scholarly journals NEW PROPERTIES OF THE TWO-LOCUS PARTIAL SELFING MODEL WITH SELECTION

Genetics ◽  
1979 ◽  
Vol 93 (1) ◽  
pp. 217-236
Author(s):  
L R Holden
Keyword(s):  
Random Mating ◽  
Analytic Solutions ◽  
Selection Model ◽  
Equilibrium Potential ◽  
Gametic Disequilibrium ◽  
Self Fertilization ◽  
Mean Fitness ◽  
Mixed Selfing

ABSTRACT Analytic solutions are obtained for the equilibria of a simple two-locus, heterotic selection model with mixed selfing and random outcrossing. T W O general phenomena are possible, depending upon the viabilities and the degree of selfing: (1) Negative disequilibrium potential, under which only gametic disequilibrium is possible; and (2) positive disequilibrium potential, which can result in permanent gametic disequilibrium provided that linkage is sufficiently tight. Under random mating (s = O), these two situations correspond to negative and positive additive epistasis, respectively. With partial self-fertilization, however, this is no longer true, and a more appropriate measure of gametc dis-equilibrium potential, ∆ (s), is introduced. A numerically aided examination of the model results in the discovery of two new properties of partial selfing with selection: (1) With negative disequilibrium potential (∆(s) < 0), the equilibrium mean fitness increases with increasing recombination. With positive disequilibrium potential (∆(s) > 0), the opposite is true. (2) Gametic disequilibrium can increase or decrease as the degree of selfing is increased. Therefore, it is apparent that partial selfing and linkage are not analogous as regards the maintenance of disequilibrium.

scholarly journals REPRODUCTIVE SYSTEM AND POLLEN FLOW IN PROGENIES OF Qualea grandiflora Mart., A TYPICAL SPECIES OF THE BRAZILIAN CERRADO

2015 ◽  
Vol 39 (2) ◽  
pp. 337-344 ◽  
Author(s):  
Lia Maris Orth Ritter Antiqueira ◽  
Paulo Yoshio Kageyama
Keyword(s):  
Reproductive System ◽  
Random Mating ◽  
Point Of View ◽  
Dispersion Pattern ◽  
Brazilian Cerrado ◽  
Fixation Rate ◽  
Pollen Dispersion ◽  
Typical Species ◽  
Environmental Recovery ◽  
Self Fertilization

This study analyzed the reproductive system and the pollen dispersion pattern of Qualea grandiflora progenies. This is a typical species from the Brazilian Cerrado about which there are not too many studies from the genetics point of view. The study was conducted in an area of 2.2 hectares located in the Conservation Unit managed by the Forest Institute of the state of São Paulo, Brazil (Assis State Forest). Total genomic DNA of 300 seeds from 25 plants (12 seeds from each plant) was extracted and amplified using specific primers to obtain microsatellite markers. Results showed that selfing is frequent among adults and progenies, and the species reproduces by outcrossing between related and unrelated individuals (0.913). The single-locus outcrossing rate was 0.632, which indicates that mating between unrelated individuals is more frequent than between related plants. The selfing rate was low (0.087), that is, the species is allogamous and self-fertilization is reduced. About 35% of the plants in the progenies were full-sibs, and about 57%, half-sibs. Besides, about 8% of the progenies were selfing siblings. The genetic differentiation coefficient within progenies was 0.139, whereas the fixation rate was about 27%. The estimate of the effective size revealed that the genetic representativeness of descent was lower than expected in random mating progenies: The analyzed samples corresponded to only 13.2 individuals of an ideal panmictic population. In environmental recovery programs, seeds, preferably from different fruits, should be collected from 95 trees to preserve the genetic diversity of the species.

scholarly journals The distribution of mutational effects on fitness in Caenorhabditis elegans inferred from standing genetic variation

2020 ◽  
Author(s):  
Kimberly J. Gilbert ◽  
Stefan Zdraljevic ◽  
Daniel E. Cook ◽  
Asher D. Cutter ◽  
Erik C. Andersen ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Caenorhabditis Elegans ◽  
Population Size ◽  
Genomic Structure ◽  
Random Mating ◽  
Population Substructure ◽  
C Elegans ◽  
Fitness Effects ◽  
Self Fertilization ◽  
New Mutations

