SEARCH · PubMed Health

Results for “Genetic Variation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 649 records · Page 36Linked to original sources

PubMed1998

Genetic variation and differentiation at microsatellite loci in Drosophila simulans. Evidence for founder effects in new world populations.

Drosophila simulans isofemale lines from Africa, South America, and two locations in North America were surveyed for variation at 16 microsatellite loci on the X, second, and third chromosomes, and 18 microsatellites, which are unmapped. D. simulans is thought to have colonized New World habitats only relatively recently (within the last few hundred years). Consistent with a founder effect occurring as colonizers moved into these New World habitats, we find less microsatellite variability in North and South American D. simulans populations than for an African population. Population subdivision as measured at microsatellites is moderate when averaged across all loci (FST = 0.136), but contrasts sharply with previous studies of allozyme variation, which have showed significantly less differentiation in D. simulans than in D. melanogaster. There are substantially fewer private alleles observed in New World populations of D. simulans than seen in a similar survey of D. melanogaster. In addition to possible differences in population size during their evolutionary histories, varying colonization histories or other demographic events may be necessary to explain discrepancies in the patterns of variation observed at various genetic markers between these closely related species.

Animals↗

PubMed2005

Patterns of genetic variation do not correlate with geographical distance in the reef-building coral Pocillopora meandrina in the South Pacific.

Dispersal may be a critical factor in the ability of reef-building corals to recover after major disturbances. We studied patterns of geographical structure using four microsatellite markers in seven South Pacific populations of Pocillopora meandrina, a major coral species from Polynesia. Variation within populations showed evidence of heterozygote deficiency. Genetic differentiation between populations was detected at a large scale (2000 km) between the Tonga and the Society Islands. Within the Society Islands, four of the five studied populations from Bora Bora, Moorea and Tahiti were not significantly different from each other. Unexpectedly, one of the three populations surveyed in Moorea was genetically different from the other two populations of this island (that were 5 and 10 km apart), and from the populations of the other two surveyed islands in this archipelago. We cannot rule out the possibility that this pattern is an equilibrium state, whereby short-range dispersal is locally more differentiating than long-range dispersal, as has been suggested by similar patterns reported in other studies. An alternative explanation that is globally consistent with all observations is that this is the signature of a large-scale destruction event, as for instance a bleaching event, followed by the recent restoration of populations by new colonists.

Animals↗

PubMed2000

An analysis of genetic variation in natural populations of Sticherus flabellatus [R. Br. (St John)] using amplified fragment length polymorphism (AFLP) markers.

Amplified fragment length polymorphisms (AFLPs) were used to characterize the genetic diversity within and among natural populations of Sticherus flabellatus. Eight populations within the Sydney region of New South Wales, Australia were surveyed using 11 primer combinations. A total of 1108 reproducible bands were detected of which 469 (42%) were polymorphic. FST estimates averaged over all polymorphic loci indicated that significant genomic differentiation occurs among populations (average = 0.783). Genetic diversity within populations was assessed according to average heterozygosity (H) and percentage polymorphic loci (P) per population. Within-population diversity ranged from H = 0.12 and P = 33.69 to H = 0.04 and P = 15.99. Analysis of genetic similarity among populations suggested that the eight populations studied fall into two groups of four populations, based on population size and the condition of the habitat. Phenetic analysis (AMOVA) indicated that genetic variation is greater among populations (74.34%) than within populations (25.66%). These findings suggest that the breeding system of S. flabellatus is predominantly inbreeding, with genetic diversity maintained by occasional outcrossing in larger populations. The results presented in this study could provide evidence to support the proposal to protect natural stands of S. flabellatus, which has implications for the Australian horticulture industry.

Crosses, Genetic↗

PubMed2000

Genetic variation among populations of the Hessian fly Mayetiola destructor (Diptera: Cecidomyiidae) in Morocco and Syria.

The RAPD-PCR technique was used to study genetic variation within and among geographical populations of the Hessian fly, Mayetiola destructor (Say), from Morocco and Syria, associated with the fly's ability to overcome resistance in three wheat cultivars containing H5, H13 and H22 resistance genes. Variation was detected both for the level of susceptibility of the cultivars and RAPD profiles of M. destructor populations. By the use of RAPD-PCR, high genetic variability was detected among individuals and populations of M. destructor within and between areas separated geographically. The DNA fingerprints of populations of M. destructor were area-specific with Nei's measures of genetic distance ranging from 0.156 (between Abda and Beni Mellal, Morocco) to 1.977 (between Marchouch, Morocco and Lattakia, Syria). Cluster analysis of the genetic distances among the populations, identified the Syrian population as an outlier. A highly significant correlation (r = 0.81) observed between the genetic and geographic distances among the populations, provided genetic support for dispersal of the fly from its presumed origin in West Asia to Morocco.

