Showing papers on "Selection (genetic algorithm) published in 1971"

The Effect of Selection on Genetic Variability

Abstract: If a metric character is determined by an effectively infinite number of loci, selection cannot cause any permanent change in the genetic variance but will cause a temporary change which is rapidly reversed when selection ceases. This change is due entirely to the correlation between pairs of loci which is induced by selection; the correlation is negative, leading to a reduction in the genetic variance under stabilizing or directional selection, and is positive, leading to an increase in the variance under disruptive selection. When selection ceases, the correlation rapidly disappears as joint equilibrium at pairs of loci is reestablished, and the variance returns to its original value. An expression is derived for the predicted amount of change in the genetic variance due to disequilibrium in the absence of linkage. The change is likely to be small under selection intensities found under natural conditions, but it may be appreciable under intense artificial selection. This limiting result shows that the ...

An Optimization Model of Food Selection

Abstract: An optimization model has been developed for the analysis of food selection behavior. The model determines the numbers and typed of prey species consumed given predator preferences and prey availability. Preferences are expressed as an ordinal ranking of all possible prey combinations. The model generates hypotheses concerning conditions for "predator switching" and other predator strategies.

Design and efficiency of selection experiments for estimating genetic parameters.

Abstract: (i) Formulae are derived for the sampling variance of selection response and for estimates of realised heritability and realised genetic correlation. (ii) If a control population is maintained, or divergent selection practised, the greater part of the sampling variance comes from genetic drift and depends primarily on the total number of individuals recorded in the whole experiment, rather than on its duration. (iii) The optimal selection intensity for estimating realised heritabilities is investigated-proportions selected of about 15 per cent should be satisfactory. Similar designs will also be efficient for estimation of realised genetic correlations. (iv) Several methods of estimating heritability are compared, of these the realised heritability has least variance. (v) Some selection indices for improving a single trait are evaluated. Mass selection is likely to be best for comparing response from alternative selection programmes or populations.

Portfolio Selection: The Effects of Uncertain Means, Variances, and Covariances

Abstract: Present models for selecting portfolios according to the mean-variance criteria do not account for the simultaneous effect of error in estimating means, variances, and covariances of security returns. This paper describes an experiment in which the impact of estimation error is so strong that the usefulness of present mean-variance approaches to portfolio selection is brought into question.

Some Models of Racial Discrimination in the Labor Market

Abstract: : The intention of the report is to demonstrate the advantages and disadvantages of neoclassical analysis as a tool for studying racial discrimination in the economic sphere and to suggest possible areas of fruitful research.

Behavioral Aspects of Population Dynamics in Unisexual‐Bisexual Poeciliopsis (Pisces: Poeciliidae)

Abstract: Unisexual forms of Poeciliopsis require sperm from males of gonochoristic species. Selection pressures dictate that males discriminate against unisexuals until the latter become extinct. Most Poeciliopsis unisexual—bisexual populations have a unisexual—bisexual female ratio that favors unisexuals, indicating that selection for conspecific mating by males has either not been operative, not persisted for a sufficient period of time, or been disrupted by unknown factors. In mate selection and insemination tests single males show almost absolute preference for conspecific females, but social interactions among males result in unisexual inseminations. Mate selection reduces unisexual fecundity in natural populations, but the all—female forms receive sufficient sperm to sustain themselves. See full-text article at JSTOR

Genetic Equilibrium and Population Growth Under Density-Regulated Selection

Abstract: A maximization principle relating gene frequency changes and population growth is formulated for a simple model of density-regulated selection. The selective value of each genotype is altered by density in a way analogous to logistic population growth. The growth of the population as a whole is logistic, its maximal rate of increase being a weighted arithmetic mean of the genotypic rates, and its carrying capacity a weighted harmonic mean of the genotypic carrying capacities. A stable genetic polymorphism occurs at a maximum, and an unstable equilibrium at a minimum, of the mean genotypic carrying capacity.

Age-Specific Selection. II. The Interaction between r and K during Population Growth

Abstract: The interplay between density-independent (r) and density-dependent (K) components of selection is investigated using models of Mendelian populations with breeding at discrete intervals and overlapping generations. Selection within each genotype is age-specific, while the contribution of each genotype to population growth is logistic. The interaction between the r- and K-characteristics of the genotypes, in conjunction with the initial population structure, determines the patterns of population growth and gene frequency change. Moreover, these patterns may be strikingly different from the sigmoid curves obtained with simpler models. In a constant environment, K-characteristics alone determine the ultimate outcome of selection. Heterozygote advantage with respect to K is necessary for a balanced genetic polymorphism. The situation is different if the environment varies. We have investigated the effects of two kinds of environmental variation on the interaction between r- and K-selection. In the first of th...

Selection and processing system for signals, including frequency discriminator

Abstract: A signal selection and processing system for use with a broadband LORAN receiver in which the average of the strongest interfering signal having a predetermined duty cycle sets the AGC level and, via a special frequency discriminator, controls the frequency of a voltage controlled oscillator (VCO). The VCO output is used to shift the entire band of input frequencies so that said strongest signals fall into the attenuating notch of a notch filter while passing the other signals to the LORAN receiver.

