scholarly journals Genetic linkage and natural selection

2010 ◽  
Vol 365 (1552) ◽  
pp. 2559-2569 ◽  
Author(s):  
N. H. Barton
Keyword(s):  
Deleterious Mutation ◽  
Balancing Selection ◽  
Selective Sweeps ◽  
Deleterious Mutations ◽  
Mutation Load ◽  
Random Drift ◽  
Selection For ◽  
Genomic Regions ◽  
Significant Interference ◽  
General Explanation

The prevalence of recombination in eukaryotes poses one of the most puzzling questions in biology. The most compelling general explanation is that recombination facilitates selection by breaking down the negative associations generated by random drift (i.e. Hill–Robertson interference, HRI). I classify the effects of HRI owing to: deleterious mutation, balancing selection and selective sweeps on: neutral diversity, rates of adaptation and the mutation load. These effects are mediated primarily by the density of deleterious mutations and of selective sweeps. Sequence polymorphism and divergence suggest that these rates may be high enough to cause significant interference even in genomic regions of high recombination. However, neither seems able to generate enough variance in fitness to select strongly for high rates of recombination. It is plausible that spatial and temporal fluctuations in selection generate much more fitness variance, and hence selection for recombination, than can be explained by uniformly deleterious mutations or species-wide selective sweeps.

scholarly journals Harmful mutation load in the mitochondrial genomes of cattle breeds

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Sankar Subramanian
Keyword(s):  
Population Size ◽  
Artificial Selection ◽  
Deleterious Mutation ◽  
Genetic Diseases ◽  
Mitochondrial Genomes ◽  
Deleterious Mutations ◽  
Founder Population ◽  
Mutation Load ◽  
Effective Population ◽  
Cattle Breeds

Abstract Objective Domestication of wild animals results in a reduction in the effective population size, and this could affect the deleterious mutation load of domesticated breeds. Furthermore, artificial selection will also contribute to the accumulation of deleterious mutations due to the increased rate of inbreeding among these animals. The process of domestication, founder population size, and artificial selection differ between cattle breeds, which could lead to a variation in their deleterious mutation loads. We investigated this using mitochondrial genome data from 364 animals belonging to 18 cattle breeds of the world. Results Our analysis revealed more than a fivefold difference in the deleterious mutation load among cattle breeds. We also observed a negative correlation between the breed age and the proportion of deleterious amino acid-changing polymorphisms. This suggests a proportionally higher deleterious SNPs in young breeds compared to older breeds. Our results highlight the magnitude of difference in the deleterious mutations present in the mitochondrial genomes of various breeds. The results of this study could be useful in predicting the rate of incidence of genetic diseases in different breeds.

scholarly journals The mutation load under tetrasomic inheritance and its consequences for the evolution of the selfing rate in autotetraploid species

1999 ◽  
Vol 74 (1) ◽  
pp. 31-42 ◽  
Author(s):  
J. RONFORT
Keyword(s):  
Inbreeding Depression ◽  
Deleterious Mutation ◽  
Stable State ◽  
Approximate Solutions ◽  
Balance Model ◽  
Deleterious Mutations ◽  
Selfing Rate ◽  
Mutation Load ◽  
Mean Fitness ◽  
The Mean

Single-locus equilibrium frequencies of a partially recessive deleterious mutation under the mutation–selection balance model are derived for partially selfing autotetraploid populations. Assuming multiplicative fitness interactions among loci, approximate solutions for the mean fitness and inbreeding depression values are also derived for the multiple locus case and compared with expectations for the diploid model. As in diploids, purging of deleterious mutations through consanguineous matings occurs in autotetraploid populations, i.e. the equilibrium mutation load is a decreasing function of the selfing rate. However, the variation of inbreeding depression with the selfing rate depends strongly on the dominance coefficients associated with the three heterozygous genotypes. Inbreeding depression can either increase or decrease with the selfing rate, and does not always vary monotonically. Expected issues for the evolution of the selfing rate consequently differ depending on the dominance coefficients. In some cases, expectations for the evolution of the selfing rate resemble expectations in diploids; but particular sets of dominance coefficients can be found that lead to either complete selfing or intermediate selfing rates as unique evolutionary stable state.

