scholarly journals Deleterious Mutation Accumulation and the Long-Term Fate of Chromosomal Inversions

2019 ◽  
Author(s):  
Emma L. Berdan ◽  
Alexandre Blanckaert ◽  
Roger K. Butlin ◽  
Claudia Bank
Keyword(s):  
Selective Advantage ◽  
Inversion Polymorphism ◽  
Adaptive Divergence ◽  
Deleterious Mutations ◽  
Dynamic Features ◽  
Chromosomal Inversions ◽  
Recessive Mutations ◽  
Standard Arrangement

AbstractChromosomal inversions contribute widely to adaptation and speciation, yet they present a unique evolutionary puzzle as both their allelic content and frequency evolve in a feedback loop. In this simulation study, we quantified the role of the allelic content in determining the long-term fate of the inversion. Recessive deleterious mutations accumulated on both arrangements with most of them being private to a given arrangement. This led to increasing overdominance, allowing for the maintenance of the inversion polymorphism and generating strong non-adaptive divergence between arrangements. The accumulation of mutations was mitigated by gene conversion but nevertheless led to the fitness decline of at least one homokaryotype under all considered conditions. Surprisingly, this fitness degradation could be permanently halted by the branching of an arrangement into multiple highly divergent haplotypes. Our results highlight the dynamic features of inversions by showing how the non-adaptive evolution of allelic content can play a major role in the fate of the inversion.Author SummaryA chromosomal inversion is a segment of the chromosome that is flipped (inverted arrangement) relative to the normal orientation (standard arrangement). Such structural mutations may facilitate evolutionary processes such as adaptation and speciation, because reduced recombination in inverted regions allows beneficial combinations of alleles to behave as a “single unit”. This locally reduced recombination can have major consequences for the evolution of the allelic content inside the inversion. We used simulations to investigate some of these consequences. Inverted regions tended to accumulate more deleterious recessive mutations than the rest of the genome, which decreased the fitness of homokarotypes (individuals with two copies of the same arrangement). This led to a strong selective advantage for heterokaryotypes (individuals with one copy of each arrangement), maintaining the inversion polymorphism in the population. The accumulation of deleterious mutations also resulted in strong divergence between arrangements. We occasionally observed an arrangement that diverged into a small number of highly differentiated haplotypes, stopping the fitness decrease in homokaryotypes. Our results highlight the dynamic features of inversions by showing how the evolution of allelic content can greatly affect the fate of an inversion.

scholarly journals Deleterious mutation accumulation and the long-term fate of chromosomal inversions

PLoS Genetics ◽  
2021 ◽  
Vol 17 (3) ◽  
pp. e1009411
Author(s):  
Emma L. Berdan ◽  
Alexandre Blanckaert ◽  
Roger K. Butlin ◽  
Claudia Bank
Keyword(s):  
Adaptive Evolution ◽  
Simulation Study ◽  
Feedback Loop ◽  
Deleterious Mutation ◽  
Adaptive Divergence ◽  
Deleterious Mutations ◽  
Dynamic Features ◽  
Chromosomal Inversions

Chromosomal inversions contribute widely to adaptation and speciation, yet they present a unique evolutionary puzzle as both their allelic content and frequency evolve in a feedback loop. In this simulation study, we quantified the role of the allelic content in determining the long-term fate of the inversion. Recessive deleterious mutations accumulated on both arrangements with most of them being private to a given arrangement. This led to increasing overdominance, allowing for the maintenance of the inversion polymorphism and generating strong non-adaptive divergence between arrangements. The accumulation of mutations was mitigated by gene conversion but nevertheless led to the fitness decline of at least one homokaryotype under all considered conditions. Surprisingly, this fitness degradation could be permanently halted by the branching of an arrangement into multiple highly divergent haplotypes. Our results highlight the dynamic features of inversions by showing how the non-adaptive evolution of allelic content can play a major role in the fate of the inversion.

