scholarly journals POPULATION SIZE AND SELECTION INTENSITY EFFECTS ON LONG-TERM SELECTION RESPONSE IN MICE

Genetics ◽  
1975 ◽  
Vol 79 (2) ◽  
pp. 305-323
Author(s):  
E J Eisen
Keyword(s):  
Inbreeding Depression ◽  
Genetic Correlations ◽  
Selection Response ◽  
Second Phase ◽  
Selection Intensity ◽  
Total Response ◽  
Family Selection ◽  
Effective Population ◽  
The Difference

ABSTRACT Long-term response to within full-sib family selection for increased postweaning gain was evaluated in lines having different effective population sizes (Ne) and selection intensities (i). Line designations were I4(4), I8(2), I16(2), M4(4), M8(2) and M16(2), where I and M indicate selection of the top 50% and 25%, respectively; 4, 8 and 16 represent the number of parental pairs per replicate and number of replicates is given in parentheses. Realized within full-sib family heritabilities (hR  2) in the first phase of selection (0-14 generations) were larger in 16-pair lines than in 4- and 8-pair lines. In the second phase of selection (>14 generations), hR  2 declined significantly (P<.01) in all lines, and only the I16 and M16 lines had hR  2 values significantly (P<.01) greater than zero. Realized genetic correlations involving number born, 12-day litter weight, weaning weight and six-week weight tended to decline in the second phase of selection. The I16, M16 and control (C16) replicates were crossed in all combinations at generation 14. Crosses were then selected within litters for high postweaning gain. The hR  2 values in the crossbred lines were all larger than those in the second selection phase for M16-1, M16-2 and I16-1, but not for I16-2. Within each Ne level, total response was significantly (P<.01) less for I lines compared with M lines. Total response increased as Ne increased, within each level of i. Relatively small differences in realized i values among Ne lines could not account for this result. The difference in total response among the Ne lines at a given selection intensity may be due to inbreeding depression and a combination of interactions involving "drift" and selection. By crossing replicates of the M lines with the C16 control, the effects of inbreeding depression were removed. Inbreeding depression and genetic drift, as defined herein, were equally important in accounting for differences among Ne lines in total response.

scholarly journals Selection Response in Finite Populations

Genetics ◽  
1996 ◽  
Vol 144 (4) ◽  
pp. 1961-1974 ◽  
Author(s):  
Ming Wei ◽  
Armando Caballero ◽  
William G Hill
Keyword(s):  
Linkage Disequilibrium ◽  
Inbreeding Depression ◽  
Genetic Variance ◽  
Relative Rate ◽  
Selection Response ◽  
Rate Of Change ◽  
Effective Population ◽  
Short Term ◽  
Model Account

Formulae were derived to predict genetic response under various selection schemes assuming an infinitesimal model. Account was taken of genetic drift, gametic (linkage) disequilibrium (Bulmer effect), inbreeding depression, common environmental variance, and both initial segregating variance within families (σAW02) and mutational (σM2) variance. The cumulative response to selection until generation t(CRt) can be approximated asCRt≈R0[t−β(1−σAW∞2σAW02)t24Ne]−Dt2Ne,where Ne is the effective population size, σAW∞2=NeσM2 is the genetic variance within families at the steady state (or one-half the genic variance, which is unaffected by selection), and D is the inbreeding depression per unit of inbreeding. R  0 is the selection response at generation 0 assuming preselection so that the linkage disequilibrium effect has stabilized. β is the derivative of the logarithm of the asymptotic response with respect to the logarithm of the within-family genetic variance, i.e., their relative rate of change. R  0 is the major determinant of the short term selection response, but σM2, Ne and β are also important for the long term. A selection method of high accuracy using family information gives a small Ne and will lead to a larger response in the short term and a smaller response in the long term, utilizing mutation less efficiently.

scholarly journals EFFECTS OF POPULATION SIZE AND SELECTION INTENSITY ON SHORT-TERM RESPONSE TO SELECTION FOR POSTWEANING GAIN IN MICE

Genetics ◽  
1973 ◽  
Vol 73 (3) ◽  
pp. 513-530
Author(s):  
J P Hanrahan ◽  
E J Eisen ◽  
J E Legates
Keyword(s):  
Population Size ◽  
Selection Response ◽  
Selection Intensity ◽  
Realized Heritability ◽  
Family Selection ◽  
Effective Population ◽  
Population Sizes ◽  
Selection For ◽  
Selection Intensities ◽  
Term Response