scholarly journals The Sheltered Genetic Load Linked to the S Locus in Plants: New Insights From Theoretical and Empirical Approaches in Sporophytic Self-Incompatibility

Genetics ◽  
2009 ◽  
Vol 183 (3) ◽  
pp. 1105-1118 ◽  
Author(s):  
Violaine Llaurens ◽  
Lucy Gonthier ◽  
Sylvain Billiard
Keyword(s):  
Inbreeding Depression ◽  
Balancing Selection ◽  
Genetic Load ◽  
Relative Fitness ◽  
Self Incompatibility ◽  
Deleterious Mutations ◽  
Gas Treatment ◽  
Genomic Inbreeding ◽  
Genomic Regions ◽  
Empirical Approaches

Inbreeding depression and mating systems evolution are closely linked, because the purging of deleterious mutations and the fitness of individuals may depend on outcrossing vs. selfing rates. Further, the accumulation of deleterious mutations may vary among genomic regions, especially for genes closely linked to loci under balancing selection. Sporophytic self-incompatibility (SSI) is a common genetic mechanism in angiosperm that enables hermaphrodite plants to avoid selfing and promote outcrossing. The SSI phenotype is determined by the S locus and may depend on dominance relationships among alleles. Since most individuals are heterozygous at the S locus and recombination is suppressed in the S-locus region, it has been suggested that deleterious mutations could accumulate at genes linked to the S locus, generating a “sheltered load.” In this article, we first theoretically investigate the conditions generating sheltered load in SSI. We show that deleterious mutations can accumulate in linkage with specific S alleles, and particularly if those S alleles are dominant. Second, we looked for the presence of sheltered load in Arabidopsis halleri using CO2 gas treatment to overcome self-incompatibility. By examining the segregation of S alleles and measuring the relative fitness of progeny, we found significant sheltered load associated with the most dominant S allele (S15) of three S alleles tested. This sheltered load seems to be expressed at several stages of the life cycle and to have a larger effect than genomic inbreeding depression.

scholarly journals A deleterious mutation-sheltering theory for the evolution of sex chromosomes and supergenes

2021 ◽  
Author(s):  
Paul Jay ◽  
Tatiana Giraud ◽  
Emilie Tezenas
Keyword(s):  
Mathematical Modeling ◽  
Sex Chromosomes ◽  
Deleterious Mutation ◽  
Stochastic Simulations ◽  
Recessive Mutation ◽  
Deleterious Mutations ◽  
Evolution Of Sex ◽  
Mutation Load ◽  
Recombination Suppression ◽  
Chromosomal Inversions

Many organisms have sex chromosomes with large non-recombining regions having expanded stepwise, the reason why being still poorly understood. Theories proposed so far rely on differences between sexes but are poorly supported by empirical data and cannot account for the stepwise suppression of recombination around sex chromosomes in organisms without sexual dimorphism. We show here, by mathematical modeling and stochastic simulations, that recombination suppression in sex chromosomes can evolve simply because it shelters recessive deleterious mutations, which are ubiquitous in genomes. The permanent heterozygosity of sex-determining alleles protects linked chromosomal inversions against expression of their recessive mutation load, leading to an accumulation of inversions around these loci, as observed in nature. We provide here a testable and widely applicable theory to explain the evolution of sex chromosomes and of supergenes in general.

scholarly journals Harmful Mutation Load in the Mitochondrial Genomes of Cattle Breeds 

2021 ◽  
Author(s):  
Sankar Subramanian
Keyword(s):  
Amino Acid ◽  
Population Size ◽  
Artificial Selection ◽  
Deleterious Mutation ◽  
Mitochondrial Genomes ◽  
Deleterious Mutations ◽  
Founder Population ◽  
Mutation Load ◽  
Effective Population ◽  
Cattle Breeds

