Showing papers on "Selection (genetic algorithm) published in 1988"

Estimating the form of natural selection on a quantitative trait.

Abstract: The fitness function f relates fitness of individuals to the quantitative trait under natural selection. The function is useful in predicting fitness differences among individuals and in revealing whether an optimum is present within the range of phenotypes in the population. It may also be thought of as describing the ecological environment in terms of the trait. Quadratic regression will approximate the fitness function from data (e.g., Lande and Arnold, 1983), but the method does not reliably indicate features of f such as the presence of modes (stabilizing selection) or dips (disruptive selection). I employ an alternative procedure requiring no a priori model for the function. The method is useful in two ways: it provides a nonparametric estimate of f, of interest by itself, and it can be used to suggest an appropriate parametric model. I also discuss measures of selection intensity based on the fitness function. Analysis of six data sets yields a variety of forms of f and provides new insights for some familiar cases. Low amounts of variation and a low density of data points near the tails of many phenotype distributions emerge as limitations to gaining information on fitness functions. An experimental approach in which the distribution of a quantitative trait is broadened through manipulation would minimize these problems.

Taguchi techniques for quality engineering : loss function, orthogonal experiments, parameter and tolerance design

Abstract: The Economics of Reducing Variation The Design of Experiment Process. Orthogonal Array Selection and Utilization. Conducting Tests. Analysis and Interpretation Methods for Experiments. Confirmation Experiment. Parameter Design. Tolerance Design. Appendices: A: Problem Solutions. B: Two-Level Orthogonal Arrays. C: Three-Level Orthogonal Arrays. D: Design and Analysis Tables. E: Proofs. F: Definitions and Symbols. G: Exmaple Experiiments.

The coalescent process in models with selection.

Abstract: Statistical properties of the process describing the genealogical history of a random sample of genes are obtained for a class of population genetics models with selection. For models with selection, in contrast to models without selection, the distribution of this process, the coalescent process, depends on the distribution of the frequencies of alleles in the ancestral generations. If the ancestral frequency process can be approximated by a diffusion, then the mean and the variance of the number of segregating sites due to selectively neutral mutations in random samples can be numerically calculated. The calculations are greatly simplified if the frequencies of the alleles are tightly regulated. If the mutation rates between alleles maintained by balancing selection are low, then the number of selectively neutral segregating sites in a random sample of genes is expected to substantially exceed the number predicted under a neutral model.

Frequency-dependent selection in bacterial populations.

Abstract: There are many situations in which the direction and intensity of natural selection in bacterial populations will depend on the relative frequencies of genotypes. In some cases, this selection will favour rare genotypes and result in the maintenance of genetic variability; this is termed stabilizing frequency-dependent selection. In other cases, selection will only favour genotypes when they are common. Rare types cannot invade and genetic variability will not be maintained; this is known as disruptive frequency-dependent selection. Phage-mediated selection for bacteria with novel restriction-modification systems is frequency-dependent and stabilizing. In mass culture, selection for the production of toxins and allelopathic agents is likely to be frequency-dependent but disruptive. This also occurs in selection favouring genes and transposable elements that cause mutations. Here I review the results of theoretical and experimental studies of stabilizing and disruptive frequency-dependent selection in bacterial populations, and speculate on the importance of this kind of selection in the adaptation and evolution of these organisms and their accessory elements (plasmid, phage and transposons).

Alternative formulations of multilevel selection

Abstract: Hierarchical expansions of the theory of natural selection exist in two distinct bodies of thought in evolutionary biology, the group selection and the species selection traditions. Both traditions share the point of view that the principles of natural selection apply at levels of biological organization above the level of the individual organism. This leads them both to considermultilevel selection situations, where selection is occurring simultaneously at more than one level. Impeding unification of the theoretical approaches of the multilevel selection traditions are the different goals of investigators in the different subdisciplines and the different types of data potentially available for analysis. We identify two alternative approaches to multilevel situations, which we termmultilevel selection [1] andmultilevel selection [2]. Of interest in the former case are the effects of group membership onindividual fitnesses, and in the latter the tendencies for the groups themselves to go extinct or to found new groups (i.e., group fitnesses). We argue that: neither represents the entire multilevel selection process; both are aspects of any multilevel selection situation; and both are legitimate approaches, suitable for answering different questions. Using this formalism, we show that: multilevel selection [2] does not require “emergent” group properties in order to provide an explanatory mechanism of evolutionary change; multilevel selection [1] is usually more appropriate for neontological group selection studies; and species selection is most fruitfully considered from the point of view of multilevel selection [2]. Finally we argue that the “effect hypothesis” of macroevolution, requiring, in selection among species, both the absence of group effects on organismic fitness (multilevel selection [1]), and the direct determination of species fitnesses by those of organisms, is untestable with paleontological data. Furthermore, the conditions for the effect hypothesis to hold are extremely restrictive and unlikely to apply to the vast majority of situations encountered in nature.

