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Bünger L, Herrendörfer G. Analysis of a long-term selection experiment with an exponential model. J Anim Breed Genet 2011; 111:1-13. [DOI: 10.1111/j.1439-0388.1994.tb00432.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Abstract
SUMMARYA line of mice, at its limit to selection for high body weight did not decline in performance over 11 generations of random mating, neither did it respond when selection was renewed. The experiment tested a method of improving body weight by a scheme which had earlier increased litter size under similar circumstances. The scheme was to derive partially inbred lines from the plateaued line, to select during inbreeding and, finally, to cross the best inbreds. Body weight was not increased, but the study allowed further examination of the residual genetic variance in the line.During inbreeding, the inbred lines became clearly differentiated in body weight, proving that loci controlling body weight had not become fixed. There was also a significant response to selection for a lower body weight during inbreeding. The pattern of results suggested the segregation of recessive genes, detrimental to high body weight but which selection had become inefficient at removing. A genetic model compatible with the results accommodated several such recessives, perhaps as many as 10, each with an effect of about two-thirds of a standard deviation (or some equivalent combination of gene number and effect), and at frequencies of around 0·2. Nevertheless, the total improvement in body weight to be gained by their elimination was only half a gram, or less than 2 %. Thus, substantial genetic effects can occur at individual loci despite trivially low heritabilities and negligible potential gains.
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STEANE DE, ROBERTS RC. Selection for total weaning weight in the mouse, and its implications for domestic livestock. ACTA ACUST UNITED AC 2010. [DOI: 10.1111/j.1439-0388.1982.tb00380.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Mgheni M, Christensen K. Selection Experiment on Growth and Litter Size in Rabbits. ACTA ACUST UNITED AC 2009. [DOI: 10.1080/00015128509435784] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Genetic differences between populations of Drosophila melanogaster for a quantitative trait: I. Laboratory populations. Genet Res (Camb) 2009. [DOI: 10.1017/s0016672300012830] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
SUMMARYAn experiment was carried out to test whether two laboratory cage populations of Drosophila melanogaster from different origins (Kaduna and Pacific) differed in the genes for sternopleural bristle number. The means, variances and heritabilities of the two populations and the synthetic formed from crosses between them were very similar.Selection for low bristle number was practised in small replicate lines, six of each pure population and nine of the synthetic. On average, Pacific responded to selection rather more rapidly than either Kaduna or the synthetic, but there was little difference in the limit achieved.Crosses between replicates within populations were made and selection continued, and these lines subsequently crossed between populations and reselected. Additional response was obtained by this procedure but the crosses between the replicates of the pure and synthetic populations attained similar selection limits.An analysis of effects of individual chromosomes from the selected lines on bristle number indicated that the contribution of each chromosome to total response was about the same in Pacific, Kaduna and the synthetic.It is concluded that differences in gene frequency, rather than the presence or absence of particular alleles, are mainly responsible for the differences observed between the populations.
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BAFFOUR-AWUAH O, BARKER JSF. Selection responses in synthetic populations of Drosophila melanogaster. J Anim Breed Genet 1988. [DOI: 10.1111/j.1439-0388.1988.tb00281.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Schüler L. Selection for fertility in mice - the selection plateau and how to overcome it. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 1985; 70:72-79. [PMID: 24254117 DOI: 10.1007/bf00264485] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/1984] [Accepted: 11/28/1984] [Indexed: 06/02/2023]
Abstract
A long-term experiment for increasing the traits first day litter size (LS1) and litter weight (LW1) was conducted with two populations for 33 generations. The selection plateau was reached in population DU-C (selection and estrus synchronization (h(2) = 0.02±0.01); in population DU-K (selection) the plateau (h(2) = 0.05±0.2) was nearly reached. Selection progress per generation was in LS1 b = 0.11±0.02; b = 0.12±0.04 (1st to 18th generation DU-K, DU-C) and b = 0.10±0.03; b = 0.07±0.05 (19th to 33rd generation, DU-K, DU-C) in LW1 b = 0.16±0.04 g; 0.19±0.07 g (DU-K, DU-C) b = 0.20±0.09 g; 0.001±0.09 g (DU-K, DU-C). Reverse and relaxe selection as well as systematic inbreeding was applied for 10 generations. Reverse selection yielded h(2) = 0.28±0.11 (R-DU-K) and h(2) = 0.17±0.05 (R-DU-C) and showed that there was still additive genetic variance. Relaxe selection did not cause alterations in the selection parameters, whereas inbreeding lead to inbred depressions (b = LS1 = -0.42±0.15; -0.45±0.12; b = LW1 = -1.13±0.20; -0.82±0.18 I-DU-K, I-DU-C). The plateau was based upon the heterozygote advantage. Several methods for overcoming the plateau were applied. A new selective useful variance could be created by crossing the plateau populations (h(2) = 0.14±0.04). A short-term progress in overcoming the plateau (1st to 3rd generation) could be obtained by litter size standardization (LS = 388). Tandem selection (selection for body weight - BW42) as well as crossing of inbred strains were not suitable for overcoming the selection plateau. Altering the environmental conditions as a possibility for overcoming the plateau has been discussed.
