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PubMedDate not supplied

Effects of the parents' age on the level of polymorphism at the Adh locus in Drosophila melanogaster: I. Effects on the genic and genotypic segregation of the offspring.

Several parameters (genetic and nongenetic) are involved in allele frequency changes and in the maintenance of the level of polymorphism at the Adh locus in Drosophila melanogaster. In this article, we have investigated the effect that parental age has on the genetic and genotypic segregation of the offspring. Comparing the offspring from crosses between heterozygous individuals of different ages (young x young, young x old, and old x old), we observed an association between adult age and allele frequencies of the offspring. The offspring of the "older" parents have a greater frequency of the Adh-F allele compared to the offspring of "younger" parents. However, this effect is not independent of the sex of parents. The age of the male has more importance than the female age. Furthermore, the duration of the parent egg-laying period also affects the genic frequencies among the offspring. The frequency of the F allele, in each cross, gradually decreases while the egg-laying period increases.

Age Factors↗
PubMed1984

The properties of meiotic gene conversion important in its effects on evolution.

In order to determine how important gene conversion is as a force in populations, extensive surveys have been made to determine the limits, distributions and typical values of evolution-related conversion parameters from various fungi, Drosophila and maize. The conversion frequency, c, had an enormous range for different mutations within a species, with loci often having different means and limits for c. b, the frequency of a particular allelle in the products of meiotic tetrads or octads with aberrant segregation ratios, often showed values near the theoretical extremes; d, disparity in direction of conversion, was frequent and often extreme. b and d could only be studied in fungi, and their less extreme values in Saccharomyces than in Sordaria or Ascobolus are clearly related to the lack of frame-shift mutations in the yeast data. For different mutations at a locus, neither c nor b showed normal distributions; both gave dispersed distributions, sometimes multi-modal for b; c and b were not usually correlated. y, the force of meiotic gene conversion on allele frequencies, had a large range of positive and negative values, with different loci often having quite different limits and mean absolute values. For different mutations at a locus, y showed dispersed distributions, with little tendency to cluster around zero. The high proportion of non-zero y values in all fungi where this could be studied, with large departures from zero being most extreme in Ascobolus and Sordaria brevicollis, shows that gene conversion could often be an important force in changing allele frequencies in favour of mutant or wild-type in these organisms. Even in organisms with much lower c or absolute d values, conversion could still be important, depending on dominance, selection coefficients and mutation rates. Presumed frame-shifts tended to have more extreme disparity and hence higher absolute y values than did presumed base-substitutions, but with no consistent c differences. Induced mutations had similar or slightly higher absolute y values compared with spontaneous mutations.

Animals↗
PubMed1976

Survivorship and gene frequencies of Drosophila melanogaster populations in abnormal oxygen atmospheres.

Vestigial wing and wild type populations of Drosophila melanogaster were exposed to 5%, 20%, and 60% oxygen at normal atmospheric pressure. Adult mortality rates, larval production, and allele frequency changes in four gene-enzymes were examined in the populations. All flies in 60% oxygen survived as well as controls until day 20 and then died out within the next 10 to 12 d. In 5% oxygen, vestigial wing flies had mortality rates greater than the 20% controls initially, but the rate eventually approached that of the controls. Wild type flies in 5% oxygen survived as well as controls. Larval production and rate of eclosure in 60% oxygen were similar to controls, but reduced in 5% oxygen. Allele frequency shifts to 6-phosphogluconate dehydrogenase and phosphoglucomutase were observed in 5% oxygen, and a shift of alpha-glycerophosphate dehydrogenase allele frequencies occurred in 60% oxygen. There was no evidence of in vivo inactivation of ADH, 6-PGD, alpha-GPD or PGM in 60% oxygen.

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↗
PubMed1993

Heterogeneous selection in subdivided populations.