Animals↗

PubMed1986

Genetic variation in HTLV-III/LAV over time in patients with AIDS or at risk for AIDS.

In a study of genetic variation in the AIDS virus, HTLV-III/LAV, sequential virus isolates from persistently infected individuals were examined by Southern blot genomic analysis, molecular cloning, and nucleotide sequencing. Four to six virus isolates were obtained from each of three individuals over a 1-year or 2-year period. Changes were detected throughout the viral genomes and consisted of isolated and clustered nucleotide point mutations as well as short deletions or insertions. Results from genomic restriction mapping and nucleotide sequence comparisons indicated that viruses isolated sequentially had evolved in parallel from a common progenitor virus. The rate of evolution of HTLV-III/LAV was estimated to be at least 10(-3) nucleotide substitutions per site per year for the env gene and 10(-4) for the gag gene, values a millionfold greater than for most DNA genomes. Despite this relatively rapid rate of sequence divergence, virus isolates from any one patient were all much more related to each other than to viruses from other individuals. In view of the substantial heterogeneity among most independent HTLV-III/LAV isolates, the repeated isolation from a given individual of only highly related viruses raises the possibility that some type of interference mechanism may prevent simultaneous infection by more than one major genotypic form of the virus.

Acquired Immunodeficiency Syndrome↗

PubMed2005

Genetic variation in selenoprotein S influences inflammatory response.

Chronic inflammation has a pathological role in many common diseases and is influenced by both genetic and environmental factors. Here we assess the role of genetic variation in selenoprotein S (SEPS1, also called SELS or SELENOS), a gene involved in stress response in the endoplasmic reticulum and inflammation control. After resequencing SEPS1, we genotyped 13 SNPs in 522 individuals from 92 families. As inflammation biomarkers, we measured plasma levels of IL-6, IL-1beta and TNF-alpha. Bayesian quantitative trait nucleotide analysis identified associations between SEPS1 polymorphisms and all three proinflammatory cytokines. One promoter variant, -105G --> A, showed strong evidence for an association with each cytokine (multivariate P = 0.0000002). Functional analysis of this polymorphism showed that the A variant significantly impaired SEPS1 expression after exposure to endoplasmic reticulum stress agents (P = 0.00006). Furthermore, suppression of SEPS1 by short interfering RNA in macrophage cells increased the release of IL-6 and TNF-alpha. To investigate further the significance of the observed associations, we genotyped -105G --> A in 419 Mexican American individuals from 23 families for replication. This analysis confirmed a significant association with both TNF-alpha (P = 0.0049) and IL-1beta (P = 0.0101). These results provide a direct mechanistic link between SEPS1 and the production of inflammatory cytokines and suggest that SEPS1 has a role in mediating inflammation.

Adult↗

PubMed1976

Genetic variation in two widespread species of salamanders, Taricha granulosa and Taricha torosa.

Two species of the genus Taricha are widely distributed. T. granulosa ranges from southern Alaska to central California. T. torosa is comprised of two described subspecies, T. t. torosa, which occupies much of the coast ranges of California, and T. t. sierrae, which inhabits the western slopes of the Sierra Nevada Mountains. A starch gel electrophoretic survey for genetic variation at 34 loci in four population samples of T. granulosa and at 40 loci in five population samples of T. torosa reveals differences among these taxa both in amounts of intrapopulational variability and in patterns of geographic variation. Average observed heterozygosity is 9.6% +/- 0.3% in T. granulosa, 3.3% +/- 0.5% in T. t. torosa, and 7.2% +/- 1.2% in T. t. sierrae. Average numbers of alleles per lon T. t. sierrae, and lowest in T. t. torosa. Oregon and California granulosa are genetically nearly as different as the subspecies of torosa, but geographic variation is continuous in the former. T. torosa on the other hand is comprised of three distinct gene pools--T. t. sierrae and northern and southern races of T. t. torosa. Strikingly different amounts of intrapopulational genetic variation and patterns of geographic variation may be explained by steady-state species differences, but historical causes may also exist.

