Genetics of quantitative traits with dominance under stabilizing and directional selection in partially selfing species

Evolution ◽  
2021 ◽  
Author(s):  
Josselin Clo ◽  
Øystein H. Opedal
Keyword(s):  
Quantitative Traits ◽  
Directional Selection ◽  
Selfing Species

scholarly journals Genetic differentiation of neutral markers and quantitative traits in predominantly selfing metapopulations: confronting theory and experiments with Arabidopsis thaliana

2006 ◽  
Vol 87 (1) ◽  
pp. 1-12 ◽  
Author(s):  
EMMANUELLE PORCHER ◽  
TATIANA GIRAUD ◽  
CLAIRE LAVIGNE
Keyword(s):  
Arabidopsis Thaliana ◽  
Genetic Differentiation ◽  
Quantitative Traits ◽  
Natural Populations ◽  
Additive Model ◽  
Linkage Disequilibria ◽  
Large Populations ◽  
Selfing Species ◽  
Theory And Experiments

The comparison of the genetic differentiation of quantitative traits (QST) and molecular markers (FST) can inform on the strength and spatial heterogeneity of selection in natural populations, provided that markers behave neutrally. However, selection may influence the behaviour of markers in selfing species with strong linkage disequilibria among loci, therefore invalidating this test of detection of selection. We address this issue by monitoring the genetic differentiation of five microsatellite loci (FST) and nine quantitative traits (QST) in experimental metapopulations of the predominantly selfing species Arabidopsis thaliana, that evolved during eight generations. Metapopulations differed with respect to population size and selection heterogeneity. In large populations, the genetic differentiation of neutral microsatellites was much larger under heterogeneous selection than under uniform selection. Using simulations, we show that this influence of selection heterogeneity on FST can be attributable to initial linkage disequilibria among loci, creating stronger genetic differentiation of QTL than expected under a simple additive model with no initial linkage. We found no significant differences between FST and QST regardless of selection heterogeneity, despite a demonstrated effect of selection on QST values. Additional data are required to validate the role of mating system and linkage disequilibria in the joint evolution of neutral and selected genetic differentiation, but our results suggest that FST/QST comparisons can be conservative tests to detect selection in selfing species.

scholarly journals Effects of linkage on response to directional selection from new mutations

1983 ◽  
Vol 42 (2) ◽  
pp. 193-206 ◽  
Author(s):  
P. D. Keightley ◽  
W. G. Hill
Keyword(s):  
Quantitative Traits ◽  
Directional Selection ◽  
Small Populations ◽  
Additive Effects ◽  
Steady Rate ◽  
Mutant Genes ◽  
Mutational Variance ◽  
Rate Of Response ◽  
Selection Of ◽  
New Mutations

SUMMARYThe influence of linkage on the rates of response to continued directional selection of quantitative traits deriving from variation contributed by new mutations in finite populations is investigated. Mutant genes are assumed to have additive effects which are randomly sampled from a symmetric distribution, and to be randomly located on the chromosome. Results were obtained by Monte Carlo simulation.The expected steady rate of response, when variability from new mutations is balanced by that lost by drift and selection, is reduced the tighter the linkage, but the reduction is small unless there are few, short chromosomes. For a given rate of new mutational variance per haploid chromosome set per generation, greater effects of linkage are obtained in large than in small populations, because more mutants segregate. The response and influence of linkage are essentially the same whether the new variance is due to many genes of small effect or few of large effect.The variability of response between replicates and generations was investigated, and the contribution to this of new mutants or recombination of existing mutants compared. Usually most genetic variability was due to the occurrence of a new favourable mutant of large effect.

The Neutral Divergence of Quantitative Traits

2018 ◽  
Author(s):  
Bruce Walsh ◽  
Michael Lynch
Keyword(s):  
Gene Expression ◽  
Genetic Drift ◽  
Joint Action ◽  
Quantitative Traits ◽  
Directional Selection ◽  
Stabilizing Selection ◽  
Data Sets ◽  
Diverse Range ◽  
Over Time

The joint action of genetic drift and mutation results in the divergence of trait means over time. This chapter examines the expected amount of divergence, which forms the basis for a number of tests on whether an observed pattern is either too large relative to drift (suggesting directional selection) or two small (suggesting stabilizing selection). It then applies these results to examine tests for selection over a very diverse range of data sets, ranging from a stratophenetic series of fossils to divergence in gene expression over time. It also examines a number of trait-augmented marked-based tests (such as using the QTLs or GWAS hits for a trait) for departures from neutrality.

scholarly journals On epistasis: why it is unimportant in polygenic directional selection

2010 ◽  
Vol 365 (1544) ◽  
pp. 1241-1244 ◽  
Author(s):  
James F. Crow
Keyword(s):  
Quantitative Traits ◽  
Developmental Process ◽  
Directional Selection ◽  
Rate Of Change ◽  
Accurate Prediction ◽  
Additive Variance ◽  
Evo Devo ◽  
Epistatic Variance

There is a difference in viewpoint of developmental and evo-devo geneticists versus breeders and students of quantitative evolution. The former are interested in understanding the developmental process; the emphasis is on identifying genes and studying their action and interaction. Typically, the genes have individually large effects and usually show substantial dominance and epistasis. The latter group are interested in quantitative phenotypes rather than individual genes. Quantitative traits are typically determined by many genes, usually with little dominance or epistasis. Furthermore, epistatic variance has minimum effect, since the selected population soon arrives at a state in which the rate of change is given by the additive variance or covariance. Thus, the breeder's custom of ignoring epistasis usually gives a more accurate prediction than if epistatic variance were included in the formulae.