The dynamics of allele frequencies changing under migration and heterogeneous selection in a subdivided population are investigated. Using perturbation techniques, a stationary state is obtained when migration and selection are both small. Heterogeneous selection leads to a positive correlation between values of F-statistics and heterozygosities when these are compared among sets of subdivided populations. This contrast with a negative value of the correlation obtained under Wright's classical model of homogeneous selection, and with the absence of correlation in the completely neutral situation.

Alleles↗
PubMed2003

Demographic and genetic structures of two partially isolated communities of Santa Catarina Island, southern Brazil.

The objectives of this study were to analyze the population structure and genetic variability of two communities, Costa da Lagoa (CLG) and São João do Rio Vermelho (SJRV), located on Santa Catarina Island in southern Brazil. The two populations descend from Azores Archipelago immigrants (Portuguese), with a minor contribution of sub-Saharan Africans and Amerindians. To estimate the relative contribution of the different ethnic groups to the current gene pool of the two communities, values of admixture were obtained using the weighted least-squares method based on allelic frequencies of the loci ABO, RHD-RHCE, GPA-GPB (MNSs), HBB, HP, TF, CP, AK, and ACP1. The origins of the studied populations can be quantified as follows: for CLG, sub-Saharan Africans (A) = 17.3%, Iberian Europeans (P) = 75.0%, and Southern Amerindians (I) = 7.7%; for SJRV, A = 48.8%, P = 44.5%, and I = 6.7%. Because haplotype frequencies of the GPA-GPB loci in SJRV were unusual, possibly as a consequence of random genetic drift, the values of admixture were recalculated after exclusion of GPA-GPB, as follows: A = 28.0%; P = 53.3%, and I = 18.7%. The total diversity (HT) was estimated as 42.29%, of which 99.6% can be attributed to the intrapopulational variability (HS). The interpopulational genetic variation (or standard distance, DST) corresponds to 0.19%, while the gene differentiation coefficient is 0.28%, indicative of low genetic difference. These results led to the conclusion that random genetic drift may have had an important effect on the Costa da Lagoa community, while presently gene flow might be the predominant evolutionary factor potentially capable of changing allele frequencies in SJRV.

Africa↗
PubMed1978

The alcohol dehydrogenase polymorphism in populations of Drosophila melanogaster. I. Selection in different environments.

The allozyme polymorphism at the alcohol dehydrogenase locus in Drosophila melanogaster was studied in order to obtain experimental evidence about the maintenance of this polymorphism. Populations started with different initial allele frequencies from homozygous F and S lines showed a convergence of frequencies on regular food at 25 degrees, leading to values equal to those in the base populations. These results were interpreted as due to some kind of balancing selection. In populations kept at 29.8 degrees, a lower equilibrium F frequency was attained. Addition of ethanol and some other alcohols to the food gave a rapid increase in F frequency, and high humidity decreased the F frequency slightly. Combination or alternation of ethanol and high humidity had variable effects in the populations tested. For a further analysis of the allele-frequency changes, estimates were obtained for egg-to-adult survival under different conditions and for adult survival on ethanol-supplemented food. On ethanol food (both at regular and high humidity), egg-to-adult survival of SS homozygotes was considerably lower than that of the FF and FS genotypes. Under regular conditions of food, temperature and humidity, a tendency to heterozygote superiority was observed, while at high humidity a relative high survival of SS was noticed in some tests. Adult survival of SS was lower than that of FF, but FS was generally intermediate, though the degree of dominance differed between populations. The results are consistent with the hypothesis of the occurrence of selection at the Adh locus.

Alcohol Oxidoreductases↗
PubMed2003

Effective number of breeders and maintenance of genetic diversity in the captive bearded vulture population.