Mutation, developmental selection, and plant evolution

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Joint Venture Partner Selection: Strategies for Developed Countries

Abstract: Introduction, Hypotheses and Methods Introduction Review of Selection Criteria Literature Research Hypotheses Research Methodology Results for Partner Selection Criteria Variable Partner Selection Criteria Variable Results for Task -Related Variables Critical Success Factor Variable Competitive Position Variable Difficulty of Internal Development Variable Part IV: Results for Partner-Related Variables Perceived Task Environment Uncertainty Variable Diversity of Line Functions Variable Extent of Shared Control Variable Conclusion and Implications Conclusions Implications Evaluation of Method and Future Research

Automatic smoothing parameter selection: A survey

Abstract: This is a survey of recent developments in smoothing parameter selection for curve estimation. The first goal of this paper is to provide an introduction to the methods available, with discussion at both a practical and also a nontechnical level, including comparison of methods. The second goal is to provide access to the literature, especially on smoothing parameter selection, but also on curve estimation in general. The two main settings considered here are nonparametric regression and probability density estimation, although the points made apply to other settings as well. These points also apply to many different estimators, although the focus is on kernel estimators, because they are the most easily understood and motivated, and have been at the heart of the development in the field.

An Integer Programming Approach to the Optimal Product Line Selection Problem

Abstract: A zero-one integer mathematical programming formulation is proposed to solve the optimal product line selection problem. Based on individual consumer measurements from conjoint analysis, the formulation seeks to find an optimal subset of products that is drawn from a proposed set of product alternatives with specified product characteristics. In addition to its inherent flexibility in incorporating various realistic constraints, a feature of the proposed approach is its potential determination of verifiable optimal solutions to the product line selection problem. The results of computational experience with an optimization code, known as the X-system, are presented. Using a variety of representative simulated cases, it is shown that the X-system can be used to effectively solve product line selection problems on both mainframe and AT personal computers.

Long-term correlated response, interpopulation covariation, and interspecific allometry

Abstract: A model of long-term correlated evolution of multiple quantitative characters is analyzed, which partitions selection into two components: one stabilizing and the other directional. The model assumes that the stabilizing component is less variable than the directional component among populations. The major result is that, within a population, the responses of characters to selection in the short term differ qualitatively from those in the long term. In the short term, the responses depend on genetic correlations between characters, but in the long term they are only determined by the fitness functions of stabilizing and directional selection, independent of genetic and phenotypic correlations. Treating the stabilizing component as a constant and assuming the directional component to vary among populations, I present formulas for the interpopulation covariation and interspecific allometry, which are functions of the intensity matrix of stabilizing selection. Particular attention is paid to the relationship between intra- and interpopulation correlations.

Multiple genetic mechanisms for the evolution of senescence in Drosophila melanogaster

Abstract: We present the results of selection experiments designed to distinguish between antag- onistic pleiotropy and mutation accumulation, two mechanisms for the evolution of senescence. Reverse selection for early-life fitness was applied to laboratory populations of Drosophila mela- nogaster that had been previously selected for late-life fitness. These populations also exhibited reduced early-age female fecundity and increased resistance to the stresses of starvation, desiccation, and ethanol, when compared to control populations. Reverse selection was carried out at both uncontrolled, higher larval rearing density and at controlled, lower larval density. In the uncon- trolled-density selection lines, early-age female fecundity increased to control-population levels in response to the reintroduction of selection for early-age fitness. Concomitantly, resistance to star- vation declined in agreement with previous observations of a negative genetic correlation between these two characters and in accordance with the antagonistic-pleiotropy mechanism. However, resistance to stresses of desiccation and ethanol did not decline in the uncontrolled-density lines during 22 generations of reverse selection for early-life fitness. The latter results provide evidence that mutation accumulation has also played a role in the evolution of senescence in this set of Drosophila populations. No significant response in early-age fecundity or starvation resistance was observed in the controlled-density reverse-selection lines, supporting previous observations that selection on Drosophila life-history characters is critically sensitive to larval rearing density.

Rate tests for selection on quantitative characters during macroevolution and microevolution.

