scholarly journals A genetic model of interpopulation variation and covariation of quantitative characters

1989 ◽  
Vol 53 (3) ◽  
pp. 215-221 ◽  
Author(s):  
Zhao-Bang Zeng
Keyword(s):  
Natural Selection ◽  
Genetic Model ◽  
Environment Interaction ◽  
Effective Population ◽  
Genotype Environment Interaction ◽  
Quantitative Characters ◽  
Special Cases ◽  
Population Sizes ◽  
Interpopulation Variation ◽  
Evolutionary Consequences

SummaryEvolutionary consequences of natural selection, migration, genotype–environment interaction, and random genetic drift on interpopulation variation and covariation of quantitative characters are analysed in terms of a selection model that partitions natural selection into directional and stabilizing components. Without migration, interpopulation variation and covariation depend mainly on the pattern and intensities of selection among populations and the harmonic mean of effective population sizes. Both transient and equilibrium covariance structures are formulated with suitable approximations. Migration reduces the differentiation among populations, but its effect is less with genotype–environment interaction. In some special cases of genotype–environment interaction, the equilibrium interpopulation variation and covariation is independent of migration.

scholarly journals The evolution of the Y chromosome with X-Y recombination.

Genetics ◽  
1988 ◽  
Vol 119 (3) ◽  
pp. 711-720
Author(s):  
A G Clark
Keyword(s):  
Natural Selection ◽  
Y Chromosome ◽  
Meiotic Recombination ◽  
Population Genetic ◽  
Sex Chromosome ◽  
Genetic Model ◽  
Chromosome Polymorphism ◽  
Significant Finding ◽  
Special Cases ◽  
Theoretical Population

Abstract A theoretical population genetic model is developed to explore the consequences of X-Y recombination in the evolution of sex chromosome polymorphism. The model incorporates one sex-determining locus and one locus subject to natural selection. Both loci have two alleles, and the rate of classical meiotic recombination between the loci is r. The alleles at the sex-determining locus specify whether the chromosome is X or Y, and the alleles at the selected locus are arbitrarily labeled A and a. Natural selection is modeled as a process of differential viabilities. The system can be expressed in terms of three recurrence equations, one for the frequency of A on the X-bearing gametes produced by females, one for each of the frequency of A on the X- and Y-bearing gametes produced by males. Several special cases are examined, including X chromosome dominance and symmetric selection. Unusual equilibria are found with the two sexes having very different allele frequencies at the selected locus. A significant finding is that the allowance of recombination results in a much greater opportunity for polymorphism of the Y chromosome. Tighter linkage results in a greater likelihood for equilibria with a large difference between the sex chromosomes in allele frequency.

scholarly journals Genetic differentiation of quantitative characters between populations or species: I. Mutation and random genetic drift

1982 ◽  
Vol 39 (3) ◽  
pp. 303-314 ◽  
Author(s):  
Ranajit Chakraborty ◽  
Masatoshi Nei
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
Genetic Drift ◽  
Genetic Variance ◽  
Genetic Model ◽  
Neutral Evolution ◽  
Random Genetic Drift ◽  
Effective Population ◽  
Quantitative Characters ◽  
Allelic State

SummaryIntroducing a new genetic model called the discrete allelic-state model, the evolutionary change of genetic variation of quantitative characters within and between populations is studied under the assumption of no selection. This model allows us to study the effects of mutation and random genetic drift in detail. It is shown that when the allelic effects on phenotype are additive, the rate of approach of the genetic variance within populations to the equilibrium value depends only on the effective population size. It is also shown that the distribution of genotypic value often deviates from normality particularly when the effective population size and the number of loci concerned are small. On the other hand, the interpopulational variance increases linearly with time, if the intrapopu-lational variance remains constant. Therefore, the ratio of interpopulational variance to intrapopulational variance can be used for testing the hypothesis of neutral evolution of quantitative characters.

scholarly journals Climate change has increased genotype-environment interactions in wheat breeding

2020 ◽  
Author(s):  
Wei Xiong ◽  
Matthew Reynolds ◽  
Jose Crossa ◽  
Thomas Payne ◽  
Urs Schulthess ◽  
...  
Keyword(s):  
Climate Change ◽  
Genetic Model ◽  
Climatic Factors ◽  
Wheat Breeding ◽  
Environment Interaction ◽  
Genotype Environment Interaction ◽  
Quantitative Genetic ◽  
Quantitative Genetic Model ◽  
Yield Responses ◽  
Wheat Lines

