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Results for “evolutionary genetics”

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PubMed2002

[Secretin--the first hormone].

Secretin was discovered by Starling & Bayliss in 1902. Three years later the hormone concept and hormonal regulation were described and early regulatory physiology took a major step forward. After several years of unsuccessful investigations, secretin was isolated with new chromatographic techniques and subsequently synthesised in the 1960s. Radioimmunoassays in the 1970s confirmed the final endocrine role of secretin. Cloning and molecular hybridisation in the 1990s have identified the size of production, precursor, genetic structure, and evolutionary relation to other gastrointestinal peptides. In addition, the secretin receptor has been described. In recent years, synthetic secretin has been applied in the functional and structural diagnostics of pancreatic function and in experimental therapy. Although it was the first bioactive substance to be identified as a hormone, our knowledge of secretin today, 100 years on, is still incomplete.

Endocrinology↗
PubMed2002

[Molecular-ecological technology of microorganisms and its application to research on environmental pollution].

Nucleicacid probe detection, PCR technique using primer, DNA sequential analysis, and electrophoresis separation and display were summarized and the application of these techniques to research on environmental pollution and future developing directions were discussed. It was pointed out that molecular-ecological technology of microorganisms are playing an important role in studying on relationships between microorganisms and contaminated environment. There are some important advances such as genetic adaptation and evolutionary mechanisms of microorganisms in contaminated environment, the positioning of pollutant-degrading genes of microorganisms and the construction of microbiological engineering bacteria, thus promoting the development of molecular ecology for bioremediation of contaminated environment.

Bacteria↗
PubMed2002

[Trans-gram gene transfer: the case of beta-lactamases].

Lateral or horizontal gene transfer is a phenomenon that has influenced the evolution of microorganisms. Despite the evolutionary trend toward genetic isolation, lateral transfer seems to take place relatively frequently, bridging the gap between very separate species. The acquisition of foreign genes may have accelerated in recent years because of the increase in the adaptive needs of bacteria, particularly through the use of antibiotics. Transfer of genes encoding beta-lactamases from Gram-positive to Gram-negative bacteria (trans-gram transfer) may be suggested on the basis of sequence analysis. We found that the sequences of the beta-lactamases BRO-1 and ACl-1, from the Gram-negative bacterial organisms Moraxella and Acidaminococcus, respectively are abnormally placed among sequences from Gram-positive beta-lactamases in phylogenetic trees. In both cases, the topology of the enzyme (attached to the cellular membrane), the structure of the signal peptide, and the Shine-Dalgarno region suggest that these enzymes originated from Gram-positive organisms. Results remain inconclusive for Haemophilus ROB-1 beta-lactamase.

Gene Transfer, Horizontal↗
PubMedDate not supplied

[Molecular mechanisms of macroevolution].

The present paper is devoted to the evolutionary role of genetic modules shuffing. The mechanisms capable to produce new molecular functions and significant complications of ontogenesis are reviewed. Two-step model of macroevolution is proposed. This model comprises: (1) Arising of a new combination of genetic modules. This step does not result in formation of a new taxon but makes necessary ground for that process. (2) Precise structure completing of the new combination of modules and corresponding genome optimization by use of various mechanisms including point mutations. This step concerns many genes and finally leads to formation of a new taxon. It is shown that arising of new combinations of genetic modules might work out as molecular basis for progressive evolution, while alternative structural completing of the same combination might result in adaptive radiation.

Adaptation, Physiological↗
PubMed2005

Different optimal offspring sizes for sons versus daughters may favor the evolution of temperature-dependent sex determination in viviparous lizards.

Temperature-dependent sex determination (TSD) has evolved independently in at least two lineages of viviparous Australian scincid lizards, but its adaptive significance remains unclear. We studied a montane lizard species (Eulamprus heatwolei) with TSD. Our data suggest that mothers can modify the body sizes of their offspring by selecting specific thermal regimes during pregnancy (mothers with higher and more stable temperatures produced smaller offspring), but cannot influence sons versus daughters differentially in this way. A field mark-recapture study shows that optimal offspring size differs between the sexes: larger body size at birth enhanced the survival of sons but reduced the survival of daughters. Thus, a pregnant female can optimize the fitness of either her sons or her daughters (via yolk allocation and thermoregulation), but cannot simultaneously optimize both. One evolutionary solution to reduce this fitness cost is to modify the sex-determining mechanism so that a single litter consists entirely of either sons or daughters; TSD provides such a mechanism. Previous work has implicated a sex difference in optimal offspring size as a selective force for TSD in turtles. Hence, opposing fitness determinants of sons and daughters may have favored evolutionary transitions from genetic sex determination to TSD in both oviparous turtles and viviparous lizards.

Animals↗
PubMed1992

Cultural barriers associated with large gene frequency differences among Italian populations.