Variation for metrical characters in drosophila populations. 3. The nature of selection.

Abstract: AN earlier paper (Kearsey and Barnes, 1970) reported the results of experiments investigating the relationship between sternopleural chaeta number and fitness in a cage population of Drosophila melanoaster. The population studied was derived from a cross between two lines, produced by selection for high and for low number of chaetae from our "Texas" population (Barnes and Kearsey, 1970), and subsequently allowed to evolve under cage conditions. It was shown that the phenotypic variance of adults captured in the cage, the survivors of intense larval competition, was approximately onequarter that of their contemporaries raised at very low density. Furthermore, this decrease in phenotypic variance was shown to be due, almost exclusively, to a decrease in genetic variance. That is, there has been selective elimination of certain genotypes at the pre-adult stage. This selective elimination was related to chaeta number. It was then possible to estimate the relative fitness of different phenotypes by comparing their relative frequencies at the two larval densities. By this means fitness was shown to be greatest for phenotypes with a value close to that of the F1 between the parental selection lines and to decline markedly with deviations in both directions from this optimum, reaching a fitness of zero within the phenotypic range. Such a reduced fitness of extreme phenotypes might be due to association between genes controlling chaeta number and subvital genes fixed during the establishment of the parental selection lines. That is, the selection lines may contain a number of recessive subvital genes linked to genes for sternopleural chaeta number and this association might still be present at the time of the experiment. Extreme phenotypes will tend to be homozygous for such subvitals, whereas intermediate phenotypes will be heterozygous and hence have higher fitness. However, the detailed relationship between phenotype and fitness was not consistent with the relationship generally found in such cases. Although linked subvitals might in part be the cause, it was argued that the results are more compatible with stabilising selection. The relationship between chaeta number and fecundity, on the other hand, was entirely consistent with a system of dispersed subvital genes. However, females extreme for chaeta number do not reach adulthood under cage conditions and as a consequence the variation in fecundity had no impact on fitness. The major component of fitness in this case appears to be egg to adult survival.

Analysis of some portfolio selection models for R&D

Abstract: This paper presents an analytical review of mathematical programming models that have been proposed as aids to the related problems of resource allocation and project selection in RD built-in assumptions; ease of computation; usefulness of outputs; versatility of application.

Evidence for the Evolution of Unpalatability Through Kin Selection in the Heliconinae (Lepidoptera)

Abstract: The relative palatabilities of seven species of heliconiine butterflies from Trinidad studied by Brower, Brower, and Collins (1963) correlate with variables directly related to individual dispersal and presumably inbreeding. The more unpalatable a species, the greater the number of geographic races and the higher the probability that populations will form site-specific roosting aggregations indicative of home-range behavior and inbreeding. These correlations are expected if kin selection has been important in the evolution of unpalatability in the Heliconiinae, but not if individual selection has been of overriding importance. The evidence supports the hypothesis that genes responsible for the production of unpalatability gain their advantage in part by having individuals carrying genes identical by descent nearby, so that a predator attacking one of these individuals will learn subsequently to avoid attacking other related individuals in the same area.

Quantitative inheritance studies in sugar-cane. II. Correlations and predicted responses to selection

Abstract: Predicted responses to selection for a number of characters, and genotypic and phenotypic correlations between characters were studied in sugar-cane seedling populations. Predicted response from family selection was found to be much greater than from mass selection for all characters except Brix value. A selection system incorporating family selection for grade (phenotypic score) and mass selection for Brix value was proposed for further investigation. Many genotypic correlations between important characters were positive and quite high with the notable exception of the correlation between stalks per stool and weight per stalk, which was high and negative. Genotypic correlations between arrowing percentage (an undesirable character) and all other characters except stalks per stool were high and negative, but most had large standard errors.

Long Term Selection for Body Weight in Mice

Abstract: IN 1930 H. D. Goodale began an experiment with mice in which he selected for body weight at 60 days of age. This study sought to determine the limits of change that could be produced through the utilization of individual, progeny test, and family methods of selection continuing for 84 generations. Dr. Goodale's stated objective was to breed mice as large as possible, and he felt it conceivable that by selection mice exceeding the size of rats could be produced. At that time, little was known of selection limits, so his ideas concerning plateaus were not illogical. Reports by Goodale" on the early results of this study showed a consistent increase in body size with no evidence of a plateau. MacArthur', utilizing information from the individual's phenotype plus those of relatives, reported a consistent divergence of lines of mice selected for high and low 60-day body weight. After 23 generations of selection, the males and females of the high line were approximately 3.2 and 3.6 times as heavy as the males and females in the low line, respectively. After 11 generations of within-family selection for large and small body size at 42 days, Falconer reported a divergence between the two lines of 11 grams, or 50 percent of the initial weight. Heritability was about 20 percent for upward selection and 50 percent for downward. Continued selection by Falconer and King for high 6-week body weight in samples of the Goodale and MacArthur lines at (approximately) generations 43 and 26, respectively, yielded little or no additional increase in body size. Roberts, working with several populations, found that selection for large and small size produced mice with mean 6week body weights of approximately 30 and 12 grams at cessation of response. These limits were realized after 10 to 30 generations of selection. Considerable information is now available indicat-