We combined pedigree data with data derived from 14 microsatellite loci to investigate genetic diversity and its maintenance in the captive source population for the reintroduction of the bearded vulture into the Alps. We found the captive population to be genetically more variable than the largest natural population in Europe, both in terms of mean number of alleles per locus and mean observed and expected heterozygosity. Allelic diversity of the captive population was higher than, and mean heterozygosity measurements were comparable with the ones found in two large, extinct populations from Sardinia and the Alps represented by museum specimens. The amount of genetic variability recruited with the founders was still present in the captive population of the year 2000, mainly because the carriers of rare alleles were still alive. However, the decline in expected heterozygosity and the loss of alleles over generations in captivity was significant. Point estimates of effective population size, N(e), based on pedigree data and estimates of effective number of breeders, N(b), based on allele frequency changes, ranged from 20 to 30 and were significantly smaller than the census size. The results demonstrate that the amount of genetic variability in the captive bearded vulture population is comparable or even larger than the amount present in natural populations. However, the population is in danger to lose genetic variability over time because of genetic drift. Management strategies should therefore aim at preserving genetic variability by minimising kinship, and at increasing N(e) by recruiting additional founders and enhancing gene flow between the released, the captive and natural populations.

Alleles↗
PubMed2005

Selectionism and neutralism in molecular evolution.

Charles Darwin proposed that evolution occurs primarily by natural selection, but this view has been controversial from the beginning. Two of the major opposing views have been mutationism and neutralism. Early molecular studies suggested that most amino acid substitutions in proteins are neutral or nearly neutral and the functional change of proteins occurs by a few key amino acid substitutions. This suggestion generated an intense controversy over selectionism and neutralism. This controversy is partially caused by Kimura's definition of neutrality, which was too strict (|2Ns|< or =1). If we define neutral mutations as the mutations that do not change the function of gene products appreciably, many controversies disappear because slightly deleterious and slightly advantageous mutations are engulfed by neutral mutations. The ratio of the rate of nonsynonymous nucleotide substitution to that of synonymous substitution is a useful quantity to study positive Darwinian selection operating at highly variable genetic loci, but it does not necessarily detect adaptively important codons. Previously, multigene families were thought to evolve following the model of concerted evolution, but new evidence indicates that most of them evolve by a birth-and-death process of duplicate genes. It is now clear that most phenotypic characters or genetic systems such as the adaptive immune system in vertebrates are controlled by the interaction of a number of multigene families, which are often evolutionarily related and are subject to birth-and-death evolution. Therefore, it is important to study the mechanisms of gene family interaction for understanding phenotypic evolution. Because gene duplication occurs more or less at random, phenotypic evolution contains some fortuitous elements, though the environmental factors also play an important role. The randomness of phenotypic evolution is qualitatively different from allele frequency changes by random genetic drift. However, there is some similarity between phenotypic and molecular evolution with respect to functional or environmental constraints and evolutionary rate. It appears that mutation (including gene duplication and other DNA changes) is the driving force of evolution at both the genic and the phenotypic levels.

Animals↗
PubMed1973

Allozyme genotype-environment relationships. I. Variation in natural populations of Drosophila pachea.

Remarkable geographic and seasonal uniformities in gene and genotype frequencies were found for four enzyme loci. Principal component analysis revealed two patterns of allele frequency changes in three of the allozyme loci (Est-b, Est-c and Acph) and one pattern in the Mdh-d locus. These patterns accounted for 90% to 100% of the variability at these loci. Significant positive correlations were obtained between several of the components and the variability in the non-saponifiable and alkaloid fractions of the senita cactus host plant. The genetic variance within a single locality (Guaymas, Mexico) was as great as the variance between all localities sampled. This is interpreted as a local founder effect. The temporary nature of the rotting cactus breeding site, the delayed maturation and the differential maturation rate of females and males are three factors proposed to cause forced outbreeding and counter the local founder effect. A combination of selection resulting from a direct interaction of the genotype and the environment, in addition to migration, is proposed to maintain the uniform gene frequencies.

Acid Phosphatase↗
PubMed1985

Enzyme polymorphism in Drosophila melanogaster populations in Iraq.