Animals↗

PubMed1992

The molecular through ecological genetics of abnormal abdomen. IV. Components of genetic variation in a natural population of Drosophila mercatorum.

Natural populations of Drosophila mercatorum are polymorphic for a phenotypic syndrome known as abnormal abdomen (aa). This syndrome is characterized by a slow-down in egg-to-adult developmental time, retention of juvenile abdominal cuticle in the adult, increased early female fecundity, and decreased adult longevity. Previous studies revealed that the expression of this syndrome in females is controlled by two closely linked X chromosomal elements: the occurrence of an R1 insert in a third or more of the X-linked 28S ribosomal genes (rDNA), and the failure of replicative selection favoring uninserted 28S genes in larval polytene tissues. The expression of this syndrome in males in a laboratory stock was associated with the deletion of the rDNA normally found on the Y chromosome. In this paper we quantify the levels of genetic variation for these three components in a natural population of Drosophila mercatorum found near Kamuela, Hawaii. Extensive variation is found in the natural population for both of the X-linked components. Moreover, there is a significant association between variation in the proportion of R1 inserted 28S genes with allelic variation at the underreplication (ur) locus such that both of the necessary components for aa expression in females tend to cosegregate in the natural population. Accordingly, these two closely linked X chromosomal elements are behaving as a supergene in the natural population. Because of this association, we do not believe the R1 insert to be actively transposing to an appreciable extent. The Y chromosomes extracted from nature are also polymorphic, with 16% of the Ys lacking the Y-specific rDNA marker. The absence of this marker is significantly associated with the expression of aa in males. Hence, all three of the major genetic determinants of the abnormal abdomen syndrome are polymorphic in this natural population.

Abdomen↗

PubMed2003

Characterization of genetic variation in and phylogenetic relationships among diploid Aegilops species by AFLP: incongruity of chloroplast and nuclear data.

Intra- and inter-specific genetic variation was investigated in seven diploid Aegilops species using the amplified fragment length polymorphism (AFLP) technique. Of the seven species, the cross-pollinating Aegilops speltoides and Aegilops mutica showed high levels of intraspecific variation whereas the remaining five self-pollinating species showed low levels. Aegilops bicornis, Aegilops searsii and Ae. speltoides formed one cluster in the dendrograms, while Aegilops caudata and Aegilops umbellulata formed another. Relationships among the species inferred were more consistent with the relationships inferred from studies of chromosome pairing in interspecific hybrids, and previous molecular phylogenetic reconstructions based on nuclear DNA, than they were with those based on molecular plasmon analysis, suggesting that the nuclear genome has evolved differently from the cytoplasmic genome in the genus Aegilops.

DNA Primers↗

PubMed2004

Genetic variation in structure-function relationships for the inbred mouse lumbar vertebral body.

UNLABELLED: Structure-function relationships were determined for L(5) vertebral bodies from three inbred mouse strains. Genetic variability in whole bone mechanical properties could be explained by a combination of the traits specifying the amount, distribution, and quality of the cortical and trabecular bone tissue. INTRODUCTION: Although phenotypically correlated with fracture, BMD may be disadvantageous to use in genetic and biomechanical analyses because BMD does not distinguish the contributions of the underlying morphological and compositional bone traits. Developing functional relationships between the underlying bone traits and whole bone mechanical properties should further our understanding of the genetics of bone fragility. MATERIALS AND METHODS: Microarchitecture and composition of L(5) vertebral bodies (n = 10/strain) from A/J, C57BL/6J, and C3H/HeJ inbred mouse strains were determined using muCT with an isotropic voxel size of 16 mum(3). Failure load, stiffness, and total deformation as a measure of ductility were measured in compression using a noncontact strain extensometer imaging system. A correlation analysis related morphological and compositional bone traits to whole bone mechanical properties. A multivariate analysis identified structure-function relationships for each genotype. RESULTS: No single bone trait accurately explained the genetic variation in mechanical properties. However, a combination of traits describing the amount, distribution, and quality of cortical and trabecular bone tissue explained >70% of the variation in vertebral mechanical properties. Importantly, structure-function relationships were unique among genotypes. CONCLUSIONS: Different genetic backgrounds use different combinations of underlying bone traits to create mechanically functional structures. Using a single complex trait such as BMD or BV/TV as the sole phenotypic marker in genetic analyses may prove to be disadvantageous because of the complex relationship between mechanical properties and the underlying bone traits. Therefore, considering multiple bone traits and the interaction among these bone traits is necessary to understand the relationship between genetic background and complex whole bone mechanical properties.

