ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

The effect of gametic-phase disequilibrium on the prediction of response to recurrent selection in plants (1993)

Mackay, I. J. ; Gibson, J. P.

Springer

Theoretical and applied genetics 87 (1993), S. 152-160

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ISSN: 1432-2242

Keywords: Recurrent selection ; Gametic phase disequilibrium ; Sugar beet

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Selection reduces additive genetic variation by generating gametic-phase disequilibrium, a phenomenon largely ignored when predicting response in plant breeding programs. The development of gametic-phase disequilibrium is here taken into account when predicting the response to selection for various schemes of recurrent selection applicable to plant populations. A general program permits prediction of response to selection from schemes of recurrent selection in which two or more rounds of selection occur in each cycle. An example from Sugar Beet, with alternate rounds of half-sib and S1 family selection, is illustrated. It is shown that failure to take into account the effects of gametic-phase disequilibrium can result in substantial overestimation of the response to selection as well as to changes in rank of the merits of alternative breeding schemes. For a given scheme, ignoring gametic-phase disequilibrium has only small effects on defining the optimum allocation of plots and the numbers of families tested.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00223759

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2

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Estimation of additive genetic variance in commercial layer poultry and simulated populations under selection (1996)

Jeyaruban, M. G. ; Gibson, J. P.

Springer

Theoretical and applied genetics 92 (1996), S. 483-491

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ISSN: 1432-2242

Keywords: Key words Parameter estimation ; Poultry ; Relationship matrix

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Changes in genetic parameters over generations for a selected commercial population and simulated populations of poultry with different sizes were studied. The traits analyzed from the commercial population were rate of lay, age at first egg, egg weight, deformation, and body weight. In the simulated population, a trait measured on both sexes and a sex-limited trait, measured only on one sex, each with a heritability of 0.1 and 0.5, were analyzed. In the commercial and simulated populations, males and females were selected on the basis of family selection indexes and data was available only after many generations of selection. Parameters for each generation were estimated by fitting an animal model using derivative free maximum likelihood (DFREML) with different data structures. In structure 1, data included the given (base) generation for which the parameters were to be estimated, and all subsequent generations. In structure 2, only data on birds in the given generation and their progeny were included. In both structures, parents of base-generation birds were assumed unrelated and pedigrees traced back to these parents. With commercial data using structure 1, estimates of σ a 2 and h2 decreased by 14 to 37% across five generations. With structure 2, no trends were observed, though estimates were lower than for structure 1. For simulated data, with a heritability of 0.1, both structures yielded apparently unbiased estimates of the observed additive genetic variances in the (selected) base generation, no matter how many generations of data were utilized, for both sex-limited and normal traits. However, with a heritability of 0.5 the estimated additive genetic variance for both types of trait decreased with a decrease in the number of generations used in the estimation. Estimates based on the first two generations underestimated, while estimates based on five generations of data overestimated, the observed genetic variances in the defined base. The combinations of conditions that lead to varying degrees of bias remain undefined.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s001220050153

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3

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Balancing selection response and rate of inbreeding by including genetic relationships in selection decisions (1995)

Brisbane, J. R. ; Gibson, J. P.

Springer

Theoretical and applied genetics 91 (1995), S. 421-431

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ISSN: 1432-2242

Keywords: Inbreeding ; Selection ; Genetic improvement

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract An iterative selection strategy, based on estimated breeding values (EBV) and average relationship among selected individuals, is proposed to optimise the balance between genetic response and inbreeding. Stochastic simulation was used to compare rates of inbreeding and genetic gain with those of other strategies. For a range of heritabilities, population sizes and mating ratios, the iterative strategy, denoted ADJEBV, outperforms other strategies, giving the greatest genetic gain at a given rate of inbreeding and the least breeding at a given genetic gain. Where selection is currently by truncation on the EBV, with a restriction on the number of full-sibs selected, it should be possible to maintain similar levels of genetic gain and inbreeding with a reduction in population size of 10–30%, by changing to the iterative strategy. If performance is measured by the reduction in cumulative inbreeding without losing more than a given amount of genetic gain relative to results obtained under truncation selection on the EBV, then with the EBV based on a family index, the performance of ADJEBV is greater at low heritability, and is generally greater than where EBV are based on individual records. When comparisons of genetic response and inbreeding are made for alternative breeding scheme designs, schemes which give higher genetic gain within acceptable inbreeding levels would usually be favoured. If comparisons are made on this basis, then the selection method used should be ADJEBV, which maximises the genetic gain for a given level of inbreeding. The results indicated that all selection strategies used to reduce inbreeding had very small effects on the variance of gain, and so differences in this respect are unlikely to affect choices among selection strategies. Selection criteria are recommended based on maximising a selection objective which specifies the desired balance between genetic gain and inbreeding.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00222969

