Recessive Mutations and the Maintenance of Sex in Structured Populations

Genetics ◽  
2001 ◽  
Vol 158 (2) ◽  
pp. 913-917 ◽  
Author(s):  
Aneil F Agrawal ◽  
J R Chasnov
Keyword(s):  
Population Structure ◽  
Structured Populations ◽  
Deleterious Mutations ◽  
Recessive Mutations ◽  
Maintenance Of Sex ◽  
Controversial Problem ◽  
Low Levels ◽  
Asexual Populations ◽  
The Cost ◽  
Cost Of Sex

AbstractThe evolutionary maintenance of sexual reproduction remains a controversial problem. It was recently shown that recessive deleterious mutations create differences in the mutation load of sexual vs. asexual populations. Here we show that low levels of population structure or inbreeding can greatly enhance the importance of recessive deleterious mutations in the context of sexual vs. asexual populations. With population structure, the cost of sex can be substantially reduced or even eliminated for realistic levels of dominance.

scholarly journals Mutation-Selection Balance, Dominance and the Maintenance of Sex

Genetics ◽  
2000 ◽  
Vol 156 (3) ◽  
pp. 1419-1425
Author(s):  
J R Chasnov
Keyword(s):  
Mutation Rate ◽  
Gene Locus ◽  
Necessary Conditions ◽  
Deleterious Mutations ◽  
Sexual Population ◽  
Recessive Mutations ◽  
Maintenance Of Sex ◽  
A Genome ◽  
Evolutionary Function ◽  
Mean Fitness

Abstract A leading hypothesis for the evolutionary function of sex postulates that sex is an adaptation that purges deleterious mutations from the genome, thereby increasing the equilibrium mean fitness of a sexual population relative to its asexual competitor. This hypothesis requires two necessary conditions: first, the mutation rate per genome must be of order one, and, second, multiple mutations within a genome must act with positive epistasis, that is, two or more mutations of different genes must be more harmful together than if they acted independently. Here, by reconsidering the theory of mutation-selection balance at a single diploid gene locus, we demonstrate a significant advantage of sex due to nearly recessive mutations provided the mutation rate per genome is of order one. The assumption of positive epistasis is unnecessary, and multiple mutations may be assumed to act independently.

The Impact of Lethal Recessive Alleles on Bottlenecks with Implications for Conservation Genetics

2016 ◽  
Author(s):  
R. B. Campbell
Keyword(s):  
Large Population ◽  
Genetic Load ◽  
Ancestral Population ◽  
Deleterious Mutations ◽  
Recessive Mutations ◽  
Deleterious Alleles ◽  
Endangered Population ◽  
Population Breeding ◽  
The Cost ◽  
The Impact

AbstractWhen a bottleneck occurs, lethal recessive alleles from the ancestral population provide a genetic load. The purging of lethal recessive mutations may prolong the bottleneck, or even cause the population to become extinct. But the purging is of short duration, it will be over before near neutral deleterious alleles accumulate. Lethal recessive alleles from the parental population and near neutral deleterious mutations which occur during a bottleneck are temporally separated threats to the survival of a population. Breeding individuals from a large population into a small endangered population will provide the benefit of viable alleles to replace near neutral deleterious alleles but also the cost of lethal recessive mutations from the large population.

scholarly journals Population structure promotes the evolution of costly sex in artificial gene networks

2018 ◽  
Keyword(s):  
Population Structure ◽  
Network Model ◽  
Gene Networks ◽  
Gene Network ◽  
Critical Role ◽  
Effective Rate ◽  
Structured Populations ◽  
Evolution Of Sex ◽  
Short Term ◽  
Asexual Populations

AbstractWe build on previous observations that Hill-Robertson interference generates an advantage of sex that, in structured populations, can be large enough to explain the evolutionary maintenance of costly sex. We employed a gene network model that explicitly incorporates interactions between genes. Mutations in the gene networks have variable effects that depend on the genetic background in which they appear. Consequently, our simulations include two costs of sex—recombination and migration loads—that were missing from previous studies of the evolution of costly sex. Our results suggest a critical role for population structure that lies in its ability to align the long- and short-term advantages of sex. We show that the addition of population structure favored the evolution of sex by disproportionately decreasing the equilibrium mean fitness of asexual populations, primarily by increasing the strength of Muller’s Ratchet. Population structure also increased the ability of the short-term advantage of sex to counter the primary limit to the evolution of sex in the gene network model—recombination load. On the other hand, highly structured populations experienced migration load in the form of Dobzhansky–Muller incompatibilities, decreasing the effective rate of migration between demes and, consequently, accelerating the accumulation of drift load in the sexual populations.

