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At least 19 recordsLinked to original sources
PubMed2000

Budding yeast as a model organism for population genetics.

Population genetics is a highly theoretical field in which many models and theories of broad significance have received little experimental testing. Microbes are well-suited for empirical population genetics since populations of almost any size may be studied genetically, and because many have easily controlled life cycles. Saccharomyces cerevisiae is almost ideal for such studies as the growing body of knowledge and techniques that have made it the best characterized eukaryote genome also allow the experimental manipulation and analysis of its population genetics. In experiments to date, the evolution of laboratory yeast populations has been observed for up to 1000 generations. In several cases, adaptation has occurred by gene duplications. The interaction between mutation, selection and genetic drift at varying population sizes is a major area of theoretical study in which yeast experiments can provide particularly valuable data. Conflicts between gene-level and among-cell selection, and co-evolution between genes within a genome, are additional topics in which a population genetics perspective may be particularly helpful. The growing field of genomics is increasingly complementary with that of population genetics. The characterization of the yeast genome presents unprecedented opportunities for the detailed study of evolutionary and population genetics. Conversely, the redundancy of the yeast genome means that, for many open reading frames, deletion has only a quantitative effect that is most readily observed in competitions with a wild-type strain.

Adaptation, Biological↗
PubMedDate not supplied

[Anopheline population genetics].

Population genetic studies of vectors are essential for (i) the determination of their taxonomic status and consequently the definition of their vectorial role in the transmission of pathogenic agents; (ii) the evaluation of the species genetic variability and the estimation of their capacities of adaptation to selection pressure; (iii) an estimation of gene flow among populations in order to evaluate their degree of isolation and gene circulation, especially resistance genes. Among the malaria vectors taken as examples on three continents, Africa, South-East Asia and Latin America, the large majority of the species showed an important polymorphism. The Gambiae Complex, which is by far the most studied one, includes at present 7 species with the recent description of An. quadriannulatus A and B from Ethiopia. An. gambiae s.s. includes itself 5 chromosomal forms. One of them, the Mopti form, should be considered as a species unto itself. For An. arabiensis, a strong differentiation has been observed among the populations from Senegal and the Indian Ocean Islands. The kdr mutation, which confers resistance to pyrethroid knockdown effect, has never been found either in the Mopti form, or An. arabiensis, indicating a restricted gene flow between these latter two and An. gambiae s.s. The speciation process of the Gambiae Complex seems to be a recent phenomenon due to environmental selection pressure. Species of the Funestus Group are distinguishable by morphological characters. The genetic study of An. funestus s.s. did not show the presence of a complex, in spite of high polymorphism and population structure. Anophelines from eastern areas present an important biodiversity. The Minimus Complex includes two species, A and C, which are widely distributed in South-East Asia. Species A is strongly endophilic, on the contrary species C is at once more exophilic and zoophilic. The latter species might have been selected by DDT indoor house spraying. After numerous taxonomic investigations, the Dirus Complex includes now 7 species. In Latin America, An. pseudopunctipennis clustered into three geographic populations which are under a speciation process. One covers North America and Guatemala, the other South America and Belize, whilst the last one is restricted to Grenada Island. On the contrary, An. darlingi showed little morphologic and genetic variability throughout the species geographic range suggesting the existence of a single species. The main objective of these studies is to implement a more selective approach of vector control programs in relation to the incriminated species, their bioecology and their role in malaria transmission. The improvement of efficiency and selectivity of vector control is becoming a major goal in order to make the best out of the available tools and control the impact of interventions on the environment.

Africa↗
PubMed1998

[Man and the diversity of his genome. An extraordinary phase in the history of population genetics].

Population genetics is almost eighty years old, but benefited only very recently from the advantages of direct DNA analysis. Nevertheless, much knowledge had already accumulated and was completely confirmed by the study of DNA markers. Major benefits of the latter came with microsatellites. It allowed to discover an error made with classical markers but even more seriously with RFLPs, because of the practically involuntary sampling of individuals almost exclusively of European origin for the detection of polymorphisms. Among other evolutionary application of microsatellites, the most attractive is their very recent use for dating population separations during the recent migration out of Africa of modern humans. They confirm the theory that this expansion was quite recent. Single nucleotide substitutions are the major material of evolution, and so far markers of this kind were rare. A new method, DHPLC, is excellent for their detection and testing. In humans it has been applied almost exclusively to the Y chromosome, and in a year it has given a completely new picture of Y chromosome genetics. Some applications of statistical methods to genetic geography of classical markers and ADN markers will show the power of the geographical approach, and therefore the need of a wide collection of population samples, as will be made possible by the HGDP (Human Genome Diversity Project).

Africa↗
PubMed1976

On the genetics and population genetics of Gm(4).

Investigations on 70 German families with 142 children confirmed the autosomal-dominant inheritance of Gm(4). However, in our material as well as in the materials published so far, Gm(4) X Gm(-4) parental combinations show clear surplusses of Gm(4) and deficits of Gm(-4) children, which might indicate prenatal selection. The world distribution of Gm4 alleles reveals a remarkable racial heterogeneity. Furthermore, marked North-South distribution gradients in Caucasoids and Mongoloids were found. The genetical and population genetical observations are discussed.

Adult↗
PubMed1982

Use of restriction fragment length polymorphisms for genetic counseling: population genetic considerations.

