Maintenance of genetic variability by mutation–selection balance: a child's guide through the jungle

Genome ◽  
1989 ◽  
Vol 31 (2) ◽  
pp. 761-767 ◽  
Author(s):  
M. G. Bulmer
Keyword(s):  
Genetic Variability ◽  
Theoretical Work ◽  
Complex Problem ◽  
Recurrent Mutation ◽  
Mutation Rates ◽  
Stabilizing Selection ◽  
House Of Cards ◽  
Model Account ◽  
Optimal Value ◽  
Selection For

Metric characters closely connected with fitness have little additive genetic variability, presumably because it is quickly exhausted under continuous directional selection on fitness. Other metric characters have substantial additive genetic variability with a typical heritability of about 0.5. A popular model is that the second class of characters is subject to weak stabilizing selection for an optimal value, which depletes genetic variability, while recurrent mutation tends to restore it. Can this model account for the variability observed, given the evidence available about the strength of selection and mutation rates? Much theoretical work has been done on this complex problem. This work is reviewed, with the intention of simplifying it as much as possible.Key words: mutation–selection balance, genetic variability, continuum-of-alleles model, house-of-cards approximation.

scholarly journals Natural Selection for an Intermediate Optimum

1960 ◽  
Vol 13 (1) ◽  
pp. 30 ◽  
Author(s):  
BDH Latter
Keyword(s):  
Natural Selection ◽  
Genetic Variability ◽  
Recurrent Mutation ◽  
Quantitative Character ◽  
Equilibrium Situation ◽  
Selection For

Natural selection against extreme metric deviation is a process which is known to lead to the elimination of genetic variability in the particular quantitative character concerned. Recurrent mutation at loci affecting the character will be expected to oppose this tendency to genetic fixation, and the resulting equilibrium situation is discussed in detail in this paper.

scholarly journals The maintenance of the genetic variability of polygenic characters by heterozygous advantage

1973 ◽  
Vol 22 (1) ◽  
pp. 9-12 ◽  
Author(s):  
M. G. Bulmer
Keyword(s):  
Genetic Variability ◽  
Population Size ◽  
Finite Population ◽  
Stable Equilibrium ◽  
The Other ◽  
Gene Substitution ◽  
Optimal Value ◽  
Selection For ◽  
As If

SUMMARYThe results of a previous paper on the effect of optimizing selection, mutation and drift on a metric character determined by a large number of loci have been extended to include the possibility that, in addition to selection for an optimal value, there may be independent selection in favour of heterozygotes; it is assumed for simplicity that at each locus the heterozygote has the same advantage, s, over each of the homozygotes. Under selection alone there is a stable equilibrium if s > ca2, where c is a measure of the intensity of the optimizing selection and a is the effect of a gene substitution. Under the additional forces exerted by mutation and by drift due to finite population size each locus behaves independently of the other loci as if it had a heterozygous advantage equal to (s − ca2).

scholarly journals Mutation-selection balance and metabolic control theory.

Genetics ◽  
1991 ◽  
Vol 129 (3) ◽  
pp. 909-923 ◽  
Author(s):  
A G Clark
Keyword(s):  
Control Theory ◽  
Metabolic Control ◽  
Enzyme Activities ◽  
Theoretical Work ◽  
Stabilizing Selection ◽  
House Of Cards ◽  
Metabolite Pool ◽  
Equilibrium Distributions ◽  
Non Gaussian ◽  
Metabolic Control Theory