scholarly journals The Advantages of Segregation and the Evolution of Sex

Genetics ◽  
2003 ◽  
Vol 164 (3) ◽  
pp. 1099-1118 ◽  
Author(s):  
Sarah P Otto
Keyword(s):  
Sexual Reproduction ◽  
Asexual Reproduction ◽  
Deleterious Mutations ◽  
Evolution Of Sex ◽  
Beneficial Mutations ◽  
Selection Regime ◽  
Strong Selection ◽  
Genome Wide ◽  
Low Levels

AbstractIn diploids, sexual reproduction promotes both the segregation of alleles at the same locus and the recombination of alleles at different loci. This article is the first to investigate the possibility that sex might have evolved and been maintained to promote segregation, using a model that incorporates both a general selection regime and modifier alleles that alter an individual’s allocation to sexual vs. asexual reproduction. The fate of different modifier alleles was found to depend strongly on the strength of selection at fitness loci and on the presence of inbreeding among individuals undergoing sexual reproduction. When selection is weak and mating occurs randomly among sexually produced gametes, reductions in the occurrence of sex are favored, but the genome-wide strength of selection is extremely small. In contrast, when selection is weak and some inbreeding occurs among gametes, increased allocation to sexual reproduction is expected as long as deleterious mutations are partially recessive and/or beneficial mutations are partially dominant. Under strong selection, the conditions under which increased allocation to sex evolves are reversed. Because deleterious mutations are typically considered to be partially recessive and weakly selected and because most populations exhibit some degree of inbreeding, this model predicts that higher frequencies of sex would evolve and be maintained as a consequence of the effects of segregation. Even with low levels of inbreeding, selection is stronger on a modifier that promotes segregation than on a modifier that promotes recombination, suggesting that the benefits of segregation are more likely than the benefits of recombination to have driven the evolution of sexual reproduction in diploids.

RPD3 encodes a second factor required to achieve maximum positive and negative transcriptional states in Saccharomyces cerevisiae

1991 ◽  
Vol 11 (12) ◽  
pp. 6317-6327 ◽  
Author(s):  
M Vidal ◽  
R F Gaber
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Target Genes ◽  
Current Data ◽  
Regulatory Function ◽  
Fourfold Increase ◽  
Recessive Mutations ◽  
Activation Of Transcription ◽  
Transcriptional Regulatory ◽  
Low Levels ◽  
Full Activation

In Saccharomyces cerevisiae, TRK1 and TRK2 encode the high- and low-affinity K+ transporters, respectively. In cells containing a deletion of TRK1, transcription levels of TRK2 are extremely low and are limiting for growth in media containing low levels of K+ (Trk- phenotype). Recessive mutations in RPD1 and RPD3 suppress the TRK2, conferring an approximately fourfold increase in transcription. rpd3 mutations confer pleiotropic phenotypes, including (i) mating defects, (ii) hypersensitivity to cycloheximide, (iii) inability to sporulate as homozygous diploids, and (iv) constitutive derepression of acid phosphatase. RPD3 was cloned and is predicted to encode a 48-kDa protein with no extensive similarity to proteins contained in current data bases. Deletion of RPD3 is not lethal but confers phenotypes identical to those caused by spontaneous mutations. RPD3 is required for both full repression and full activation of transcription of target genes including PHO5, STE6, and TY2. RPD3 is the second gene required for this function, since RPD1 is also required. The effects of mutations in RPD1 and RPD3 are not additive, suggesting that these genes are involved in the same transcriptional regulatory function or pathway.

scholarly journals A novel coalescent method insensitive to population structure

2020 ◽  
Author(s):  
Zeqi Yao ◽  
Kehui Liu ◽  
Shanjun Deng ◽  
Xionglei He
Keyword(s):  
Population Structure ◽  
Phylogenetic Tree ◽  
Simulated Data ◽  
Structured Populations ◽  
Population History ◽  
Cell Populations ◽  
Developmental History ◽  
Coalescent Analysis ◽  
History Of ◽  
Larger Sample

AbstractConventional coalescent inferences of population history make the critical assumption that the population under examination is panmictic. However, most populations are structured. This complicates the prevailing coalescent analyses and sometimes leads to inaccurate estimates. To develop a coalescent method unhampered by population structure, we perform two analyses. First, we demonstrate that the coalescent probability of two randomly sampled alleles from the immediate preceding generation (one generation back) is independent of population structure. Second, motivated by this finding, we propose a new coalescent method: i-coalescent analysis. i-coalescent analysis computes the instantaneous coalescent rate (iCR) by using a phylogenetic tree of sampled alleles. Using simulated data, we broadly demonstrate the capability of i-coalescent analysis to accurately reconstruct population size dynamics of highly structured populations, although we find this method often requires larger sample sizes for structured populations than for panmictic populations. Overall, our results indicate i-coalescent analysis to be a useful tool, especially for the inference of population histories with intractable structure such as the developmental history of cell populations in the organs of complex organisms.

scholarly journals Genetic sex determination and sex-specific lifespan in tetrapods – evidence of a toxic Y effect

