Deviation from Equilibrium: Genetic Drift – Random Changes in Small Populations

2006 ◽  
pp. 31-40
Author(s):  
David Wool
Keyword(s):  
Genetic Drift ◽  
Small Populations

scholarly journals Recombination Can Evolve in Large Finite Populations Given Selection on Sufficient Loci

Genetics ◽  
2003 ◽  
Vol 165 (4) ◽  
pp. 2249-2258 ◽  
Author(s):  
Mark M Iles ◽  
Kevin Walters ◽  
Chris Cannings
Keyword(s):  
Experimental Evidence ◽  
Genetic Drift ◽  
Finite Population ◽  
Selective Advantage ◽  
Indirect Selection ◽  
Small Populations ◽  
Finite Populations ◽  
Population Sizes ◽  
Population Recombination

AbstractIt is well known that an allele causing increased recombination is expected to proliferate as a result of genetic drift in a finite population undergoing selection, without requiring other mechanisms. This is supported by recent simulations apparently demonstrating that, in small populations, drift is more important than epistasis in increasing recombination, with this effect disappearing in larger finite populations. However, recent experimental evidence finds a greater advantage for recombination in larger populations. These results are reconciled by demonstrating through simulation without epistasis that for m loci recombination has an appreciable selective advantage over a range of population sizes (am, bm). bm increases steadily with m while am remains fairly static. Thus, however large the finite population, if selection acts on sufficiently many loci, an allele that increases recombination is selected for. We show that as selection acts on our finite population, recombination increases the variance in expected log fitness, causing indirect selection on a recombination-modifying locus. This effect is enhanced in those populations with more loci because the variance in phenotypic fitnesses in relation to the possible range will be smaller. Thus fixation of a particular haplotype is less likely to occur, increasing the advantage of recombination.

scholarly journals Impact of mutation rate and selection at linked sites on fine-scale DNA variation across the homininae genome

2018 ◽  
Author(s):  
David Castellano ◽  
Adam Eyre-Walker ◽  
Kasper Munch
Keyword(s):  
Gene Conversion ◽  
Mutation Rate ◽  
Genetic Drift ◽  
Recombination Rate ◽  
Small Populations ◽  
Conserved Sequences ◽  
Positive Correlation ◽  
Dna Diversity ◽  
Biased Gene Conversion ◽  
The Impact

AbstractDNA diversity varies across the genome of many species. Variation in diversity across a genome might arise for one of three reasons; regional variation in the mutation rate, selection and biased gene conversion. We show that both non-coding and non-synonymous diversity are correlated to a measure of the mutation rate, the recombination rate and the density of conserved sequences in 50KB windows across the genomes of humans and non-human homininae. We show these patterns persist even when we restrict our analysis to GC-conservative mutations, demonstrating that the patterns are not driven by biased gene conversion. The positive correlation between diversity and our measure of the mutation rate seems to be largely a direct consequence of regions with higher mutation rates having more diversity. However, the positive correlation with recombination rate and the negative correlation with the density of conserved sequences suggests that selection at linked sites affect levels of diversity. This is supported by the observation that the ratio of the number of non-synonymous to non-coding polymorphisms is negatively correlated to a measure of the effective population size across the genome. Furthermore, we find evidence that these genomic variables are better predictors of non-coding diversity in large homininae populations than in small populations, after accounting for statistical power. This is consistent with genetic drift decreasing the impact of selection at linked sites in small populations. In conclusion, our comparative analyses describe for the first time how recombination rate, gene density, mutation rate and genetic drift interact to produce the patterns of DNA diversity that we observe along and between homininae genomes.

Evolutionary Conservation Biology

2001 ◽  
Author(s):  
Philip W. Hedrick
Keyword(s):  
Genetic Variation ◽  
Endangered Species ◽  
Inbreeding Depression ◽  
Genetic Drift ◽  
Conservation Biology ◽  
The Other ◽  
Small Populations ◽  
Desert Bighorn Sheep ◽  
Endangered Fish ◽  
Evolutionary Aspects