Abstract The evolution of metabolic control is examined with models that unify approaches of classical quantitative genetics and metabolic control theory. The quantitative traits considered are the activities of enzymes embedded within metabolic pathways. In the models, polygenic mutation alters the enzyme activities (Vmax/Km) according to prescribed distributions, and the population evolves following classical haploid viability selection. Stabilizing selection operates on global properties of the metabolic pathway, including either flux or metabolite pool concentration. Analytical results and numerical simulations demonstrate several important properties of these characters, including skewed, non-Gaussian equilibrium distributions, and an expected positive correlation between activities of enzymes flanking a substrate pool undergoing stabilizing selection. The house-of-cards approximation proved to be accurate in predicting the equilibrium distribution of allelic effects for a biologically reasonable segment of the parameter space. Further experimental and theoretical work is needed before a clear assessment can be made whether the observed variance in enzyme activities is explicable by a mutation-selection balance, and this system provides an excellent opportunity for such a test.

scholarly journals STABILIZING SELECTION FOR PUPA WEIGHT IN TRIBOLIUM CASTANEUM

Genetics ◽  
1977 ◽  
Vol 87 (2) ◽  
pp. 327-341
Author(s):  
Pamela K Kaufman ◽  
Franklin D Enfield ◽  
Ralph E Comstock
Keyword(s):  
Genetic Variability ◽  
Tribolium Castaneum ◽  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Heterozygote Advantage ◽  
Stabilizing Selection ◽  
Phenotypic Variance ◽  
Sources Of Variation ◽  
Selection For

ABSTRACT Ninety-five generations of stabilizing selection for pupa weight in Tribolium castaneum resulted in a significant decrease in phenotypic variance, moderate reductions in additive genetic variance, but only slight changes in heritability for the trait. Sterility was significantly lower and the average number of live progeny per fertile mating was significantly higher in populations where stabilizing selection was practiced as compared with random selected populations. The results indicate that more genetic variability is being maintained than would be expected unless a fraction of the genes have a heterozygote advantage on the fitness scale. The reduction in phenotypic variance indicated that the populations with stablizing selection became somewhat more buffered against environmental sources of variation over the course of the experiment.

scholarly journals Stabilizing selection on individual pattern elements of aposematic signals

2017 ◽  
Vol 284 (1861) ◽  
pp. 20170926 ◽  
Author(s):  
Anne E. Winters ◽  
Naomi F. Green ◽  
Nerida G. Wilson ◽  
Martin J. How ◽  
Mary J. Garson ◽  
...  
Keyword(s):  
Pattern Analysis ◽  
Marine Organism ◽  
Warning Signal ◽  
Colour Pattern ◽  
Stabilizing Selection ◽  
Warning Signals ◽  
Fish Predator ◽  
Selection For ◽  
Aposematic Signals ◽  
Behavioural Experiments

Warning signal variation is ubiquitous but paradoxical: low variability should aid recognition and learning by predators. However, spatial variability in the direction and strength of selection for individual elements of the warning signal may allow phenotypic variation for some components, but not others. Variation in selection may occur if predators only learn particular colour pattern components rather than the entire signal. Here, we used a nudibranch mollusc, Goniobranchus splendidus , which exhibits a conspicuous red spot/white body/yellow rim colour pattern, to test this hypothesis. We first demonstrated that secondary metabolites stored within the nudibranch were unpalatable to a marine organism. Using pattern analysis, we demonstrated that the yellow rim remained invariable within and between populations; however, red spots varied significantly in both colour and pattern. In behavioural experiments, a potential fish predator, Rhinecanthus aculeatus , used the presence of the yellow rims to recognize and avoid warning signals. Yellow rims remained stable in the presence of high genetic divergence among populations. We therefore suggest that how predators learn warning signals may cause stabilizing selection on individual colour pattern elements, and will thus have important implications on the evolution of warning signals.

scholarly journals Substitution Rates Under Stabilizing Selection

Genetics ◽  
1987 ◽  
Vol 116 (3) ◽  
pp. 479-486
Author(s):  
Alan Hastings
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Quantitative Traits ◽  
Strong Dependence ◽  
Phenotypic Selection ◽  
Analytical Models ◽  
Stabilizing Selection ◽  
Substitution Rates ◽  
Quantitative Characters ◽  
Selection For

ABSTRACT Allelic substitutions under stabilizing phenotypic selection on quantitative traits are studied in Monte Carlo simulations of 8 and 16 loci. The results are compared and contrasted to analytical models based on work of M. Kimura for two and "infinite" loci. Selection strengths of S = 4Nes approximately four (which correspond to reasonable strengths of selection for quantitative characters) can retard substitution rates tenfold relative to rates under neutrality. An important finding is a strong dependence of per locus substitution rates on the number of loci.

