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Results for “variable gene flow”

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PubMed2000

Genetic diversity in tetraploid populations of the endangered daisy Rutidosis leptorrhynchoides and implications for its conservation.

Polyploidy is an important variable in assessing the genetics of endangered plant species. Species consisting of populations with different chromosome numbers pose questions as to the mode of inheritance, relative variability status, population divergence and gene flow. The self-incompatible species Rutidosis leptorrhynchoides (Asteraceae) in south-eastern Australia is a good example. The remnant populations in the northern sector of the species range are diploid, whereas southern ones are either diploid or tetraploid. Allozyme analysis of the tetraploid populations showed tetrasomic inheritance confirming an autopolyploid genetic system, a modest increase in their allelic richness over diploid populations in the same region and a lack of genetic divergence. Conservation and replenishment strategies should take account of these genetic features of mixed ploidy.

Asteraceae↗

PubMed2002

Temporal and geographic genetic variation in Culex nigripalpus theobald (Culicidae: Diptera), a vector of St. Louis encephalitis virus, from Florida.

A field population of Culex (Culex) nigripalpus Theobald from Vero Beach, FL sampled monthly over a period of 24 mo, a colony sample and 10 geographic samples were analyzed for genetic variation at 14 enzyme loci using polyacrylamide gel electrophoresis. The Cx. nigripalpus colony sample showed significantly lower genetic variation than the field-collected samples, measured by mean number of alleles per locus (colony 1.4 +/- 0.1 versus field 2.1 +/- 0.22), percentage of polymorphic loci (colony 35.7% versus field 54.8 +/- 7.7%), but mean observed heterozygosity (Ho = colony 0.16 +/- 0.07 versus field 0.17 +/- 0.03) and mean Hardy-Weinberg expected heterozygosity (He = colony 0.14 +/- 0.06 versus field 0.18 +/- 0.02) did not differ significantly. Three of the 14 loci (Aldox, Gpd, and Gpi) from the Vero Beach field samples showed distinct temporal patterns in the frequency of the most common allele. Higher mean observed heterozygosity (Ho) occurred during months following high rainfall in the Vero Beach field samples than during months following low rainfall. The average Nm value of 3.6 indicated high gene flow among the temporally distributed samples of the Vero Beach population. Genetic variability values between geographic samples from Panhandle, FL and south Florida were not significant. Gene flow estimates based on F(ST) = 0.039 provided a Nm of 6.2 indicating high levels of gene flow among the geographic samples of Cx. nigripalpus. The average Nei's and modified Rogers' genetic distances among the 10 populations were 0.009 +/- 0.001 and 0.081 +/- 0.004, respectively. The cluster analysis did not suggest geographic clustering, Because Cx. nigripalpus is the vector of St. Louis encephalitis (SLE) in Florida, temporal and geographic genetic variation in this species is discussed in relation to the seasonal and geographic SLE virus activity in Florida.

Animals↗

PubMed1978

[Variation of the profile phenotype M of alpha-1-chymotrypsine : trial of interpretation (author's transl)].

Cross immunoelectrophoresis of serum A1AT (Pi M) shows "frequent" patterns with M2 less than M6 less than M4. Other "particular" patterns were found with M6 greater than M4 and M6 less than M2. The most often found patterns among the Negroid population in our study appeared dissimilar to that found among Caucasians. The "super-gene" concept and the variability of genetic flow may explain this difference. The "particular" patterns are often found in cord blood samples and in patients with hepatocarcinoma. They show similaritis between embryonic and cancerous processes. These different patterns also agree with the "super-gene" concept.

Carcinoma, Hepatocellular↗

PubMed1996

Riverine barriers and gene flow in Amazonian saddle-back tamarins.

We describe patterns of genotypic and phenotypic variation in saddle-back tamarin (Saguinus fuscicollis) populations along the central and upper Rio Juruá, western Brazilian Amazonia. The genetic data are sequence haplotypes of the mitochondrial cytochrome b gene; phenotypic data are pelage colour variants that define sharply demarcated subspecies of this extremely variable tamarin species. We show that gene flow occurs between adjacent subspecies, but that this phenomenon is restricted to the headwater section of the river, which is consistent with expectations from the riverine barrier hypothesis. In this model, the major first-order tributaries of the Amazon form effective barriers to dispersal, with between-bank gene flow limited to the narrowed sections of headwater streams and parallel divergence increasing along both banks from the headwaters to the mouth of a given river. In meandering rivers such as the Rio Juruá, we suggest passive transfer through river channel dynamics as the main mechanism permitting genetic contact between populations on opposite banks of the river. Finally, we argue that in the case of plant and animal species that are largely restricted to unflooded (terra firme) forests, such as tamarins, seasonally flooded (várzea) forest can operate as a critical additional barrier to between-bank gene flow.

