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 55 records · Page 3Linked to original sources

PubMed1985

Two-dimensional gel studies of genetic variation in the plasma proteins of Amerindians and Japanese.

Genetic variation has been studied in plasma samples from 107 Amerindian children and their parents, and 110 Japanese children and their parents by means of two-dimensional polyacrylamide gel electrophoresis. Twenty-three polypeptides were scored; the identity of nine of these is at present still unknown. Genetic variation was encountered in 11 of these polypeptides. We have previously reported that the index of heterozygosity was 6.2 +/- 0.7% for 20 "randomly selected", silver stained polypeptides scored for genetic variation in Caucasoids (Rosenblum et al. 1983b). For technical reasons only 11 of these 20 polypeptides could be routinely scored in preparations from the Amerindian samples. For these 11 polypeptides, the indices of heterozygosity in the three populations were: Amerindians, 4.5 +/- 0.6%; Japanese, 5.7 +/- 0.7%; Caucasoids, 8.0 +/- 1.1%. Even with these relatively small numbers some striking ethnic differences as regards individual polypeptides are apparent.

Adult↗

PubMed1980

Genetical variation for enzyme activity in a population of Drosophila melanogaster. V. The genetical architecture, as shown by diallel analysis, of alcohol dehydrogenase (ADH) activity.

Fifteen highly inbred lines extracted by sib-mating from the laboratory cage population, "Texas", of Drosophila melanogaster were crossed in a half-diallel mating design. Female progeny were assayed individually for ADH activity at 25 degrees and 35 degrees C and for total protein. At 25 degrees C there was considerable additive genetical variation and the dominance variation was attributable to specific parents and to specific crosses at random in the diallel table. The character total protein also showed considerable additive variation but less dominance variation. Largely independent gene action was shown by the characters ADH activity and total protein. There were strong genotype-environment interactions for heat-stability. At 35 degrees C most of the genetical variation was additive and mainly due to modifier loci. It was concluded that at 25 degrees C dominance was ambidirectional and almost complete. This genetical architecture was compatible with a past history of stabilising selection for ADH activity in the "Texas" population.

Alcohol Oxidoreductases↗

PubMed2025

Gut fungi are associated with human genetic variation and disease risk.

Human genetic determinants of the gut mycobiome remain uninvestigated despite decades of research highlighting tripartite relationships between gut bacteria, genetic background, and disease. Here, we present the first genome-wide association study on the number and types of human genetic loci influencing gut fungi relative abundance. We detect 148 fungi-associated variants (FAVs) across 7 chromosomes that statistically associate with 9 fungal taxa. Of these FAVs, several occur in the protein-coding genes PTPRC, ANAPC10, NAV2, and CDH13. Additional FAVs link to tissue-specific gene expression as fungi-associated expression quantitative trait loci. Notably, the relative abundance of gut yeast Kazachstania associates with genetic variation in CDH13 encoding T-cadherin, a protein linked to cardiovascular disease. Kazachstania forms a causal relationship with cardiovascular disease risk in a mendelian two-sample randomization analysis. These findings establish previously unrecognized connections between human genetics, gut fungi, and chronic disease, broadening the paradigm of human-microbe interactions in the gut to the mycobiome.

Humans↗

PubMed1996

Genetic variation in the population of Ibiza (Spain): genetic structure, geography, and language.

A sample of 203 individuals from Ibiza (Balearic Islands, Spain) were tested for blood group and serum protein genetic variation and compared with other circum-Mediterranean populations. Allele frequencies were calculated for the following blood group and serum systems: ABO, Rh, MNSs, P, Lewis, Duffy, Kell, ORM, GC, TF, PI, and HP. The allele frequencies from Ibiza were compared with those from other Balearic Islands (Majorca and Minorca) and with related European and North African groups using an assortment of analytical methods (genetic distances, R matrix analysis, and Mantel tests). R matrix analysis revealed that Ibiza is genetically different from the other Balearic populations and, because of gene flow from Spain, clusters with European groups. The level of genetic microdifferentiation of the Mediterranean populations, measured by RST (average of the R matrix diagonal elements, rii), is 0.028. An examination of the relationship between genetic, geographic, and linguistic distances by Mantel tests revealed that genetic distances are significantly correlated with linguistic distances, whereas the genetic distances are not significantly correlated with geographic distances. The plot of mean per locus heterozygosity versus the genetic distance from the centroid of distribution revealed that all three Balearic Islands have experienced considerable gene flow but that Ibiza has been most affected by the action of stochastic processes.

Blood Group Antigens↗

PubMedDate not supplied

Substantial genetic variation in southern African black rhinoceros (Diceros bicornis).

