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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↗

PubMed2006

Additive genetic variation and the distribution of QTN effects among sites.

Early quantitative genetic theories emphasize the distribution of gene effects at individual loci or the distribution of mutant effects in maintaining quantitative genetic variation, but infrequently stress the distribution of gene effects among loci. In this study, we analyse the effects of the distribution of quantitative trait nucleotides (QTN) effects among sites under artificial and stabilizing selection. Wright's formula is applied to describing the density distribution of allele frequencies of multiple diallelic QTN at the equilibrium of mutation-drift-selection. Our results demonstrate that the distribution of QTN effects among sites can affect additive genetic variation in terms of total additive variance, average gene diversity, per-class contribution of QTN effects and per-QTN contribution. When the distribution of QTN effects among sites is changed from L-shaped to bell-shaped or to be a flatter, both the total additive variance and the average gene diversity are changed. Per-class and per-QTN contributions exhibit different distribution patterns. The L-shaped distribution indicates the predominant role of the aggregative effects from the QTN of small finite effects. The bell-shaped or flatter distributions indicate the predominance of the QTN of intermediate and large effects. These predictions highlight the significance of the distribution of QTN effects among sites in interpreting the maintenance of quantitative genetic variation at the fine genome scale.

Animals↗

PubMed2006

Genetic variation for outcrossing among Caenorhabditis elegans isolates.

The evolution of breeding systems results from the existence of genetic variation and selective forces favoring different outcrossing rates. In this study we determine the extent of genetic variation for characters directly related to outcrossing, such as male frequency, male mating ability, and male reproductive success, in several wild isolates of the nematode Caenorhabditis elegans. This species is characterized by an androdioecious breeding system in which males occur with hermaphrodites that can either self-fertilize or outcross with males. We find genetic variation for all characters measured, but also find that environmental variation is a large fraction of the total phenotypic variance. We further determine the existence of substantial genetic variation for population competitive performance in several laboratory environments. However, these measures are uncorrelated with outcrossing characters. The data presented here contribute to an understanding of male maintenance in natural populations through their role in outcrossing.

Animals↗

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↗

PubMed2003

Genetic variation in male effects on female reproduction and the genetic covariance between the sexes.

Males of many insect species increase the fecundity and/or egg size of their mates through the amount or composition of their nuptial gifts or ejaculate. The genetic bases of such male effects on fecundity or egg size are generally unknown, and thus their ability to evolve remains speculative. Likewise, the genetic relationship between male and female investment into reproduction in dioecious species, which is expected to be positive if effects on fecundity are controlled by at least some of the same genes in males and females, is also unknown. Males of the seed beetle Stator limbatus contribute large ejaculates to females during mating, and the amount of donated ejaculate is positively correlated with male body mass. Females mated to large males lay more eggs in their lifetime than females mated to small males. We describe an experiment in which we quantify genetic variation in the number of eggs sired by males (mated to a single female) and found that a significant proportion of the phenotypic variance in the number of eggs sired by males was explained by their genotype. Additionally, the number of eggs sired by a male was highly positively genetically correlated with his body mass. The between-sex genetic correlation, that is, the genetic correlation between the number of eggs sired by males and the number of eggs laid by females, was highly positive when eggs were laid on Acacia greggii seeds. This indicates that males that sire many eggs have sisters that lay many eggs. Thus, some of the genes that control male ejaculate size (or some other fecundity-enhancing factor) when expressed in males appear to control fecundity when expressed in females. We found no significant interaction between male and female genotype on fecundity.

Animals↗

PubMed2003

Genetic variation of Avicennia marina (Forsk.) Vierh. (Avicenniaceae) in Vietnam revealed by microsatellite and AFLP markers.