ABSTRACT The effects of population size and selection intensity on the mean response was examined after 14 generations of within full-sib family selection for postweaning gain in mice. Population sizes of 1, 2, 4, 8 and 16 pair matings were each evaluated at selection intensities of 100% (control), 50% and 25% in a replicated experiment. Selection response per generation increased as selection intensity increased. Selection response and realized heritability tended to increase with increasing population size. Replicate variability in realized heritability was large at population sizes of 1, 2 and 4 pairs. Genetic drift was implicated as the primary factor causing the reduced response and lowered repeatability at the smaller population sizes. Lines with intended effective population sizes of 62 yielded larger selection responses per unit selection differential than lines with effective population sizes of 30 or less.

scholarly journals Breeding schemes in reindeer husbandry

Rangifer ◽  
2003 ◽  
Vol 23 (2) ◽  
pp. 45 ◽  
Author(s):  
Lars Rönnegård ◽  
J. A. Woolliams ◽  
Öje Danell
Keyword(s):  
Genetic Gain ◽  
Mass Selection ◽  
Effective Population ◽  
Selection Programme ◽  
Breeding Schemes ◽  
The Difference ◽  
Genetic Contributions ◽  
Parameter Values ◽  
Open Nucleus

The objective of the paper was to investigate annual genetic gain from selection (G), and the influence of selection on the inbreeding effective population size (Ne), for different possible breeding schemes within a reindeer herding district. The breeding schemes were analysed for different proportions of the population within a herding district included in the selection programme. Two different breeding schemes were analysed: an open nucleus scheme where males mix and mate between owner flocks, and a closed nucleus scheme where the males in non-selected owner flocks are culled to maximise G in the whole population. The theory of expected long-term genetic contributions was used and maternal effects were included in the analyses. Realistic parameter values were used for the population, modelled with 5000 reindeer in the population and a sex ratio of 14 adult females per male. The standard deviation of calf weights was 4.1 kg. Four different situations were explored and the results showed: 1. When the population was randomly culled, Ne equalled 2400. 2. When the whole population was selected on calf weights, Ne equalled 1700 and the total annual genetic gain (direct + maternal) in calf weight was 0.42 kg. 3. For the open nucleus scheme, G increased monotonically from 0 to 0.42 kg as the proportion of the population included in the selection programme increased from 0 to 1.0, and Ne decreased correspondingly from 2400 to 1700. 4. In the closed nucleus scheme the lowest value of Ne was 1300. For a given proportion of the population included in the selection programme, the difference in G between a closed nucleus scheme and an open one was up to 0.13 kg. We conclude that for mass selection based on calf weights in herding districts with 2000 animals or more, there are no risks of inbreeding effects caused by selection.

scholarly journals Optimum selection intensities in artificial selection programmes: an experimental evaluation

1977 ◽  
Vol 30 (2) ◽  
pp. 115-119 ◽  
Author(s):  
R. Frankham
Keyword(s):  
Experimental Evaluation ◽  
Selection Intensity ◽  
Effective Population ◽  
Term Selection ◽  
Optimum Selection ◽  
Selection For ◽  
Selection Intensities ◽  
Selection Of ◽  
Better Than

SUMMARYAn experimental evaluation of Robertson's (1970) theory concerning optimum intensities of selection for selection of varying durations has been carried out using published results from a long term selection study in Drosophila. Agreement of predicted rankings of treatments with expectations was excellent for low values of t/T (generations/total number scored) but poor for larger values of t/T. This was due to the 20% selection intensity treatments responding worse than expected and the 40% treatments relatively better than expected. Several possible reasons for the discrepancies exist but the most likely explanation is considered to be the greater reduction in effective population size due to selection in treatments with more intense selection.

