Genetic load and effective size of natural populations ofDrosophila melanogaster in Korea

1985 ◽  
Vol 41 (1) ◽  
pp. 127-129 ◽  
Author(s):  
Y. Choi
Keyword(s):  
Natural Populations ◽  
Genetic Load ◽  
Effective Size

scholarly journals GENETIC LOAD IN NATURAL POPULATIONS: IS IT COMPATIBLE WITH THE HYPOTHESIS THAT MANY POLYMORPHISMS ARE MAINTAINED BY NATURAL SELECTION?

Genetics ◽  
1974 ◽  
Vol 77 (3) ◽  
pp. 569-589
Author(s):  
Martin L Tracey ◽  
Francisco J Ayala
Keyword(s):  
Drosophila Melanogaster ◽  
Natural Selection ◽  
Natural Population ◽  
Natural Populations ◽  
Genetic Load ◽  
Structural Genes ◽  
Invertebrate Species ◽  
Average Proportion ◽  
Mean Fitness ◽  
The Mean

ABSTRACT Recent studies of genetically controlled enzyme variation lead to an estimation that at least 30 to 60% of the structural genes are polymorphic in natural populations of many vertebrate and invertebrate species. Some authors have argued that a substantial proportion of these polymorphisms cannot be maintained by natural selection because this would result in an unbearable genetic load. If many polymorphisms are maintained by heterotic natural selection, individuals with much greater than average proportion of homozygous loci should have very low fitness. We have measured in Drosophila melanogaster the fitness of flies homozygous for a complete chromosome relative to normal wild flies. A total of 37 chromosomes from a natural population have been tested using 92 experimental populations. The mean fitness of homozygous flies is 0.12 for second chromosomes, and 0.13 for third chromosomes. These estimates are compatible with the hypothesis that many (more than one thousand) loci are maintained by heterotic selection in natural populations of D. melanogaster.

scholarly journals “Genetic Load”: How the Architects of the Modern Synthesis Became Trapped in a Scientific Ideology

2018 ◽  
pp. 118
Author(s):  
Alexandra Soulier
Keyword(s):  
Theoretical Basis ◽  
Policy Making ◽  
Natural Populations ◽  
Genetic Load ◽  
Social Progress ◽  
Human Populations ◽  
Complex Phenomenon ◽  
Science And Policy ◽  
Theodosius Dobzhansky ◽  
Combined Actions

The term “genetic load” first emerged in a paper written in 1950 by the geneticist H. Muller. It is a mathematical model based on biological, social, political and ethical arguments describing the dramatic accumulation of disadvantageous mutations in human populations that will occur in modern societies if eugenic measures are not taken. The model describes how the combined actions of medical and social progress will supposedly impede natural selection and make genes of inferior quality likely to spread across populations – a process which in fine loads their progress. Genetic load is based on optimal fitness and emerges from a “typological view” of evolution. This model of evolution had previously, however, been invalidated by Robert Wright and Theodosius Dobzhansky who, as early as 1946, showed that polymorphism was the rule in natural populations. The blooming and persistence of the concept of genetic load, after its theoretical basis had already expired, are a historical puzzle. This persistence reveals the intricacy of science and policy-making in eugenic matters. The Canguilhemian concept of ‘scientific ideology’ (1988) is used along with the concept of ‘immutable mobile’ (Latour 1986) and compared with the concept of ‘co-production’ (Jasanoff 1998), to provide complementary perspectives on this complex phenomenon.

GENETICS OF NATURAL POPULATIONS. XXVIII. THE MAGNITUDE OF THE GENETIC LOAD IN POPULATIONS OF DROSOPHILA PSEUDOOBSCURA

Genetics ◽  
1960 ◽  
Vol 45 (6) ◽  
pp. 723-740 ◽  
Author(s):  
B Spassky ◽  
N Spassky ◽  
O Pavlovsky ◽  
M G Krimbas ◽  
C Krimbas ◽  
...  
Keyword(s):  
Natural Populations ◽  
Genetic Load ◽  
Drosophila Pseudoobscura

scholarly journals Seasonally fluctuating selection can maintain polymorphism at many loci via segregation lift

2017 ◽  
Vol 114 (46) ◽  
pp. E9932-E9941 ◽  
Author(s):  
Meike J. Wittmann ◽  
Alan O. Bergland ◽  
Marcus W. Feldman ◽  
Paul S. Schmidt ◽  
Dmitri A. Petrov
Keyword(s):  
Seasonal Changes ◽  
Fitness Function ◽  
Natural Populations ◽  
Genetic Load ◽  
General Mechanism ◽  
Large Contribution ◽  
Multilocus Genotype ◽  
Fluctuating Selection ◽  
Previous Theory ◽  
Future Work