Thirty protein-coding loci of southern African black rhinoceros (Diceros bicornis) from four isolated populations were studied using starch gel electrophoresis and polyacrylamide gel electrophoresis. Gene diversity estimates varied between 0.036 and 0.058, with the Zambezi Valley population having the largest amount of protein variation. These levels are higher than those in other studies of genetic variation in black rhinoceros and are similar to the amount of genetic variation observed for outbred natural populations that are not genetically depauperate. Because the observed levels of genetic variation vastly exceed the expectations for current effective population sizes, the current levels apparently reflect large black rhinoceros populations which have existed until recently. Observed levels of genetic variation within populations are consistent with the expectations when recent demographic events are taken into account.

Africa, Southern↗

PubMed1983

Solomon Islander skin pigmentation: ultrastructural differences related to genetic variation in Melanesia.

Genetic differences between Solomon Islander populations are distinguishable on the basis of melanosome packaging in epidermal keratinocytes. By electron microscopic study of skin pigmentation in various Melanesian populations, we have found distinct inter-island differences in the mode of melanosome packaging. Melanosomes are found as singlets in the skin of Bougainville Islanders but are found aggregated in melanosome complexes in Malaita Islanders and Ontong Javanese. This variation in melanosome packaging represents an important biologic difference found between Solomon Islanders and may reflect the genetic diversity existing in the original Melanesian founding population or the genetic diversity existing in the original Melanesian founding population or populations.

Genetic Variation↗

PubMed1979

Genetic variation in prenatal survival and litter size.

The nature of genetic variation in litter size and its components was examined using results of long term selection and of crossing selected lines of mice. Selection for small and for large litters produced strains with mean litter size of approximately 6 and 15, respectively. The large litter size line showed a period of renewed response after 45 generations of selection, following a period of 15 generations with no response. The relative contribution of genotype of the dam and of the embryo to prenatal survival was examined using results of selection, crossing and embryo transfer. Genotype of female carrying the litter was responsible for most of the observed differences. Genes for poor survival expressed by the embryo were present in some strains, but accounted for less variation than did maternal genotype. Information from the selected lines and from crosses among them provided evidence for dominance of genes affecting fertility and prenatal survival and additivity of genes affecting ovulation rate and body weight. The information was used to suggest a model for more effective exploitation of heterosis using breeds or strains of animals of known performance for different components. The extent of genetic variation for prenatal survival suggests that natural selection in this species may not always be for maximum survival. It is suggested that the ability to reduce litter size after conception, in response to nutritional or other stress, may at times be of selective advantage, contributing to maintenance of genetic variation in survival rate.

Animals↗

PubMed1988

Population amalgamation and genetic variation: observations on artificially agglomerated tribal populations of Central and South America.

The interpretation of data on genetic variation with regard to the relative roles of different evolutionary factors that produce and maintain genetic variation depends critically on our assumptions concerning effective population size and the level of migration between neighboring populations. In humans, recent population growth and movements of specific ethnic groups across wide geographic areas mean that any theory based on assumptions of constant population size and absence of substructure is generally untenable. We examine the effects of population subdivision on the pattern of protein genetic variation in a total sample drawn from an artificial agglomerate of 12 tribal populations of Central and South America, analyzing the pooled sample as though it were a single population. Several striking findings emerge. (1) Mean heterozygosity is not sensitive to agglomeration, but the number of different alleles (allele count) is inflated, relative to neutral mutation/drift/equilibrium expectation. (2) The inflation is most serious for rare alleles, especially those which originally occurred as tribally restricted "private" polymorphisms. (3) The degree of inflation is an increasing function of both the number of populations encompassed by the sample and of the genetic divergence among them. (4) Treating an agglomerated population as though it were a panmictic unit of long standing can lead to serious biases in estimates of mutation rates, selection pressures, and effective population sizes. Current DNA studies indicate the presence of numerous genetic variants in human populations. The findings and conclusions of this paper are all fully applicable to the study of genetic variation at the DNA level as well.

Alleles↗

PubMedDate not supplied

Genetic variation and inferences about perceived taste intensity in mice and men.

The study of genetic variation in taste produces parallels between mice and men. In mice, genetic variation across strains has been documented with psychophysical and anatomical measures as well as with recordings from whole nerves. In humans, the variation has been documented with psychophysical and anatomical measures. Whole-nerve recordings from animals and psychophysical ratings of perceived intensities from human subjects have a similar logical limitation: absolute comparisons across individuals require a standard stimulus that can be assumed equally intense to all. Comparisons across whole-nerve recordings are aided by single-fiber recordings. Comparisons across psychophysical ratings of perceived intensity have been aided by recent advances in methodology; these advances now reveal that the magnitude of genetic variation in human subjects is larger than previously suspected. In females, hormones further contribute to variation in taste. There is evidence that the ability to taste (particularly bitter) cycles with hormones in women of child-bearing age, rises to a maximum early in pregnancy and declines after menopause. Taste affects food preferences, which in turn affect dietary behavior and thus disease risks. Valid assessment of taste variation now permits measurement of the impact of taste variation on health. Advances in psychophysical methodology were essential to understanding genetic variation in taste. In turn, the association of perceived taste intensities with tongue anatomy now provides a new tool for psychophysics. The ability of a psychophysical scale to provide across-subject comparisons can be assessed through its ability to show the fungiform papillae density-taste association.