Conservation biology as a discipline focused on endangered species is young and dates only from the late 1970s. Although conservation of endangered species encompasses many different biological disciplines, including behavior, ecology, and genetics, evolutionary considerations always have been emphasized (e.g., Frankel and Soule 1981). Many of the applications of evolutionary concepts to conservation are ones related to genetic variation in small or subdivided populations. However, the critical status of many endangered species makes both more precision and more caution necessary than the general findings for evolutionary considerations. On the other hand, the dire situations of many endangered species often require recommendations to be made on less than adequate data. Overall, one can think of the evolutionary aspects of conservation biology as an applied aspect of the evolution of small populations with the important constraint that any conclusions or recommendations may influence the actual extinction of the populations or species under consideration. From this perspective, all of the factors that influence continuing evolution (i.e., selection, inbreeding, genetic drift, gene flow, and mutation; e.g., Hedrick 2000) are potentially important in conservation. The evolutionary issues of widest concern in conservation biology—inbreeding depression and maintenance of genetic variation— can be seen in their simplest form as the joint effects of inbreeding and selection, and of genetic drift and mutation, respectively. However, even in model organisms such as Drosophila, the basis of inbreeding depression and the maintenance of genetic variation are not clearly understood. In addition, findings from model laboratory organisms may not provide good insight into problems in many endangered species, the most visible of which are generally slowly reproducing, large vertebrates with small populations. Here we will first focus on introductions to two important evolutionary aspects of conservation biology: the units of conservation and inbreeding depression. Then, we will discuss studies in two organisms as illustrations of these and related principles—an endangered fish species, the Gila topminnow, and desert bighorn sheep—to illustrate some evolutionary aspects of conservation. In the discussion, we will mention some of the other evolutionary topics that are relevant to conservation biology.

Predicting the genetic drift in small populations

1985 ◽  
Vol 13 (3) ◽  
pp. 207-218 ◽  
Author(s):  
C. Chevalet ◽  
H. De Rochambeau
Keyword(s):  
Genetic Drift ◽  
Small Populations

scholarly journals Low RAPD Variation and Female-Biased Sex Ratio Indicate Genetic Drift in Small Populations of the Dioecious Conifer Taxus Baccata in Switzerland

2004 ◽  
Vol 5 (3) ◽  
pp. 357-365 ◽  
Author(s):  
Karin Hilfiker ◽  
Felix Gugerli ◽  
Jean-Philippe Schütz ◽  
Peter Rotach ◽  
Rolf Holderegger
Keyword(s):  
Sex Ratio ◽  
Genetic Drift ◽  
Taxus Baccata ◽  
Small Populations ◽  
Biased Sex Ratio ◽  
Rapd Variation

scholarly journals GENETIC DRIFT IN SMALL POPULATIONS OF TRIBOLIUM

Evolution ◽  
1979 ◽  
Vol 33 (2) ◽  
pp. 579-584 ◽  
Author(s):  
S. S. Rich ◽  
A. E. Bell ◽  
S. P. Wilson
Keyword(s):  
Genetic Drift ◽  
Small Populations

scholarly journals Genetic loads at a polymorphic locus which is maintained by frequency-dependent selection

1970 ◽  
Vol 16 (2) ◽  
pp. 145-150 ◽  
Author(s):  
Motoo Kimura ◽  
Tomoko Ohta
Keyword(s):  
Population Size ◽  
Effective Population Size ◽  
Genetic Drift ◽  
Gene Frequency ◽  
Polymorphic Locus ◽  
Small Populations ◽  
Effective Population ◽  
Frequency Dependent ◽  
Frequency Dependent Selection ◽  
Selective Neutrality

SUMMARYIf a polymorphic locus is maintained in finite populations by frequency-dependent selection with selective neutrality at equilibrium, it is generally accompanied by two genetic loads, i.e. the dysmetric and the drift loads. The former arises because the fitness of the population may not be at a maximum at the equilibrium gene frequency and the latter because genetic drift in small populations displaces the gene frequency from its equilibrium value.In some simple models of frequency-dependent selection considered, the drift load is independent of selection coefficients and is approximately equal to (n−1)/(2Ne), where n is the number of alleles and Ne is the effective population size.

scholarly journals The fertility effects of pericentric inversions in Drosophila melanogaster.

Genetics ◽  
1993 ◽  
Vol 134 (2) ◽  
pp. 487-496 ◽  
Author(s):  
J A Coyne ◽  
W Meyers ◽  
A P Crittenden ◽  
P Sniegowski
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Genetic Drift ◽  
Small Populations ◽  
Closely Related Species ◽  
Chromosome Inversions ◽  
Pericentric Inversions ◽  
In The Wild ◽  
Suppressed Recombination ◽  
Length Analysis