Animals↗

PubMed2004

Patterns of variation within and between Greek populations of Ceratitis capitata suggest extensive gene flow and latitudinal clines.

Four natural Greek populations of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), was studied for genetic variability at 25 enzyme loci. The comparison of polymorphism within and between populations shows two loci with high between-population heterozygosity (HT) and very high fixation index (F(ST)) values, suggesting the presence of balancing selection. The gradual decline of common allele frequency of the polymorphic loci tested indicated that latitudinal clines are present in Greece. Indirect estimates of gene flow based both on Wright's method (Nm*) and on the Slatkin's method (Nm*), which depends on the frequencies of rare alleles found in only one population, revealed a substantial amount of gene flow (Nm = 3.493 and Nm* = 3.197). These estimates of gene flow may well explain why the "introduced" Greek populations of C. capitata, in spite of their low genetic variability, display the same polymorphic loci. Gene flow in combination with natural selection and genetic drift may have played an important role to genetic differentiation in this species in Greece.

Alleles↗

PubMed2004

Population genetics of the potentially invasive African fruit fly species, Ceratitis rosa and Ceratitis fasciventris (Diptera: Tephritidae).

A set of 10 microsatellite markers was used to survey the levels of genetic variability and to analyse the genetic aspects of the population dynamics of two potentially invasive pest fruit fly species, Ceratitis rosa and C. fasciventris, in Africa. The loci were derived from the closely related species, C. capitata. The degree of microsatellite polymorphism in C. rosa and C. fasciventris was extensive and comparable to that of C. capitata. In C. rosa, the evolution of microsatellite polymorphism in its distribution area reflects the colonization history of this species. The mainland populations are more polymorphic than the island populations. Low levels of differentiation were found within the Africa mainland area, while greater levels of differentiation affect the islands. Ceratitis fasciventris is a central-east African species. The microsatellite data over the Uganda/Kenya spatial scale suggest a recent expansion and possibly continuing gene flow within this area. The microsatellite variability data from C. rosa and C. fasciventris, together with those of C. capitata, support the hypothesis of an east African origin of the Ceratitis spp.

Africa↗

PubMed2004

Variation of female frequency and cytoplasmic male-sterility gene frequency among natural gynodioecious populations of wild radish (Raphanus sativus L.).

In gynodioecious plant populations, sex determination often involves both cytoplasmic male-sterility (CMS) genes and specific nuclear genes that restore male function. How gynodioecy is maintained under the joint dynamics of CMS and restorer genes remains controversial. Although many theoretical models deal with interactions between CMS genes and restorer genes with sexual phenotypes and predict changes in their frequencies, it is difficult to observe the frequencies because no molecular markers have been established for either CMS or restorer genes in well-studied gynodioecious plants. This is the first report of the frequency of a CMS gene determined using a molecular marker in natural populations of a gynodioecious plant. Using a set of CMS gene-specific polymerase chain reaction primers, we compared female and CMS gene frequencies in 18 natural populations of Raphanus sativus. Female frequency was relatively low, ranging from 0 to 0.21. In contrast, the CMS gene frequency was highly variable among populations, ranging from 0 to 1. Estimated restorer gene frequency seemed less variable than observed CMS gene frequency, probably due to higher gene flow than in the CMS gene. Genetic drift may play a role in maintaining high variability of the CMS gene, although other possibilities are not excluded.

DNA Primers↗

PubMed2001

A review on the origin and spread of deleterious mutants of the beta-globin gene in Indian populations.

