scholarly journals Directional selection can drive the evolution of modularity in complex traits

2014 ◽  
Vol 112 (2) ◽  
pp. 470-475 ◽  
Author(s):  
Diogo Melo ◽  
Gabriel Marroig
Keyword(s):  
Complex Traits ◽  
Directional Selection ◽  
Stabilizing Selection ◽  
Simulation Framework ◽  
Full Agreement ◽  
Central Concept ◽  
Modern Biology ◽  
Living Organisms ◽  
Multivariate Systems ◽  
Evolutionary Consequences

Modularity is a central concept in modern biology, providing a powerful framework for the study of living organisms on many organizational levels. Two central and related questions can be posed in regard to modularity: How does modularity appear in the first place, and what forces are responsible for keeping and/or changing modular patterns? We approached these questions using a quantitative genetics simulation framework, building on previous results obtained with bivariate systems and extending them to multivariate systems. We developed an individual-based model capable of simulating many traits controlled by many loci with variable pleiotropic relations between them, expressed in populations subject to mutation, recombination, drift, and selection. We used this model to study the problem of the emergence of modularity, and hereby show that drift and stabilizing selection are inefficient at creating modular variational structures. We also demonstrate that directional selection can have marked effects on the modular structure between traits, actively promoting a restructuring of genetic variation in the selected population and potentially facilitating the response to selection. Furthermore, we give examples of complex covariation created by simple regimes of combined directional and stabilizing selection and show that stabilizing selection is important in the maintenance of established covariation patterns. Our results are in full agreement with previous results for two-trait systems and further extend them to include scenarios of greater complexity. Finally, we discuss the evolutionary consequences of modular patterns being molded by directional selection.

Complex Traits in Natural Populations

2020 ◽  
pp. 263-290
Author(s):  
Daniel L. Hartl
Keyword(s):  
Complex Traits ◽  
Population Genomics ◽  
Association Studies ◽  
Natural Populations ◽  
Complex Diseases ◽  
Stabilizing Selection ◽  
Phenotypic Evolution ◽  
Genetic Changes ◽  
Number Of Genes ◽  
Almost All

This chapter could as well be titled “Population Genomics,” although many aspects of population genomics are integrated throughout the other chapters. It includes estimates of mutational variance and standing variance, phenotypic evolution under directional selection as measured by the linear selection gradient, and phenotypic evolution under stabilizing selection. It explores the strengths and limitations of genome-wide association studies of quantitative trait loci (QTLs) and expression (eQTLs) to detect genetic influencing complex traits in natural populations and genetic risk factors for complex diseases such as heart disease or diabetes. The number of genes affecting complex traits is considered, as well as evidence bearing on the issue of whether complex diseases are primarily affected by a very large number of genes, almost all of small effect, and how this bears on direct-to-consumer and over-the-counter genetic testing. The population genomics of adaptation is considered, including drug resistance, domestication, and local selection versus gene flow. The chapter concludes with the population genomics of speciation as illustrated by reinforcement of mating barriers, the reproducibility of phenotypic and genetic changes, and the accumulation of genetic incompatibilities.

scholarly journals Quantitative genetic variability maintained by mutation-stabilizing selection balance: sampling variation and response to subsequent directional selection

1989 ◽  
Vol 54 (1) ◽  
pp. 45-58 ◽  
Author(s):  
Peter D. Keightley ◽  
William G. Hill
Keyword(s):  
Genetic Variance ◽  
Directional Selection ◽  
Quantitative Character ◽  
Stabilizing Selection ◽  
Effective Population ◽  
Selection Responses ◽  
Quantitative Genetic ◽  
Before And After ◽  
Cage Population ◽  
Selection Of

SummaryA model of genetic variation of a quantitative character subject to the simultaneous effects of mutation, selection and drift is investigated. Predictions are obtained for the variance of the genetic variance among independent lines at equilibrium with stabilizing selection. These indicate that the coefficient of variation of the genetic variance among lines is relatively insensitive to the strength of stabilizing selection on the character. The effects on the genetic variance of a change of mode of selection from stabilizing to directional selection are investigated. This is intended to model directional selection of a character in a sample of individuals from a natural or long-established cage population. The pattern of change of variance from directional selection is strongly influenced by the strengths of selection at individual loci in relation to effective population size before and after the change of regime. Patterns of change of variance and selection responses from Monte Carlo simulation are compared to selection responses observed in experiments. These indicate that changes in variance with directional selection are not very different from those due to drift alone in the experiments, and do not necessarily give information on the presence of stabilizing selection or its strength.