Abstract Heterozygotes for pericentric inversions are expected to be semisterile because recombination in the inverted region produces aneuploid gametes. Newly arising pericentric inversions should therefore be quickly eliminated from populations by natural selection. The occasional polymorphism for such inversions and their fixation among closely related species have supported the idea that genetic drift in very small populations can overcome natural selection in the wild. We studied the effect of 7 second-chromosome and 30 third-chromosome pericentric inversions on the fertility of heterokaryotypic Drosophila melanogaster females. Surprisingly, fertility was not significantly reduced in many cases, even when the inversion was quite large. This lack of underdominance is almost certainly due to suppressed recombination in inversion heterozygotes, a phenomenon previously observed in Drosophila. In the large sample of third-chromosome inversions, the degree of underdominance depends far more on the position of breakpoints than on the inversion's length. Analysis of these positions shows that this chromosome has a pair of "sensitive sites" near cytological divisions 68 and 92: these sites appear to reduce recombination in a heterozygous inversion whose breakpoints are nearby. There may also be "sensitive sites" near divisions 31 and 49 on the second chromosome. Such sites may be important in initiating synapsis. Because many pericentric inversions do not reduce the fertility of heterozygotes, we conclude that the observed fixation or polymorphism of such rearrangements in nature does not imply genetic drift in very small populations.

scholarly journals Dynamics of inbreeding depression due to deleterious mutations in small populations: mutation parameters and inbreeding rate

1999 ◽  
Vol 74 (2) ◽  
pp. 165-178 ◽  
Author(s):  
JINLIANG WANG ◽  
WILLIAM G. HILL ◽  
DEBORAH CHARLESWORTH ◽  
BRIAN CHARLESWORTH
Keyword(s):  
Inbreeding Depression ◽  
Genetic Drift ◽  
Ancestral Population ◽  
Small Populations ◽  
Weak Selection ◽  
Recessive Mutations ◽  
Rate Of Decay ◽  
Inbreeding Rate ◽  
Lethal Equivalents ◽  
Reproductive Rates

A multilocus stochastic model is developed to simulate the dynamics of mutational load in small populations of various sizes. Old mutations sampled from a large ancestral population at mutation–selection balance and new mutations arising each generation are considered jointly, using biologically plausible lethal and deleterious mutation parameters. The results show that inbreeding depression and the number of lethal equivalents due to partially recessive mutations can be partly purged from the population by inbreeding, and that this purging mainly involves lethals or detrimentals of large effect. However, fitness decreases continuously with inbreeding, due to increased fixation and homozygosity of mildly deleterious mutants, resulting in extinctions of very small populations with low reproductive rates. No optimum inbreeding rate or population size exists for purging with respect to fitness (viability) changes, but there is an optimum inbreeding rate at a given final level of inbreeding for reducing inbreeding depression or the number of lethal equivalents. The interaction between selection against partially recessive mutations and genetic drift in small populations also influences the rate of decay of neutral variation. Weak selection against mutants relative to genetic drift results in apparent overdominance and thus an increase in effective size (Ne) at neutral loci, and strong selection relative to drift leads to a decrease in Ne due to the increased variance in family size. The simulation results and their implications are discussed in the context of biological conservation and tests for purging.

scholarly journals Adaptive and maladaptive genetic diversity in small populations; insights from the Brook Charr (Salvelinus fontinalis) case study

2019 ◽  
Author(s):  
Anne-Laure Ferchaud ◽  
Maeva Leitwein ◽  
Martin Laporte ◽  
Damien Boivin-Delisle ◽  
Bérénice Bougas ◽  
...  
Keyword(s):  
Transposable Elements ◽  
Genetic Drift ◽  
Environmental Variables ◽  
Evolutionary Biology ◽  
Salvelinus Fontinalis ◽  
Small Populations ◽  
Deleterious Mutations ◽  
Brook Charr ◽  
Main Driver ◽  
Genomic Regions

AbstractInvestigating the relative importance of neutral versus selective processes governing the accumulation of genetic variants is a key goal in evolutionary biology. This is particularly true in the context of small populations, where genetic drift can counteract the effect of selection. In this study, we investigated the accumulation of putatively beneficial and harmful variations using 7,950 high-quality filtered SNPs among 36 lacustrine, seven riverine and seven anadromous Brook Charr (Salvelinus fontinalis) populations (n = 1,193) from Québec, Canada. Using the Provean algorithm, we observed an accumulation of deleterious mutations that tend to be more prevalent in isolated lacustrine and riverine populations than the more connected anadromous populations. In addition, the absence of correlation between the occurrence of putative beneficial nor deleterious mutations and local recombination rate supports the hypothesis that genetic drift might be the main driver of the accumulation of such variants. Despite the effect of pronounced genetic drift and limited gene flow in non-anadromous populations, several loci representing biological functions of potential adaptive significance were associated with environmental variables, and particularly with temperature. We also identified genomic regions associated with anadromy. We also observed an overrepresentation of transposable elements associated with variation in environmental variables, thus supporting the importance of transposable elements in adaptation.

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