Abstract ObjectiveDomestication of wild animals results in a reduction in the effective population size and this could affect the deleterious mutation load of domesticated breeds. Furthermore, artificial selection will also contribute to accumulation deleterious mutations due to the increased rate of inbreeding among these animals. The process of domestication, founder population size, and artificial selection differ between cattle breeds, which could lead to a variation in their deleterious mutation loads. We investigated this using mitochondrial genome data from 252 animals belonging to 15 cattle breeds of the world. ResultsOur analysis revealed more than fivefold difference in the deleterious mutation load among cattle breeds. We also observed a negative correlation between the neutral heterozygosity and the ratio of amino acid changing diversity to silent diversity. This suggests a proportionally higher amino acid changing variants in breeds with low diversity. Our results highlight the magnitude of difference in the deleterious mutations present in the mitochondrial genomes of various breeds. The results of this study could be useful in predicting the rate of incidence of genetic diseases in different breeds.

scholarly journals The effects of a deleterious mutation load on patterns of influenza A/H3N2's antigenic evolution in humans

eLife ◽  
2015 ◽  
Vol 4 ◽  
Author(s):  
Katia Koelle ◽  
David A Rasmussen
Keyword(s):  
Influenza Virus ◽  
Genetic Linkage ◽  
Influenza A ◽  
Deleterious Mutation ◽  
Rna Virus ◽  
Phylogenetic Analyses ◽  
Molecular Pathways ◽  
Deleterious Mutations ◽  
Mutation Load ◽  
Antigenic Evolution

Recent phylogenetic analyses indicate that RNA virus populations carry a significant deleterious mutation load. This mutation load has the potential to shape patterns of adaptive evolution via genetic linkage to beneficial mutations. Here, we examine the effect of deleterious mutations on patterns of influenza A subtype H3N2's antigenic evolution in humans. By first analyzing simple models of influenza that incorporate a mutation load, we show that deleterious mutations, as expected, act to slow the virus's rate of antigenic evolution, while making it more punctuated in nature. These models further predict three distinct molecular pathways by which antigenic cluster transitions occur, and we find phylogenetic patterns consistent with each of these pathways in influenza virus sequences. Simulations of a more complex phylodynamic model further indicate that antigenic mutations act in concert with deleterious mutations to reproduce influenza's spindly hemagglutinin phylogeny, co-circulation of antigenic variants, and high annual attack rates.

scholarly journals EXPECTED LINKAGE DISEQUILIBRIUM FOR A NEUTRAL LOCUS LINKED TO A CHROMOSOMAL ARRANGEMENT

Genetics ◽  
1983 ◽  
Vol 103 (3) ◽  
pp. 545-555
Author(s):  
Curtis Strobeck
Keyword(s):  
Linkage Disequilibrium ◽  
Balancing Selection ◽  
Natural Populations ◽  
Transient Behavior ◽  
Random Drift ◽  
Strong Linkage ◽  
Linkage Disequilibria ◽  
Chromosomal Arrangement ◽  
Neutral Locus ◽  
Selection For

ABSTRACT The expected value of the squared linkage disequilibrium is derived for a neutral locus associated with a chromosomal arrangement that is maintained in the population by strong balancing selection. For a given value of recombination, the expected squared linkage disequilibrium is shown to decrease as the intensity of selection maintaining the arrangement increases. The transient behavior of the expected square linkage disequilibrium is also derived. This theory applies to loci that are closely linked to inversions in Drosophila species and to loci closely linked to the differential segments of the translocation complexes in ring-forming species of Oenothera. In both cases the strong linkage disequilibria that have been observed in natural populations can be explained by random drift.

scholarly journals Purging of highly deleterious mutations through severe bottlenecks in Alpine ibex

2019 ◽  
Author(s):  
Christine Grossen ◽  
Frederic Guillaume ◽  
Lukas F. Keller ◽  
Daniel Croll
Keyword(s):  
Deleterious Mutation ◽  
Conservation Status ◽  
Population Bottlenecks ◽  
Deleterious Mutations ◽  
Population Declines ◽  
Mutation Load ◽  
Current Conservation ◽  
Term Survival ◽  
Alpine Ibex ◽  
Species Survival