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 Expansion load: recessive mutations and the role of standing genetic variation

2014 ◽  
Author(s):  
Stephan Peischl ◽  
Laurent Excoffier
Keyword(s):  
Genetic Variation ◽  
Species Range ◽  
Human Populations ◽  
Deleterious Mutations ◽  
Recessive Mutations ◽  
Mutation Burden ◽  
Natural Range ◽  
Mean Fitness ◽  
Expansion Load

Expanding populations incur a mutation burden – the so-called expansion load. Previous studies of expansion load have focused on co-dominant mutations. An important consequence of this assumption is that expansion load stems exclusively from the accumulation of new mutations occurring in individuals living at the wave front. Using individual-based simulations we study here the dynamics of standing genetic variation at the front of expansions, and its consequences on mean fitness if mutations are recessive. We find that deleterious genetic diversity is quickly lost at the front of the expansion, but the loss of deleterious mutations at some loci is compensated by an increase of their frequencies at other loci. The frequency of deleterious homozygotes therefore increases along the expansion axis whereas the average number of deleterious mutations per individual remains nearly constant across the species range. This reveals two important differences to co-dominant models: (i) mean fitness at the front of the expansion drops much faster if mutations are recessive, and (ii) mutation load can increase during the expansion even if the total number of deleterious mutations per individual remains constant. We use our model to make predictions about the shape of the site frequency spectrum at the front of range expansion, and about correlations between heterozygosity and fitness in different parts of the species range. Importantly, these predictions provide opportunities to empirically validate our theoretical results. We discuss our findings in the light of recent results on the distribution of deleterious genetic variation across human populations, and link them to empirical results on the correlation of heterozygosity and fitness found in many natural range expansions.

scholarly journals On the origin of species: insights from the ecological genomics of lake whitefish

2010 ◽  
Vol 365 (1547) ◽  
pp. 1783-1800 ◽  
Author(s):  
Louis Bernatchez ◽  
Sébastien Renaut ◽  
Andrew R. Whiteley ◽  
Nicolas Derome ◽  
Julie Jeukens ◽  
...  
Keyword(s):  
Research Programme ◽  
Adaptive Divergence ◽  
Population Divergence ◽  
Ecological Genomics ◽  
Model Species ◽  
Sequencing Technologies ◽  
Sympatric Forms ◽  
Genomic Tools

In contrast to the large amount of ecological information supporting the role of natural selection as a main cause of population divergence and speciation, an understanding of the genomic basis underlying those processes is in its infancy. In this paper, we review the main findings of a long-term research programme that we have been conducting on the ecological genomics of sympatric forms of whitefish ( Coregonus spp.) engaged in the process of speciation. We present this system as an example of how applying a combination of approaches under the conceptual framework of the theory of adaptive radiation has yielded substantial insight into evolutionary processes in a non-model species. We also discuss how the joint use of recent biotechnological developments will provide a powerful means to address issues raised by observations made to date. Namely, we present data illustrating the potential offered by combining next generation sequencing technologies with other genomic approaches to reveal the genomic bases of adaptive divergence and reproductive isolation. Given increasing access to these new genomic tools, we argue that non-model species studied in their ecological context such as whitefish will play an increasingly important role in generalizing knowledge of speciation.

scholarly journals Obstruction of adaptation in diploids by recessive, strongly deleterious alleles

2015 ◽  
Vol 112 (20) ◽  
pp. E2658-E2666 ◽  
Author(s):  
Zoe June Assaf ◽  
Dmitri A. Petrov ◽  
Jamie R. Blundell
Keyword(s):  
Genetic Disorders ◽  
Natural Populations ◽  
Selective Advantage ◽  
Adaptive Mutation ◽  
Heterozygote Advantage ◽  
Deleterious Mutations ◽  
Beneficial Mutation ◽  
Recessive Mutations ◽  
Deleterious Alleles ◽  
Signature Of Selection

