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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical and applied genetics 83 (1992), S. 451-458 
    ISSN: 1432-2242
    Schlagwort(e): Independent culling ; Cost function ; Selection index ; Multi-stage selection ; Optimum ; Transformed culling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary When traits become evident at different ages or there are large differences in the costs of measuring various traits, selection by independent culling levels may give a higher aggregate economic return than index selection because not all traits need to be measured on all individuals. The problems with optimum independent culling selection is that general solutions are not possible and numerical integration is needed for specific cases. Recently, Xu and Muir (1991) developed a new independent culling level procedure by use of orthogonal transformation of the original characters. With their procedure, explicit solutions for optimum truncation points are possible without numerical integration. As such, the procedure is proficient for any number of stages, and generalized theoretical comparisons of alternative breeding strategies are possible. However, their procedure was limited to the case where selection is for one character at each stage. In this paper, our previous results are extended to the general case of multi-stage index selection, called selection index updating. This procedure is called selection index updating because as traits become available in latter stages, each subsequent index contains all of the traits available up to that stage. The procedure is to develop sequential indices for each stage such that correlations among indices at different stages are zero. Optimum culling points are obtained for the updating procedure by using Xu and Muir's (1991) iterative equations. Due to the property of orthogonality of the updated indices, aggregate gain can be partitioned into gains due to various stages of selection. Partitioning of aggregate economic gain is useful to breeders who desire to adjust individual trait selection intensity based on facilities available at that stage. Methods are discussed to modify the procedure to obtain maximum aggregate economic return per unit of cost associated with obtaining measures on each trait. An application of multi-stage selection is demonstrated using a set of data for Rhode Island Red layer type chickens. A second example demonstrates the use of multi-stage selection optimized with respect to aggregate economic gain and costs associated with obtaining measurements.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Theoretical and applied genetics 82 (1991), S. 457-465 
    ISSN: 1432-2242
    Schlagwort(e): Artificial selection ; Independent culling ; Multiple traits ; Optimum ; Selection methods
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary An approximate method with explicit solutions to apply independent culling levels for multiple traits in n-stages of selection was developed. An approximate solution was found for sequentially selected traits. Two assumptions were necessary. The first was to assume that subsequent selection would not appreciably change the mean of traits already selected, and the second was to approximate the variance of a correlated trait in a selected population with an upward biased projection. The procedure was shown to give near optimal results regardless of selection intensity or genetic correlations if phenotypic correlations among traits were low. The procedure gave poor results only for certain sequences of selection when phenotypic correlations were high. However, in those cases good results were obtained using a different sequence of selection. With high correlations, the procedure is recommended only after comparing solutions and expected genetic gain for all sequences of selection. If the expected aggregate gain for the sequence of selection desired is less than that of another order, culling points associated with the optimal ordering must be determined. Genetic gain from use of culling points is independent of order of selection. The procedure is recommended for use with computer programs that attempt to find optimal culling points to reduce computational time and to check results.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Crop science 38 (1998), S. 1526-1535 
    ISSN: 1435-0653
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The choice of a marker-aided recurrent selection (MARS) strategy depends on a number of factors. An experimental comparison of these factors can be costly or infeasible, but a theoretical comparison can provide some guidelines. This study was conducted to evaluate the genetic aspects of expected responses to various MARS methods and to compare the efficiencies of MARS relative to traditional phenotypic recurrent selection (PRS) and to marker-aided mass selection (MS). The MARS methods examined here are MS, half-sib family (HSF), full-sib family (FSF), S1 family (S1F), testcross progeny (TC), combined FSF selection with within-family MS (CSFS), and combined HSF selection with within-family MS (CSHS). If a large fraction of the additive genetic variance (p) in a character can be explained by marker loci, the efficiencies of MARS relative to corresponding PRS can be great. This is most pronounced when family size (n) is small and decreases as n increases. An exception to this is for CSHS, where MARS is superior to PRS across all family sizes. Similarly, CSFS performs better than FSF selection under a wider range of family sizes (1 〈 n 〈 50). With a constant rate selected and a relatively large family size, S1F, CSFS and CSHS selection are superior to MS, whereas HSF selection is inferior to MS. With constraints of the same effective size selected for each method, MS, which takes advantage of the greatest selection intensity, is the most efficient method. Nevertheless, MARS among small families or individual plants can produce substantial increases in selection responses.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    Genetica 104 (1998), S. 9-19 
    ISSN: 1573-6857
    Schlagwort(e): identical by descent ; quantitative trait loci ; random model ; sib mating design
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The power to separate the variance of a quantitative trait locus (QTL) from the polygenic variance is determined by the variability of genes identical by descent (IBD) at the QTL. This variability may increase with inbreeding. Selfing, the most extreme form of inbreeding, increases the variability of the IBD value shared by siblings, and thus has a higher efficiency for QTL mapping than random mating. In self-incompatible organisms, sib mating is the closest form of inbreeding. Similar to selfing, sib mating may also increase the power of QTL detection relative to random mating. In this study, we develop an IBD-based method under sib mating designs for QTL mapping. The efficiency of sib mating is then compared with random mating. Monte Carlo simulations show that sib mating designs notably increase the power for QTL detection. When power is intermediate, the power to detect a QTL using full-sib mating is, on average, 7% higher than under random mating. In addition, the IBD-based method proposed in this paper can be used to combine data from multiple families. As a result, the estimated QTL parameters can be applied to a wide statistical inference space relating to the entire reference population.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1573-6857