Analysis of Variance↗

PubMed1996

Use of PCR-RFLP assays to detect genetic variation at single-copy nuclear loci in striped bass (Morone saxatilis).

We developed three assays that detect genetic variation at single-copy nuclear loci in striped bass (Morone saxatilis). Because these assays are based on restriction enzyme digests of DNA amplified by the polymerase chain reaction (PCR-RFLP), they are easy to perform on large numbers of samples. Breeding trials demonstrated that the alleles identified in each of the three assays are inherited in a Mendelian fashion as codominant alleles at single-copy loci. To demonstrate the utility of these PCR-RFLP assays, we compared the genetic composition of striped bass populations from the Congaree River in South Carolina and from the Choptank River in Maryland. Allele frequencies were significantly different at the SB14 locus, suggesting that the two populations may be genetically distinct. Furthermore, during the development of the PCR-RFLP assays, we demonstrated that the GT(n) microsatellite-associated DNA regions (MSA regions) contained RFLPs at a frequency 9-fold higher than that observed for randomly chosen segments of DNA. If MSA regions proved to be variable in other organisms as well, they could provide a valuable source of intraspecific variation.

Animals↗

PubMed1975

Implications of genetic variation in mouse brain structure for electrode placement by stereotaxic surgery.

The spatial locations of several forebrain and midbrain fibre tracts have been compared across seven commonly used inbred, hybrid and outbred mouse strains using a series of electrolytic lesions of known positions with respect to a stereotaxic instrument. Highly significant genetic variation was found in the position of lambda, bregma and several major fibre tracts with respect to interaural zero; in the locations of fibre tracts with respect to bregma; and in the location of fibre tracts with respect to each other. It was demonstrated that stereotaxic coordinates of a structure for one strain could not be used for other strains. Errors resulting from improper alignment of the head in the instrument and histological artifact were also determined. These errors showed no significant group differences, but they revealed that within-group variation was substantially affected by such imperfections.

Animals↗

PubMed1987

Dietary fat clearance in normal subjects is regulated by genetic variation in apolipoprotein E.

Apolipoprotein E (apo E) plays an important role in receptor mediated clearance of lipoprotein particles from plasma. Common genetic variation in apo E exists with three alleles coding for proteins called E2, E3, and E4. In in vitro receptor binding assays, E2 binds poorly, whereas E3 and E4 function normally. Recently, the apo E phenotype has been shown to have an effect on low density lipoprotein (LDL) cholesterol levels with levels in subjects with E2 lower and E4 higher than E3. We have examined the effect of the apo E polymorphism on dietary fat clearance using the vitamin A-fat loading test, which specifically labels intestinally derived lipoproteins with retinyl palmitate (RP). 27 normal subjects were studied, 10 with E3/3, 9 with E3/2, 7 with E4/3, and 1 with E4/4. After a vitamin A-containing fatty meal, postprandial RP concentrations were measured in chylomicron (Sf greater than 1,000) and nonchylomicron (Sf less than 1,000) fractions for 14 h. Compared with E3/3 subjects, E3/2 subjects had a significantly higher nonchylomicron RP concentration (P less than 0.05) (peak heights and areas below the curves) indicating slower clearance and the E4/3, E4/4 group had a significantly lower nonchylomicron RP concentration (P less than 0.05) indicating faster clearance. The clearance in the latter group was twice that of E3/2 subjects (P less than 0.01). Thus, heterozygosity for the defective form of apo E, E2, delays, and the surprising presence of a functionally normal allele, E4, increases clearance. This apo E effect on exogenous fat clearance may explain the recently described effect of the apo E phenotypes on LDL cholesterol levels.

Adult↗

PubMed1985

Clinal genetic variation at enzyme loci in bald eagles (Haliaeetus leucocephalus) from the western United States.

Five polymorphic enzyme loci of about 50 sampled were discovered in blood extracts of bald eagles from Alaska, Washington, Oregon, and Arizona, representing the first biochemical genetic variation described for the species. All five loci exhibited trends of north-to-south clinal geographic variation in gene frequencies. Gene frequencies at three loci culminated in fixation in the Arizona population, which consists of 12 known breeding pairs. The Arizona birds were maximally heterozygous at the other two loci, suggesting the possibility of maintenance of some clines by natural selection. No significant discontinuities in gene frequencies were observed which correlated with earlier descriptions of two subspecies (northern and southern races) of bald eagles.

