Estimates of genetic load in small populations suggest extensive purging of deleterious alleles

2019 ◽  
Author(s):  
Neetha Iyer
Keyword(s):  
Genetic Load ◽  
Small Populations ◽  
Deleterious Alleles

scholarly journals Inbreeding Depression in Small Populations of Self-Incompatible Plants

Genetics ◽  
2001 ◽  
Vol 159 (3) ◽  
pp. 1217-1229
Author(s):  
Sylvain Glémin ◽  
Thomas Bataillon ◽  
Joëlle Ronfort ◽  
Agnès Mignot ◽  
Isabelle Olivieri
Keyword(s):  
Inbreeding Depression ◽  
Genetic Load ◽  
Joint Effect ◽  
Breeding Systems ◽  
Small Populations ◽  
S Locus ◽  
Frequency Dependent ◽  
Frequency Dependent Selection ◽  
Deleterious Alleles ◽  
Negative Frequency Dependent Selection

Abstract Self-incompatibility (SI) is a widespread mechanism that prevents inbreeding in flowering plants. In many species, SI is controlled by a single locus (the S locus) where numerous alleles are maintained by negative frequency-dependent selection. Inbreeding depression, the decline in fitness of selfed individuals compared to outcrossed ones, is an essential factor in the evolution of SI systems. Conversely, breeding systems influence levels of inbreeding depression. Little is known about the joint effect of SI and drift on inbreeding depression. Here we studied, using a two-locus model, the effect of SI (frequency-dependent selection) on a locus subject to recurrent deleterious mutations causing inbreeding depression. Simulations were performed to assess the effect of population size and linkage between the two loci on the level of inbreeding depression and genetic load. We show that the sheltering of deleterious alleles linked to the S locus strengthens inbreeding depression in small populations. We discuss the implications of our results for the evolution of SI systems.

scholarly journals Estimates of genetic load in small populations suggest extensive purging of deleterious alleles

2019 ◽  
Author(s):  
Tom van der Valk ◽  
Marc de Manuel ◽  
Tomas Marques-Bonet ◽  
Katerina Guschanski
Keyword(s):  
Large Population ◽  
Genetic Load ◽  
Small Population ◽  
Small Populations ◽  
Population Declines ◽  
Current Conservation ◽  
Low Genetic Diversity ◽  
Deleterious Alleles ◽  
Declining Populations ◽  
Genetic Purging

AbstractDeclining populations are expected to experience negative genetic consequences of inbreeding, which over time can drive them to extinction. Yet, many species have survived in small populations for thousands of generations without apparent fitness effects, possibly due to genetic purging of partially deleterious recessive alleles in inbred populations. We estimate the abundance of deleterious alleles in a range of mammals and find that conversely to current conservation thinking species with historically small population size and low genetic diversity generally have lower genetic load compared to species with large population sizes. Rapid population declines will thus disproportionally affect species with high diversity, as they carry many deleterious alleles that can reach fixation before being removed by genetic purging.

Genetic load and biological changes to extant humans

2020 ◽  
pp. 1-4
Author(s):  
Arthur Saniotis ◽  
Maciej Henneberg ◽  
Kazhaleh Mohammadi
Keyword(s):  
Natural Selection ◽  
Current Knowledge ◽  
Genetic Load ◽  
Differential Fertility ◽  
Medical Interventions ◽  
Deleterious Alleles ◽  
Gradual Process ◽  
Genetic Complexity ◽  
Sexual Recombination ◽  
Improved Sanitation

Abstract Extant humans are currently increasing their genetic load, which is informing present and future human microevolution. This has been a gradual process that has been rising over the last centuries as a consequence of improved sanitation, nutritional improvements, advancements in microbiology and medical interventions, which have relaxed natural selection. Moreover, a reduction in infant and child mortality and changing societal attitudes towards fertility have led to a decrease in total fertility rates (TFRs) since the 19th century. Generally speaking, decreases in differential fertility and mortality have meant that there is less opportunity for natural selection to eliminate deleterious mutations from the human gene pool. It has been argued that the average human may carry ~250–300 mutations that are mostly deleterious, as well as several hundred less-deleterious variants. These deleterious alleles in extant humans mean that our fitness is being constrained. While such alleles are viewed as reducing human fitness, they may also have had an adaptive function in the past, such as assisting in genetic complexity, sexual recombination and diploidy. Saying this, our current knowledge on these fitness compromising alleles is still lacking.

scholarly journals Sex differences in deleterious genetic variants in a haplodiploid social insect

2021 ◽  
Author(s):  
Sara E. Miller ◽  
Michael J. Sheehan
Keyword(s):  
Genetic Load ◽  
Low Frequency ◽  
Paper Wasp ◽  
Deleterious Mutations ◽  
Wild Populations ◽  
Nonsense Mutations ◽  
Low Frequencies ◽  
Complete Dominance ◽  
Deleterious Alleles ◽  
Population Allele Frequency

