonization by southwest Pacific birds. II. The effect of species diversity on total population density.

Among southwest Pacific birds colonizing a species-poor island from a species-rich island, spatial expansion of the niche to include a wider range of altitudes, habitats, or vertical strata is often an immediate response, while changes in foraging techniques and diet usually occur more slowly and require genotypic change. Despite occupation of spatially broader niches by some colonizing species and increases in abundance by others, the total population density of the whole avifauna is up to nine times lower on a species-poor island than in a comparable habitat on a species-rich island. Total population density varies among islands approximately linearly with the number of species in the lowlands, supralinearly at higher elevations. Part of the explanation is that many birds on small islands expand into niche space which is suboptimal for them and from which they would be excluded by species utilizing this niche space optimally on a species-rich island. The other suggested explanation is an intrinsic inefficiency or loss of fitness among populations on small Pacific islands compared to large-island populations, due to impoverished gene pools, reduced selection pressure, and low degree of endemism.

Animals↗
PubMed1975

Allozymic and chromosomal similarity in two Drosophila species.

D. setosimentum and ochrobasis are a pair of very close, partly sympatric species endemic to Hawaii island. Males of the two species differ strikingly in wing-pattern and there are altitudinal and breeding-site differences. Similarity indices have been calculated for both chromosomal (C) ald allozymic (A) variants. Within the main populations of each species both kinds of data give coefficients above 0.98. Interspecific comparison of the main populations shows 0.66 (C) and 0.79 (A). An isolated population of ochrobasis from Kohala Volcano (Ohu), when compared with setosimentum, shows 0.68 (C) and 0.98 (A). Chromosomes are thus much more sensitive than allozymes in distinguishing these species; the same is true in the case of D. silvestris and heteroneura from the same forests. These morphologically distinct species, when compared, show 0.96 (A). All four species appear to be very new in the historical sense. In one area, about 2% of wild-caught D. setosimentum/ochrobasis are interspecific hybrids although adequate samples indicate that the separate gene pools have not broken down. The specific names should be retained but the two entities are perhaps best described as quite advanced semispecies in which reproductive isolation in nature is now nearly complete.

Animals↗
PubMed1986

Mitochondrial DNA analysis of hybridization between sympatric white-tailed deer and mule deer in west Texas.

Sympatric populations of white-tailed deer and mule deer (Odocoileus virginianus and Odocoileus hemionus, respectively) on a west Texas ranch share a common mitochondrial DNA restriction map genotype. Phylogenetic analysis indicates that this genotype is more characteristic of O. virginianus than of O. hemionus. The genotype of west Texas deer differs from that of O. virginianus from South Carolina by five mutational events (1.3% sequence divergence), whereas it differs from that of O. hemionus from California by 17 events (5.5% divergence). We suggest that interspecies hybridization has occurred, primarily between mule deer bucks and white-tailed deer does, with preferential absorption of hybrid offspring into the mule deer gene pool. Introgressive hybridization may be involved in ongoing displacement of mule deer by white-tailed deer in west Texas.

Animals↗
PubMed1989

Chromosomal inversion patterning and population differentiation in a young insular species, Drosophila silvestris.

The recently evolved Hawaiian species Drosophila silvestris has a subdivided population structure and shows great spatial heterogeneity in chromosome inversion distributions and frequencies within its extremely limited geographic range. Pattern analysis of the 11 chromosomal polymorphisms in the context of the recently discovered morphological and behavioral divergence within the species has elucidated the history of the chromosomal differentiation. We identify four chronological groups of inversions and their probable sites of origin. Spread of the derived "3-row" bristle morphotype on the Hilo side of the Island of Hawaii has been accompanied by the acquisition of six new inversion polymorphisms. Three phylogenetically old inversions show correlations with altitude, and there are multiple cross-correlations between inversions on the same and different chromosomes, reflecting complex interaction systems. Quantification of the genetic population structure of D. silvestris by hierarchical F statistics reveals a dramatic level of genetic differentiation for an evolutionarily new species of such restricted range. This level exceeds that of older, continental Drosophila species. There is, however, minimal concordance between the chromosomal variation and the morphological-behavioral discontinuity, a consequence of the extensive cytological variation within each morphotype. Such a fragmented gene pool favors the rapid evolution and continued divergence of this insular species.

Animals↗
PubMed1997

Endosperm balance number manipulation for direct in vivo germplasm introgression to potato from a sexually isolated relative (Solanum commersonii Dun.).

Diploid (2n = 2x = 24) Solanum species with endosperm balance number (EBN) = 1 are sexually isolated from diploid 2EBN species and both tetraploid (2n = 4x = 48, 4EBN) and haploid (2n = 2x = 24, 2EBN) S. tuberosum Group Tuberosum. To sexually overcome these crossing barriers in the diploid species S. commersonii (1EBN), the manipulation of the EBN was accomplished by scaling up and down ploidy levels. Triploid F1 hybrids between an in vitro-doubled clone of S. commersonii (2n = 4x = 48, 2EBN) and diploid 2EBN clones were successfully used in 3x x 4x crosses with S. tuberosum Group Tuberosum, resulting in pentaploid/near pentaploid BC1 progenies. This provided evidence of 2n (3x) egg formation in the triploid female parents. Two selected BC1 pentaploid hybrids were successfully backcrossed both as male and as female parents with S. tuberosum Group Tuberosum. The somatic chromosome number varied greatly among the resulting BC2 progenies, which included hyperaneuploids, but also a number (4.8%) of 48-chromosome plants. The introgression of S. commersonii genomes was confirmed by the presence of S. commersonii-specific randomly amplified polymorphic DNA markers in the BC2 population analyzed. The results clearly demonstrate the feasibility of germplasm introgression from sexually isolated diploid 1EBN species into the 4x (4EBN) gene pool of the cultivated potato using sexual hybridization. Based on the amount and type of genetic variation generated, cumbersomeness, general applicability, costs, and other factors, it would be interesting to compare the approach reported here with other in vitro or in vivo, direct or indirect, approaches previously reported.

Journal Article↗
PubMed1992

The relationship between homozygosity and the occurrence of specific diseases in Bouvier Belge des Flandres dogs in The Netherlands.

Since purebred dog populations represent closed gene pools, a relatively high level of consanguinity between individuals, and hence of inbreeding, is common. This case control study was conducted to establish the possible connection between the actual level of homozygosity due to inbreeding and specific diseases (flea allergy, osteochondrosis, laryngeal paralysis, neoplasm, autoimmune disease, hypoplastic trachea, and food allergy) occurring in the Bouvier Belge des Flandres breed. One hundred and sixty-eight animals referred to the Utrecht University Clinic formed the patient group. Each of the seven diseases was chosen because of the demonstrability of the diagnosis. Each animal was chosen because one of the selected diseases was established in that individual, and because its pedigree was complete. All dogs of the patient group were born between 1 January 1980 and 31 December 1985. A control group (n = 123) was randomly chosen from the total population of registered Bouviers born in the Netherlands in the same period. pedigree data were obtained from the Dutch Kennel Club. The extent of inbreeding was determined for all animals using Wright's inbreeding coefficient. The distribution of inbreeding coefficients in each patient group was compared with the distribution in controls. Inbreeding coefficients in the control group ranged from 0.0 to 0.406. Animals in which osteochondrosis, food allergy, autoimmune disease, neoplasm, or hypoplastic trachea was diagnosed had higher inbreeding coefficients than controls. It was concluded that in the Bouvier Belge des Flandres dog population examined, the level of homozygosity was positively correlated with occurrence of these diseases.

Animals↗