Animals↗

PubMed2000

Metazoan parasite species richness and genetic variation among freshwater fish species: cause or consequence?

The factors responsible for the maintenance of genetic variation among natural populations remain a mystery. Recent models of host-parasite co-evolution assume that parasites exert frequency-dependent selection on their hosts by favouring rare alleles that may confer resistance against infection. We tested this prediction in a comparative analysis that sought relationships between levels of genetic variation and the number of metazoan parasite species exploiting each host species. We used data on 40 species of North American freshwater fishes. After controlling for sampling effort and phylogenetic influences, we found no relationship between genetic polymorphism and parasite species richness among fish species. However, we found a marginal negative correlation between parasite species richness and heterozygosity. This result goes against the prediction that increased selective pressure by parasites should be associated with higher levels of genetic variation. Instead, it suggests that parasites may be colonising host species showing low levels of genetic variation with greater success than genetically more variable host species.

Animals↗

PubMed1996

Genetic variation and nutrition.

Advances in genetics and molecular biology indicate that susceptibility to chronic diseases such as coronary artery disease (CAD), hypertension, diabetes, obesity, osteoporosis, alcoholism, cancer, etc., to a great extent is genetically determined. Studies have shown that 50% of the variance in plasma cholesterol concentration is genetically determined, whereas 30%-60% of the variance in blood pressure is genetically determined. For fibrinogen, an independent risk factor for CAD, 15%-50% of the variance is genetically determined. In the U.K. population the variance for the fibrinogen level is 15% whereas in the Hawaiian population, the variance is 50%, indicating significant differences between populations. Among Australians, 75% of the variance in bone density is found to be genetically determined. Genetic variation influences the response to diet. For example, individuals with ApoE4 have higher cholesterol levels and a higher risk of CAD than those with ApoE3. Additional studies show that women of the ApoE 3/2 phenotype stand to benefit the least from a high polyunsaturate: saturate (P:S) diet because of reduction in the more 'protective' high density lipoprotein cholesterol (HDL-C), whereas men of the ApoE 4/3 phenotype showed the greatest improvement in the LDL/HDL ratio. Therefore a general recommendation to increase the polyunsaturated content of the diet in order to decrease the risk for CAD is not appropriate for women with ApoE 3/2 phenotype. Thus, specific information is needed to define the optimal diet for an individual.

Adaptation, Physiological↗

PubMed1988

Analysis of genetic variation reveals human immunoglobulin VH-region gene organization.

We have investigated the extent of genetic variation and the number of germ-line heavy-chain-variable (VH) genes to obtain information on the organization and repertoire of the VH genes. Our studies revealed extensive genetic variation in this region, indicated by restriction-endonuclease site polymorphisms. Analysis of the distribution of selected polymorphic loci revealed evidence of linkage disequilibrium, particularly between VH2 and VH3 subclass loci, indicating that the subclasses are interdispersed in the human germ-line chromosome. Absolute correlation was detected between alleles of a VH2 locus and the alleles of three VH3 loci, evidence for an extra set of VH genes, which are present in 48% of the Caucasian population. A preliminary estimate of the number of VH genes, approximately 50, indicates a smaller number of VH genes than suggested by the amount of protein variation. The extensive genetic variation we have observed may be associated with genetic differences in the immune response and potentially with variable susceptibility to autoimmune disorders.

Alleles↗

PubMed1990

Multipoint analysis of human quantitative genetic variation.

A unique method of partitioning human quantitative genetic variation into effects due to specific chromosomal regions is presented. This method is based on estimating the proportion of genetic material, R, shared identical by descent (IBD) by sibling pairs in a specified chromosomal region, on the basis of their marker genotypes at a set of marker loci spanning the region. The mean and variance of the distribution of R conditional on IBD status and recombination pattern between two marker loci are derived as a function of the distance between the two loci. The distribution of the estimates of R is exemplified using data on 22 loci on chromosome 7. A method of using the estimated R values and observed values of a quantitative trait in a set of sibships to estimate the proportion of total genetic variance explained by loci in the region of interest is presented. Monte Carlo simulation techniques are used to show that this method is more powerful than existing methods of quantitative linkage analysis based on sib pairs. It is also shown through simulation studies that the proposed method is sensitive to genetic variation arising from both a single locus of large effect as well as from several loosely linked loci of moderate phenotypic effect.

