Differences In Gene Frequencies Research Articles

Spatial and temporal population structure of Brevicoryne brassicae

AbstractAllozymes from individual aphids were used as markers to examine the structure of Brevicoryne brassicae colonies collected from field experiments at Horticulture Research International, Wellesbourne, during the summers of 1991, 1992 and 1993. Eighteen enzyme systems were examined using cellulose acetate electrophoresis, but only 6‐phosphogluconate dehydrogenase (6‐PGDH) showed polymorphism (three alleles) in the samples. There were significant differences in gene frequencies between populations at some sites within 1 kilometre and between times of sampling, with an increase in the proportion of the most common genotype AA later in the season, possibly due to selection during the summer of the best adapted clones. These changes in gene frequency might produce biased results in trials screening brassica crops against aphids.

THE SELECTION BARRIER BETWEEN POPULATIONS SUBJECT TO STABILIZING SELECTION.

The introgression of genes carried by a small group of immigrants is studied. The recipient and the donor populations differ at several autosomal loci subject to weak selection, and two allelic forms of each gene are considered. Fitness variation is determined by additive allelic effects, by dominance effects, and by two-locus additive-by-additive epistatic interaction of the effects of the alleles. The fate of the group of immigrants is quantified by the selection barrier that describes the cumulative mean fitness of the hybrids and hybrid descendants relative to the fitness of the resident population. The monomorphic and the polymorphic loci of the recipient population contribute differently to the selection barrier. If the genetic difference between recipient and donor population is small, then the contribution of the monomorphic loci is dominated by a positive term dependent on the difference in gene frequencies. The contribution of the polymorphic loci depends only on the difference of the leading order in the pairwise linkage disequilibria between the two populations. This contribution may be positive or negative; and, thus, polymorphic loci may either contribute to the barrier or inflate the introgression.

CYP2E1 and ALDH2 genotypes and alcohol dependence in Japanese.

The genotypes of the CYP2E1 and ALDH2 loci of alcoholic (alcohol dependence) and nonalcoholic (healthy) Japanese were investigated to examine the relationship between the polymorphism of CYP2E1 (C1/C2) and ALDH2 (ALDH2*1/ALDH2*2), and the susceptibility to alcoholism. There was no significant difference in C2 gene frequency between alcoholics (0.19) and nonalcoholics (controls) (0.20), whereas there was a significant difference in ALDH2 allele frequency, suggesting that, in Japanese, the C2 genotype of CYP2E1 may have nothing to do with the risk of developing alcohol dependence. However, the ALDH2*1 allele may influence drinking behavior and the development of alcohol dependence. Furthermore, racial interethnic differences in the frequency of the mutated allele of the CYP2E1 gene (C2) were found, like the ALDH2 gene. Japanese healthy controls showed a significantly higher frequency of the C2 allele than did Swedish healthy controls (0.05; reported by Persson et al., FEBS Lett. 319:207-211, 1993).

Patterns of genetic variation among Canadian populations of the bird cherry-oat aphid, Rhopalosiphum padi L. (Homoptera: Aphididae)

Past allozyme studies have shown a very low level of genetic variation among aphid populations. Attempts have been made to link this lack of diversity to the biological characteristics of aphids. This study examines the effect of host-alternation on genetic diversity in Canadian populations of the aphid Rhopalosiphum padi. Allozyme analysis of 15 populations on the primary host and 14 on the secondary hosts revealed polymorphism at only three of 51 loci. Little geographical differentiation was observed among populations from a single host category. However, gene frequency differences were noted between populations on primary and those on secondary hosts at two of three polymorphic loci and the mean heterozygosity was substantially reduced on secondary hosts. This pattern might result from the admixture on secondary hosts of resident clones and relatively invariant migrants from southern areas. Alternatively, the decreased heterozygosity might result from either a selective disadvantage of heterozygotes on secondary hosts or their selective migration to other hosts.