AbstractDeleterious variants are selected against but can linger in populations at low frequencies for long periods of time, decreasing fitness and contributing to disease burden in humans and other species. Deleterious variants occur at low frequency but distinguishing deleterious variants from low frequency neutral variation is challenging based on population genetics data. As a result, we have little sense of the number and identity of deleterious variants in wild populations. For haplodiploid species, it has been hypothesized that deleterious alleles will be directly exposed to selection in haploid males, but selection can be masked in diploid females due to partial or complete dominance, resulting in more efficient purging of deleterious mutations in males. Therefore, comparisons of the differences between haploid and diploid genomes from the same population may be a useful method for inferring rare deleterious variants. This study provides the first formal test of this hypothesis. Using wild populations of Northern paper wasps (Polistes fuscatus), we find that males have fewer overall variants, and specifically fewer missense and nonsense variants, than females from the same population. Allele frequency differences are especially pronounced for rare missense and nonsense mutations and these differences lead to a lower genetic load in males than females. Based on these data we estimate that a large number of highly deleterious mutations are segregating in the paper wasp population. Stronger selection against deleterious alleles in haploid males may have implications for adaptation in other haplodiploid insects and provides evidence that wild populations harbor abundant deleterious variants.

scholarly journals Sexual selection and inbreeding: two efficient ways to limit the accumulation of deleterious mutations

2018 ◽  
Author(s):  
E. Noël ◽  
E. Fruitet ◽  
D. Lelaurin ◽  
N. Bonel ◽  
A. Ségard ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Experimental Evolution ◽  
Genetic Load ◽  
Deleterious Mutations ◽  
Mutation Load ◽  
Male Function ◽  
Female Function ◽  
Deleterious Alleles ◽  
Self Fertilization ◽  
Male Specific

AbstractTheory and empirical data showed that two processes can boost selection against deleterious mutations, thus facilitating the purging of the mutation load: inbreeding, by exposing recessive deleterious alleles to selection in homozygous form, and sexual selection, by enhancing the relative reproductive success of males with small mutation loads. These processes tend to be mutually exclusive because sexual selection is reduced under mating systems that promote inbreeding, such as self-fertilization in hermaphrodites. We estimated the relative efficiency of inbreeding and sexual selection at purging the genetic load, using 50 generations of experimental evolution, in a hermaphroditic snail (Physa acuta). To this end, we generated lines that were exposed to various intensities of inbreeding, sexual selection (on the male function) and nonsexual selection (on the female function). We measured how these regimes affected the mutation load, quantified through the survival of outcrossed and selfed juveniles. We found that juvenile survival strongly decreased in outbred lines with reduced male selection, but not when female selection was relaxed, showing that male-specific sexual selection does purge deleterious mutations. However, in lines exposed to inbreeding, where sexual selection was also relaxed, survival did not decrease, and even increased for self-fertilized juveniles, showing that purging through inbreeding can compensate for the absence of sexual selection. Our results point to the further question of whether a mixed strategy combining the advantages of both mechanisms of genetic purging could be evolutionary stable.

Population improvement in lucerne (Medicago sativa L.): components of inbreeding depression are different in original and improved populations

1998 ◽  
Vol 38 (8) ◽  
pp. 831 ◽  
Author(s):  
C. A. Kimbeng ◽  
E. T. Bingham
Keyword(s):  
Inbreeding Depression ◽  
Chromosome Doubling ◽  
Genetic Load ◽  
Field Trials ◽  
Improvement Strategy ◽  
Improvement Program ◽  
Original Population ◽  
Deleterious Alleles ◽  
Herbage Yield ◽  
Population Improvement

Summary. Inbreeding depression, the lowered fitness of inbred individuals compared with their non-inbred counterparts, is an important concept in lucerne improvement; but is poorly understood. Two-allele autotetraploid populations are suitable for studying inbreeding depression, especially when the population improvement strategy involves inbreeding, because they are derived from chromosome-doubling of hybrid diploid plants. They have a maximum of 2 alleles and a single allelic interaction per locus. Inbreeding depression was compared in original 2-allele autotetraploid populations and populations that had undergone inbreeding and selection. The original and improved (selected) populations were produced by intercrossing 2 single-cross lines from the original and improved 2-allele autotetraploid populations respectively. Herbage yield of the S1 and intercrossed generations derived from these populations was evaluated in field trials at Arlington, Wisconsin, USA, and used to estimate inbreeding depression. Herbage yield of the S1 and intercrossed generations derived from the improved population were significantly (P<0.01) higher, by 13.3 and 24%, respectively, than those derived from the original population. Selection during inbreeding probably decreased the frequency of deleterious alleles and accumulated favourable alleles. Inbreeding depression values were higher in the improved compared with the original population. Genetic load of deleterious alleles may account for much of the inbreeding depression observed in the original population, whereas, in the improved population, loss of heterozygosity or non-additive gene interactions between favourable alleles on linked chromosome segments may account for the substantial inbreeding depression. Therefore, in a population improvement program, the causes of inbreeding depression seem to be more important than their estimated value.

scholarly journals When is selection effective?