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4

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Including genetic relationships in selection decisions: alternative methodologies (1995)

Brisbane, J. R. ; Gibson, J. P.

Springer

Theoretical and applied genetics 91 (1995), S. 769-775

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ISSN: 1432-2242

Keywords: Inbreeding ; Selection ; Genetic improvement

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Investigations are made of variations in an iterative methodology previously introduced for reducing inbreeding by including genetic relationships in selection decisions, using adjusted estimated breeding values (EBV). An alternative computing strategy for maximising the value of the population selection criterion is shown to involve less computation, which results in function values as great or greater than the original method. Alteration of weights for different types of relationships in the adjusted EBV has no detectable effect on genetic gain at a given level of inbreeding. Selection using the adjusted EBV method in one sex and truncation on EBV in the other sex results in less genetic gain at a given level of inbreeding than using adjusted EBV in both sexes, but results in more gain at a given level of inbreeding than three selection strategies that do not include genetic relationships in selection decisions. The advantage of the adjusted EBV method over these three methods is retained when selection is for a sexlimited trait.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00220957

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5

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Selection strategies and artificial evolution (1989)

Gibson, J. P.

Springer

Theoretical and applied genetics 78 (1989), S. 87-92

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ISSN: 1432-2242

Keywords: Selection indexes ; Biological responses

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Artificial selection results in biolgical changes, creating artificial evolution. When using selection indexes, the artificial evolution depends on the relative economic (or other) weight of traits in the breeding objective, and on the phenotypic and genetic variances and covariances among these traits and the traits recorded in the selection index. As shown here, the selection strategy (in this case, individual selection versus progeny test selection) can also have marked effects on the kind of artificial evolution produced. Thus, where economic weights are uncertain, choice between alternative selection strategies might take into account the different types of animal or plant resulting.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00299759

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6

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The use of constrained selection indexes in breeding for economic merit (1990)

Gibson, J. P. ; Kennedy, B. W.

Springer

Theoretical and applied genetics 80 (1990), S. 801-805

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ISSN: 1432-2242

Keywords: Economic weights ; Restricted indexes ; Desired gains

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary Various methods exist for the derivation of restricted and/or desired gains selection indexes, and their use in applied breeding has been advocated. It is shown that there exists a set of implied linear economic weights for all constrained indexes and their derivation is given. Where economic weights are linear and known, a standard selection index is, by definition, optimal and thus a constrained index will usually be suboptimal. It is argued that economic weights can always be estimated and that the effects of uncertain weights can be examined by sensitivity analysis. If economic weights are nonlinear, use of the first order (linear) economic weights or a derived linear index, using previously described methods, will give very close to optimum economic selection responses. Examples from the literature indicate that severe losses of potential economic gain can possibly occur through use of a constrained index. It is concluded that constrained indexes should be avoided for economic genetic selection.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00224195

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7

Electronic Resource

Estimation of additive genetic variance in commercial layer poultry and simulated populations under selection (1996)

Jeyaruban, M. G. ; Gibson, J. P.