Evolution and Man

Antiquity ◽  
1957 ◽  
Vol 31 (124) ◽  
pp. 188-198
Author(s):  
Ronald Singer
Keyword(s):  
Biological Sciences ◽  
Comparative Anatomy ◽  
Modern Biology ◽  
Political Situation ◽  
Morphological Studies ◽  
Technical Advances ◽  
Theories Of Evolution ◽  
Post War ◽  
Living Organisms ◽  
The 19Th Century

The whole of modern biology has been called ‘ a commentary on the Origin of Species ’ (Charles Singer, 1949). In a sense this is true. Following the endeavours to trace the natural histories of the various living organisms, attempts are still in progress to determine the modes, patterns and directive forces of evolution. The end of the 19th and the first quarter of the 20th centuries were characterized by morphological studies in comparative anatomy, the rise of geology and the birth of genetics. The second quarter of this century has witnessed a phenomenal expansion in technical advances leading to critical appraisals of previous concepts and to maturation of new, revolutionary theories based upon seemingly disconnected disciplines-experimental embryology, genetics, physkal anthropology, palaeontology and geology. One of the unacclaimed causes of the correlation of knowledge is the post-war mastery of air travel. The spectacular rise of the ' basic ' biological sciences due to emergent industrial and atomic competitive needs in an era of socio-economic enlightenment is another factor giving rise to the pursuit of such knowledge. In a general sense this is the end of a Darwinian ' cycle ' ; the favourable socio-political situation of the 19th century formed the ' overture ' to the Darwinian theory. Act One saw the development, championing and triumphs of the intellectual interpretations of ' Darwinists '. In Act Two the weaknesses and the vital issues of the application of the theory to various living forms and particularly to Homo sapims were exposed, mainly through the clashes of ' neo-Darwinists ' and ' neo-Lamarckists '. This led to Act Three in which the various sciences (and especially genetics), competing to illustrate and develop alternative theories of evolution, blossomed out, particularly in their search for the mechanisms of the evolutionary processes. In the final scene of this Act the socio-political situation once again formed an important background as the diverse disciplines combine tq unify concepts, and, in fact, to prove evolution.

Sexual difference in modes of selection on the pleopods of crayfish (Decapoda: Astacoidea) revealed by the allometry of developmentally homologous traits

2003 ◽  
Vol 81 (6) ◽  
pp. 971-978 ◽  
Author(s):  
Naoko Kato ◽  
Tadashi Miyashita
Keyword(s):  
Sexual Difference ◽  
Procambarus Clarkii ◽  
Regression Line ◽  
Directional Selection ◽  
Stabilizing Selection ◽  
Allometric Relationships ◽  
Selective Force ◽  
Developmental Constraints ◽  
Selection Pressures ◽  
Males And Females

Crayfish have five pairs of abdominal limbs called pleopods. In males, the first and second pairs of pleopods are used for transferring spermatophores to the female during copulation. The remaining pleopods in males have no obvious function. Female crayfish use their pleopods to carry eggs. Accordingly, it is expected that the selection pressures that act on the pleopods differ between males and females. To test this hypothesis, we estimated modes of selection on pleopods in two species of crayfish (Procambarus clarkii and Pacifastacus trowbridgii) by comparing allometric relationships in functional and nonfunctional pleopods. Since pleopods are serially homologous traits, developmental constraints on these traits appear to be minimal. The lengths of the first male pleopods, used in copulation, showed lower allometric values and less dispersion around the regression line, suggesting that they have been under stabilizing selection. This likely occurs because the major selective force is the ability of males to copulate with females of various sizes. The pleopods of females showed higher allometric values than pleopods of males without an assigned function. This suggests that the pleopods of females have been under directional selection, most likely because they are longer and can therefore carry more eggs.

scholarly journals Evidence for stabilizing selection at pleiotropic loci for human complex traits

2017 ◽  
Author(s):  
Emily S Wong ◽  
Steve Chenoweth ◽  
Mark Blows ◽  
Joseph E Powell
Keyword(s):  
Complex Traits ◽  
Allelic Diversity ◽  
Complex Trait ◽  
Stabilizing Selection ◽  
Single Nucleotide ◽  
Risk Alleles ◽  
History Of ◽  
Genetic Constraint ◽  
Disease Risks ◽  
Disease Loci