Genetic differences among black-lipped pearl oyster (Pinctada margaritifera) populations in the western Pacific

Seven populations of the black-lipped pearl oyster, Pinctada margaritifera, from the western Pacific were assayed for allozyme variation at 17 polymorphic loci from mantle biopsies. Levels of within population variation were high (mean number of alleles per locus averaged 6.8, mean direct-count heterozygosities averaged 0.575). Gene frequencies within populations conformed to those expected under random mating. Significant genetic differentiation between populations within reef groups and additionally between the Great Barrier Reef (GBR) and the Pacific islands (Kiribati and the Cook Islands) was revealed by hierarchical FST analysis. The average numbers of migrants per generation (Nem) among the Pacific islands and among the GBR populations was 6–8 and twice that between the Pacific islands and the GBR. This suggests a relatively high gene flow among populations in Kiribati and the Cook Islands on an evolutionary time scale. However, the occurrence of significant differences in gene frequencies among populations within reef groups suggests that genetic surveys of local populations should be undertaken prior to making any transfers of pearl oysters from other reefs in order to protect these genetic resources.

Factor IX gene haplotypes in Brazilian Blacks and characterization of unusual Ddel alleles

Analysis of factor IX gene polymorphisms is considered the best approach for prenatal diagnosis and carrier detection of haemophilia B when the identification of the gene mutation is not possible. Studies involving factor IX gene polymorphisms in Black populations are scarce and essentially restricted to the North-American Black population whose composition is substantially different from that of the Brazilian and presumably other Black populations of South America. In this paper we report the analysis of eight factor IX gene polymorphisms in Brazilian Blacks: 5' BamHI, DdeI, intron 2 BamHI, XmnI, TaqI, TaqI, MspI, MnlI and HhaI. Characterization of the VNTR-like DdeI polymorphism revealed six different alleles: B, AB, A2B, A2B2, A3B and A5B, the last being described here for the first time. The 5' BamHI, DdeI, MspI and HhaI polymorphisms showed the highest heterozygosities (0.40-0.50) and are in linkage equilibrium with one another. 19 complete haplotypes could be identified in this population. Based on the results we propose a systematic strategy for carrier detection and prenatal diagnosis of haemophilia B in this population. The combined analysis of four polymorphisms (5' BamHI, HhaI, MspI and DdeI) provided an informative genetic marker in 85% of the females. The use of all eight polymorphisms allows information in 95% of females. Additionally, differences in gene frequencies and haplotype distribution suggest dissimilarities in factor IX gene polymorphisms between the Brazilian and the North-American Black populations.

Genetic Risk and Carcinogen Exposure: a Common Inherited Defect of the Carcinogen-Metabolism Gene Glutathione S-Transferase M1 (GSTM1) That Increases Susceptibility to Bladder Cancer