Recessive deleterious mutations are common, causing many genetic disorders in humans and producing inbreeding depression in the majority of sexually reproducing diploids. The abundance of recessive deleterious mutations in natural populations suggests they are likely to be present on a chromosome when a new adaptive mutation occurs, yet the dynamics of recessive deleterious hitchhikers and their impact on adaptation remains poorly understood. Here we model how a recessive deleterious mutation impacts the fate of a genetically linked dominant beneficial mutation. The frequency trajectory of the adaptive mutation in this case is dramatically altered and results in what we have termed a “staggered sweep.” It is named for its three-phased trajectory: (i) Initially, the two linked mutations have a selective advantage while rare and will increase in frequency together, then (ii), at higher frequencies, the recessive hitchhiker is exposed to selection and can cause a balanced state via heterozygote advantage (the staggered phase), and (iii) finally, if recombination unlinks the two mutations, then the beneficial mutation can complete the sweep to fixation. Using both analytics and simulations, we show that strongly deleterious recessive mutations can substantially decrease the probability of fixation for nearby beneficial mutations, thus creating zones in the genome where adaptation is suppressed. These mutations can also significantly prolong the number of generations a beneficial mutation takes to sweep to fixation, and cause the genomic signature of selection to resemble that of soft or partial sweeps. We show that recessive deleterious variation could impact adaptation in humans and Drosophila.

scholarly journals Population genetics of Drosophila ananassae: genetic differentiation among Indian natural populations at the level of inversion polymorphism

2007 ◽  
Vol 89 (4) ◽  
pp. 191-199 ◽  
Author(s):  
PRANVEER SINGH ◽  
B. N. SINGH
Keyword(s):  
Natural Populations ◽  
Chromosomal Polymorphism ◽  
Inversion Polymorphism ◽  
Drosophila Ananassae ◽  
Geographic Pattern ◽  
Important Conclusion ◽  
Chromosomal Inversions ◽  
Comprehensive Manner ◽  
Different Parts

SummaryThe present study, which is one of the longest temporal (two decades) and largest spatial (different parts of India covered) investigations on inversion polymorphism in natural populations of D. ananassae, was undertaken to understand the dynamics of inversion polymorphism in a broad and comprehensive manner. Forty-five natural populations from different ecogeographic regions of the country (covering the regions from Kashmir to Kanniyakumari and Gujarat to Nagaland) were analysed for chromosomal inversions. All the populations show the presence of the three cosmopolitan inversions, frequencies of which vary among the populations analysed. Simple correlations between frequencies of different inversions and regression analysis of inversion frequencies with latitude, longitude and altitude were insignificant. This reinforces the concept of rigid polymorphism in D. ananassae. Genetic divergence (spatial and temporal) at the level of chromosomal polymorphism among natural populations was calculated. Results show spatial divergence but no temporal divergence. Rigid polymorphic systems of D. ananassae did not show long-term directional trends. On the basis of the present study, and after including comparisons with the studies conducted more than two decades ago, the most important conclusion to be drawn is that the three cosmopolitan inversions in D. ananassae segregate within populations at fairly similar frequencies, and the general geographic pattern has remained constant.

Abusive head trauma (AHT) outcome at long-term follow-up and the role of elective neurosurgical approach: A report of 22 cases

2013 ◽  
Author(s):  
Francesca Menegazzo ◽  
Melissa Rosa Rizzotto ◽  
Martina Bua ◽  
Luisa Pinello ◽  
Elisabetta Tono ◽  
...  
Keyword(s):  
Head Trauma ◽  
Abusive Head Trauma ◽  
Long Term Follow Up

Negative emotion differentiation and long-term physical health—The moderating role of neuroticism.

2020 ◽  
Vol 39 (2) ◽  
pp. 127-136
Author(s):  
Vincent Y. S. Oh ◽  
Eddie M. W. Tong
Keyword(s):  
Physical Health ◽  
Negative Emotion ◽  
Emotion Differentiation ◽  
Moderating Role

Central role of mycophenolate (MMF) in different immunosuppressive protocols influencing long-term survival after 305 lung transplantations

2008 ◽  
Vol 56 (S 1) ◽  
Author(s):  
P Brenner ◽  
M Kraft ◽  
K Jaros ◽  
F Kur ◽  
J Behr ◽  
...  
Keyword(s):  
Term Survival ◽  
Long Term Survival
Sign in / Sign up

Export Citation Format

Share Document