AbstractHow genetic variation contributes to phenotypic variation is a central question in genetics. Association signals for a complex trait are found throughout the majority of the genome suggesting much of the genome is under some degree of genetic constraint. Here, we develop a intraspecific population genetics approach to define a measure of population structure for each single nucleotide polymorphism (SNP). Using this approach, we test for evidence of stabilizing selection at complex traits and pleiotropic loci arising from the evolutionary history of 47 complex traits and common diseases. Our approach allowed us to identify traits and regions under stabilizing selection towards both global and subpopulation optima. Strongest depletion of allelic diversity was found at disease loci, indicating stabilizing selection has acted on these phenotypes in all subpopulations. Pleiotropic loci predominantly displayed evidence of stabilizing selection, often contributed to multiple disease risks, and sometimes also affected non-disease traits such as height. Risk alleles at pleiotropic disease loci displayed a more consistent direction of effect than expected by chance suggesting that stabilizing selection acting on pleiotropic loci is amplified through multiple disease phenotypes.

scholarly journals The relative impact of evolving pleiotropy and mutational correlation on trait divergence

2019 ◽  
Author(s):  
Jobran Chebib ◽  
Frédéric Guillaume
Keyword(s):  
Stochastic Model ◽  
Directional Selection ◽  
Population Variation ◽  
The Other ◽  
Common Mechanism ◽  
Stabilizing Selection ◽  
Relative Impact ◽  
Relative Importance ◽  
Trait Evolution ◽  
Trait Divergence

AbstractBoth pleiotropic connectivity and mutational correlations can restrict the divergence of traits under directional selection, but it is unknown which is more important in trait evolution. In order to address this question, we create a model that permits within-population variation in both pleiotropic connectivity and mutational correlation, and compare their relative importance to trait evolution. Specifically, we developed an individual-based, stochastic model where mutations can affect whether a locus affects a trait and the extent of mutational correlations in a population. We find that traits can diverge whether there is evolution in pleiotropic connectivity or mutational correlation but when both can evolve then evolution in pleiotropic connectivity is more likely to allow for divergence to occur. The most common genotype found in this case is characterized by having one locus that maintains connectivity to all traits and another that loses connectivity to the traits under stabilizing selection (subfunctionalization). This genotype is favoured because it allows the subfunctionalized locus to accumulate greater effect size alleles, contributing to increasingly divergent trait values in the traits under directional selection without changing the trait values of the other traits (genetic modularization). These results provide evidence that partial subfunctionalization of pleiotropic loci may be a common mechanism of trait divergence under regimes of corridor selection.

scholarly journals History of development of the biological microworld

2020 ◽  
Vol 2 (1) ◽  
pp. 152-178
Author(s):  
Vsevolod V. Borisov
Keyword(s):  
Amino Acid Sequences ◽  
Cell Nuclei ◽  
Modern Biology ◽  
Regular Sequences ◽  
Hereditary Factors ◽  
History Of ◽  
Living Nature ◽  
Living Organisms ◽  
Real Essence ◽  
The 19Th Century

The history of modern biology may be considered to begin with the penetration of scientists to biological mini-world, formed by microorganisms, cells and sub-cellular entities. The main problem to be solved was the nature of biological (genetic) heredity. In the middle of the 19th century a conception was put forward about presence in living organisms of hereditary factors, later referred as genes, whose nature for a long period remained unknown. A significant progress was achieved with elaboration of the chromosomal theory of heredity based on the presence in cell nuclei of sub-cellular structures – chromosomes. In further search of hereditary agents the plausible candidate seemed to be a polymer chemically identified as deoxyribonucleic acid (DNA). But no fantasy was enough to establish any connection of DNA with phenotypical features of living organisms. In 1953 James Watson and Francis Crick in the process of construction of space model of DNA molecule succeeded to reveal a mechanism of copying non-regular sequences of four heterocyclic bases present as one per monomer in DNA. It was suggested that these sequences might be recognized as a hereditary information. But the real essence of heredity happens to be found not so in copying as in coding. This revolutionary idea was soon (in 1954) put forward by a physicist George Gamow who suggested that a sequence of bases in DNA is a genetic text and that living cells possess a genetic code which in fact is a mechanism of transformation of sequences of triplets of DNA monomers (the “letters” of genetic text) to amino acid sequences of a multitude of various proteins which are the main functional molecules of the living nature. Now a plenty of genetic texts were elucidated which made it possible for researchers to achieve a new level of knowledge about living nature.

scholarly journals The quantitative genetic consequences of pleiotropy under stabilizing and directional selection.