Electrophoretic studies of the degree and pattern of polymorphism at two third-chromosome loci, esterase-6 (Est-6) and phosphoglucomutase (PGM), were carried out in three Drosophila melanogaster populations collected from different localities in Iraq: Mosul, Tuwaitha, and Basrah. The results show that only the Tuwaitha population was polymorphic for both loci; the other two populations were polymorphic for Est-6 and monomorphic for PGM. The allele frequency changes at both loci were followed for 20 generations in an experimental cage derived from the Tuwaitha population; it was found that there is a deviation from Hardy-Weinberg equilibrium at both loci toward the homozygote.

Animals↗
PubMed2000

Identification of 187 single nucleotide polymorphisms (SNPs) among 41 candidate genes for ischemic heart disease in the Japanese population.

To investigate whether common variants in the human genetic background are associated with pathogenesis of ischemic heart diseases, we systematically surveyed 41 possible candidate genes for single-nucleotide polymorphisms (SNPs) by directly sequencing 96 independent alleles at each locus, derived from 48 unrelated Japanese patients with myocardial infarction, including 25.8 kb 5' flanking regions, 56.8 kb exonic and 35.4 kb intronic sequences, and 1.8 kb 3' flanking regions. In this genomic DNA of nearly 120 kb, we identified 187 SNPs: 55 in 5' flanking regions, seven in 5' untranslated regions (UTRs), 52 in coding elements, 64 in introns, eight in 3' UTRs, and one in a 3' flanking region. Among the 52 coding SNPs, 26 were non-synonymous changes. Allelic frequencies of some of the polymorphisms were significantly different from those reported in European populations. For example, the Q506R substitution in the coagulation factor V gene, the so-called "Leiden mutation", has a reported frequency of 2.3% in Europeans, but we detected the Leiden mutation in none of the Japanese genomes that we investigated. The allelic frequencies of the -33A>G SNP in the thrombomodulin gene were also very different; this allele occurred at a 12% frequency in the Japanese patients that we examined, although it had been detected in none of 82 Caucasians reported previously. These data support the hypothesis that some SNPs are specific to particular ethnic groups.

3' Untranslated Regions↗
PubMed1988

Inclusive fitness models with two sexes.

Much recent work has focused on the transition from G. R. Price's (1970, Nature 227, 520-521) formula for allele frequency change to an inclusive fitness condition for the selective advantage of a certain behaviour. In case there is any kind of asymmetry between the sexes, the analysis must keep track of the two sexes separately, and this leads to a number of different forms of the expression for inclusive fitness. In this paper I gather these forms together and note the assumptions needed to make each valid. I also show how inclusive fitness should be formulated when the behaviour of the actor is controlled by another individual. I illustrate the inclusive fitness approach with a sex allocation example in a haplodiploid population with a local breeding structure.

Animals↗
PubMed2026

Ancient DNA as a temporal lens: reconstructing evolution, migration, and disease dynamics.

Ancient DNA (aDNA) has transformed evolutionary biology and anthropology by providing direct, chronologically validated genetic evidence over millennia. This review synthesizes significant findings from the paleogenomic era (2010-2025), demonstrating how ancient DNA has resolved persistent debates across four interconnected themes: (i) human migration and admixture, revealing complex population transitions from archaic hominins to Holocene expansions; (ii) adaptation, tracking allele frequency changes during domestication and selection; (iii) pathogen history, clarifying the origins of pandemics and the evolution of microbiomes; and (iv) ecosystem dynamics, identifying extinction causes through sedimentary DNA and conservation genomics. We contend that scientific rigor and ethical stewardship are crucial for accurate conclusions, given ancient DNA study requires the destructive collection of culturally significant remains. This review argues that continued advancement will depend on the integration of genomic data with archaeological, isotopic, and proteomic evidence, and highlights the necessity for equitable involvement with descendant communities. By conceptualizing the past as a continuum of dynamic processes rather than static events, ancient DNA provides a revised historical narrative and insights relevant to contemporary concerns in conservation, health, and social justice.

Evolution↗
PubMed1998

Polymorphic DNA markers in the genome of parasitic nematodes.

