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Types of Selection

Types of Selection

Natural selection influences the frequencies of particular alleles and phenotypes within populations in several different ways. Primarily, natural selection can be directional, stabilizing, or disruptive. Directional selection favors one extreme trait and shifts the population towards that phenotype while selecting against individuals displaying alternate traits. Stabilizing selection favors an intermediate trait with a narrow range of variation. Deviation from the optimal phenotype towards an...

Frequency-dependent Selection

Frequency-dependent Selection

When the fitness of a trait is influenced by how common it is (i.e., its frequency) relative to different traits within a population, this is referred to as frequency-dependent selection. Frequency-dependent selection may occur between species or within a single species. This type of selection can either be positive—with more common phenotypes having higher fitness—or negative, with rarer phenotypes conferring increased fitness.

Law of Independent Assortment

Law of Independent Assortment

While Mendel’s Law of Segregation states that the two alleles for one gene are separated into different gametes, a different question of how different genes are inherited remains. For example, is the gene for tall plants inherited with the gene for green peas? Mendel asked this question by experimenting with a dihybrid cross; a cross in which both parents are homozygous for two distinct traits resulting in an F1 generation that are heterozygous for both traits.

Mutation, Gene Flow, and Genetic Drift

Mutation, Gene Flow, and Genetic Drift

In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time. Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size).

Background and Environment Affect Phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
An example of how genetic background affects phenotype can be seen in horses. The Extension gene in horses is responsible for their coat color. A wild-type gene (EE) produces black pigment in the coat, while a mutant gene (ee) produces red pigment. A...

Law of Segregation

Law of Segregation

When crossing pea plants, Mendel noticed that one of the parental traits would sometimes disappear in the first generation of offspring, called the F1 generation, and could reappear in the next generation (F2). He concluded that one of the traits must be dominant over the other, thereby causing masking of one trait in the F1 generation. When he crossed the F1 plants, he found that 75% of the offspring in the F2 generation had the dominant phenotype, while 25% had the recessive phenotype.

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Shifting Zebrafish Lethal Skeletal Mutant Penetrance by Progeny Testing

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Phenotypic Assortment Changes the Landscape of Selection.

Edmund D Brodie¹, Phoebe A Cook¹, Robin A Costello¹

¹Mountain Lake Biological Station and Department of Biology, University of Virginia, Charlottesville, VA, USA.

The Journal of Heredity

|December 8, 2021

Summary

This summary is machine-generated.

Social selection impacts fitness through trait expression. Phenotypic assortment in forked fungus beetles varied across populations but was consistent yearly, changing with social context.

Keywords:

beetle indirect genetic effects kin selection social behavior social network social selection

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Area of Science:

Evolutionary Biology
Behavioral Ecology
Quantitative Genetics

Background:

Social interactions significantly influence individual fitness.
Social selection pathways link expressed traits to the fitness of others.
Phenotypic assortment patterns mediate the effects of social selection.

Purpose of the Study:

To estimate interactant covariance (Cij') in forked fungus beetles.
To investigate the consistency and plasticity of phenotypic assortment in natural populations.
To understand how social selection varies with environmental and social contexts.

Main Methods:

Estimating interactant covariance (Cij') from field and experimental studies.
Analyzing phenotypic assortment based on body size and horn length in forked fungus beetles.
Manipulating resource distribution and social properties to assess plasticity.

Main Results:

Phenotypic assortment of male beetles by size or horn length varied significantly among subpopulations.
Assortment patterns showed broad year-to-year consistency within subpopulations.
Interactant covariance strength and direction rapidly changed with experimental alterations in resource distribution and social density.
Covariances were generally more negative in contexts with higher social interaction rates.

Conclusions:

Phenotypic assortment is a key factor in the variability of multilevel selection.
Social selection gradients are mediated by patterns of phenotypic assortment.
The plasticity of phenotypic assortment suggests its dynamic role in evolutionary processes.