Springer

Theoretical and applied genetics 92 (1996), S. 483-491

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ISSN: 1432-2242

Keywords: Parameter estimation ; Poultry ; Relationship matrix

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Changes in genetic parameters over generations for a selected commercial population and simulated populations of poultry with different sizes were studied. The traits analyzed from the commercial population were rate of lay, age at first egg, egg weight, deformation, and body weight. In the simulated population, a trait measured on both sexes and a sex-limited trait, measured only on one sex, each with a heritability of 0.1 and 0.5, were analyzed. In the commercial and simulated populations, males and females were selected on the basis of family selection indexes and data was available only after many generations of selection. Parameters for each generation were estimated by fitting an animal model using derivative free maximum likelihood (DFREML) with different data structures. In structure 1, data included the given (base) generation for which the parameters were to be estimated, and all subsequent generations. In structure 2, only data on birds in the given generation and their progeny were included. In both structures, parents of base-generation birds were assumed unrelated and pedigrees traced back to these parents. With commercial data using structure 1, estimates of σ a 2 and h2 decreased by 14 to 37% across five generations. With structure 2, no trends were observed, though estimates were lower than for structure 1. For simulated data, with a heritability of 0.1, both structures yielded apparently unbiased estimates of the observed additive genetic variances in the (selected) base generation, no matter how many generations of data were utilized, for both sex-limited and normal traits. However, with a heritability of 0.5 the estimated additive genetic variance for both types of trait decreased with a decrease in the number of generations used in the estimation. Estimates based on the first two generations underestimated, while estimates based on five generations of data overestimated, the observed genetic variances in the defined base. The combinations of conditions that lead to varying degrees of bias remain undefined.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00223697

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8

Electronic Resource

Genetic improvement of production while maintaining fitness (1995)

Meuwissen, T. H. E. ; Gibson, J. P. ; Quinton, M.

Springer

Theoretical and applied genetics 90 (1995), S. 627-635

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ISSN: 1432-2242

Keywords: Genetic improvement ; Fitness Finite locus models ; Production

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Selection for production tends to decrease fitness, in particular, major components such as reproductive performance. Under an infinitesimal genetic model restricted index selection can maintain reproductive performance while improving production. However, reproductive traits are thought to be controlled by a finite number of recessive alleles at low frequency. Culling for low reproduction may weed out the negative homozygous genotypes for reproduction in any generation, thus controlling the frequencies of alleles negative for reproduction. Restricted index selection, culling for low reproduction and a new method called empirical restricted index selection were compared for their efficiency in improving production while maintaining reproduction. Empirical restricted index selection selects animals that have on average the highest estimated breeding values for production and on average the same estimated breeding values for reproduction as the base population. An infinitesimal genetic model and models with a finite number of loci for reproduction with rare deleterious recessive alleles, which have additive, dominant or no pleiotropic effects on production, were considered. When reproduction was controlled by a finite number of loci with rare recessive alleles, restricted index selection could not maintain reproduction. The culling of 20% of the animals on reproduction maintained reproduction with all genetic models, except for the model where loci for reproduction had additive effects on production. Empirical restricted selection maintained reproduction with all models and yielded higher production responses than culling on reproduction, except when there were dominant pleiotropic effects on production.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00222126

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9

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The genetics of selfing with concurrent backcrossing in breeding hybrid sugar beet (Beta vulgaris altissima L.) (1999)

Mackay, I. J. ; Gibson, J. P. ; Caligari, P. D. S.

Springer

Theoretical and applied genetics 98 (1999), S. 1156-1162

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ISSN: 1432-2242

Keywords: Key words Hybrid selection ; Concurrent backcrossing ; Additive genetic relationship ; Doubled haploids ; Inbreeding

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Sugar beet hybrids are produced by crossing a cytoplasmic male-sterile (CMS) line with a pollinator. New CMS lines are produced by crossing a fertile plant to an existing CMS line. The fertile plant is also selfed. In the following generation, one of the selfed, fertile progeny is paired and isolated with one of the crossed, CMS progeny, to give a second generation of selfing and crossing. Over a series of such crosses and selfs, a new fertile inbred line and its corresponding, near-isogenic CMS partner are produced. Selection among lines takes place at one or more stages of the backcrossing programme. A method is presented here for calculating the genetic variances and covariances within and between lines and generations based on a derivation of additive genetic relationships modified from an approach widely employed in animal breeding. The genetic variances and covariances are used to predict response to selection from varying strategies, from which optimum schemes can be determined. Results suggest that selection should generally take place after three generations of backcrossing when the fertile plant used to initiate the backcrossing process is not inbred, but can take place after generation two when the fertile plant is inbred. Doubled haploid production is unlikely to provide an extra advantage that would be worthwhile in such a system. The method developed here can be used to explore a wide range of more complex breeding systems.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s001220051180

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