Abstract The International Maize and Wheat Improvement Center (CIMMYT) develops and distributes annually elite wheat lines as international trials worldwide to assess their performance in different environments and utilization by partners for use in breeding or release as varieties. However, as elsewhere, the collaborator test sites where trials are evaluated have experienced climate change, with implications for how adapted wheat genotypes are bred. Using a standard quantitative genetic model and archived datasets for four global spring wheat trials, we show that the genotype-environment-interaction (GEI) has increased by up to 500% over recent decades. Notably crossover has increased over time, a critical indicator of changes in the ranking of cultivar performance in different environments. Climatic factors explain over 70% of the year-to-year variability in GEI and crossover interactions for yield. Examining yield responses of all genotypes in all trial environments from 1985 to 2017 reveals that climate change has increased GEI by ~ 49% and ranking change by ~38%. Genetic improvement of wheat targeted to high-yielding environments has exacerbated this increase, but the performance of new wheat germplasm developed to withstand heat and drought stress is more adapted and stable, offsetting the increase in ranking changes due to the warmer climate.

scholarly journals Molecular evolutionary consequences of island colonisation

2015 ◽  
Author(s):  
Jennifer James ◽  
Robert Lanfear ◽  
Adam Eyre-Walker
Keyword(s):  
Genetic Diversity ◽  
Population Bottleneck ◽  
Surprising Result ◽  
Population Bottlenecks ◽  
Adaptive Potential ◽  
Effective Population ◽  
Island Species ◽  
Population Sizes ◽  
Evolutionary Consequences ◽  
The Relationship

Island endemics are likely to experience population bottlenecks; they also have restricted ranges. Therefore we expect island species to have small effective population sizes (Ne) and reduced genetic diversity compared to their mainland counterparts. As a consequence, island species may have inefficient selection and reduced adaptive potential. We used both polymorphisms and substitutions to address these predictions, improving on the approach of recent studies that only used substitution data. This allowed us to directly test the assumption that island species have small values of Ne. We found that island species had significantly less genetic diversity than mainland species; however, this pattern could be attributed to a subset of island species that had undergone a recent population bottleneck. When these species were excluded from the analysis, island and mainland species had similar levels of genetic diversity, despite island species occupying considerably smaller areas than their mainland counterparts. We also found no overall difference between island and mainland species in terms of effectiveness of selection or mutation rate. Our evidence suggests that island colonisation has no lasting impact on molecular evolution. This surprising result highlights gaps in our knowledge of the relationship between census and effective population size.

scholarly journals Estimation of effective population sizes from data on genetic markers

2005 ◽  
Vol 360 (1459) ◽  
pp. 1395-1409 ◽  
Author(s):  
Jinliang Wang
Keyword(s):  
Genetic Markers ◽  
Evolutionary Biology ◽  
Genetic Model ◽  
Spatial Scales ◽  
Effective Population ◽  
Future Developments ◽  
The Past ◽  
Heterozygosity Excess ◽  
Population Sizes ◽  
The Many

The effective population size ( N e ) is an important parameter in ecology, evolutionary biology and conservation biology. It is, however, notoriously difficult to estimate, mainly because of the highly stochastic nature of the processes of inbreeding and genetic drift for which N e is usually defined and measured, and because of the many factors (such as time and spatial scales, systematic forces) confounding such processes. Many methods have been developed in the past three decades to estimate the current, past and ancient effective population sizes using different information extracted from some genetic markers in a sample of individuals. This paper reviews the methodologies proposed for estimating N e from genetic data using information on heterozygosity excess, linkage disequilibrium, temporal changes in allele frequency, and pattern and amount of genetic variation within and between populations. For each methodology, I describe mainly the logic and genetic model on which it is based, the data required and information used, the interpretation of the estimate obtained, some results from applications to simulated or empirical datasets and future developments that are needed.

scholarly journals Genotype × Environment Interaction in Psychiatric Genetics: Deep Truth or Thin Ice?