Analysis of geographic variation for eight red cell markers in Italy shows significant spatial structure for most alleles. Effective population sizes estimated from FST values at these loci are much smaller than those predicted from data on consanguineous marriage, suggesting the presence of factors (presumably barriers) that have reduced gene flow and enhanced the evolutionary weight of genetic drift. Most regions of sharp gene frequency change correspond to geographic and linguistic barriers. Two allele frequencies are significantly correlated with measures of linguistic differentiation but not with indexes describing broad religious and social attitudes. The similarity between patterns of genetic and linguistic variation in Italy, also observed in a previous study, suggests that in specific areas linguistic diversity has acted as a biological barrier constraining mating, dispersal, or both. There is no evidence for a similar role of other extent cultural barriers.

Communication Barriers↗
PubMedDate not supplied

Surface morphology and characteristics of hemocytes of Biomphalaria glabrata (Pulmonata: Planorbidae) from two geographic sources.

Biomphalaria glabrata is a fresh water snail of medical importance since it is the intermediate host of the trematode Schistosoma mansoni. The internal defense system of mollusks is mostly represented by circulating elements of the hemolymph (hemocytes). The infectivity of S. mansoni to B. glabrata is determined by genetic factors and evolutionary adaptations. In the present work factors about the parasite/snail relationship were evaluated, especially those related to the morphology and characteristics of the surface of cells present in the hemolymph of two strains of B. glabrata: a strain with high susceptibility to S. mansoni (Puerto Rico, PR) and a strain with medium susceptibility (Caripe, Ca). Hemolymph was collected by cephalopodal puncture; a total and a differential count of hemocytes were done in dyed preparations and through scanning electron microscopy (SEM). Results from both strains show a high quantitative variability of the total hemocyte count. Hemocytes dyed with May-Grünwald Giemsa showed cells with a basophilic nucleus predominantly in PR (61.7%), dense and strongly basophilic in Ca (71.2%) with significant differences between them. Through SEM round cells with a corrugated surface were observed (6-10microm), hemocytes with an irregular spongy surface (12microm), others with many projections (16microm) and cells not reported in similar to erythrocytes (21microm). Hemocytic cells from both strains confirmed cytoadherence and encapsulation were confirmed in the hemocytic cells from both strains, while no differences associated to the susceptibility of the strains were observed after 2 h of parasite-hemocyte incubation.

Animals↗
PubMed2006

Functional origins of fitness effect-sizes of compensatory mutations in the DNA bacteriophage phiX174.

Epistasis is an important and poorly understood aspect of mutations and strongly influences the evolutionary impact of genetic variation on adaptation and fitness. Although recent studies have begun to characterize the distribution of epistatic effects between mutations affecting fitness, there is currently a lack of empirical information on the underlying biological causes of these epistatic interactions. What are the functional constraints that determine the effectiveness of a compensatory mutation at restoring fitness? We have measured the effect-sizes of 52 compensatory mutations affecting nine different deleterious mutations in the major capsid and spike proteins of the DNA bacteriophage phiX174. On average, an experimentally detectable compensatory mutation recovers about two-thirds of the fitness cost of the preceding deleterious mutation. Variation in fitness effect-sizes is only weakly associated with measures of the distance separating the deleterious and compensatory mutations in the amino acid sequence or the folded protein structure. However, there is a strong association of fitness effect-size with the correlation in the effects of the mutations on the biochemical properties of amino acids. A compensatory mutation has the largest effect-size, on average, when both the compensatory and deleterious mutations have radical effects on the overall biochemical make-up of the amino acids. By examining the relative contributions of specific biochemical properties to variation in fitness effect-size, we find that the area and charge of amino acids have a major influence, which suggests that the complexity of the amino acid phenotype is simplified by selection into a reduced number of phenotypic components.

Bacteriophage phi X 174↗
PubMed1994

[Pollen of gramineae and its botanical, taxonomical, and ecological aspects].

This is a review of tropical pollens (Gramineae) which cause allergy, addressed to medical workers and with emphasis in the Costa Rican. The graminean family Poaceae is widely distributed and has great genetic plasticity. An evolutionary tendency to floral reduction has led to anemophily, with pollens ranging from large (e.g. corn, Zea mays) to very small (e.g. tribes Poae and Avenae). This family produces a large number of pollens per panicle. The early morning production of free pollen (before 8 am) enhances allergic problems. In contrast, in rice (Oryza sativa) most pollen is liberated near mid day, which favours long range dispersal because of more appropriate environmental temperature and humidity. This can explain why rice is the first cause of allergic sensitivization in the asthmatic patients of the Costa Rican driest provinces (Guanacaste and Puntarenas). Despite the small size of several temperate and tropical species are present, because of geographic position, climatic diversity, irregular topography, etc. This paper presents a general description of the subfamilies Pooideae, Panicoideae, Chlorideae (Eragrostoideae) and Oryzoideae (including the medically most important tribes). Their pollens are illustrated with light and electron microscopy.