Numerous studies have associated bladder cancer with exposure to carcinogens present in tobacco smoke and other environmental or occupational exposures. Approximately 50% of all humans inherit two deleted copies of the GSTM1 gene which encodes for the carcinogen-detoxification enzyme glutathione S-transferase M1. Recent findings suggest that the GSTM1 gene may modulate the internal dose of environmental carcinogens and thereby affect the risk of developing bladder cancer. We investigated whether the absence of the GSTM1 gene affects bladder cancer risk and whether there are racial differences in GSTM1 genotype frequency. Using a polymerase chain reaction (PCR)-based method, we examined the frequency of the homozygous deleted genotype (GSTM1 0/0) in 229 patients with transitional cell carcinoma of the bladder and 211 control subjects who were enrolled from the Urology Clinics at Duke University Medical Center and the University of North Carolina Hospitals. Control subjects were urology clinic patients who primarily presented with benign prostatic hypertrophy or impotence, who had no history of any cancer other than nonmelanoma skin cancer, and who were frequency matched to case patients on race, sex, and age (10-year age intervals). In order to explore racial differences in GSTM1 gene frequency, genotype was also determined in a community-based sample of 466 paid, healthy, unrelated volunteers from Durham and Chapel Hill, N.C. The presence or absence of the GSTM1 gene locus was determined by using a differential PCR, a semiquantitative technique in which multiple genes are coamplified. Overall, the GSTM1 0/0 genotype conferred a 70% increased risk of bladder cancer (odds ratio [OR] = 1.7; 95% confidence interval [CI] = 1.2-2.5; P = .004). Absence of the GSTM1 gene encoding the glutathione S-transferase M1 enzyme significantly increased risk to persons with exposure to the carcinogens in tobacco smoke (OR = 1.8; 95% CI = 1.2-3.0; P = .01) but poses little increased risk to persons without such exposure. Persons with smoking exposure of more than 50 pack-years who had the GSTM1 0/0 genotype had a sixfold greater risk relative to persons in the lowest risk group (i.e., nonsmokers who were GSTM1 +/+ or +/0). In the pooled clinic control and community sample groups (677 individuals), the GSTM1 0/0 genotype occurred less frequently among Blacks (35%) than among Whites (49%, P < .001). These findings support a protective role for the GSTM1 gene in bladder cancer. From these findings, it is estimated that 25% of all bladder cancer may be attributable to the at-risk GSTM1 0/0 genotype.

Genetic Polymorphism of Milk Proteins in Hungarian Spotted and Hungarian Grey Cattle: A Possible New Genetic Variant of β-Lactoglobulin

Genetic variants of αs1-, β-, and κ-caseins and of β-lactoglobulin were studied with PAGE and isoelectric focusing in milk samples of 101 Hungarian Spotted and 120 Hungarian Grey cows. Gene frequencies and genotypic frequencies were estimated. Significant differences in gene frequencies between the two breeds were observed at the κ-casein and β-lactoglobulin locus. The variants β-casein C, κ-casein C, and β-lactoglobulin D were not found in Hungarian Grey cows. On immobilized pH gradient, isoelectric focusing gels containing carrier ampholytes, a new unidentified protein band appeared near β-lactoglobulin B in about 10% of the milk samples of Hungarian Grey cattle.

GENETIC VARIABILITY OF GELIDIUM CANARIENSIS (RHODOPHYTA) DETERMINED BY ISOZYME ELECTROPHORESIS1

ABSTRACTThe populations of Gelidium canariensis (Grunow) Seoane‐Camba from the Canary Islands were analyzed for genetic variability by isozyme electrophoresis in 1989 and 1990. Each population was divided into sporophytic and gametophytic subpopulations. Twenty‐three to 27 putative alleles corresponding to 22 gene loci were analyzed. Sev‐enteen loci were monomorphic in all six subpopulations, and five were polymorphic in at least one subpopulation. Significant deviations from Hardy‐Weinberg equilibrium were found. The amount of genetic variability (percentage of polymorphic loci, mean number of alleles per locus, and average gene diversity) of haploid subpopulations was lower than that of diploid subpopulations. No correlation between genetic distance and geographical distance was found. Low genetic differentiation between sporophytic and gametophytic subpopulations of the same locality was obsewed in two populations. The low genetic diversity and genetic differentiation suggest that the genetic structure of the populations of G. canariensis from the Canary Islands is due to a combination of founder effects and the predominance of asexual reproduction. Initial differences in gene frequencies may have persisted because of insufficient time to reach a higher level of differentiation.

Genetic segregation analysis of red blood cell (RBC) histamine N-methyltransferase (HNMT) activity.