Deleterious mutations of the human beta-globin gene are responsible for beta-thalassaemia and other haemoglobinopathies, which are the most common genetic diseases in Indian populations. A highly heterogeneous distribution of those mutations is observed in India and certain mutations are restricted to some extent to particular groups only. The reasons behind the geographical clustering and origin of the mutations in India is a highly debated issue and the evidence is conflicting. Our present article aims at tracing the origin of the deleterious beta-globin mutation and evaluates the role of different evolutionary forces responsible for the spread and present distribution of those mutations in Indian populations, using data from molecular biology and statistical methods. Mutations are generated essentially randomly, but "hot-spot" sites for mutation are reported for the beta-globin gene cluster, indicating sequence dependency of mutation. A single origin of a deleterious beta-globin mutation, followed by recombination (in a hot spot region) and/or interallelic gene conversion (within beta-globin gene) through time is the most plausible hypothesis to explain the association of those mutations with multiple haplotype backgrounds and frameworks. It is suggested that India is the place of origin of HbE and HbD mutations and that they dispersed to other parts of the would by migration. HbS mutants present in Indian populations are not of Middle East origin but rather a fresh mutation is the probable explanation for the prevalence among tribal groups. beta-thalassaemia represents a heterogeneous group of mutant alleles in India. Five common and twelve rare mutations have been reported in variable frequencies among different Indian populations. Gene flow of those mutant alleles from different populations of the world by political, military and commercial interactions possibly accounts for the heterogenous nature of beta-thalassaemia among Indians. A multiple allelic polymorphic system of the beta-globin gene exists in different populations. Dynamic interaction of the mutant alleles in the presence of different selective forces including falciparum malaria and biosocial patterns of Indian populations is discussed in order to explain the variable distribution and maintenance of those mutant alleles.

Biological Evolution↗

PubMed2005

Estimating pollen flow using SSR markers and paternity exclusion: accounting for mistyping.

Highly informative genetic markers, such as simple sequence repeats (SSRs), can be used to directly measure pollen flow by parentage analysis. However, mistyping (i.e. false inference of genotypes caused by the occurrence of null alleles, mutations, and detection errors) can lead to substantial biases in the estimates obtained. Using computer simulations, we evaluated a direct method for estimating pollen immigration using SSR markers and a paternity exclusion approach. This method accounts for mistyping and does not rely on assumptions about the distribution of male reproductive success. If ignored, even minor rates of mistyping (1.5%) resulted in overestimating pollen immigration by up to 150%. When we required at least two mismatching loci before excluding candidate fathers from paternity, the resulting pollen immigration estimates had small biases for rates of mistyping up to 4.5%. Requiring at least three mismatches for exclusion was needed to minimize the upward biases of pollen immigration caused by rates of mistyping up to 10.5%. The minimum number of highly variable SSR loci needed to minimize cryptic gene flow and obtain reliable estimates of pollen immigration varied from five to seven for a sampling scheme applicable to most conifers (i.e. when paternal haplotypes can be unambiguously determined). Between five and nine highly variable SSR loci were needed for a more general sampling scheme that is applicable to all diploid seed plants. With moderately variable SSR markers, consistently accurate estimates of pollen immigration could be obtained only for rates of mistyping up to 4.5%. We developed the POLLEN FLOW (PFL) computer program which can be used to obtain unbiased and precise estimates of pollen immigration under a wide range of conditions, including population sizes as large as 600 parents and mistyping rates as high as 10.5%.

Alleles↗

PubMed2002

Population variability in Chironomus (Camptochironomus) species (Diptera, Nematocera) with a Holarctic distribution: evidence of mitochondrial gene flow.

Phylogenetic analysis of DNA sequences from mitochondrial (mt) genes (Cytochrome b and Cytochrome oxidase I) and one nuclear gene (globin 2b) was used for the investigation of Nearctic and Palearctic populations representing four Chironomus species of the subgenus Camptochironomus, namely C. biwaprimus, C. pallidivittatus, C. tentans sensu stricto and C. dilutus (the last two species constitute Holarctic C. tentans sensu lato). Phenograms constructed on the basis of mt sequences were not congruent with trees based on nuclear genes, or with morphological and cytological data. The mt tree divided the populations by continental region, rather than by the species groupings recognized by the other data sets. The incongruence is explained by mt gene flow resulting from hybridization between the sympatric species on each continent. Calculation of divergence times, based on the sequence data, suggest that C. tentans (s.l.) and C. pallidivittatus have both been in North America for about 2.5 My.

Animals↗

PubMed1999

Genetic and Floral Divergence among Sympatric Populations of Gymnadenia conopsea s.l. (Orchideaceae) with Different Flowering Phenology.

