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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.

Hardy-Weinberg Principle

Hardy-Weinberg Principle

Diploid organisms have two alleles of each gene, one from each parent, in their somatic cells. Therefore, each individual contributes two alleles to the gene pool of the population. The gene pool of a population is the sum of every allele of all genes within that population and has some degree of variation. Genetic variation is typically expressed as a relative frequency, which is the percentage of the total population that has a given allele, genotype or phenotype.

Genetic Screens

Genetic Screens

Genetic screens are tools used to identify genes and mutations responsible for phenotypes of interest. Genetic screens help identify individuals or a group of people at risk of developing genetic diseases and help them with early intervention, targeted therapy, and reproductive options.
Forward genetic screens
Forward or “classical” genetic screens involve creating random mutations in an organism’s DNA using radiation, mutagens, or insertion of additional bases, which...

Conservative Site-specific Recombination and Phase Variation

Conservative Site-specific Recombination and Phase Variation

Because the DNA segments are cut and reorganized in a direction-specific manner, site-specific recombination has emerged as an efficient genetic engineering technique. Flippase and Cyclization recombinases or Flp and Cre, respectively, are two members of the tyrosine recombinase family derived from bacteriophages, that are used to mediate site-specific DNA insertions, deletions, and targeted expression of proteins in mammalian cell lines.
The recognition sites for Cre recombinase called LoxP...

Confirmation Biases

Confirmation Biases

The confirmation bias is the tendency to focus on information that confirms our existing beliefs and ignore information that is inconsistent with our expectations. For example, if you think that your professor is not very nice, you notice all of the instances of rude behavior exhibited by the professor while ignoring the countless pleasant interactions he is involved in on a daily basis. Have you ever fallen prey to the confirmation bias, either as the source or target of such bias?

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...

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Related Experiment Video

Updated: Apr 21, 2026

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity

Published on: March 25, 2020

On the unfounded enthusiasm for soft selective sweeps.

Jeffrey D Jensen¹

¹1] School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1007, Switzerland [2] Swiss Institute of Bioinformatics (SIB), Lausanne 1007, Switzerland.

Nature Communications

|October 28, 2014

Summary

This summary is machine-generated.

Adaptation in populations may not be limited by new mutations, according to two genetic models. However, current evidence from humans and Drosophila challenges these models, questioning their broad applicability in evolutionary studies.

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Last Updated: Apr 21, 2026

In Vitro Directed Evolution of a Restriction Endonuclease with More Stringent Specificity

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Area of Science:

Evolutionary biology
Population genetics
Molecular evolution

Background:

Understanding the pace and drivers of adaptation is crucial in evolutionary biology.
The role of new mutations in limiting adaptation rates has been a long-standing question.

Purpose of the Study:

To evaluate recent population genetic models suggesting adaptation is not mutation-limited.
To assess the empirical and experimental evidence supporting or refuting these models.

Main Methods:

Review of theoretical population genetic models.
Analysis of empirical data from studies on humans and Drosophila.

Main Results:

Two models propose that adaptation rates are not significantly constrained by the supply of new beneficial mutations.
Existing empirical and experimental data challenge the widespread applicability of these mutation-independent adaptation models.

Conclusions:

Recent theoretical models propose non-mutation-limited adaptation.
Current evidence suggests these models may not fully explain observed variation in natural populations like humans and Drosophila.