2017 ◽  
Vol 20 (3) ◽  
pp. 187-196 ◽  
Author(s):  
Lindon Eaves
Keyword(s):  
Genetic Model ◽  
Clinical Symptoms ◽  
Theory Of Measurement ◽  
Risk Scores ◽  
Environment Interaction ◽  
Psychiatric Genetics ◽  
Environmental Covariates ◽  
Genotype Environment Interaction ◽  
Sum Scores ◽  
Method Of Assessment

Background:There continues to be significant investment in the detection of genotype × environment interaction (G × E) in psychiatric genetics. The implications of the method of assessment for the genetic analysis of psychiatric disorders are examined for simulated twin data on symptom scores and environmental covariates.Methods: Additive and independent genetic and environmental risks were simulated for 10,000 monozygotic (MZ) and 10,000 dizygotic (DZ) twin pairs and the ‘subjects’ administered typical simulated checklists of clinical symptoms and environmental factors. A variety of standard tests for G × E were applied to the simulated additive risk scores, sum scores derived from the checklists and transformed sum scores.Results:All analyses revealed no evidence for G × E for latent risk but marked evidence for G × E and other effects of modulation in the sum scores. These effects were all removed by transformation. An integrated genetic and psychometric model, accounting for both the causes of latent liability and a theory of measurement, was fitted to a sample of the simulated sum-score data and showed that there was no significant modulation of the parameters of the genetic model by environmental covariates (i.e., no G × E).Conclusions:Claims to detect G × E based on analytical methods that ignore the theory of measurement must be subjected to greater scrutiny prior to publication.

scholarly journals Dissecting the Effects of Selection and Mutation on Genetic Diversity in Three Wood White (Leptidea) Butterfly Species

2019 ◽  
Vol 11 (10) ◽  
pp. 2875-2886 ◽  
Author(s):  
Venkat Talla ◽  
Lucile Soler ◽  
Takeshi Kawakami ◽  
Vlad Dincă ◽  
Roger Vila ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Natural Selection ◽  
Nucleotide Diversity ◽  
Gene Annotation ◽  
Rate Variation ◽  
Butterfly Species ◽  
Relative Role ◽  
Effective Population ◽  
Genome Wide ◽  
Population Sizes

Abstract The relative role of natural selection and genetic drift in evolution is a major topic of debate in evolutionary biology. Most knowledge spring from a small group of organisms and originate from before it was possible to generate genome-wide data on genetic variation. Hence, it is necessary to extend to a larger number of taxonomic groups, descriptive and hypothesis-based research aiming at understanding the proximate and ultimate mechanisms underlying both levels of genetic polymorphism and the efficiency of natural selection. In this study, we used data from 60 whole-genome resequenced individuals of three cryptic butterfly species (Leptidea sp.), together with novel gene annotation information and population recombination data. We characterized the overall prevalence of natural selection and investigated the effects of mutation and linked selection on regional variation in nucleotide diversity. Our analyses showed that genome-wide diversity and rate of adaptive substitutions were comparatively low, whereas nonsynonymous to synonymous polymorphism and substitution levels were comparatively high in Leptidea, suggesting small long-term effective population sizes. Still, negative selection on linked sites (background selection) has resulted in reduced nucleotide diversity in regions with relatively high gene density and low recombination rate. We also found a significant effect of mutation rate variation on levels of polymorphism. Finally, there were considerable population differences in levels of genetic diversity and pervasiveness of selection against slightly deleterious alleles, in line with expectations from differences in estimated effective population sizes.

scholarly journals DEVELOPMENTAL STABILITY OF DROSOPHILA MELANOGASTER UNDER ARTIFICIAL AND NATURAL SELECTION IN CONSTANT AND FLUCTUATING ENVIRONMENTS

Genetics ◽  
1980 ◽  
Vol 95 (4) ◽  
pp. 1033-1042
Author(s):  
Brian P Bradley
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Developmental Stability ◽  
Stabilizing Selection ◽  
Phenotypic Variance ◽  
Environment Interaction ◽  
Total Phenotypic Variance ◽  
Environmental Variance ◽  
Genotype Environment Interaction ◽  
Fluctuating Environments

ABSTRACT Populations of Drosophila melanogaster in constant 25λ and fluctuating 20/29λ environments showed increases in developmental stability, indicated by decreases in bilateral asymmetry of sterno-pleural chaeta number. In both environments, rates of decrease in asymmetry were greater under natural selection (control lines) than under artificial stabilizing selection. Overall mean asymmetry was greater in the fluctuating environment.—There was no evidence that decreased asymmetry was due to heterozygosity, and the decline in asymmetry was not explained by the decline in chaeta number in the lines under only natural selection. However, the decline was consistent with changes in total phenotypic variance and environmental variance.— The divergence between lines after 39 generations of selection was seen in differences in asymmetry and also in the genotype-environment interaction expressed in cross-culturing experiments.

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