Gymnadenia conopsea s.l. is a common orchid in central Europe, where early- and late-flowering populations can be distinguished. The early-flowering form is recognized as subspecies conopsea and the late-flowering form as subspecies densiflora. The two subspecies can occur in sympatry, but their flowering periods are separated. We investigated whether early- and late-flowering subspecies are genetically differentiated, whether they diverged once or repeatedly, and we tried to identify potential evolutionary forces involved in the divergence of the two subspecies. We used genetic markers to estimate genetic divergence within and among populations of early- and late-flowering G. conopsea, and to reconstruct their evolutionary history. In addition, we assessed morphological variation between subspecies. Allozyme variation indicated that subspecies conopsea was significantly more variable than ssp. densiflora and that gene flow among populations of ssp. conopsea was higher than among populations of ssp. densiflora. Gene flow between subspecies was low, indicating that the difference in flowering phenology represented an effective barrier to gene flow. A neighbor-joining tree based on allozyme frequencies indicated that early- and late- flowering populations did not diverge repeatedly in sympatry. Levels of cpDNA variation were generally low, even between G. conopsea s.l. and Gymnadenia odoratissima, chosen as an outgroup. Four cpDNA haplotypes were found, which differed only in the number of microsatellite repeats. Their distribution among subspecies of G. conopsea s.l. and G. odoratissima indicates that microsatellite haplotypes have evolved repeatedly, and their occurrence in different taxa thus represents a homoplasy. Floral characters were variable within and among populations and subspecies but did not consistently separate early- from late-flowering populations. A weak separation between subspecies was found in vegetative characters that presumably reflected habitat and competitive differences experienced by early- and late-flowering populations.

Journal Article↗

PubMed1999

Genetic structure and gene flow among Komodo dragon populations inferred by microsatellite loci analysis.

A general concern for the conservation of endangered species is the maintenance of genetic variation within populations, particularly when they become isolated and reduced in size. Estimates of gene flow and effective population size are therefore important for any conservation initiative directed to the long-term persistence of a species in its natural habitat. In the present study, 10 microsatellite loci were used to assess the level of genetic variability among populations of the Komodo dragon Varanus komodoensis. Effective population size was calculated and gene flow estimates were compared with palaeogeographic data in order to assess the degree of vulnerability of four island populations. Rinca and Flores, currently separated by an isthmus of about 200 m, retained a high level of genetic diversity and showed a high degree of genetic similarity, with gene flow values close to one migrant per generation. The island of Komodo showed by far the highest levels of genetic divergence, and its allelic distinctiveness was considered of great importance in the maintenance of genetic variability within the species. A lack of distinct alleles and low levels of gene flow and genetic variability were found for the small population of Gili Motang island, which was identified as vulnerable to stochastic threats. Our results are potentially important for both the short- and long-term management of the Komodo dragon, and are critical in view of future re-introduction or augmentation in areas where the species is now extinct or depleted.

Alleles↗

PubMed1994

Factors affecting calculation and use of conversion equations for genetic merit of dairy bulls.

Factors affecting calculation and use of conversion equations were reviewed. Methods of expressing reliability of converted evaluations were surveyed. Of 16 countries responding, 6 did not calculate reliability for converted evaluations, 5 accepted reliability from the exporting country, and 5 assumed genetic correlations of .6 to 1.0 with the US. Genetic correlations between the US and 8 other countries were estimated and generally were > or = .9; estimated correlations between the US and Canada were 1.0. Estimated correlations averaged .93 for milk, .89 for fat, and .92 for protein yields. Correlation estimates were lowest for countries differing most from the US in management conditions (Australia, New Zealand) or trait definition (Germany), which suggests that correlation estimates < 1.0 indicate differences in trait measurement as well as differences in biological expression. Conversion equations were computed from data of US and Canadian Holstein bulls with and against the gene flow. Equations against the gene flow generally had regression coefficients and intercepts lower than those calculated with the gene flow. Lower regression coefficients were explained by selection on the dependent variable. Lower intercepts were attributed to preferential treatment of daughters from imported semen, which would lower intercepts for equations against the gene flow and inflate intercepts with the gene flow.

Animals↗

PubMed1996

Rapid detection of recombinant antibody fragments directed against cell-surface antigens by flow cytometry.

Cloning the correct genes coding for antibody variable domains (especially VL kappa) from hybridomas is often complicated by the presence of several immunoglobulin transcripts, some of them arising from the myeloma cell line. Indeed, four different VL genes were obtained after the amplification of immunoglobulin genes by PCR from the hybridoma HD37, which produces an antibody against the human CD19 B cell differentiation antigen. Most of the variants (eight out of 15) were derived from the kappa chain of the myeloma MOPC-21. For the rapid functional evaluation of recombinant antibody fragments against cell surface antigens, we established an efficient expression and detection system. First, deleted and mutated genes were eliminated by a colony screening procedure. Bacteria from picked colonies were then induced and grown in the presence of 0.4 M sucrose to increase the accumulation of soluble scFv in the periplasm (5-10 micrograms per ml of bacterial shake-tube culture). Finally, the cell-specific binding of scFv in crude periplasmic extracts was detected by flow cytometry. This procedure facilitated the efficient cloning of a functional anti-CD19 VH/VL combination from the hybridoma cDNA.