scholarly journals Recombination load associated with selection for increased recombination

1996 ◽  
Vol 67 (1) ◽  
pp. 27-41 ◽  
Author(s):  
B. Charlesworth ◽  
N. H. Barton
Keyword(s):  
Transposable Elements ◽  
Direct Effect ◽  
Quantitative Traits ◽  
Genetic Variance ◽  
Genetic Recombination ◽  
Additive Genetic Variance ◽  
Directional Selection ◽  
Additive Variance ◽  
Linkage Disequilibria ◽  
Selection For

SummaryExperiments on Drosophila suggest that genetic recombination may result in lowered fitness of progeny (a ‘recombination load’). This has been interpreted as evidence either for a direct effect of recombination on fitness, or for the maintenance of linkage disequilibria by epistatic selection. Here we show that such a recombination load is to be expected even if selection favours increased genetic recombination. This is because of the fact that, although a modifier may suffer an immediate loss of fitness if it increases recombination, it eventually becomes associated with a higher additive genetic variance in fitness, which allows a faster response to directionselection. This argument applies to mutation-selection balance with synergistic epistasis, directional selection on quantitative traits, and ectopic exchange among transposable elements. Further experiments are needed to determine whether the selection against recombination due to trie immediate load is outweighed by the increased additive variance in fitness produced by recombination.

Effect of ignoring major genes when predicting response to selection

1990 ◽  
Vol 1990 ◽  
pp. 10-10
Author(s):  
S.P. Simpson
Keyword(s):  
Standard Deviation ◽  
Genetic Improvement ◽  
Quantitative Traits ◽  
Major Gene ◽  
Animal Breeding ◽  
Directional Selection ◽  
Index Selection ◽  
Response To Selection ◽  
Phenotypic Standard Deviation ◽  
Breeding Programmes

Selection is an important component of animal breeding theory. Directional selection is used extensively in animal breeding programmes as a method of obtaining genetic improvement. Much of the theory used to explain the consequences of selection assumes that the quantitative traits under consideration, eg. leanness or index scores, are under the control of many genes with small effects (polygenes). However, many traits are under the control of both polygenes and a major gene. Conventionally, the expected response to index selection is taken to be R=ih2σp, where σP is the phenotypic standard deviation of the index, h2 its heritability and i the intensity of selection. The intensity of selection is the expected mean of the index scores of the selected animals and has been tabulated by Falconer (1989).

Analysis of phenotypic selection among locations in Impatiens pallida and Impatiens capensis

1990 ◽  
Vol 68 (5) ◽  
pp. 1098-1105 ◽  
Author(s):  
Jonathan T. Brassard ◽  
Daniel J. Schoen
Keyword(s):  
Quantitative Traits ◽  
Environmental Heterogeneity ◽  
Light Availability ◽  
Natural Populations ◽  
Phenotypic Selection ◽  
Directional Selection ◽  
Impatiens Capensis ◽  
Selection Analysis ◽  
Sib Families ◽  
Selection Of

Selection analysis of a set of quantitative traits was carried out in environmentally similar quadrats within natural populations of Impatiens capensis and Impatiens pallida to examine whether spatially heterogeneous directional selection is detectable when the range of environmental variation is restricted. While 25 of 96 different estimates of directional selection were significantly different from zero, there was only one instance in which directional selection of a quantitative trait was spatially heterogeneous among quadrats within species. The discovery of a low level of spatially heterogeneous selection supports previous results showing that spatially heterogeneous selection in these species is likely due to heterogeneity in abiotic features of the habitat, such as water and light availability, or to environmental factors correlated with these features. Measurements of the same set of characters examined in the selection analysis for 33 self-sib families of I. pallida indicate significant among-family variation in all instances. The evolutionary implications of these findings are discussed. Key words: natural selection, environmental heterogeneity, genetic variation, Impatiens pallida, Impatiens capensis.

Additive-multiplicative approximation of genotype-environment interaction.

Genetics ◽  
1994 ◽  
Vol 138 (4) ◽  
pp. 1339-1349 ◽  
Author(s):  
A Gimelfarb
Keyword(s):  
Drosophila Melanogaster ◽  
Environmental Effects ◽  
Experimental Evaluation ◽  
Quantitative Traits ◽  
Directional Selection ◽  
Environment Interaction ◽  
Broad Sense Heritability ◽  
Degree Polynomial ◽  
Environmental Variance ◽  
Genotype Environment Interaction

Abstract A model of genotype-environment interaction in quantitative traits is considered. The model represents an expansion of the traditional additive (first degree polynomial) approximation of genotypic and environmental effects to a second degree polynomial incorporating a multiplicative term besides the additive terms. An experimental evaluation of the model is suggested and applied to a trait in Drosophila melanogaster. The environmental variance of a genotype in the model is shown to be a function of the genotypic value: it is a convex parabola. The broad sense heritability in a population depends not only on the genotypic and environmental variances, but also on the position of the genotypic mean in the population relative to the minimum of the parabola. It is demonstrated, using the model, that G x E interaction may cause a substantial non-linearity in offspring-parent regression and a reversed response to directional selection. It is also shown that directional selection may be accompanied by an increase in the heritability.

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