Genetics ◽  
1990 ◽  
Vol 125 (1) ◽  
pp. 207-213 ◽  
Author(s):  
M Slatkin ◽  
S A Frank
Keyword(s):  
Directional Selection ◽  
Stabilizing Selection ◽  
Normal Model ◽  
Multivariate Normal ◽  
Genetic Covariance ◽  
Phenotypic Characters ◽  
House Of Cards ◽  
Quantitative Genetic ◽  
Stepwise Mutation ◽  
Multivariate Normal Model

Abstract The independence of two phenotypic characters affected by both pleiotropic and nonpleiotropic mutations is investigated using a generalization of M. Slatkin's stepwise mutation model of 1987. The model is used to determine whether predictions of either the multivariate normal model introduced in 1980 by R. Lande or the house-of-cards model introduced in 1985 by M. Turelli can be regarded as typical of models that are intermediate between them. We found that, under stabilizing selection, the variance of one character at equilibrium may depend on the strength of stabilizing selection on the other character (as in the house-of-cards model) or not (as in the multivariate normal model) depending on the types of mutations that can occur. Similarly, under directional selection, the genetic covariance between two characters may increase substantially (as in the house-of-cards model) or not (as in the multivariate normal model) depending on the kinds of mutations that are assumed to occur. Hence, even for the simple model we consider, neither the house-of-cards nor the multivariate normal model can be used to make predictions, making it unlikely that either could be used to draw general conclusions about more complex and realistic models.

scholarly journals The statistical mechanics of a polygenic character under stabilizing selection, mutation and drift

2010 ◽  
Vol 8 (58) ◽  
pp. 720-739 ◽  
Author(s):  
Harold P. de Vladar ◽  
Nick H. Barton
Keyword(s):  
Population Genetics ◽  
Statistical Mechanics ◽  
Generating Function ◽  
Genetic Drift ◽  
Infinite Series ◽  
Genetic Variance ◽  
Directional Selection ◽  
Entropy Measure ◽  
Stabilizing Selection ◽  
Approximation Procedure

By exploiting an analogy between population genetics and statistical mechanics, we study the evolution of a polygenic trait under stabilizing selection, mutation and genetic drift. This requires us to track only four macroscopic variables, instead of the distribution of all the allele frequencies that influence the trait. These macroscopic variables are the expectations of: the trait mean and its square, the genetic variance, and of a measure of heterozygosity, and are derived from a generating function that is in turn derived by maximizing an entropy measure. These four macroscopics are enough to accurately describe the dynamics of the trait mean and of its genetic variance (and in principle of any other quantity). Unlike previous approaches that were based on an infinite series of moments or cumulants, which had to be truncated arbitrarily, our calculations provide a well-defined approximation procedure. We apply the framework to abrupt and gradual changes in the optimum, as well as to changes in the strength of stabilizing selection. Our approximations are surprisingly accurate, even for systems with as few as five loci. We find that when the effects of drift are included, the expected genetic variance is hardly altered by directional selection, even though it fluctuates in any particular instance. We also find hysteresis, showing that even after averaging over the microscopic variables, the macroscopic trajectories retain a memory of the underlying genetic states.

scholarly journals Selection in natural populations V. Indian Rats (Rattus Rattus)

1966 ◽  
Vol 8 (3) ◽  
pp. 261-267 ◽  
Author(s):  
Leigh Van Valen ◽  
Robin Weiss
Keyword(s):  
Environmental Effects ◽  
Rattus Rattus ◽  
Natural Populations ◽  
Directional Selection ◽  
Stabilizing Selection ◽  
Selection Intensity ◽  
Average Difference ◽  
Age Classes ◽  
Tooth Width ◽  
The Difference

In samples of sixteen populations of Rattus rattus from southern India, the oldest individuals have less variable molar widths than the younger ones. This is probably due to stabilizing selection by mortality. There is no detectable heterogeneity between sexes or teeth or among populations in this selection. Although there is no average difference between age classes in mean tooth width, the difference between age classes is heterogeneous among populations. This heterogeneity may reflect heterogeneity in directional selection or in direct environmental effects. The selection intensity on the variance is about 0·04.

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