AbstractHuman activity caused dramatic population declines in many wild species. The resulting bottlenecks have a profound impact on the genetic makeup of a species with unknown consequences for health. A key genetic factor for species survival is the evolution of deleterious mutation load, but how bottleneck strength and mutation load interact lacks empirical evidence. Here, we take advantage of the exceptionally well-characterized population bottlenecks of the once nearly extinct Alpine ibex. The species survived one of the most dramatic bottlenecks known for successfully restored species. We analyze 60 complete genomes of six ibex species and the domestic goat. We show that historic bottlenecks rather than the current conservation status predict levels of genome-wide variation. By retracing the recolonization of the Alps by Alpine ibex, we find genomic evidence of concurrent purging of highly deleterious mutations but accumulation of mildly deleterious mutations. This demonstrates how human-induced severe bottlenecks caused both relaxed selection and purging, thus reshaping the landscape of deleterious mutation load. Our findings also highlight that even populations of ~1000 individuals can accumulate mildly deleterious mutations. Hence, conservation efforts should focus on preventing population declines below such levels to ensure long-term survival of species.

scholarly journals The Evolution of Bacterial Transformation: Sex With Poor Relations

Genetics ◽  
1997 ◽  
Vol 146 (1) ◽  
pp. 27-38 ◽  
Author(s):  
Rosemary J Redfield ◽  
Matthew R Schrag ◽  
Antony M Dean
Keyword(s):  
Natural Transformation ◽  
Deleterious Mutation ◽  
Fitness Function ◽  
Dna Uptake ◽  
Deleterious Mutations ◽  
Limited Data ◽  
Bacterial Populations ◽  
Selection For ◽  
Transformation Systems ◽  
Selection Of

Bacteria are the only organisms known to actively take up DNA and recombine it into their genomes. While such natural transformation systems may provide many of the same benefits that sexual reproduction provides eukaryotes, there are important differences that critically alter the consequences, especially when recombination's main benefit is reducing the mutation load. Here, analytical and numerical methods are used to study the selection of transformation genes in populations undergoing deleterious mutation. Selection for transformability depends on the shape of the fitness function against mutation. If the fitness function is linear, then transformation would be selectively neutral were it not for the possibility that transforming cells may take up DNA that converts them into nontransformable cells. If the selection includes strong positive (synergistic) epistasis, then transformation can be advantageous in spite of this risk. The effect of low quality DNA (from selectively killed cells) on selection is then studied analytically and found to impose an additional cost. The limited data available for real bacterial populations suggest that the conditions necessary for the evolution of transformation are unlikely to be met, and thus that DNA uptake may have some function other than recombination of deleterious mutations.

scholarly journals Deleterious mutations as an evolutionary factor: 1. The advantage of recombination

1984 ◽  
Vol 44 (2) ◽  
pp. 199-217 ◽  
Author(s):  
Alexey S. Kondrashov
Keyword(s):  
Recombination Frequency ◽  
Decisive Role ◽  
Crossing Over ◽  
Whole Genome ◽  
Critical Number ◽  
Deleterious Mutations ◽  
Mutation Load ◽  
Sexual Population ◽  
Physiological Cost ◽  
Selection For

SUMMARYA population with u deleterious mutations per genome per generation is considered in which only those individuals that carry less than a critical number of k mutations are viable. It has been shown previously that under such conditions sexual reproduction is advantageous. Here we consider selection at a locus that determines recombination frequency of the whole genome. The value v = u/ √ k has been found to play the decisive role. When v < 0·35 the direction of selection for recombination may be different for different cases, but the intensity of selection is always very small. The advantage of recombination becomes considerable when v > 0·5, its growth under increasing v being approximately linear. If v > 2 no less than 95% of the progeny are bound to die because of the selection against deleterious mutations. Since this seems to be too great a mutation load, we may assume 0·5 < v < 2·0 for any sexual population if mutation really maintains crossing-over. Results on selection at a locus which controls mutability provide evidence that v is located within the specified interval if the physiological cost of a twofold reduction of the mutation rate is within the range 10–80%. A number of consequences of this hypothesis about the mechanism of selection for sex and recombination are discussed.

Sign in / Sign up

Export Citation Format

Share Document