The relationship between greasy fleece weight and clean fleece weight in the South Australian Merino

1961 ◽  
Vol 1 (1) ◽  
pp. 34
Author(s):  
GH Ford
Keyword(s):  
Genetic Variability ◽  
Covariance Analysis ◽  
The South ◽  
Weight Relationship ◽  
Different Seasons ◽  
Sire Group ◽  
Selection For ◽  
Fleece Weight ◽  
The Relationship ◽  
Australian Merino

The correlation between clean fleece weight and greasy fleece weight in South Australian strain Merino hoggets of both sexes in three widely different seasons was found to be Rams, 0.841, 0.890, 0.701 and Ewes, 0.846, 0.850 and 0.839. A covariance analysis of clean and greasy fleece weights showed no significant differences between slopes of individual sires, but significant differences between sire group means, indicating genetic variability for these two traits. It is concluded that the correlations are high enough to make selection for clean fleece weight by partial culling on the basis of greasy fleece weight, followed by scouring of midside samples of the fleece from the top sheep for greasy fleece weight, as advocated by Beattie (1956), practicable. The use of the clean fleece weight, greasy fleece weight relationship will rarely be sufficient on its own to formulate a selection plan. The conditions for the use of other aids to estimate clean fleece weight, such as the Neale squeeze machine, are discussed.

Genetic, geographical and temporal variation of porcine reproductive and respiratory syndrome virus in Illinois

Microbiology ◽  
2000 ◽  
Vol 81 (1) ◽  
pp. 171-179 ◽  
Author(s):  
Tony L. Goldberg ◽  
Edwin C. Hahn ◽  
Ronald M. Weigel ◽  
Gail Scherba
Keyword(s):  
Genetic Variability ◽  
Genetic Similarity ◽  
Pseudorabies Virus ◽  
Amino Acid Level ◽  
Effective Vaccine ◽  
Respiratory Syndrome Virus ◽  
Stabilizing Selection ◽  
Gene Sequences ◽  
Long Distance ◽  
Geographical Regions

Porcine reproductive and respiratory syndrome virus (PRRSV) ORF5 gene sequences were generated by RT–PCR from 55 field isolates collected in Illinois and eastern Iowa. Spatial and temporal patterns of genetic variation in the virus were examined on a local geographical scale in order to test the hypothesis that the genetic similarity of PRRSV isolates (measured as their percentage pairwise ORF5 nucleotide similarity) was positively correlated with their geographical proximity. Levels of genetic variability in the Illinois/eastern Iowa PRRSV sample were similar to levels of variability seen across broader geographical regions within North America. The genetic similarity of isolates did not correlate with their geographical distance. These results imply that the movement of PRRSV onto farms does not generally occur via distance-limited processes such as wind or wildlife vectors, but more typically occurs via the long-distance transport of animals or semen. Genetic distances between PRRSV isolates collected from the same farms at different times increased as the time separating the collection events increased. This result implies rapid movement of new genetic types of PRRSV into and out of farms. PRRSV ORF5 displayed a pattern of third-codon-position diversity bias that was not evident in a geographically comparable sample of pseudorabies virus (a swine alphaherpesvirus) gC gene sequences. This result provides evidence that PRRSV ORF5 is experiencing stabilizing selection against structural novelty. Despite high genetic variability at all geographical levels, PRRSV ORF5 nevertheless contained potentially antigenic regions that were invariant at the amino acid level. These regions should make effective vaccine targets if they prove to be immunogenic.

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