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Related Concept Videos

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.

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 result in visible changes...

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: May 30, 2026

Examination of Thymic Positive and Negative Selection by Flow Cytometry

Examination of Thymic Positive and Negative Selection by Flow Cytometry

Published on: October 8, 2012

Detecting past positive selection through ongoing negative selection.

Georgii A Bazykin¹, Alexey S Kondrashov

¹Department of Bioengineering and Bioinformatics, M. V. Lomonosov Moscow State University, Moscow, Russia.

Genome Biology and Evolution

|August 24, 2011

Summary

This summary is machine-generated.

Detecting positive selection is difficult. This new method identifies positive selection by observing ongoing negative selection, offering new insights into evolutionary adaptation in species like Drosophila and humans.

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Examination of Thymic Positive and Negative Selection by Flow Cytometry

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Following the Dynamics of Structural Variants in Experimentally Evolved Populations

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Published on: February 3, 2023

Area of Science:

Evolutionary biology
Population genetics
Molecular evolution

Background:

Detecting positive selection is a significant challenge in evolutionary studies.
Understanding the balance between positive and negative selection is crucial for evolutionary insights.

Purpose of the Study:

To develop a novel method for detecting past positive selection.
To analyze evolutionary adaptation by comparing selection pressures at different genetic sites.

Main Methods:

Comparing intraspecies polymorphism at functionally important and neutral sites.
Analyzing nucleotide substitutions and allele frequencies.
Utilizing a method similar to the McDonald-Kreitman test but with improved capabilities.

Main Results:

The fraction of adaptive amino acid replacements in Drosophila melanogaster has remained stable at approximately 0.5.
In the human lineage, this fraction decreased significantly after the Ponginae-Homininae divergence, dropping to near zero.
The proposed method offers advantages over existing tests, especially with extensive genotypic data.

Conclusions:

The developed method effectively detects positive selection by identifying ongoing negative selection.
Evolutionary adaptation rates differ significantly between Drosophila and human lineages.
This approach provides new avenues for studying selection pressures, particularly in species with abundant genetic information.