scholarly journals Natural Selection for an Intermediate Optimum

1960 ◽  
Vol 13 (1) ◽  
pp. 30 ◽  
Author(s):  
BDH Latter
Keyword(s):  
Natural Selection ◽  
Genetic Variability ◽  
Recurrent Mutation ◽  
Quantitative Character ◽  
Equilibrium Situation ◽  
Selection For

Natural selection against extreme metric deviation is a process which is known to lead to the elimination of genetic variability in the particular quantitative character concerned. Recurrent mutation at loci affecting the character will be expected to oppose this tendency to genetic fixation, and the resulting equilibrium situation is discussed in detail in this paper.

scholarly journals A SIMULATION STUDY OF TRUNCATION SELECTION FOR A QUANTITATIVE TRAIT OPPOSED BY NATURAL SELECTION

Genetics ◽  
1980 ◽  
Vol 94 (4) ◽  
pp. 989-1000
Author(s):  
Francis Minvielle
Keyword(s):  
Natural Selection ◽  
Artificial Selection ◽  
Random Mating ◽  
Selection Response ◽  
Quantitative Character ◽  
Mass Selection ◽  
Frequency Selection ◽  
Selection Experiments ◽  
Selection For ◽  
Selective Process

ABSTRACT A quantitative character controlled at one locus with two alleles was submitted to artificial (mass) selection and to three modes of opposing natural selection (directional selection, overdominance and underdominance) in a large random-mating population. The selection response and the limits of the selective process were studied by deterministic simulation. The lifetime of the process was generally between 20 and 100 generations and did not appear to depend on the mode of natural selection. However, depending on the values of the parameters (initial gene frequency, selection intensity, ratio of the effect of the gene to the environmental standard deviation, fitness values) the following outcomes of selection were observed: fixation of the allele favored by artificial selection, stable nontrivial equilibrium, unstable equilibrium and loss of the allele favored by artificial selection. Finally, the results of the simulation were compared to the results of selection experiments.

Maintenance of genetic variability by mutation–selection balance: a child's guide through the jungle

Genome ◽  
1989 ◽  
Vol 31 (2) ◽  
pp. 761-767 ◽  
Author(s):  
M. G. Bulmer
Keyword(s):  
Genetic Variability ◽  
Theoretical Work ◽  
Complex Problem ◽  
Recurrent Mutation ◽  
Mutation Rates ◽  
Stabilizing Selection ◽  
House Of Cards ◽  
Model Account ◽  
Optimal Value ◽  
Selection For

Metric characters closely connected with fitness have little additive genetic variability, presumably because it is quickly exhausted under continuous directional selection on fitness. Other metric characters have substantial additive genetic variability with a typical heritability of about 0.5. A popular model is that the second class of characters is subject to weak stabilizing selection for an optimal value, which depletes genetic variability, while recurrent mutation tends to restore it. Can this model account for the variability observed, given the evidence available about the strength of selection and mutation rates? Much theoretical work has been done on this complex problem. This work is reviewed, with the intention of simplifying it as much as possible.Key words: mutation–selection balance, genetic variability, continuum-of-alleles model, house-of-cards approximation.

Frequency-dependent selection in bacterial populations

1988 ◽  
Vol 319 (1196) ◽  
pp. 459-472 ◽  
Keyword(s):  
Natural Selection ◽  
Genetic Variability ◽  
Mass Culture ◽  
Experimental Studies ◽  
Frequency Dependent ◽  
Bacterial Populations ◽  
Frequency Dependent Selection ◽  
Selection For ◽  
Restriction Modification ◽  
Restriction Modification Systems

There are many situations in which the direction and intensity of natural selection in bacterial populations will depend on the relative frequencies of genotypes. In some cases, this selection will favour rare genotypes and result in the maintenance of genetic variability; this is termed stabilizing frequency-dependent selection. In other cases, selection will only favour genotypes when they are common. Rare types cannot invade and genetic variability will not be maintained; this is known as disruptive frequency-dependent selection. Phage-mediated selection for bacteria with novel restriction-modification systems is frequency-dependent and stabilizing. In mass culture, selection for the production of toxins and allelopathic agents is likely to be frequency-dependent but disruptive. This also occurs in selection favouring genes and transposable elements that cause mutations. Here I review the results of theoretical and experimental studies of stabilizing and disruptive frequency-dependent selection in bacterial populations, and speculate on the importance of this kind of selection in the adaptation and evolution of these organisms and their accessory elements (plasmid, phage and transposons).