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Affiliation(s)
- L Schüler
- Forschungszentrum für Tierproduktion Dummerstorf-Rostock der Akademie der Landwirtschaftswissenschaften der DDR, DDR-2551, Dummerstorf, German Democratic Republic
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Abstract
SUMMARYA strain of mice that had ceased to respond to selection for high litter size was inbred with continued selection. Depression of the mean proved the existence of residual genetic variance. Four lines survived the inbreeding, and one reached 20 generations with a mean equal to the original strain, thus disproving overdominance as a major cause of the residual variation. The four selected inbred lines were crossed and a new strain derived from the cross was maintained in parallel with the original strain. The new strain showed an improvement of 1·5 mice per litter over the original strain. Thus selection with inbreeding was able to achieve an advance beyond the limit attained by the original selection.The hypothesis that the residual variation was due to genes with simple dominance was tested by seeing if it could account for the observations with reasonable values of the relevant parameters. The improvement made by the inbreeding and crossing required the elimination of about 30 recessive genes with effects (homozygote difference) of 0·5 phenotypic standard deviations and gene frequencies of 0·2. Consideration of the mean levels of the selected inbred lines in conjunction with the rate of depression found on inbreeding without selection showed that the selection with inbreeding had eliminated about 75% of the segregating reces-sives. The number of genes contributing to the residual variance was therefore about 40. The additive variance generated by these genes was just consistent with the estimate of zero from the realized heritability. Consideration of the original selection showed that about half the genes could have been still segregating when the response ceased. The hypothesis therefore requires the number of genes in the base population to have been about 80. The number of genes required, though large, does not seem impossible, and the hypothesis of genes with simple dominance can account for all the observations.
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Kress DD, Enfield FD, Braskerud O. Correlated response in male and female sterility to selection for pupa weight in Tribolium castaneum. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 1971; 41:197-202. [PMID: 24430243 DOI: 10.1007/bf00279769] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/1970] [Indexed: 06/03/2023]
Abstract
The correlated responses in male and female sterility to 50 generations of individual selection for pupa weight in Tribolium were analyzed. Two replicate lines (S-lines) were selected for heavier pupa weight and stabilizing selection for pupa weight was practiced in two replicate control lines (C-lines). There was close agreement between replicates in both sets of lines for direct and correlated responses. The rate of inbreeding has been constant for all lines (approximately 0.5% per generation).Regression of generation means for pupa weight on generation of selection indicated a significant linear regression in the direct response for both lines. The linear increases of 46 and 55 μg. per generation in the S-lines accounted for 98% of the variation among generations and the linear decreases of 5 and 10 μg. per generation in the C-lines accounted for 70-90% of the variation in the generation means.Maximum likelihood estimators were used to calculate the frequency of male and female sterility for each generation and line. Average sterility in the base population ranged from about 4 to 12% for both sexes. Polynomial regressions of percent sterility on generation of selection showed that quadratic and higher order regressions were occasionally significant but accounted for a relatively small fraction of the total variation. In the two S-line replicates, linear regression coefficients of percent sterility on generation number were 0.16±.09 and 0.20±.07 for males and 0.72±.08 and 0.54±.08 for females, suggesting a larger correlated response in female than in male sterility. In the C-lines, linear regression coefficients were 0.02±.08 and -.12±.05 for males in the two replicates and -.05±.05 and -.05±.05 for females. Estimates of realized genetic correlations between pupa weight and sterility in the S-lines ranged from 0.04 to 0.14 for males and from 0.14 to 0.37 for females when the heritability of sterility was allowed to take on values from 0.05 to 0.25.