Genetic variation of Avicennia marina in the costal area of Vietnam was examined using microsatellite and AFLP markers. By using five microsatellite loci a total of 21 alleles were detected. The average number of alleles per locus per population ranged from 1.667 to 3.000. The observed heterozygosity varied from 0.180 to 0.263, with an average of 0.210 indicating relatively low level of genetic variation comparing to the previous studies on A. marina in the worldwide range. The expected heterozygosity was larger than the observed heterozygosity leading to positive inbreeding coefficients in all the six populations. Highly significant departures from Hardy-Weinberg Equilibrium were detected in four populations. AFLP analysis revealed a total of 386 loci, of which 232 (60.1%) were polymorphic. In congruent with microsatellite markers relatively low levels of genetic variation were detected at both gene and nucleotide levels (H = 0.086; pi = 0.0054). Reduced level of genetic variation was found in the central population, and in the southern populations. Both microsatellite and AFLP markers revealed large genetic differentiation (F(ST) = 0.262 and 0.338, respectively) indicating strong genetic structure among regional populations. Pairwise genetic distance by AFLP showed two populations in the north and the other two in the south are closely related each other.

Alleles↗

PubMed2005

Genetic variation at the ACE gene is associated with persistent microalbuminuria and severe nephropathy in type 1 diabetes: the DCCT/EDIC Genetics Study.

The development and progression of microvascular complications have been extensively documented in a cohort of type 1 diabetic subjects enrolled in the Diabetes Control and Complications Trial (DCCT) and followed in the Epidemiology of Diabetes Interventions and Complications (EDIC) study. We describe the association of genetic variation in the ACE gene in 1,365 DCCT/EDIC subjects with incident persistent microalbuminuria (n = 312) and severe nephropathy (n = 115). We studied three markers (rs1800764, insertion/deletion, and rs9896208) in the ACE gene that allowed us to capture genetic variation in the common haplotypes occurring at frequencies of >5% in Caucasians. Compared with the more frequent genotype (D/I) for the insertion/deletion polymorphism, in multivariate models, the I/I genotype conferred a lower risk for persistent microalbuminuria (hazard ratio [HR] 0.62 [95% CI 0.43-0.89], P = 0.009) and severe nephropathy (0.56 [0.32-0.96], P = 0.033). Variation at the two other markers, rs1800764 and rs9896208, were also associated with these renal outcomes. In addition, homozygosity for the common haplotype TIC (which corresponded to the T, insertion, and C alleles at the three markers, rs1800764, insertion/deletion, and rs9896208, respectively) versus the CDT/TIC haplotype pair was associated with lower risk for development of persistent microalbuminuria (HR 0.49 [0.32-0.75], P = 0.0009) and severe nephropathy (0.41 [0.22-0.78], P = 0.006). Our findings in the DCCT/EDIC cohort provide strong evidence that genetic variation at the ACE gene is associated with the development of nephropathy in patients with type 1 diabetes.

Albuminuria↗

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↗

PubMed2006

Genome-wide scan reveals that genetic variation for transcriptional plasticity in yeast is biased towards multi-copy and dispensable genes.

One of the most important aspects of the evolution of development and physiology is the interplay between gene expression and the environment, by which traits become altered in response to environmental triggers. This feature is known as phenotypic plasticity. When different genotypes show different levels of plasticity for a trait, then they show genotype-by-environment interaction, or GEI. It is now clear that gene expression plays an important role in organismic-level phenotypic plasticity, but we know very little about whether gene expression itself is subject to genetic variation for phenotypic plasticity (GEI). Given that gene regulation is likely to have evolved to respond to environmental changes, it is of central importance to understand how environmental and genetic variation interact to produce variation in gene expression. Here we investigate genetic variation for phenotypic plasticity in the yeast transcriptome for the whole genome. Six strains of Saccharomyces cerevisiae were grown in four different environments representing a continuum of rich and poor natural conditions. Using DNA-microarray data and an ANOVA analysis with a stringent criterion of significance, we found significant genetic variation for transcriptional plasticity (GEI) among strains for approximately 5% of the genes in the genome. There are about twice as many genes that show genetic variation for phenotypic plasticity as show genetic variation in transcription level independent of the environment. We also found that genes with genetic variation for plasticity were less likely to be essential and were significantly biased towards genes that have paralogs.