ABSTRACTThe distribution of fitness effects for new mutations is one of the most theoretically important but difficult to estimate properties in population genetics. A crucial challenge to inferring the distribution of fitness effects (DFE) from natural genetic variation is the sensitivity of the site frequency spectrum to factors like population size change, population substructure, and non-random mating. Although inference methods aim to control for population size changes, the influence of non-random mating remains incompletely understood, despite being a common feature of many species. We report the distribution of fitness effects estimated from 326 genomes of Caenorhabditis elegans, a nematode roundworm with a high rate of self-fertilization. We evaluate the robustness of DFE inferences using simulated data that mimics the genomic structure and reproductive life history of C. elegans. Our observations demonstrate how the combined influence of self-fertilization, genome structure, and natural selection can conspire to compromise estimates of the DFE from extant polymorphisms. These factors together tend to bias inferences towards weakly deleterious mutations, making it challenging to have full confidence in the inferred DFE of new mutations as deduced from standing genetic variation in species like C. elegans. Improved methods for inferring the distribution of fitness effects are needed to appropriately handle strong linked selection and selfing. These results highlight the importance of understanding the combined effects of processes that can bias our interpretations of evolution in natural populations.

Mating system and genetic polymorphism in populations of Secale cereale and S. vavilovii

1984 ◽  
Vol 26 (3) ◽  
pp. 308-317 ◽  
Author(s):  
M. Pérez De La Vega ◽  
R. W. Allard
Keyword(s):  
Mating System ◽  
Secale Cereale ◽  
Random Mating ◽  
Genetic Studies ◽  
Banding Patterns ◽  
Enzyme Systems ◽  
Incompatibility System ◽  
Secale Cereale L ◽  
Isozyme Polymorphism ◽  
Self Fertilization

Electrophoretic banding patterns were determined for nine enzyme systems (IPO, PGM, PGI, LAP, GOT, EST, PHOS, MDH, CPX) in four populations of Secale cereale L. from widely different geographical areas, and in one population of S. vavilovii Grossh. Secale cereale was found to be extensively variable and S. vavilovii invariant for these enzyme systems. Formal genetic studies of nine polymorphic banding zones in S. cereale revealed that each zone was under single locus control. Mating system studies based on these loci indicated that 8% of self-fertilization occurred under field conditions in a population of S. cereale, a species with a highly developed self-incompatibility system. Each population was characterized by fewer heterozygotes than expected in random mating populations. Genotypic and allelic frequencies were nearly identical in four populations of S. cereale, despite their diverse origins and different cytological characteristics.Key words: mating system, Secale, rye, isozyme polymorphism.

scholarly journals Association between mendelian factors with mixed selfing and random mating

Heredity ◽  
1956 ◽  
Vol 10 (1) ◽  
pp. 51-55 ◽  
Author(s):  
J H Bennett ◽  
F E Binet
Keyword(s):  
Random Mating ◽  
Mixed Selfing

scholarly journals Mutation-selection balance and the evolutionary advantage of sex and recombination

1990 ◽  
Vol 55 (3) ◽  
pp. 199-221 ◽  
Author(s):  
Brian Charlesworth
Keyword(s):  
Mutation Rate ◽  
Genetic Recombination ◽  
Random Mating ◽  
Quantitative Character ◽  
Sexual Population ◽  
Evolutionary Advantage ◽  
Diminishing Returns ◽  
Mean Fitness ◽  
Locus System ◽  
Asexual Populations

SummaryMutation-selection balance in a multi-locus system is investigated theoretically, using a modification of Bulmer's infinitesimal model of selection on a normally-distributed quantitative character, taking the number of mutations per individual (n) to represent the character value. The logarithm of the fitness of an individual with n mutations is assumed to be a quadratic, decreasing function of n. The equilibrium properties of infinitely large asexual populations, random-mating populations lacking genetic recombination, and random-mating populations with arbitrary recombination frequencies are investigated. With ‘synergistic’ epistasis on the scale of log fitness, such that log fitness declines more steeply as n increases, it is shown that equilibrium mean fitness is least for asexual populations. In sexual populations, mean fitness increases with the number of chromosomes and with the map length per chromosome. With ‘diminishing returns’ epistasis, such that log fitness declines less steeply as n increases, mean fitness behaves in the opposite way. Selection on asexual variants and genes affecting the rate of genetic recombination in random-mating populations was also studied. With synergistic epistasis, zero recombination always appears to be disfavoured, but free recombination is disfavoured when the mutation rate per genome is sufficiently small, leading to evolutionary stability of maps of intermediate length. With synergistic epistasis, an asexual mutant is unlikely to invade a sexual population if the mutation rate per diploid genome greatly exceeds unity. Recombination is selectively disadvantageous when there is diminishing returns epistasis. These results are compared with the results of previous theoretical studies of this problem, and with experimental data.