Animals↗

PubMed2003

Hybrid origin of a cichlid population in Lake Malawi: implications for genetic variation and species diversity.

The importance of species recognition to taxonomic diversity among Lake Malawi cichlids has been frequently discussed. Hybridization - the apparent breakdown of species recognition - has been observed sporadically among cichlids and has been viewed as both a constructive and a destructive force with respect to species diversity. Here we provide genetic evidence of a natural hybrid cichlid population with a unique colour phenotype and elevated levels of genetic variation. We discuss the potential evolutionary consequences of interspecific hybridization in Lake Malawi cichlids and propose that the role of hybridization in generating both genetic variability and species diversity of Lake Malawi cichlids warrants further consideration.

Animals↗

PubMed2001

Haptoglobin polymorphism and schizophrenia: genetic variation on chromosome 16.

Recently, it was shown that schizophrenia is accompanied by an activation of the inflammatory response system with signs of an acute phase response, such as increased plasma haptoglobin (Hp) concentrations. Hp is characterized by a molecular variation with three known phenotypes, i.e. Hp 1-1, Hp 2-1 and Hp 2-2. The aim of the present study was to examine Hp phenotypic and genotypic frequencies in schizophrenic patients. Hp phenotyping was carried out in 98 Northwestern Italian schizophrenic patients and the phenotypic and genotypic distributions were compared with the distributions established in the Northwestern Italian population. Plasma Hp concentrations were determined by means of a laser nephelometric method. The allele frequency of the Hp phenotypes in schizophrenia, i.e. Hp 1-1 (9.2%), Hp 2-1 (38.8%) and Hp 2-2 (52.0%), was significantly different from that in the Northwestern Italian population, i.e. Hp 1-1 (17.0%), Hp 2-1 (51.3%) and Hp 2-2 (38.5%). The frequency of the Hp-2 gene was significantly higher in schizophrenic patients (71.7%) as compared with the observed frequency in the Northwestern Italian population (62.5%). The alterations in Hp phenotypic and genotypic distribution were more pronounced in the schizo-affective, disorganized, undifferentiated and residual schizophrenic patients than in paranoid schizophrenic patients. More than a third (35.7%) of the schizophrenic patients showed plasma Hp concentrations which were higher than the upper limits of normality. Schizophrenia is accompanied by an altered distribution of the Hp phenotypes and genotypes, suggesting that genetic variation on chromosome 16 may be associated with schizophrenia.

Adult↗

PubMed1999

A note on the relevance of human population genetic variation and molecular epidemiology to assessing radiation health risk for space travellers.

We discuss the relevance to space medicine of studies concerning human genetic variation and consequent variable disease susceptibility or sensitivity between individuals. The size of astronaut and cosmonaut populations is both presently and cumulatively small, and despite the launch of the International Space Station, unlikely to increase by orders of magnitude within the foreseeable future. In addition, astronauts-cosmonauts constitute unrepresentative samples of their national populations. While the context of exposure for the astronaut-cosmonaut group is one unlikely to be replicated elsewhere than in space, aspects of specific exposures may be simulated by events such as occupational radiation exposure or radiation therapy. Hence, population-based studies of genetic susceptibility or sensitivity to disease, especially where it is precipitated by events that may simulate consequences of the space environment, likely will prove of value in assessing long-term health risks.

Astronauts↗

PubMed1990

Genetic variation for oviposition behavior in Drosophila melanogaster. I. Quantitative genetic analysis of insertion behavior.

The genetic basis of egg insertion behavior was analyzed in two Drosophila melanogaster strains (N and E strain), which were homozygous for the Slow allele of the alcohol dehydrogenase locus. The E strain had been selected for increased tolerance to ethanol. This study originated from the observation that nearly all of the eggs laid by females of the E strain were inserted, while in the control strain (N strain) which was kept on regular food, considerable variation for egg insertion occurred. Crosses between the E and the N strains were made, and quantitative genetic tests were performed. It was shown that the inheritance of egg insertion is polygenic, some of the genes are probably sex linked, and in-laying is partly dominant over on-laying. The heritability of the trait, derived from mother-daughter regression analysis, was .59 +/- .18. The repeatability was high. Bidirectional selection in the E strain was unsuccessful, but an asymmetrical response to selection was obtained in the N strain and in lines derived from crosses between the N and the E strains. Selection for in-laying was more successful than for on-laying. The realized heritability in the former lines was .35 +/- .10.

Alcohol Dehydrogenase↗