    Schlagwort(e): chicken ; fisher‐scoring ; Marek's disease ; maximum likelihood ; QTL ; threshold trait
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A typical problem in mapping quantitative trait loci (QTLs) comes from missing QTL genotype. A routine method for parameter estimation involving missing data is the mixture model maximum likelihood method. We developed an alternative QTL mapping method that describes a mixture of several distributions by a single model with a heterogeneous residual variance. The two methods produce similar results, but the heterogeneous residual variance method is computationally much faster than the mixture model approach. In addition, the new method can automatically generate sampling variances of the estimated parameters. We derive the new method in the context of QTL mapping for binary traits in a F2 population. Using the heterogeneous residual variance model, we identified a QTL on chromosome IV that controls Marek's disease susceptibility in chickens. The QTL alone explains 7.2% of the total disease variation.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Genetica 105 (1999), S. 281-291 
    ISSN: 1573-6857
    Schlagwort(e): dominant markers ; multipoint mapping ; QTL ; random model
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We present a multipoint algorithm for mapping quantitative trait loci (QTLs) using dominant markers. The algorithm is designed for outbred populations and is particularly suited for large families. The algorithm works with either codominant or dominant markers, either of which may be interspersed within the same linkage map. Concurrently, the algorithm also partitions dominance variance at the QTL. Computer simulations show that with large families, QTL mapping with dominant markers can be almost as powerful as with bi-allelic, codominant markers. Yet despite this, other situations show a large standard deviation in the estimate of the QTL position, thus making QTL mapping with dominant markers in outbred populations a useful detection tool, albeit limited in its resolution.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Genetica 102-103 (1998), S. 145-155 
    ISSN: 1573-6857
    Schlagwort(e): beneficial mutations ; mutation accumulation ; molecular evolution
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract We present a series of models that allow beneficial mutations to arise as a consequence of small changes in mutations' selection coefficients. We do this by extending a strictly deleterious shift model into one that incorporates intragenic regions such as introns and exons. The results show that populations segregate and fix a substantial number of beneficial mutations. In these simulations, the percentage is approximately 50%, though the specific number is a function of the population size and the underlying genic model. In general, it was quite easy for populations to counter their deleterious load and rise in an unbounded increase in mean fitness. We discuss a possible application of the model to molecular evolution.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Springer
    Behavior genetics 28 (1998), S. 341-355 
    ISSN: 1573-3297
    Schlagwort(e): Four-way cross ; full-sib family ; regression ; variance ; linkage
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Psychologie
    Notizen: Abstract Mapping quantitative trait loci (QTL) is a typical problem of regression with uncertain independent variables because the genotype of a putative QTL is not observed. Rather, the genotype is inferred from marker information. The method of maximum likelihood (ML) methods is considered to be the optimal solution for this problem because the distribution of the unobserved QTL genotype is fully taken into account. The simple linear regression method (REG) is a first-order approximation to ML and usually performs very well. In this study, an iteratively reweighted least squares method (IRWLS) is proposed. The new method is a second-order approximation to ML because both the expectation and the variance of the unobserved QTL genotype are taken into consideration. The IRWLS is developed in the context of a single large outbred family. The properties of IRWLS are demonstrated and compared with REG and ML via replicated Monte Carlo simulations. The conclusions are: (1) when marker information content is high, the three methods perform equally well, but ML and IRWLS outperform REG when marker information content is low and the variance explained by the QTL is high; (2) when the residual distribution is not normal, ML can fail or have low power to detect small QTLs, but REG and IRWLS are robust to non-normality; and (3) when the residual distribution is normal, the performance of IRWLS is almost identical to ML, but the computational speed of IRWLS is many times faster than that of ML.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Chichester [u.a.] : Wiley-Blackwell
    Developmental Genetics 15 (1994), S. 92-103 
    ISSN: 0192-253X
    Schlagwort(e): Developmental quantitative genetics ; development ; epigenetic ; evolution ; genetic models ; effects ; Life and Medical Sciences ; Genetics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie
    Notizen: Discussions about evolutionary change in developmental processes or morphological structures are predicated on specific quantitative genetic models whose parameters predict whether evolutionary change can occur, its relative rate and direction, and if correlated change will occur in other related and unrelated structures. The appropriate genetic model should reflect the relevant genetical and developmental biology of the organisms, yet be simple enough in its parameters so that deductions can be made and hypotheses tested. As a consequence, the choice of the most appropriate genetic model for polygenically controlled traits is a complex tissue and the eventual choice of model is often a compromise between completeness of the model and computational expediency. Herein, we discuss several developmental quantitative genetic models for the evolution of development and morphology. The models range from the classical direct effects model to complex epigenetic models. Further, we demonstrate the algebraic equivalency of the Cowley and Atchley epigenetic model and Wagner's developmental mapping model. Finally, we propose a new multivariate model for continuous growth trajectories. The relative efficacy of these various models for understanding evolutionary change in developmental and morphological traits is discussed. © 1994 Wiley-Liss, Inc.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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