Most natural populations are affected by seasonal changes in temperature, rainfall, or resource availability. Seasonally fluctuating selection could potentially make a large contribution to maintaining genetic polymorphism in populations. However, previous theory suggests that the conditions for multilocus polymorphism are restrictive. Here, we explore a more general class of models with multilocus seasonally fluctuating selection in diploids. In these models, the multilocus genotype is mapped to fitness in two steps. The first mapping is additive across loci and accounts for the relative contributions of heterozygous and homozygous loci—that is, dominance. The second step uses a nonlinear fitness function to account for the strength of selection and epistasis. Using mathematical analysis and individual-based simulations, we show that stable polymorphism at many loci is possible if currently favored alleles are sufficiently dominant. This general mechanism, which we call “segregation lift,” requires seasonal changes in dominance, a phenomenon that may arise naturally in situations with antagonistic pleiotropy and seasonal changes in the relative importance of traits for fitness. Segregation lift works best under diminishing-returns epistasis, is not affected by problems of genetic load, and is robust to differences in parameters across loci and seasons. Under segregation lift, loci can exhibit conspicuous seasonal allele-frequency fluctuations, but often fluctuations may be small and hard to detect. An important direction for future work is to formally test for segregation lift in empirical data and to quantify its contribution to maintaining genetic variation in natural populations.

scholarly journals Segregation lift: A general mechanism for the maintenance of polygenic variation under seasonally fluctuating selection

2017 ◽  
Author(s):  
Meike J. Wittmann ◽  
Alan O. Bergland ◽  
Marcus W. Feldman ◽  
Paul S. Schmidt ◽  
Dmitri A. Petrov
Keyword(s):  
Seasonal Changes ◽  
Natural Populations ◽  
Genetic Load ◽  
General Mechanism ◽  
Large Contribution ◽  
Fluctuating Selection ◽  
Previous Theory ◽  
Increasing Function ◽  
Special Case ◽  
Polygenic Variation

AbstractMost natural populations are affected by seasonal changes in temperature, rainfall, or resource availability. Seasonally fluctuating selection could potentially make a large contribution to maintaining genetic polymorphism in populations. However, previous theory suggests that the conditions for multi-locus polymorphism are restrictive. Here we explore a more general class of models with multi-locus seasonally fluctuating selection in diploids. In these models, loci first contribute additively to a seasonal score, with a dominance parameter determining the relative contributions of heterozygous and homozygous loci. The seasonal score is then mapped to fitness via a monotonically increasing function, thereby accounting for epistasis. Using mathematical analysis and individual-based simulations, we show that stable polymorphism at many loci is possible if currently favored alleles are sufficiently dominant with respect to the additive seasonal score (but not necessarily with respect to fitness itself). This general mechanism, which we call “segregation lift”, operates for various genotype-to-fitness maps and includes the previously known mechanism of multiplicative selection with marginal overdominance as a special case. We show that segregation lift may arise naturally in situations with antagonistic pleiotropy and seasonal changes in the relative importance of traits for fitness. Segregation lift is not affected by problems of genetic load and is robust to differences in parameters across loci and seasons. Under segregation lift, loci can exhibit conspicuous seasonal allele-frequency fluctuations, but often fluctuations may also be small and hard to detect. Via segregation lift, seasonally fluctuating selection might contribute substantially to maintaining genetic variation in natural populations.

scholarly journals MICROGEOGRAPHIC DIFFERENTIATION OF CHROMOSOMAL AND ENZYME POLYMORPHISMS IN DROSOPHILA PERSIMILIS

Genetics ◽  
1977 ◽  
Vol 85 (4) ◽  
pp. 681-695 ◽  
Author(s):  
Charles E Taylor ◽  
Jeffrey R Powell
Keyword(s):  
Habitat Preferences ◽  
Natural Populations ◽  
Genetic Load ◽  
Heterogeneous Environments ◽  
Behavioral Differences ◽  
Chromosome Inversion ◽  
Enzyme Polymorphisms ◽  
Drosophila Persimilis ◽  
Spatially Varying ◽  
Spatially Varying Selection

ABSTRACT We studied microgeographic and temporal genetic differentiation in natural populations of Drosophila persimilis with respect to chromosome inversion and enzyme polymorphisms. Both inversion frequencies and allozyme frequencies varied significantly over short distances. Neither differed significantly between morning and evening collections. Because several studies of the dispersal behavior of this species have been performed, we attempt to fit the observed data to mathematical models which relate dispersion to random genetic drift and to spatially varying selection coefficients. We conclude that the observations are due at least partly to behavioral differences among genotypes. i.e., habitat preferences. These results have implications for genetic load theory and models of selection in heterogeneous environments.

scholarly journals Deleterious variation mimics signatures of genomic incompatibility and adaptive introgression

2017 ◽  
Author(s):  
Bernard Y. Kim ◽  
Christian D. Huber ◽  
Kirk E. Lohmueller
Keyword(s):  
Population Genetic ◽  
Natural Populations ◽  
Genetic Load ◽  
Population Admixture ◽  
Population Differences ◽  
Deleterious Mutations ◽  
Recombination Rates ◽  
Adaptive Introgression ◽  
Fitness Effects ◽  
New Mutations