Long-term Response: 2. Finite Population Size and Mutation

2018 ◽  
Author(s):  
Bruce Walsh ◽  
Michael Lynch
Keyword(s):  
Population Size ◽  
Quantitative Trait ◽  
Finite Population ◽  
Initial Response ◽  
Optimal Selection ◽  
Selection Intensity ◽  
Effective Population ◽  
Additive Variance ◽  
Term Response

In a finite population, drift is often more important than selection in removing any initial additive variance. This chapter examines the joint impact of selection, drift, and mutation on the long-term response in a quantitative trait. One key result is the remarkable finding of Robertson that the expected long-term response from any initial additive variance is bounded above by the product of twice the effective population size times the initial response. This result implies that the optimal selection intensity for long-term response it to save half of the population in each generation.

scholarly journals Long-term selection for a quantitative character in large replicate populations of Drosophila melanogaster: 1. Response to selection

1980 ◽  
Vol 35 (1) ◽  
pp. 1-17 ◽  
Author(s):  
B. H. Yoo
Keyword(s):  
Drosophila Melanogaster ◽  
Phenotypic Variability ◽  
Selection Response ◽  
Quantitative Character ◽  
Response Patterns ◽  
Total Response ◽  
Term Selection ◽  
Bristle Number ◽  
Selection For

SUMMARYThe response to long-term selection for increased abdominal bristle number was studied in six replicate lines of Drosophila melanogaster derived from the sc Canberra outbred strain. Each line was continued for 86–89 generations with 50 pairs of parents selected at an intensity of 20%, and subsequently for 32–35 generations without selection. Response continued for at least 75 generations and average total response was in excess of 36 additive genetic standard deviations of the base population (σA) or 51 times the response in the first generation. The pattern of longterm response was diverse and unpredictable typically with one or more accelerated responses in later generations. At termination of the selection, most of the replicate lines were extremely unstable with high phenotypic variability, and lost much of their genetic gains rapidly upon relaxation of selection.The variation in response among replicates rose in the early phase of selection to level off at approximately 7·6 around generation 25. As some lines plateaued, it increased further to a level higher than would be accommodated by most genetic models. The replicate variation was even higher after many generations of relaxed selection. The genetic diversity among replicates, as revealed in total response, the individuality of response patterns and variation of the sex-dimorphism ratio, suggests that abdominal bristle number is influenced potentially by a large number of genes, but a smaller subset of them was responsible for selection response in any one line.

scholarly journals Long-term selection for protein amount over 70 generations in mice

1998 ◽  
Vol 72 (2) ◽  
pp. 93-109 ◽  
Author(s):  
LUTZ BÜNGER ◽  
ULLA RENNE ◽  
GERHARD DIETL ◽  
SIEGFRIED KUHLA
Keyword(s):  
Body Weight ◽  
Selection Response ◽  
Direct Selection ◽  
Control Line ◽  
Phenotypic Variance ◽  
Effective Population ◽  
Term Selection ◽  
General Importance ◽  
Selection For

Based on the outbred mouse strain Fzt: Du, which has been obtained by systematic crossing of four inbred and four outbred lines, a long-term selection experiment was carried out for total protein amount (PA) in the carcass, starting in 1975. An unselected control line (CO) was kept under the same management but without continuous protein analysis. The protein amount of male carcasses at 42 days of age (P42) increased from 2·9 g in generation 0 to 5·2 g at generation 70, representing 97% of a theoretical selection limit. The total selection response amounts to 2·3 g, which is about 80% above the initial value and corresponds to 9σp or 12σA . The estimated realized heritability of protein amount decreased from 0·56 to 0·03 at generation 70, which was due to an increase in phenotypic variance from 0·065 to 0·24 g2 and a reduction in genetic variance from 0·04 to 0·01 g2. Half the selection response was obtained after about 18 to 23 generations, a half-life of 0·25 to 0·3 Ne. The maximum selection response was 0·094 g/generation and the response was 0·01 g/generation at generation 70. The measurements of body weights at 0, 10, 21, 42 and 63 days throughout the experiment showed a strong correlated effect for all weights. The PA mice are one of the heaviest lines of mice ever reported, and do not differ significantly in their body composition from control mice at 42 days. The direct selection response was due primarily to increased general growth. Body weight and protein amount are phenotypically and genetically highly correlated (rp=0·82, rA≈1); however, selection for body weight led to fatter animals, whereas selection for protein opposed increased fatness (at least until selection age). This may be of general importance in animal breeding. The comparatively high selection response in this experiment seems due to the heterogeneity of the base population, the relatively high effective population size, and the duration of the experiment.