Allergens↗
PubMed1994

[Single-primer variant of PCR-amplifications of segments of the main noncoding region of human mitochondrial DNA].

A method for amplifying segments of the main non-coding region of human mitochondrial DNA using a single-primer PCR is proposed. The method employs oligonucleotides that are homologous to this region of the human mitochondrial genome. Possible reaction mechanisms and the perspectives for using the method in evolutionary and population genetic studies are discussed.

Base Sequence↗
PubMed1997

Deletion within the D17S34 locus in a primitive neuroectodermal tumor.

Loss of heterozygosity on chromosome 17p13.3 is frequently observed in solid tumors, and the presence of a tumor suppressor gene has been predicted in this region of chromosome 17. We have analyzed a primitive neuroectodermal tumor sample exhibiting loss of heterozygosity at the D17S34 locus, a commonly used telomeric marker on the short arm of chromosome 17. The remaining allele showed a rearrangement. Cosmids spanning the D17S34 locus and probes from that region were used to demonstrate a 9-kb deletion within the D17S34 locus and were found to contain evolutionary, conserved sequences. Genetic alterations in this region may also affect expression of immediately adjacent genes, such as ABR, and could be a common mechanism in the causation of primitive neuroectodermal tumors.

Chromosomes, Human, Pair 17↗
PubMed2005

QTL mapping and the genetic basis of adaptation: recent developments.

Quantitative trait loci (QTL) mapping has been used in a number of evolutionary studies to study the genetic basis of adaptation by mapping individual QTL that explain the differences between differentiated populations and also estimating their effects and interaction in the mapping population. This analysis can provide clues about the evolutionary history of populations and causes of the population differentiation. QTL mapping analysis methods and associated computer programs provide us tools for such an inference on the genetic basis and architecture of quantitative trait variation in a mapping population. Current methods have the capability to separate and localize multiple QTL and estimate their effects and interaction on a quantitative trait. More recent methods have been targeted to provide a comprehensive inference on the overall genetic architecture of multiple traits in a number of environments. This development is important for evolutionary studies on the genetic basis of multiple trait variation, genotype by environment interaction, host-parasite interaction, and also microarray gene expression QTL analysis.

Adaptation, Biological↗
PubMed2003

Mate choice theory and the mode of selection in sexual populations.

Indirect new data imply that mate and/or gamete choice are major selective forces driving genetic change in sexual populations. The system dictates nonrandom mating, an evolutionary process requiring both revised genetic theory and new data on heritability of characters underlying Darwinian fitness. Successfully reproducing individuals represent rare selections from among vigorous, competing survivors of preadult natural selection. Nonrandom mating has correlated demographic effects: reduced effective population size, inbreeding, low gene flow, and emphasis on deme structure. Characters involved in choice behavior at reproduction appear based on quantitative trait loci. This variability serves selection for fitness within the population, having only an incidental relationship to the origin of genetically based reproductive isolation between populations. The claim that extensive hybridization experiments with Drosophila indicate that selection favors a gradual progression of "isolating mechanisms" is flawed, because intra-group random mating is assumed. Over deep time, local sexual populations are strong, independent genetic systems that use rich fields of variable polygenic components of fitness. The sexual reproduction system thus particularizes, in small subspecific populations, the genetic basis of the grand adaptive sweep of selective evolutionary change, much as Darwin proposed.

Animals↗
PubMed1985

Comparison of distance matrices in studies of population structure and genetic microdifferentiation: quadratic assignment.

Questions concerning the relative effects of various evolutionary forces in molding the genetic variability exhibited by groups of human populations have typically been investigated by comparing a variety of genetic and cultural/historical "distance" matrices. A major methodological difficulty has been the lack of formal testing procedures with which to assess the degree of confirmation or disconfirmation of an estimated measure of relationship between such matrices. In this paper, we examine a very flexible matrix combinatorial procedure which generates statistical significance levels for correlational measures of pattern similarity between distance matrices. A recent generalization of the basic procedure to the three-matrix case allows questions concerning which of two matrices best fits a third matrix to be formally tested. Applications of these hypothesis testing and inference procedures to two separate sets of genetic, geographic, and cultural distance matrices illustrates their potential for finally solving a long-standing problem in anthropological genetics.

Anthropometry↗
PubMed1989

Genetic segregation and the maintenance of sexual reproduction.