scholarly journals Gene-drive-mediated extinction is thwarted by population structure and evolution of sib mating

2019 ◽  
Vol 2019 (1) ◽  
pp. 66-81 ◽  
Author(s):  
James J Bull ◽  
Christopher H Remien ◽  
Stephen M Krone
Keyword(s):  
Population Structure ◽  
Genome Engineering ◽  
Random Mating ◽  
Structured Populations ◽  
Target Sequence ◽  
Gene Drive ◽  
Resistance Evolution ◽  
Sib Mating ◽  
Mean Fitness ◽  
Gene Drives

AbstractBackground and objectivesGenetic engineering combined with CRISPR technology has developed to the point that gene drives can, in theory, be engineered to cause extinction in countless species. Success of extinction programs now rests on the possibility of resistance evolution, which is largely unknown. Depending on the gene-drive technology, resistance may take many forms, from mutations in the nuclease target sequence (e.g. for CRISPR) to specific types of non-random population structures that limit the drive (that may block potentially any gene-drive technology).MethodologyWe develop mathematical models of various deviations from random mating to consider escapes from extinction-causing gene drives. A main emphasis here is sib mating in the face of recessive-lethal and Y-chromosome drives.ResultsSib mating easily evolves in response to both kinds of gene drives and maintains mean fitness above 0, with equilibrium fitness depending on the level of inbreeding depression. Environmental determination of sib mating (as might stem from population density crashes) can also maintain mean fitness above 0. A version of Maynard Smith’s haystack model shows that pre-existing population structure can enable drive-free subpopulations to be maintained against gene drives.Conclusions and implicationsTranslation of mean fitness into population size depends on ecological details, so understanding mean fitness evolution and dynamics is merely the first step in predicting extinction. Nonetheless, these results point to possible escapes from gene-drive-mediated extinctions that lie beyond the control of genome engineering.Lay summaryRecent gene drive technologies promise to suppress and even eradicate pests and disease vectors. Simple models of gene-drive evolution in structured populations show that extinction-causing gene drives can be thwarted both through the evolution of sib mating as well as from purely demographic processes that cluster drive-free individuals.

scholarly journals A deterministic model of cyclical selection

1975 ◽  
Vol 25 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Rolf F. Hoekstra
Keyword(s):  
Deterministic Model ◽  
Fitness Function ◽  
Natural Populations ◽  
Sufficient Conditions ◽  
Selection Model ◽  
Property A ◽  
Order Of Magnitude ◽  
Protected Polymorphism ◽  
Mean Fitness ◽  
Special Case

SUMMARYA deterministic model of cyclical selection in randomly mating populations is studied. Sufficient conditions for a protected polymorphism, which are for the special case of alternating selection also necessary conditions, are obtained using a simple graphical approach. The most important condition requires ‘marginal overdominance’ (Wallace, 1968); the other conditions seem hard to satisfy in a natural situation. Furthermore it is shown that the cyclical selection model can be regarded as a special case of a frequency-dependent selection model (Cockerham et al. 1972). Using this property, a mean fitness function for the cyclical selection model is derived. Generally, the mean fitness will not be maximized under cyclical selection. The relevance of the model to the problem of the role of cyclical selection in the maintenance of genetic polymorphism in natural populations is discussed. It is concluded that this relevance is probably rather limited with regard to the creation of protected polymorphism, but that the influence of cyclical selection on transient polymorphisms might be more significant. An approximate formula for the time needed for a given change in gene frequency under cyclical selection is derived. It appears that cyclical selection can extend considerably the time during which a transient polymorphism persists, especially if the selective differences in the different environments are of the same order of magnitude and of opposite sign.

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