scholarly journals Optimierung von Zuchtstrukturen einer Zweilinienkreuzung – Eine Monte-Carlo Studie

2003 ◽  
Vol 46 (3) ◽  
pp. 293-303
Author(s):  
N. Mielenz ◽  
M. Wensch-Dorendorf ◽  
L. Schüler
Keyword(s):  
Monte Carlo ◽  
Population Structure ◽  
Genetic Correlations ◽  
Monte Carlo Study ◽  
Pure Line ◽  
Selection Response ◽  
Optimal Number ◽  
Optimum Number ◽  
Complete Dominance ◽  
The Difference

Abstract. Title of the paper: Optimization of the population structure for a two-line crossbreeding scheme – a Monte-Carlo study A stochastic simulation was used to optimize the population structure in a two-line crossbreeding system under non-additive gene models. For different fixed test capacities, given number of offspring per dam and varying degrees of dominance the optimum number of selected sires was calculated. As criterions of the optimization the cumulative selection response on generation 10, the corresponding standard error of the response and the development of the inbreeding in the purebreds were used. If the trait was controlled by loci with partial and complete dominance, than the optimal number of selected sires was between 8 and 12 for given test capacities of 2304, 1152 and 1536 animals per generation and per the sire line. In the case of overdominance the number of selected sires increased on 24 to 48. Additionally, the level of the selection response in the three populations was affected by the difference of the allele frequencies in the initial generation and the economic weights of the additive purebred and crossbred effects. Under partial and complete dominance with corresponding purebred-crossbred genetic correlations of high and moderate level only small extra benefits were obtained from including crossbred information over pure line information.

scholarly journals Predicting the durability of ship's machine parts and mechanisms on the criterion of material fatigue

2020 ◽  
pp. 127-133
Author(s):  
В.К. Румб
Keyword(s):  
Fatigue Cracks ◽  
Experimental Studies ◽  
Fatigue Curve ◽  
Second Phase ◽  
Critical Dimensions ◽  
Material Fatigue ◽  
The Difference ◽  
Two Phases ◽  
The Moment

На основе теории о кристаллическом строении металлов рассмотрена физика усталостного разрушения. Показано, что зарождение и развитие усталостных трещин является случайным процессом, состоящим из двух фаз: первая – образование макроскопической (видимой) трещины; вторая – рост трещины до критических размеров, после которых наступает поломка детали. Приведены критерии работоспособности деталей по критерию усталости материала. Особое внимание уделено методическим положениям, позволяющим расчетным путем прогнозировать долговечность деталей для первой фазы усталости материала. Предлагаемая методика базируется на кривой усталости материала и корректированной гипотезе линейного суммирования повреждений. Отличительной особенностью методики является ее применимость для различных видов нагружения, в частности, показано как с ее помощью можно определять усталостную долговечность для режимного и блочного нагружений деталей. Отмечено, что для повышения точности прогнозирования долговечности необходимы дополнительные экспериментальные исследования прочности материала при циклическом нагружении, равном 1010 ÷ 1012циклов. В перспективе разработанная методика позволяет рассчитывать остаточную долговечность деталей как разность между расчетной долговечностью новой детали и ее наработкой до момента нового использования. Based on the theory about the crystalline structure of metals, the physics of fatigue destruction is considered. It is shown that the origin and development of fatigue cracks is a random process consisting of two phases: the first - the formation of a macroscopic (visible) crack; The second phase is the growth of the crack to critical dimensions, after which the part breaks. The criteria for the health of the parts are given on the criterion of material fatigue. Particular attention is paid to the methodical provisions, allowing the calculated way to predict the durability of parts for the first phase of material fatigue. The proposed technique is based on the material fatigue curve and the corrected hypothesis of linear summation of damage. A distinctive feature of the technique is its applicability for different types of loading, in particular, it shows how it can determine fatigue durability for the mode and block loading of parts. It is noted that additional experimental studies of the strength of the material in the cyclical load equal to 1010 ÷ 1012 cycles are needed to improve the accuracy of longevity prediction. In the long term, the developed technique allows to calculate the residual durability of parts as the difference between the calculated durability of the new part and its development until the moment of new use.

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