Adaptation, Physiological↗

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↗

PubMed1993

Genetic variation and random drift in autotetraploid populations.

The rate of decay of genetic variation is determined for randomly mating autotetraploid populations of finite size, and the equilibrium homozygosity under mutation and random drift is calculated. It is shown that heterozygosity is lost at a slower rate than in diploid populations, and that the equilibrium heterozygosity with mutation and random drift is higher than for diploids. Outcrossing populations as well as populations that randomly self are analyzed. A method of comparing genetic variation between autotetraploid and diploid populations is proposed. Our treatment suggests that the "gametic homozygosity" provides a unified approach for comparing genotypes within a population as well as comparing genetic variation between populations with different levels of ploidy.

Alleles↗

PubMed1998

Positive correlation between recombination rates and levels of genetic variation in natural populations of sea beet (Beta vulgaris subsp. maritima).

The relation between the level of genetic variation and the rate of recombination per physical unit was investigated in sea beet (Beta vulgaris subsp. maritima). The rate of recombination per physical unit was estimated indirectly through marker density in an RFLP linkage map of sugar beet. From this map, we also selected RFLP markers covering two of the nine chromosomes in Beta. The markers were used to estimate the level of genetic variation in three populations of sea beet, two from Italy and one from England. Two estimates of genetic variation were employed, one based on the number of alleles in the sample and the other on heterozygosity. A statistically significant positive correlation was found between recombination rate and genetic variation. Several theoretical explanations for this are discussed, background selection being one. A correlation similar to this has been observed previously in Drosophila, one that was higher than what we obtained for Beta. This is consistent with various biological differences between the two species.

Chenopodiaceae↗

PubMed2000

Food acceptance and genetic variation in taste.

OBJECTIVE: To determine if individuals who taste 6-n-propylthiouracil (PROP), one marker of genetic variation in taste, as exceptionally bitter can also perceive sugars as sweeter, other bitters as more intense, and dietary fats as more creamy and/or viscous than do individuals who taste PROP as weakly bitter. This study examined the association between genetic variation in taste and acceptance for sweet, high-fat, and bitter foods and beverages. DESIGN: Genetic variation was measured by perceived bitterness of PROP (influenced by genetic, hormonal, and pathologic factors) and density of fungiform papillae on the anterior portion of the tongue (influenced primarily by genetic factors). Four sweet, 3 fat, and 3 bitter groups were derived from principal components analyses of questionnaire items. SUBJECTS: Convenience sample of healthy adults (24 women, 22 men; mean age +/- standard deviation = 21 +/- 6 years) who did not report high dietary restraint. STATISTICAL ANALYSES: Pearson product moment correlations between genetic taste measures and food and beverage groups. RESULTS: The sample showed diversity in genetic taste measures: perceived bitterness of 0.0032 mol/L PROP ranged from "weak" to well above "very strong"; fungiform papillae densities ranged from 33 to 156 papillae per square centimeter. Distribution of perceived bitterness of PROP and fungiform papillae density differed in women and men. The association between genetic taste measures and acceptance of sweet and high-fat groups differed in women and men. In women, liking of sweet and high-fat food and beverage groups decreased with increasing perceived bitterness of PROP. In men, liking of these foods and beverages increased but with increasing papillae densities. Genetic taste measures were not associated with a dislike of bitter food and beverage groups. APPLICATIONS: The influence of genetic variation in taste on food intake depends on how perceptible sweet, fat, or bitter components are in foods and beverages, as well as the value of sensory factors vs other factors (e.g., health, convenience) on personal dietary choices. Female supertasters of PROP bitterness may avoid high-fat or sweet foods because these oral sensations are too intense and thus less pleasant. Supertasters may taste more bitterness in vegetables but still enjoy eating them because of their healthfulness and because condiments (especially those that are salt based) can block bitterness.

Adolescent↗