Methylation is an important pathway in the biotransformation of many drugs, neurotransmitters, and xenobiotic compounds. Histamine N-methyltransferase (HNMT) catalyzes the N tau-methylation of histamine and structurally related compounds. Measurement of HNMT activity in the RBC makes it possible to access variation in the enzyme activity that may reflect differences in less accessible tissues such as brain. Previously reported high family correlations for RBC HNMT activity suggested that genetic inheritance plays a major role in the regulation of variation in this enzyme. In the present study we completed complex segregation analyses of RBC HNMT activity of 241 individuals in 51 nuclear families that were randomly ascertained through children in the Rochester, Minnesota public school system in order to characterize the mode of inheritance of this important enzyme. We found evidence for major gene influence on the regulation of RBC HNMT activity. Both transformed and untransformed data support the presence of Mendelian major gene segregation, but the gene frequency differences do not indicate a direct correspondence between genotypes inferred from the two sets of analyses. Analyses of the skewed untransformed data indicated the presence of a relatively rare (Q = 0.121) additive major gene for high activity, with the three overlapping genotype distributions representing 77, 21, and 2% of individuals. Analyses of the normalized transformed data indicated the presence of a common (Q = 0.71) additive major gene for high activity, with the three overlapping genotype distributions accounting for 9, 41, and 50% of individuals. The analyses of transformed data give the best fit as well as the most parsimonious Mendelian major gene model.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic structure of leaf-beetles populations: microgeographic and sexual differentiation in Oreina cacaliae and O. speciosissima

We used F-statistics to quantify the population structure of two sympatric species of leaf beetles, Oreina cacaliae and O. speciosissima (Chrysomelinae, Coleoptera), which share the same microhabitat since they feed on the same herbaceous host plants. We measured genetic differentiation at six allozyme loci 1) among populations separated by relatively small distances (40 to 250 kilometers), 2) within each population, and 3) between sexes within populations. For both species, the populations studied are not panmictic. For each population, heterozygosities are relatively high, but the observed heterozygosities are generally lower than the expected values. Overall, within-population differentiation is high and similar for both species (Fis = 0.326 for O. cacaliae and 0.332 for O. speciosissima). Additionally, populations of both species are highly differentiated (Fst = 0.234 versus 0.051 for O. speciosissima). For O. cacaliae, Fis and Fst are greater among females than among males, while for O. speciosissima, Fst is sustantially greater among the males while Fis is slightly greater among males. Differences in gene frequency among the sexes were statistically tested using a modified Fst with sex as the defining category, and the sexes differed significantly with the exception of one population in O. cacaliae. Possible explanations for this difference are discussed.

Genetic structure of giant clam (Tridacna maxima) populations from reefs in the Western Coral Sea

Allozyme variation at six polymorphic loci was examined in 10 populations of Tridacna maxima from reefs in the Western Coral Sea, to test whether patterns of relatedness previously reported for foraminiferan populations reflected a fundamental structuring of the fauna in the region. Genetic distances (Nei's D) among populations of T. maxima ranged from 0–0.065 and increased with increasing geographical separation. No significant differences in gene frequencies were observed among populations within two groups of reefs identified by cluster analysis: the Great Barrier Reef (GBR), and among the offshore reefs excluding Lihou and Osprey. Significant genetic differences among these groups and the outliers Lihou and Osprey were consistent with the greater geographical separation of populations between areas than within areas. There was no evidence of differentiation along a north-south axis as reported for the foraminiferan Marginopora vertebralis, nor did populations from offshore reefs on the Queensland Plateau form a well-defined group that was genetically distinct from the GBR. The patterns observed for M. vertebralis do not appear to reflect a fundamental structuring of biota in the region. The differences in the pattern of genetic variation for M. vertebralis as compared with those for T. maxima may be due to several differences in the biological characteristics of the two species. The time of breeding in particular may influence the extent to which the divergence of the East Australian Current restricts larval dispersal among reefs in the central Queensland Plateau.

Sheep blood polymorphism and genetic divergence between French Rambouillet and Spanish Merino: role of genetic drift.