Abstract: Evolutionary biologists are increasingly interested in testing alternative models rather than simply presenting plausible explanations for their observations. Although most biologists agree that significant phenotypic changes cannot occur without natural selection, it is useful to have statistical tests that reject alternative mechanisms such as genetic drift and mutation. The first such tests were presented by Lande (1976, 1977). This note reviews previous analyses of neutral phenotypic evolution and concentrates on tests derived from two simple approximations. One describes neutral macroevolution in populations that have achieved an equilibrium level of heritable variation determined by mutation and genetic drift; the other (developed explicitly in Lande [1976, 1977]) describes neutral microevolution in recently established populations whose levels of heritable variation may be far from mutationdrift equilibrium. As our examples below demonstrate, average rates of macroevolutionary change are rarely fast or slow enough to provide sufficient evidence for rejecting neutral models. Although we state our results in terms of statistical tests, the sampling errors for many of the parameters are unknown. Thus our results are best viewed as qualitative assessments of the agreement of evolutionary rates with the expectations from simple neutral models. Lande (1976) applied quantitative-genetics theory to describe two fundamental processes that can change phenotypic means: natural selection and genetic drift. He first estimated the minimum intensity of truncation selection necessary to produce a specific change (see Charlesworth [1984a) for an analysis of another mode of selection); then, he calculated the maximum effective population size, denoted N, *, that would allow genetic drift to produce the same phenotypic change by random sampling. From this stochastic model, Lande (1977) developed a \"rate test\" for the hypothesis that drift alone could account for observed divergence among the mean phenotypes of reproductively isolated populations. Charlesworth (l984b) has developed related tests for the null hypothesis that evolutionary rates remain constant within lineages. All of these tests, including the ones discussed below, assume that changes in mean phenotype are caused by genetic changes rather than direct phenotypic responses to changing environmental conditions. An implication of Lande's (1976) test, which rejects neutrality if N, > Ne*, is that genetic drift changes the mean phenotype more rapidly in small populations than in large ones. This contradicts Kimura's (1968) original neutral theory of molecular evolution, which predicts that the rate of molecular evolution is independent of population size and is governed wholly by the rate at which neutral mutations arise. The reason for this discrepancy is that Lande's (1976) test treats the additive genetic variance as roughly constant and independent of population size. In contrast, Kimura's neutral theory is based on an explicit model of mutation and drift, which leads to the prediction that the equilibrium genetic variance depends on population size while the rate of evolution is independent of population size. Although Lande (1976 p. 326) noted that the equilibrium level of additive variance will generally depend on population size, this was not incorporated into his test for neutral phenotypic evolution. Subsequently, Lande (1979, 1980) gave explicit formulas for the dynamics of phenotypic means and both the equilibria and dynamics of genetic variances and covariances for multiple characters under mutation and drift. As discussed below, these later analyses, like Kimura's neutral theory, lead to the prediction that the longterm rate of neutral phenotypic evolution depends only on mutation parameters and is independent of population size. Lynch and Hill (1986) analyzed the implications of more general genetic assumptions for both the dynamics and equilibria ofa single polygenic character subject to mutation and genetic drift. The purpose of the present note is to clarify the relationships among these results and to emphasize the critical role played by time scales and initial conditions in determining the importance of population size to neutral phenotypic evolution.

Selection on individual phenotype and best linear unbiased predictor of breeding value in a closed swine herd.

Abstract: Computer simulation of a closed 100-sow and 4-boar swine herd was used to analyze effects of selection method on genetic change, inbreeding and genetic variance over 10 yr for traits with heritabilities (h2) of .10, .30 and .60. Selection of replacement animals was either on individual phenotype or best linear unbiased predictor (BLUP) of breeding value using an animal model. For both methods, culling of existing breeding animals was at random on age and reproductive performance. The effect of additional culling of existing breeding animals when a replacement with better individual phenotype or BLUP of breeding value was available also was evaluated. Genetic gain was greater for selection on BLUP than on individual phenotype, but relative differences narrowed with increasing heritability. At yr 10 the relative advantage of selection on BLUP was 55% for h2 = .10, 25% for h2 = .30 and 10% for h2 = .60. Culling when a replacement with better individual phenotype or BLUP of breeding value was available resulted in considerably increased genetic progress (34% to 57%). The proportional effect of culling on rate of genetic gain was relatively independent of heritability and type of selection. Inbreeding (F) was higher with selection on BLUP (F = .27 to .38 at yr 10) than on individual phenotype (F = .17 to .22 at yr 10). As heritability increased, rate of inbreeding increased for selection on individual phenotype, but rate of inbreeding tended to decrease with increasing heritability for selection on BLUP.(ABSTRACT TRUNCATED AT 250 WORDS)