Two-locus population genetic models are analyzed to evaluate the utility of restriction fragment length polymorphisms for purposes of genetic counseling. It is shown that the linkage disequilibrium between a neutral marker and a tightly linked overdominant mutant will increase rapidly as the mutant moves to its polymorphic equilibrium. The linkage disequilibrium decays for deleterious recessive mutants. Two measures involving the linkage disequilibrium are investigated to determine how much information the transmission of the neutral marker provides about the transmission of the selected gene. In certain kinds of matings, where the parental two-locus genotypes and linkage phases are known, it is possible to determine whether or not a progeny is homozygous for the selected gene on the basis of the fetal genotype at the marker locus. A quantity of primary interest is the fraction of matings between individuals heterozygous for the selected gene in which exact diagnosis can be made in this way. The expected proportion of such matings, taken over all two-locus matings involving heterozygotes at the selected locus, is calculated as a function of the gene frequencies at the two loci and the linkage disequilibrium between them. This expected value is maximized when the linkage disequilibrium is at its maximum in absolute value. Fewer than half of all matings are informative if the linkage disequilibrium is small in magnitude or if the gene frequencies at the two loci are quite different. Consideration is also given to various conditional measures of association that may be useful when the parental two-locus genotypes are unknown. The results suggest that the utility of tightly linked neutral marker genes in predicting the transmission of a selected gene is generally less when selection acts against a recessive gene than for overdominant selection.

Base Sequence↗
PubMed1985

Multiallelic restriction fragment polymorphisms in genetic counseling: population genetic considerations.

The use of selectively neutral, multiallelic molecular markers to trace the transmission of tightly linked genes is examined theoretically for all genetic counseling situations in which the diagnosis of deleterious progeny is desired. Formulae are computed in terms of the gametic frequency distribution in the population, for the expected fraction of matings (alpha i) which allow exact diagnosis on the basis of the marker alleles transmitted, assuming an arbitrary number (n) of alleles segregating at the marker locus and possibly nonrandom associations between the loci. In each case, it is shown that the diagnostic value of a multiallelic marker increases as n increases, with approximately 1-1/n matings informative, on average.

Alleles↗
PubMed2003

Disparate patterns of population genetic structure and population history in two sympatric penaeid shrimp species (Farfantepenaeus aztecus and Litopenaeus setiferus) in the eastern United States.

Analysing the population genetic structures of sympatric species provides opportunities to compare patterns of population genetic structure and phylogeography in order to gain insight into the factors that influence the development of the observed patterns. In this study, we compared the population genetic structures and phylogeographies of brown shrimp (Farfantepenaeus aztecus) and white shrimp (Litopenaeus setiferus), two sympatric penaeid shrimp species that inhabit the waters of the eastern USA, using sequence analysis of the mitochondrial DNA control region. Brown shrimp showed no significant phylogenetic structure or population subdivision, and closely related haplotypes were geographically dispersed. Mismatch analysis indicated that brown shrimp experienced a late-Pleistocene era sudden population expansion. In contrast, white shrimp had a complex haplotype phylogeny consisting of two distinct lineages and two less well-defined sublineages, and the haplotypes and lineages were geographically structured. Mismatch analysis for white shrimp also showed evidence of sudden population expansion, albeit for each lineage separately and more recently than in the brown shrimp. These disparate patterns may have developed as a result of species-specific differences in physiological tolerances and habitat preferences that caused greater fluctuations in white shrimp population sizes and reductions in long-term effective population size relative to that of the brown shrimp, and thereby increased the susceptibility of the white shrimp populations to stochastic genetic change.

Animals↗
PubMed1988

Diversity of some gene frequencies in European and Asian populations. IV. Genetic population structure assessed by the variogram.

Isolation-by-distance models of population structure predict an exponential decrease of genetic relatedness with distance. Under the Kimura-Weiss (1964) model the plots of gene frequency variance versus distance (variograms), computed at various loci, are expected to have equal slope and reach a common asymptote. The gene frequency distributions at eight loci in 192 European and Asian populations have been summarized by variograms. On the average, the Kimura-Weiss model seems to describe adequately allele frequency change up to 900 km, but gradients are apparent at greater distances for most markers studied. These patterns may result form either differential selection or long-range gene flow; however, the extensive clinal variation observed for glyoxalase, esterase D and 6-PGD cannot be entirely accounted for by the Neolithic radiation of early farmers in the Middle East and Europe.

Alleles↗
PubMed1997

Genetic selection strategies--population genetics.

This paper provides an overview of the association between population genetics and selection strategies in poultry. Relationships between artificial and natural selection and among causes contributing to limits to artificial selection are discussed. Homeostasis and resource allocations at the individual and at the population level are reviewed. Examples from poultry demonstrate where human intervention has circumvented biological limits. Lastly, this paper considers the role of population genetics in future breeding strategies for poultry.

Animal Husbandry↗
PubMed1979

Human pancreatic amylase polymorphism: formal genetics and population genetics.

The genetically determined polymorphism of human pancreatic amylase (E.C. 3.2.1.1), AMY2, is demonstrated in serum specimens by agarose gel electrophoresis. We investigated 325 mother-child pairs and 2594 unrelated individuals from southwestern Germany. This study confirms the formal hypothesis of two common alleles AMY1/2, AMY2/2 and possibly two rare alleles AMY3/2, AMY4/2 at an autosomal locus AMY2. The frequency of the AMY1/2 allele was calculated as 0.951; AMY3/2 and AMY4/2 seem to have a frequency of 0.001 in this sample.

Alleles↗