AbstractWhile it is appreciated that population size changes can impact patterns of deleterious variation in natural populations, less attention has been paid to how population admixture affects the dynamics of deleterious variation. Here we use population genetic simulations to examine how admixture impacts deleterious variation under a variety of demographic scenarios, dominance coefficients, and recombination rates. Our results show that gene flow between populations can temporarily reduce the genetic load of smaller populations, especially if deleterious mutations are recessive. Additionally, when fitness effects of new mutations are recessive, between-population differences in the sites at which deleterious variants exist creates heterosis in hybrid individuals. This can lead to an increase in introgressed ancestry, particularly when recombination rates are low. Under certain scenarios, introgressed ancestry can increase from an initial frequency of 5% to 30-75% and fix at many loci, even in the absence of beneficial mutations. Further, deleterious variation and admixture can generate correlations between the frequency of introgressed ancestry and recombination rate or exon density, even in the absence of other types of selection. The direction of these correlations is determined by the specific demography and whether mutations are additive or recessive. Therefore, it is essential that null models include both demography and deleterious variation before invoking reproductive incompatibilities or adaptive introgression to explain unusual patterns of genetic variation.

scholarly journals Genetic causes and consequences of the breakdown of self-incompatibility: case studies in the Brassicaceae

2008 ◽  
Vol 90 (1) ◽  
pp. 47-60 ◽  
Author(s):  
BARBARA K. MABLE
Keyword(s):  
Genetic Diversity ◽  
Demographic History ◽  
Natural Populations ◽  
Genetic Load ◽  
Self Incompatibility ◽  
Negative Consequences ◽  
Recessive Mutations ◽  
Mating System Evolution ◽  
History Of ◽  
Selective Forces

SummaryThe genetic consequences of inbreeding is a subject that has received thorough theoretical attention and has been of interest to empirical biologists since the time of Darwin. Particularly for species with genetically controlled mechanisms to promote outcrossing (self-incompatibility or SI systems), it is expected that high levels of genetic load should accumulate through sheltering of deleterious recessive mutations. Nevertheless, transitions to selfing are common across angiosperms, which suggests that the potentially negative consequences of reduced heterozygosity and genetic diversity are balanced by other factors, such as reproductive assurance. This mini-review focuses on empirical research in the Brassicaceae to emphasize some of the genetic consequences of shifts to inbreeding in terms of mechanisms for loss of SI, changes in genetic diversity following loss of SI, and inbreeding depression in relation to outcrossing history. Despite the long history of theoretical attention, there are still some surprisingly large gaps in our understanding in each of these areas. Rather than providing a complete overview, examples are drawn predominantly from published and emerging data from Arabidopsis thaliana and its relatives to highlight recent progress and remaining questions. We are currently on the brink of major breakthroughs in understanding due both to advances in sequencing technology and a shift in focus from crop plants to natural populations, where critical factors such as population structure, phylogeography, demographic history, partial compatibility and individual variation can be taken into account when investigating the nature of the selective forces regulating mating system evolution.

scholarly journals Mating system variation among populations, individuals and within and among fruits in Bertholletia excelsa

2015 ◽  
Vol 64 (1-6) ◽  
pp. 248-259 ◽  
Author(s):  
L.H.O. Wadt ◽  
A. B. Baldoni ◽  
V. S. Silva ◽  
T. Campos ◽  
K. Martins ◽  
...  
Keyword(s):  
Mating System ◽  
Natural Population ◽  
Natural Populations ◽  
Effective Size ◽  
Fixation Index ◽  
Bertholletia Excelsa ◽  
Selection For ◽  
Conservation Breeding ◽  
Seed Collections ◽  
Different Levels

AbstractThe aim of this study was to investigate variation in mating system among three Brazilian Amazon populations of the tree Bertholletia excelsa with different levels of anthropogenic interventions. We collected open-pollinated seeds from one natural population, remnant trees dispersed in a pasture, and trees from a plantation. Outcrossing rate not varied among the populations and indicates that all seeds were originated from outcrossing (tm=1.0). Mating among relatives was significant higher in the plantation than forest and pasture populations, probably due the fact that many trees are related in the plantation. Correlated mating was significantly higher in pasture (rp=0.47) and plantation (rp=0.51) than in the natural population (rp=0.22), suggesting that trees in natural population are pollinated by a higher number of pollen donors. The paternity correlation was significantly higher within (rp(w)=0.41) than among fruits (rp(a)=0.18), showing a higher probability to find full-sibs within than among fruits. The fixation index was generally lower in seed trees than in their seedlings, suggesting selection for heterozygous individuals from seedling to adult stages. Progeny arrays collected from the natural population had a lower proportion of pairwise full-sibs than in pasture and plantation and higher variance effective size (2.75) than trees in pasture (2.15) and plantations (2.22). Results highlight that seed collections for conservation, breeding and reforestation programs preferentially should be carried out in natural populations due low proportion highest variance effective size within progeny.

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