Rambouillet sheep originating from Spanish Merino have been maintained in France as a small and closed flock since their importation. After 190 years of independent evolution, the flock has markedly differentiated from its Spanish parental population. The observed differences between them were characterized by the fixation in Rambouillet of the Mb and F30 alleles, which occurred in Spanish Merino with frequencies of 0.90 and 0.80 respectively (at two distinct blood group loci M and F30) and by the absence in Rambouillet of other alleles or phenogroups (at the Tf and the A, B, C blood group loci) which were observed in Spanish Merino with frequencies ranging from 0.10 to 0.28. On the basis of their phenotypic distributions at 11 blood polymorphic loci, the two populations differed significantly from each other (total chi 2 values = 352.62, 23 df, P less than 0.001). By comparing the observed magnitude of gene frequency differences between Rambouillet and Spanish Merino with the estimate of inbreeding coefficient for Rambouillet obtained from pedigrees, it appeared that the observed genetic differences could be attributed to the evolutionary change due to random drift in the small and closed flock of Rambouillet.

Endogenous Viral Gene Distribution in Populations of Meat-Type Chickens

The present study was designed to document the complexity of endogenous viral (ev) genes and seek evidence for their association with production traits in selected and control strains of meat-type chickens. Three populations were studied, each consisting of a control strain and one to three strains selected for various production traits. The ev genes were revealed by digesting genomic DNA with restriction enzymes and detecting DNA fragments on Southern blots using radioactive probes from nucleotide sequences of the avian leukosis virus genome.A total of 31 polymorphic ev loci were identified in these populations from a Sac I digest, with an average of 7.3 ev genes per bird. There were no significant differences in ev genes per bird between strains within populations or between selected and control strains overall. Thirty of 62 comparisons in the three populations indicated ev gene frequency differences (P < .05). Within populations, 13 of 93 comparisons of ev gene frequencies between control and selected strains and 8 of 62 between three selected strains of a sire population showed such differences (P < .05). Selection for body weight and feed efficiency had been observed to reduce gene frequencies of the slow-feathering gene, which usually contains the ev 21 locus; however, these effects were not detected (.05 <P < .06) between strains of the dam population in the current study. Such differences suggested possible associations between ev genes and production traits in meat-type chickens.

Microgeographic and temporal genetic variation in populations of the bluetongue virus vector Culicoides variipennis (Diptera: Ceratopogonidae).

Seven Colorado populations of the bluetongue virus vector Culicoides varipennis (Coquillett) were analyzed for genetic variation at 19-21 isozyme loci. Permanent populations, which overwinter as larvae, showed little temporal genetic change at 19 loci. PGD and MDH showed seasonal changes in gene frequencies, attributable to selection at two permanent populations. Two temporary populations showed low heterozygosity compared with permanent populations. Independent estimates of gene flow, calculated using FST and the private allele method, were Nm* = 2.15 and 6.95, respectively. Colorado C. variipennis permanent populations showed high levels of gene flow which prevented significant genetic differentiation due to genetic drift. Temporary populations showed significant gene frequency differences from nearby permanent populations due to the "founder effect" associated with chance colonization.

Genetic Differentiation Among Populations of Culicoides variipennis (Diptera: Ceratopogonidae), the North American Vector of Bluetongue Virus

Genetic relationships among 24 populations of Culicoides variipennis (Coquillett) were examined using isozyme electrophoresis of 21 protein-encoding loci. Estimates of genetic similarity based on gene frequency differences among populations were consistent with the existence of three North American subspecies, C. v. occidentalis Wirth & Jones, C. v. sonorensis Wirth & Jones, and C. v. variipennis. A stepwise discriminant analysis determined several allozymes which, when used in two canonical variables, accounted for 97% of the dispersion between subspecies. The geographic and genetic relationships among the three subspecies provide support for the hypothesis that the subspecies may be different species. The genetic relationships of the three subspecies to C. gigas Root & Hoffman suggest that C. v. occidentalis diverged from a C. variipennis-like ancestor from which C. v. sonorensis and C. v. variipennis later evolved. The implications of the genetic structure of the C. variipennis complex for the epidemiology of bluetongue disease in North America are discussed.