Chromosomes, Human, Pair 7↗

PubMed1993

Mutation models and quantitative genetic variation.

Analyses of evolution and maintenance of quantitative genetic variation depend on the mutation models assumed. Currently two polygenic mutation models have been used in theoretical analyses. One is the random walk mutation model and the other is the house-of-cards mutation model. Although in the short term the two models give similar results for the evolution of neutral genetic variation within and between populations, the predictions of the changes of the variation are qualitatively different in the long term. In this paper a more general mutation model, called the regression mutation model, is proposed to bridge the gap of the two models. The model regards the regression coefficient, gamma, of the effect of an allele after mutation on the effect of the allele before mutation as a parameter. When gamma = 1 or 0, the model becomes the random walk model or the house-of-cards model, respectively. The additive genetic variances within and between populations are formulated for this mutation model, and some insights are gained by looking at the changes of the genetic variances as gamma changes. The effects of gamma on the statistical test of selection for quantitative characters during macroevolution are also discussed. The results suggest that the random walk mutation model should not be interpreted as a null hypothesis of neutrality for testing against alternative hypotheses of selection during macroevolution because it can potentially allocate too much variation for the change of population means under neutrality.

Biological Evolution↗

PubMed1986

Genetic variation in subdivided populations and conservation genetics.

The genetic differentiation of populations is usually studied by using the equilibrium theory of Wright's infinite island model. In practice, however, populations are not always in equilibrium, and the number of subpopulations is often very small. To get some insight into the dynamics of genetic differentiation of these populations, numerical computations are conducted about the expected gene diversities within and between subpopulations by using the finite island model. It is shown that the equilibrium values of gene diversities (HS and HT) and the coefficient of genetic differentiation (GST) depend on the pattern of population subdivision as well as on migration and that the GST value is always smaller than that for the infinite island model. When the number of migrants per subpopulation per generation is greater than 1, the equilibrium values of HS and HT are close to those for panmictic populations, as noted by previous authors. However, the values of HS, HT, and GST in transient populations depend on the pattern of population subdivision, and it may take a long time for them to reach the 95 per cent range of the equilibrium values. The implications of the results obtained for the conservation of genetic variability in small populations are discussed. It is argued that any single principle should not be imposed as a general guideline for the management of small populations.

Animals↗

PubMedDate not supplied

Genetic variation in Cumbrians.

Regional variation in the genetic constitution of the Cumbrian population is demonstrated in a survey of blood groups, red cell enzymes, and secretor status in a large sample of schoolchildren. In particular, the south and centre appear to be distinct from the remainder of Cumbria, but in different directions. The features of the central Lake District, tending towards gene frequencies observed in Norway, suggest that it may be a region in which the presence of a relict population is still detectable.

Adolescent↗

PubMed1978

Detection of genetic variation with radioactive ligands. III. genetic polymorphism of transcobalamin II in human plasma.

We detected genetically determined, electrophoretic variants of vitamin B12 binding proteins, most probably transcobalamin II, in human plasma. Polymorphic variants were observed in all populations tested; the two most common alleles (of at least four detected to date) attain frequencies of greater than 40% in Caucasians and Orientals. The variants are autosomally inherited and are seen as doublets in homozygotes, and four-banded patterns, the sum of two dissimilar homozygote patterns, in heterozygotes. The technique used in this survey, polyacrylamide gel electrophoresis (PAGE) autoradiography of plasma and serum labeled in vitro with 57Co-vitamin B12 is particularly applicable to the study of trace proteins such as the transcobalamins (10(-9)M). Possible functional variation in the TC II allele products is described, and the selective significance of this worldwide polymorphism is considered.

Autoradiography↗

PubMed2000

Permanence or change? The meaning of genetic variation.

Selected aspects of the evolutionary process and more specifically of the genetic variation are considered, with an emphasis in studies performed by my group. One key aspect of evolution seems to be the concomitant occurrence of dichotomic, contradictory (dialect) processes. Genetic variation is structured, and the dynamics of change at one level is not necessarily paralleled by that in another. The pathogenesis-related protein superfamily can be cited as an example in which permanence (the maintenance of certain key genetic features) coexists with change (modifications that led to different functions in different classes of organisms). Relationships between structure and function are exemplified by studies with hemoglobin Porto Alegre. The genetic structure of tribal populations may differ in important aspects from that of industrialized societies. Evolutionary histories also may differ when considered through the investigation of patrilineal or matrilineal lineages. Global evaluations taking into consideration all of these aspects are needed if we really want to understand the meaning of genetic variation.

Africa↗