Polymorphic molecular markers are being identified to characterize the genomes of parasitic nematodes. The aim is to construct a map with markers evenly spread over the six chromosomes. With such a map, regions can be identified that are under selection pressure when attempts are being made to eradicate worms, be it by drugs, vaccines or genetic resistance in the sheep. Several types of markers have been developed, microsatellites, transposon-associated markers, amplified fragment length polymorphism (AFLP) and expressed sequence tag (EST) markers. Linkage groups can be constructed using several genetic crosses between inbred and drug resistant strains. EST markers will be especially important for comparative mapping with the genome of Caenorhabditis elegans, and therefore localization of the linkage group on a chromosome. It will then be possible to identify functional genes close to markers that have changed allele frequencies under selection pressure and identify the mechanisms of resistance to parasite control.

Animals↗
PubMed1992

Population genetic models of genomic imprinting.

The phenomenon of genomic imprinting has recently excited much interest among experimental biologists. The population genetic consequences of imprinting, however, have remained largely unexplored. Several population genetic models are presented and the following conclusions drawn: (i) systems with genomic imprinting need not behave similarly to otherwise identical systems without imprinting; (ii) nevertheless, many of the models investigated can be shown to be formally equivalent to models without imprinting; (iii) consequently, imprinting often cannot be discovered by following allele frequency changes or examining equilibrium values; (iv) the formal equivalences fail to preserve some well known properties. For example, for populations incorporating genomic imprinting, parameter values exist that cause these populations to behave like populations without imprinting, but with heterozygote advantage, even though no such advantage is present in these imprinting populations. We call this last phenomenon "pseudoheterosis." The imprinting systems that fail to be formally equivalent to nonimprinting systems are those in which males and females are not equivalent, i.e., two-sex viability systems and sex-chromosome inactivation.

Dosage Compensation, Genetic↗
PubMed2003

Evolution of additive and nonadditive genetic variance in development time along a cline in Drosophila serrata.

Latitudinal clines provide natural systems that may allow the effect of natural selection on the genetic variance to be determined. Ten clinal populations of Drosophila serrata collected from the eastern coast of Australia were used to examine clinal patterns in the trait mean and genetic variance of the life-history trait egg-to-adult development time. Development time significantly lengthened from tropical areas to temperate areas. The additive genetic variance for development time in each population was not associated with latitude but was associated with the population mean development time. Additive genetic variance tended to be larger in populations with more extreme development times and appeared to be consistent with allele frequency change. In contrast, the nonadditive genetic variance was not associated with the population mean but was associated with latitude. Levels of nonadditive genetic variance were greatest in the region of the cline where the gradient in the change in mean was greatest, consistent with Barton's (1999) conjecture that the generation of linkage disequilibrium may become an important component of the genetic variance in systems with a spatially varying optimum.

Analysis of Variance↗
PubMed2006

Effective gene dispersal and female reproductive success in Mediterranean maritime pine (Pinus pinaster Aiton).

Understanding population-scale processes that affect allele frequency changes across generations is a long-standing interest in genetic, ecological and evolutionary research. In particular, individual differences in female reproductive success and the spatial scale of gene flow considerably affect evolutionary change and patterns of local selection. In this study, a recently developed maximum-likelihood (ML) method based on established offspring, the Seedling Neighbourhood Model, was applied and exponentially shaped dispersal kernels were fitted to both genetic and ecological data in a widespread Mediterranean pine, Pinus pinaster Aiton. The distribution of female reproductive success in P. pinaster was very skewed (about 10% of trees mothered 50% of offspring) and significant positive female selection gradients for diameter (gamma = 0.7293) and cone crop (gamma = 0.4524) were found. The selective advantage of offspring mothered by bigger trees could be due to better-quality seeds. These seeds may show more resilience to severe summer droughts and microsite variation related to water and nutrient availability. Both approaches, ecological and of parentage, consistently showed a long-distance dispersal component in saplings that was not found in dispersal kernels based on seed shadows, highlighting the importance of Janzen-Connell effects and microenvironmental variation for survival at early stages of establishment in this Mediterranean key forest tree.

Gene Flow↗