2014 ◽  
Author(s):  
Simon Gravel
Keyword(s):  
Genetic Load ◽  
Human Populations ◽  
Deleterious Alleles ◽  
Genome Wide ◽  
Biological Insight ◽  
Specific Allele ◽  
Mutational Damage ◽  
Modelling Assumptions ◽  
Random Fluctuations ◽  
Quantitative Explanation

AbstractDeleterious alleles can reach high frequency in small populations because of random fluctuations in allele frequency. This may lead, over time, to reduced average fitness. In that sense, selection is more ‘effective’ in larger populations. Recent studies have considered whether the different demographic histories across human populations have resulted in differences in the number, distribution, and severity of deleterious variants, leading to an animated debate. This article first seeks to clarify some terms of the debate by identifying differences in definitions and assumptions used in recent studies. We argue that variants of Morton, Crow and Muller’s ‘total mutational damage’ provide the soundest and most practical basis for such comparisons. Using simulations, analytical calculations, and 1000 Genomes data, we provide an intuitive and quantitative explanation for the observed similarity in genetic load across populations. We show that recent demography has likely modulated the effect of selection, and still affects it, but the net result of the accumulated differences is small. Direct observation of differential efficacy of selection for specific allele classes is nevertheless possible with contemporary datasets. By contrast, identifying average genome-wide differences in the efficacy of selection across populations will require many modelling assumptions, and is unlikely to provide much biological insight about human populations.

scholarly journals No evidence of positive assortative mating for genetic quality in fruit flies

2019 ◽  
Vol 286 (1912) ◽  
pp. 20191474
Author(s):  
Nathaniel P. Sharp ◽  
Michael C. Whitlock
Keyword(s):  
Sexual Selection ◽  
Assortative Mating ◽  
Genetic Variance ◽  
Genetic Load ◽  
Fruit Fly ◽  
Genetic Quality ◽  
Mating Patterns ◽  
Disassortative Mating ◽  
Deleterious Alleles ◽  
Positive Assortative Mating

In sexual populations, the effectiveness of selection will depend on how gametes combine with respect to genetic quality. If gametes with deleterious alleles are likely to combine with one another, deleterious genetic variation can be more easily purged by selection. Assortative mating, where there is a positive correlation between parents in a phenotype of interest such as body size, is often observed in nature, but does not necessarily reveal how gametes ultimately combine with respect to genetic quality itself. We manipulated genetic quality in fruit fly populations using an inbreeding scheme designed to provide an unbiased measure of mating patterns. While inbred flies had substantially reduced reproductive success, their gametes did not combine with those of other inbred flies more often than expected by chance, indicating a lack of positive assortative mating. Instead, we detected a negative correlation in genetic quality between parents, i.e. disassortative mating, which diminished with age. This pattern is expected to reduce the genetic variance for fitness, diminishing the effectiveness of selection. We discuss how mechanisms of sexual selection could produce a pattern of disassortative mating. Our study highlights that sexual selection has the potential to either increase or decrease genetic load.

scholarly journals A simulation study on detecting purging of inbreeding depression in captive populations

2005 ◽  
Vol 86 (2) ◽  
pp. 139-148 ◽  
Author(s):  
ELIZABETH BOAKES ◽  
JINLIANG WANG
Keyword(s):  
Regression Model ◽  
Inbreeding Depression ◽  
Simulation Study ◽  
Statistical Power ◽  
Simulated Data ◽  
Significant Trend ◽  
Small Populations ◽  
Deleterious Mutations ◽  
Deleterious Alleles ◽  
Captive Populations

Inbreeding depression threatens the survival of small populations of both captive and wild outbreeding species. In order to fully understand this threat, it is necessary to investigate what role purging plays in reducing inbreeding depression. Ballou (1997) undertook such an investigation on 25 mammalian populations, using an ancestral inbreeding regression model to detect purging. He concluded that there was a small but highly significant trend of purging on neonatal survival across the populations. We tested the performance of the regression model that Ballou used to detect purging on independently simulated data. We found that the model has low statistical power when inbreeding depression is caused by the build-up of mildly deleterious alleles. It is therefore possible that Ballou's study may have underestimated the effects of ancestral inbreeding on the purging of inbreeding depression in captive populations if their inbreeding depression was caused mainly by mildly deleterious mutations. We also developed an alternative regression model to Ballou's, which showed an improvement in the detection of purging of mildly deleterious alleles but performed less well if deleterious alleles were of a large effect.

Sign in / Sign up

Export Citation Format

Share Document