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Affiliation(s)
- D D Kress
- University of Minnesota, St. Paul, Minn., USA
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Morton JR. Analysis of gene action in the control of body weight and tail length in the mouse. Heredity (Edinb) 1970; 25:555-74. [PMID: 5286381 DOI: 10.1038/hdy.1970.63] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
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Papa KE. Inheritance of growth rate in Neurospora crassa: crosses between previously selected lines. CANADIAN JOURNAL OF GENETICS AND CYTOLOGY. JOURNAL CANADIEN DE GENETIQUE ET DE CYTOLOGIE 1970; 12:1-9. [PMID: 5487923 DOI: 10.1139/g70-001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Continuous selection for fast linear growth rate in Neurospora crassa at 18°, 25°, and 35 °C was effective. Crossing plateaued selection lines within the same temperature revealed that different combinations of genes were synthesized in each line. Most of these differences could be attributed to non-additive gene effects. Twelve cycles of selection within progeny from crosses between selected lines were effective, although the growth rate reached previously in the fastest parent was not surpassed.Crossing plateaued selection lines improved at different temperatures generated new genetic variance, thus indicating the fixation of different alleles in different lines with temperature. The difference between lines selected at different temperatures could be explained be the additive effect of two to three genes. Estimates of the average genetic variance were found to be highest among the progeny from crosses involving 35°-selection lines and lowest from crosses involving 18°-selection lines
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Dev D, Jaap R, Harvey W. Results of Selection for Eight-Week Body Weight in Three Broiler Populations of Chickens. Poult Sci 1969. [DOI: 10.3382/ps.0481336] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Frankham R, Jones LP, Barker JS. The effects of population size and selection intensity in selection for a quantitative character in Drosophila. 3. Analyses of the lines. Genet Res (Camb) 1968; 12:267-83. [PMID: 5713600 DOI: 10.1017/s0016672300011861] [Citation(s) in RCA: 36] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
1. In order to determine the nature of the genetic variation causing the response to selection in our lines (Joneset al.1968), various analyses were performed.2. There was no consistent change in heritability, estimated from half-sib correlation or from the phenotypic correlation between the bristle numbers of two abdominal segments, after 10 to 20 generations of selection.3. Realized heritabilities over the 10 generations subsequent to the heritability estimations were less than in the early generations but bore little relationship to the estimated values.4. Six lines contained recessive lethals with appreciable effects on bristle number as indicated by high variances, large regression on relaxation and large response to reverse selection.5. Reverse selection lines taken from the main lines at generation 40 indicated that genetic variation was still present in almost all of the lines. Only one line failed to respond to further forward or to reverse selection.6. The three highest lines were crossed in pairs and reselected. Two of the three possible crosses gave further response, exceeding the higher parent after one and three generations, but the other cross failed to pass the highest parent line.7. A combination of large gene effects, linkage, and gene interaction effects have been suggested as the cause of irregularities in the response of the lines. It has not been possible to determine the relative importance of these effects.
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Ohta T. Effect of initial linkage disequilibrium and epistasis on fixation probability in a small population, with two segregating loci. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 1968; 38:243-248. [PMID: 24442309 DOI: 10.1007/bf01245624] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The probability of ultimate fixation was studied for 2 loci small populations by the method of Monte Carlo simulation and also partly by analytical treatment. The analytical solutions for fixation probability known at present and the difficulty of their application to more complex situations were discussed. Monte Carlo experiments were carried out for large values ofN e s 1,N e s 2 andN e ε, for which the analytical solutions have not been obtained.One of the main purposes was to investigate the effect of initial linkage disequilibrium (D) on fixation probability. Whens 1,s 2 and ε are 0, the effect of disequilibrium is given by {1-2N e c/(2N e c+1)}D withKIMURA'S model and {1-2N e c/(2 N e c-c+1)}D with the model ofKARLIN andMCGREGOR. When |N e s 1| and |N e s 2| were small and ε=0, the effect of disequilibrium was shown to be almost the same as in the selectively neutral case (formulas 8). When those parameters are not small, the effect of disequilibrium is larger because of the rapid approach to fixation.Another purpose of this study was to investigate the effect of epistasis on fixation probability.KIMURA obtained the solution for joint fixation ofA andB when the selective advantage is given to genotypeAB as the joint effect ofA andB. The present study has verified his formula and showed that linkage does not affectu(AB) under initial linkage equilibrium. Also some cases of additive × additive epistasis were studied.
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Affiliation(s)
- T Ohta
- National Institute of Genetics, Mishima
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