Aspects of unconscious selection and the evolution of domesticated plants

Abstract: Unconscious selection may be defined as non-intentional human selection. The term was introduced by Darwin and its modern concept was developed by C.D. Darlington. Unconscious selection, or automatic selection as it is sometimes called, could have been responsible for most of the differences that distinguish domesticated seed crops from their wild progenitors, including loss of natural dispersal mechanisms, even and rapid seed germination, larger propagules, simultaneous ripening, and loss of mechanical protection as well as changes in the breeding system. Some differences, such as those in seed or fruit colors, may have developed from conscious selection at an early time. For unconscious selection to operate in the development of domesticated plants there would have to have been a deliberate planting of seeds by people.

The Problem of Selecting the Shape Functions for a p-Type Finite Element

Abstract: : The paper addresses the question of the optimal selection of the shape functions for p-type finite elements and discusses the effectivity of the conjugate gradient and multilevel iteration method for solving the corresponding linear system. The selection of the shape functions is of major importance for the performance of the solver based on iterative methods. Neither the theory nor practice of the optimal selection of the shape functions is available yet. We have seen that the condensation approach which has obvious advantages from the point of parallel computations is a very effective tool for keeping the condition number under the control and is especially advantageous for the conjugate gradient method.

Field measurements of natural and sexual selection in the fungus beetle, bolitotherus cornutus.

Abstract: Selection on three phenotypic traits was estimated in a natural population of a fungus beetle, Bolitotherus cornutus. Lifetime fitness of a group of males in this population was estimated, and partitioned into five components: lifespan, attendance at the mating area, number of females courted, number of copulations attempted, and number of females inseminated. Three phenotypic characters were measured-elytral length, horn length, and weight; there were strong positive correlations among the three characters. Selection was estimated by regressing each component of fitness on the phenotypic traits. Of the three traits, only horn length was under significant direct selection. This selection was for longer horns and was due mainly to differences in lifespan and access to females. The positive selection on horn length combined with the positive correlations between horn length and the other two characters resulted in positive total selection on all three characters.

Selection of wound closure materials

Abstract: Selection of wound closure materials (sutures, needles, staples, and skin tapes) is presented. The characteristics of commonly used suture materials and needles are discussed as a background for their rational selection and usage. The attributes of staples and sutureless skin closures (skin tapes) are also given and contrasted with those of sutures.

Frequency-dependent Selection

Abstract: Received 30.X.63

Plant Breeding Methodology

Abstract: Part 1 Introductory topics: introduction to methodology genetic engineering and the future. Part 2 Breeding and selection methods: primary methods shaped by historical usage - a preamble the mass selection method pedigree and f+d2-derived family methods backcross method methods shaped by competitive forces the multiblend variety the multiline method methods shaped by recurrent forces the recurrent selection method diallel selective mating method genetic male sterility male sterile facilitated recurrent selection method methods shaped by requirements of techniques heterosis and commercial hybrids the single seed descent method doubled haploid method. Part 3 Breeding and selection strategies: issues in selection - a preamble visual selection selection indices harvest index stability. Part 4 Germ plasm and crossing considerations: germ plasm choosing cross quality level predicting and choosing parents predicting and choosing crosses and lines hybridizing or crossing techniques. Part 5 Plant traits of special relevance: seed characteristics morphological and other traits. Part 6 Project management: the four stages of plant breeding minimum staff plant breeding choosing sites and environments field organization and operations 101 ways to enrich your breeding program.

Quantitative genetics of morphological differentiation in peromyscus. ii. analysis of selection and drift.

Abstract: The hypothesis that the morphological divergence of local populations of Peromyscus is due to random genetic drift was evaluated by testing the proportionality of the among-locality covariance matrix, L, and the additive genetic covariance matrix, G. Overall, significant proportionality of L and Ĝ was not observed, indicating the evolutionary divergence of local populations does not result from random genetic drift. The forces of selection needed to differentiate three taxa of Peromyscus were reconstructed to examine the divergence of species and subspecies. The selection gradients obtained illustrate the inadequacy of univariate analyses of selection by finding that some characters evolve in the direction opposite to the force of selection acting directly on them. A retrospective selection index was constructed using the estimated selection gradients, and truncation selection on this index was used to estimate the minimum selective mortality per generation required to produce the observed change. On any of the time scales used, the proportion of the population that would need to be culled was quite low, the greatest being of the same order of magnitude as the selective intensities observed in extant natural populations. Thus, entirely plausible intensities of directional natural selection can produce species-level differences in a period of time too short to be resolved in the fossil record.