The relationship between facial whorl direction and sidedness in ridden horses

2006 ◽  
Vol 35 ◽  
pp. 247-250
Author(s):  
H. Randle ◽  
E. Elworthy
Keyword(s):  
Natural Selection ◽  
Artificial Selection ◽  
Competitive Ability ◽  
Close Association ◽  
Human Behaviour ◽  
Physical Ability ◽  
Facial Hair ◽  
Selection For ◽  
The Relationship ◽  
The Brain

The influence of Natural Selection on the evolution of the horse (Equus callabus) is minimal due to its close association with humans. Instead Artificial Selection is commonly imposed through selection for features such as a ‘breed standard’ or competitive ability. It has long been considered to be useful if indicators of characteristics such as physical ability could be identified. Kidd (1902) suggested that the hair coverings of animals were closely related to their lifestyle, whether they were active or passive. In 1973 Smith and Gong concluded that hair whorl (trichloglyph) pattern and human behaviour is linked since hair patterning is determined at the same time as the brain develops in the foetus. More recently Grandin et al. (1995), Randle (1998) and Lanier et al. (2001) linked features of facial hair whorls to behaviour and production in cattle. Hair whorl features have also been related to temperament in equines (Randle et al., 2003).

scholarly journals Induced defenses alter the strength and direction of natural selection on reproductive traits in common milkweed

2016 ◽  
Author(s):  
Ken A. Thompson ◽  
Kaitlin A. Cory ◽  
Marc T. J. Johnson
Keyword(s):  
Natural Selection ◽  
Jasmonic Acid ◽  
Reproductive Traits ◽  
Induced Defenses ◽  
Asclepias Syriaca ◽  
Ecological Processes ◽  
Foliar Damage ◽  
Antiherbivore Defenses ◽  
Selection For ◽  
Generate Plant

AbstractEvolutionary biologists have long sought to understand the ecological processes that generate plant reproductive diversity. Recent evidence indicates that constitutive antiherbivore defenses can alter natural selection on reproductive traits, but it is unclear whether induced defenses will have the same effect and whether reduced foliar damage in defended plants is the cause of this pattern. In a factorial field experiment using common milkweed, Asclepias syriaca, we induced plant defenses using jasmonic acid (JA) and imposed foliar damage using scissors. We found that JA-induced plants experienced selection for more inflorescences that were smaller in size (fewer flowers), while control plants only experienced a trend toward selection for larger inflorescences (more flowers); all effects were independent of foliar damage. Our results demonstrate that induced defenses can alter both the strength and direction of selection on reproductive traits, and suggest that antiherbivore defenses may promote the evolution of plant reproductive diversity.

scholarly journals Natural Selection at an Exceptionally Long GGC Repeat in the Human RASGEF1C and Divergent Genotypes in Late-onset Neurocognitive Disorder

2021 ◽  
Author(s):  
Z Jafarian ◽  
S Khamse ◽  
H Afshar ◽  
Khorram Khorshid HR ◽  
A Delbari ◽  
...  
Keyword(s):  
Natural Selection ◽  
Evolutionary Biology ◽  
Late Onset ◽  
Core Promoter ◽  
Human Subjects ◽  
Specific Gene ◽  
Protein Coding ◽  
Repeat Allele ◽  
Complex Disorders ◽  
Selection For

Abstract Across the human protein-coding genes, the neuron-specific gene, RASGEF1C, contains the longest (GGC)-repeat, spanning its core promoter and 5′ untranslated region (RASGEF1C-201 ENST00000361132.9). RASGEF1C expression dysregulation occurs in late-onset neurocognitive disorders (NCDs), such as Alzheimer’s disease. Here we sequenced the GGC-repeat in a sample of human subjects (N = 269), consisting of late-onset NCDs (N = 115) and controls (N = 154). We also studied the status of this STR across vertebrates. The 6-repeat allele of this repeat was the predominant allele in the controls (frequency = 0.85) and NCD patients (frequency = 0.78). The NCD genotype compartment consisted of an excess of genotypes that lacked the 6-repeat (Mid-P exact = 0.004). We also detected divergent genotypes that were present in five NCD patients and not in the controls (Mid-P exact = 0.007). This STR expanded beyond 2-repeats specifically in primates, and was at maximum length in human. We conclude that there is natural selection for the 6-repeat allele of the RASGEF1C (GGC)-repeat in human, and significant divergence from that allele in late-onset NCDs. Indication of natural selection for predominantly abundant STR alleles and divergent genotypes enhance the perspective of evolutionary biology and disease pathogenesis in human complex disorders.

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