2020 ◽  
Author(s):  
Zahida Sultanova ◽  
Philip A. Downing ◽  
Pau Carazo
Keyword(s):  
Sex Chromosomes ◽  
Alternative Hypothesis ◽  
Z Chromosome ◽  
W Chromosome ◽  
Deleterious Mutations ◽  
Recessive Mutations ◽  
Y Chromosomes ◽  
Heterogametic Sex ◽  
Taxonomic Patterns

ABSTRACTSex-specific lifespans are ubiquitous across the tree of life and exhibit broad taxonomic patterns that remain a puzzle, such as males living longer than females in birds and vice versa in mammals. The prevailing “unguarded-X” hypothesis (UXh) explains this by differential expression of recessive mutations in the X/Z chromosome of the heterogametic sex (e.g., females in birds and males in mammals), but has only received indirect support to date. An alternative hypothesis is that the accumulation of deleterious mutations and repetitive elements on the Y/W chromosome might lower the survival of the heterogametic sex (“toxic Y” hypothesis). Here, we report lower survival of the heterogametic relative to the homogametic sex across 138 species of birds, mammals, reptiles and amphibians, as expected if sex chromosomes shape sex-specific lifespans. We then analysed bird and mammal karyotypes and found that the relative sizes of the X and Z chromosomes are not associated with sex-specific lifespans, contrary to UXh predictions. In contrast, we found that Y size correlates negatively with male survival in mammals, where toxic Y effects are expected to be particularly strong. This suggests that small Y chromosomes benefit male lifespans. Our results confirm the role of sex chromosomes in explaining sex differences in lifespan, but indicate that, at least in mammals, this is better explained by “toxic Y” rather than UXh effects.

scholarly journals Ordering structured populations in multiplayer cooperation games

2015 ◽  
Author(s):  
Jorge Peña ◽  
Bin Wu ◽  
Arne Traulsen
Keyword(s):  
Population Structure ◽  
Spatial Structure ◽  
Structured Populations ◽  
Evolution Of Cooperation ◽  
Multiplayer Games ◽  
Spatial Games ◽  
Population Structures ◽  
Single Structure ◽  
Containment Order ◽  
Update Rules

AbstractSpatial structure greatly affects the evolution of cooperation. While in two-player games the condition for cooperation to evolve depends on a single structure coefficient, in multiplayer games the condition might depend on several structure coefficients, making it difficult to compare different population structures. We propose a solution to this issue by introducing two simple ways of ordering population structures: the containment order and the volume order. If population structure 𝒮1 is greater than population structure 𝒮2 in the containment or the volume order, then 𝒮1 can be considered a stronger promoter of cooperation. We provide conditions for establishing the containment order, give general results on the volume order, and illustrate our theory by comparing different models of spatial games and associated update rules. Our results hold for a large class of population structures and can be easily applied to specific cases once the structure coefficients have been calculated or estimated.

Labor Activation, Social Protection and Poverty Reduction: The Case of Russia

2019 ◽  
Vol 4 (3) ◽  
pp. 328-353
Author(s):  
Esuna Dugarova
Keyword(s):  
Labor Market ◽  
Poverty Reduction ◽  
Social Protection ◽  
Decent Work ◽  
Russian Government ◽  
Core Element ◽  
Low Levels ◽  
Demographic Shifts ◽  
Working Poverty ◽  
The Cost

Social protection is an important strategy to protect people from livelihood risks, develop human capital and promote economic growth. Decent work is a core element of social protection and a critical condition for eradicating poverty. Despite high labor force participation and low unemployment, Russia’s labor market shows several negative trends, including working poverty and growing informality. Both are exacerbated by gender disparities and unfavorable demographic shifts. Over the past decade the Russian government has implemented active labor market interventions, and enhanced targeted social protection aimed at promoting employment and reducing poverty. Based on the analysis of key data and programs, the article finds that the country achieved stability in the labor market, but at the cost of deteriorating living standards caused by low levels of productivity and wages.

scholarly journals Air Pollution Control: Equity Considerations for Rural and Urban America

1973 ◽  
Vol 2 (2) ◽  
pp. 224-234
Author(s):  
Douglas E. Morris
Keyword(s):  
Air Pollution ◽  
Pollution Control ◽  
Air Pollution Control ◽  
Equity Issue ◽  
Great Magnitude ◽  
Urban America ◽  
Rural And Urban ◽  
Low Levels ◽  
The Many ◽  
The Cost

This paper deals with one of the many aspects of controlling air pollution–equity. The equity issue discussed concerns the fact that areas with high and low levels of air pollution are subjected to many of the same controls under current legislation. The equity issue is, of course, only one of several imperative questions that should be addressed and fully researched before society embarks on an abatement program of great magnitude. In fact, comparisons between expected cost outlays by firms and individuals to control air pollution, and the cost of allowing the pollution to continue, indicate that it may be less costly for firms and individuals to do nothing.

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