Amino Acid Sequence↗

PubMed2002

Genetic differentiation, gene flow and the origin of infestations of the medfly, Ceratitis capitata.

The genetic structure of natural populations of the economically important dipteran species Ceratitis capitata was analysed using both biochemical and molecular markers. This revealed considerable genetic variation in populations from different geographic regions. The nature of this variation suggests that the evolutionary history of the species involved the spread of individuals from the ancestral African populations through Europe and, more recently, to Latin America, Hawaii and Australia. The observed variation can be explained by various evolutionary forces acting differentially in the different geographic areas, including genetic drift, bottleneck effects, selection and gene flow. The analysis of the intrinsic variability of the medfly's genome and the genetic relationships among populations of this pest is a prerequisite for any control programme.

Africa↗

PubMed2000

Genetic subdivision, glacial refugia and postglacial recolonization in the golden-striped salamander, Chioglossa lusitanica (Amphibia: urodela).

The golden-striped salamander (Chioglossa lusitanica) is an ecologically specialized species, endemic to north-western Iberia. Patterns of genetic variation were assessed at seven polymorphic enzyme loci and one mitochondrial DNA (mtDNA) marker (cytochrome b) in 17 populations across its range. Estimates of enzyme genetic diversity revealed a high degree of genetic subdivision (FST = 0.68), mainly attributable to the existence of two groups of populations. The groups were located, respectively, north and south of the Mondego River, indicating that this river coincided with a major historical barrier to gene flow. A significant decrease in genetic variability from the Mondego northwards was associated with the Douro and Minho rivers. mtDNA sequence variation revealed a congruent pattern of two haplotype groups (d = 2.2%), with a geographical distribution resembling that of allozymes. The pattern and depth of genetic variation is consistent with the following hypotheses: (i) subdivision of an ancestral range of the species prior to the middle Pleistocene; (ii) secondary contact between populations representing historical refugia; (iii) relatively recent range expansion giving rise to the northern part of the species range; and (iv) loss of genetic variation through founder effects during range expansion across major rivers.

Alcohol Dehydrogenase↗

PubMed2000

Genetic diversity of North American populations of Cristatella mucedo, inferred from microsatellite and mitochondrial DNA.

Research over the past 20 years has shown, with the help of molecular markers, that the population genetics and distribution patterns of freshwater invertebrates in North America are often more complex than was previously believed. Here we extend this research to an, as yet, unstudied but widespread and common group, the freshwater bryozoans. Colonies of the bryozoan Cristatella mucedo were collected from a number of lakes across central North America, and were characterized genetically by analysis of microsatellite loci and mitochondrial DNA (mtDNA) cytochrome b sequences. The microsatellites illustrate a pattern of generally diverse and highly differentiated populations that contain little evidence of recent gene flow. The mtDNA sequences yielded highly variable levels of divergence, ranging from 0.0 to 8.8% within populations, and 0.0 to 9.8% among populations. The multiple divergent mtDNA lineages within populations provide evidence for repeated colonization events. The lack of clustering of haplotypes by site suggests that there has been widespread dispersal of multiple genetic lineages since the last ice age. While some of the haplotype lineages may have evolved in disjunct glacial refugia, the maximum levels of divergence predate the time since the last glacial-interglacial cycles. It is likely that multiple factors including vicariance events, patterns of dispersal, localized extinction, and an unusual life history, explain the unique phylogeographic patterns evident today in populations of C. mucedo.

Animals↗

PubMed2000

Genetic structure of avian populations--allozymes revisited.

Selection on allozymes has sometimes been advanced as one explanation for the low levels of population differentiation detected in avian populations by the use of enzymatic markers. Comparisons of the amount of population subdivision (estimated by FST values or analogous indices) measured by enzymatic and mitochondrial DNA (mtDNA) markers in birds were seen as evidence for this because mtDNA typically produces a more structured picture of population subdivisions. In fact, when taking into account the smaller effective population size of mtDNA, nuclear and mitochondrial markers give concordant results. Some discrepancies still exist, but I suggest that some might originate from different amounts of nuclear vs. mitochondrial gene flow due to partial reproductive isolation. Variable number of tandem repeat (VNTR) loci do not provide a dramatically different picture of population structures in birds compared to allozymes. Although more tests are needed, such as comparing the amount of genetic structure detected in the same populations with allozymes and microsatellites, the low levels of population subdivision measured with allozymes in birds seem to reflect historical and demographic processes and would not appear to result from any peculiarities of bird enzymatic loci.

Animals↗