Sexual reproduction confronts evolutionary biology with a paradox: other things being equal, an asexual (all-female) population will have twice the reproductive potential of a competing sexual population and therefore should rapidly drive the sexual population to extinction. Thus, the persistence of sexual reproduction in most life forms implies a compensatory advantage to sexual reproduction. Work on this problem has emphasized the evolutionary advantages produced by the genetic recombination that accompanies sexual reproduction. Here we show that genetic segregation produces an advantage to sexual reproduction even in the absence of an advantage from recombination. Segregation in a diploid sexual population allows selection to carry a single advantageous mutation to a homozygous state, whereas two separate mutations are required in a parthenogenetic population. The complete fixation of advantageous mutations is thus delayed in a heterozygous state in asexual populations. Calculation of the selective load incurred suggests that it may offset the intrinsic twofold reproductive advantage of asexual reproduction and maintain sexual reproduction in diploid populations.

Animals↗
PubMed2003

The mind of primitive anthropologists: hemoglobin and HLA, patterns of molecular evolution.

Frank Livingstone played a central role in defining the population genetics of the sickle cell mutation at position 6 of the human beta globin gene, the most famous amino acid substitution in evolutionary biology. Its discovery occurred at a time when traditional, 19th-century principles of natural selection were being joined with the newly discovered mechanics of DNA structure and protein synthesis to produce Neo-Darwinian theory. When combined with the epidemiology of malaria in Africa, differential mortality for both homozygotes, and the resulting advantage of the heterozygote, sickle cell became the classic balanced polymorphism. Human HLA-A has 237 molecular alleles. The histocompatibility system has as its primary function the presentation of peptides to T-cell receptors and plays an essential role in the immune system. Nearly all of the alleles are codominant and fully functional. Despite almost 30 years of disease-association studies with HLA-A, no convincing evidence has been found for differential fertility or mortality at this locus. Yet the dogma in the histocompatibility field is that this extensive human polymorphism is maintained by "balancing selection." Explaining HLA-A polymorphism is what one might call the sickle-cell-effect. This one mutation, coming as it did at the historical convergence of Darwinian theory and modern genetics, and carrying with it the strong relationship between mutation, disease, and allele frequency, has conditioned our discussion of human genetic variation and population genetics. Has the strength of this early idea made evolutionary biologists uncritical of systems like HLA-A and retarded the search for new mechanisms of molecular evolution? Is it now time to move away from a focus on mutation and polymorphism in evolutionary genetics and toward a systems theory that would explain the origin and evolution of hemoglobin and HLA-A and the biochemical pathways that surround them?

Alleles↗
PubMed1996

Cladistic approaches to identifying determinants of variability in multifactorial phenotypes and the evolutionary significance of variation in the human genome.

Genetic surveys based on detailed restriction site mapping or DNA sequencing allow one to identify many different classes of mutational change at the molecular level and to estimate the evolutionary history of the genetic variation (a haplotype tree). These two sources of information can be combined in a powerful fashion to test hypotheses about the evolutionary significance of genetic variation and to identify mutations that are associated with diseases. Hypotheses about selection on various classes of genetic variation can be tested by examining the distribution patterns of different mutational classes upon the haplotype tree. The power of this procedure can be enhanced if it is coupled with comparative data from other, closely related species. With respect to disease associations, all mutations that affect phenotypic variation in a population occurred at some point in the evolutionary history of the region of the gene containing the mutations. Even if this evolutionary history is estimated from mutations other than those causing phenotypic effects, the phenotypically important mutations are imbedded in this same evolutionary history. Hence, whole branches (clades) of the haplotype tree should display homogeneous phenotypic effects and this fact is utilized to search for phenotypic associations of haplotypes by using nested clades in a haplotype tree. This procedure has more power than alternatives that do not use evolutionary history, and it avoids several statistical and interpretative problems associated with single-marker analyses. All of these methods could be used more extensively if more human genetic surveys concentrated on greater genetic resolution in small DNA regions and included non-human apes.

Animals↗
PubMed1999

Evidence of recombination among enteroviruses.

Human enteroviruses consist of more than 60 serotypes, reflecting a wide range of evolutionary divergence. They have been genetically classified into four clusters on the basis of sequence homology in the coding region of the single-stranded RNA genome. To explore further the genetic relationships between human enteroviruses and to characterize the evolutionary mechanisms responsible for variation, previously sequenced genomes were subjected to detailed comparison. Bootstrap and genetic similarity analyses were used to systematically scan the alignments of complete genomic sequences. Bootstrap analysis provided evidence from an early recombination event at the junction of the 5' noncoding and coding regions of the progenitors of the current clusters. Analysis within the genetic clusters indicated that enterovirus prototype strains include intraspecies recombinants. Recombination breakpoints were detected in all genomic regions except the capsid protein coding region. Our results suggest that recombination is a significant and relatively frequent mechanism in the evolution of enterovirus genomes.

Enterovirus↗