The structure of Dreissena polymorpha populations from basins adjacent to the Chernobyl atomic power station

The genetic and morphological differences among seven Dreissena polymorpha populations exposed to various environmental factors in the water basins adjacent to the Chernobyl atomic power station were examined. All of the populations showed differences in gene frequencies at four polymorphic loci. The populations could be divided into two groups according to temperature regime at the breeding site. Differences in Dreissena polymorpha populations were observed largely for those loci that showed significant deviations from the Hardy-Weinberg distribution. Radiation failed to cause any significant effect on the population structure. Within the limits considered, diversity in shell coloration among Dreissena polymorpha populations was governed by conditions at the breeding site (character of the substrate, rate of water flow, etc.), and not by thermal or radioactive contamination.

An intensive study of allozyme variation in freshwater resident and anadromous trout, Salmo trutta L., in western Ireland*

Ten polymorphic enzyme coding loci were assayed using starch gel electrophoresis in anadromous (sea trout) and freshwater‐resident trout, Salmo trutta, from two neighbouring river systems draining into Clew Bay in western Ireland. Samples were collected from the Burrishoole and from the neighbouring Newport river system. In the Burrishoole system, two samples were from above waterfalls impassable to migratory trout, two consisted of anadromous smolts or post‐smolts and the remainder were freshwater‐resident trout from freely accessible areas. There were large differences in gene frequency between trout from above impassable barriers and all others sampled, and these two groups also differed substantially from each other. More minor differences were evident between some other samples, particularly between trout from the upper lake and streams entering it and a stream associated with the lower lake. Two anadromous populations therefore occur in the Burrishoole system. In contrast, no differences were evident in two sampling years between anadromous trout and cohabiting freshwater‐resident trout from the upper part of the Burrishoole system. Thus, in the upper part of this system, anadromous trout do not appear to comprise a separate population from non‐migratory trout and interbreeding may occur.

Geographical variation ion allozyme frequencies of populations of Penaeus monodon (Crustacea : Decapoda) in Australia

This first systematic survey of genetic variation in P. monodon populations in Australia over a wide geographical range demonstrated highly significant differences in gene frequencies between the west-coast population and those on the northern and eastern coastlines. Some variation in gene frequencies among populations within the northern and eastern coastlines was detected in chi-square tests. Several loci (GPI*, PGM* and MPI*) contributed to the significant differences among populations. Genetic diversity decreased from east to west, suggesting colonization of the northern and western coasts by populations from the east after the last opening of the Torres Strait (c. 8000 BP). Evidence of genetic differences between western compared with northern and eastern populations is now available for three species of penaeid. These differences suggest, at least, that gene flow over several thousand years has been insufficient to erase genetic differences evolved during separation. Penaeid populations may therefore be more structured than has been thought, and the genetic homogeneity emphasized to date may be a result of the lack of genetic markers rather than a lack of population structure.

Genetic structure of milk proteins in Argentinian Holstein and Argentinian Creole cattle

The genetic structure of milk proteins was studied in two completely different breeds: Argentinian Holstein (dairy breed; n = 377) and Argentinian Creole cattle (native breed; n = 161). Fairly large similarities were observed among Argentinian Holstein allelic frequencies reported in the present study and the values described in the literature for other Holstein populations. The high frequency of αs1-Cn gene was the most remarkable gene frequency difference between Holstein and Creole breeds. Gametic phase disequilibrium was found among three casein loci but not between casein and β-lactoglobulin loci. Both breeds showed the same gametic disequilibrium in β-Cn A/k-Cn A and β-Cn A/k-Cn B haplotypes; however, the αs1-Cn B/β-Cn A haplotype was only in disequilibrium in Holstein breed. In general, the gametic phase disequilibrium found in both breeds was similar to those described for other breeds. The possible causes of gametic disequilibrium are discussed, and the results suggest that natural selection could be the most likely explanation.