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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.

Genome Size and the Evolution of New Genes

Genome Size and the Evolution of New Genes

Genome Size and the Evolution of New Genes

Genome Size and the Evolution of New Genes

While every living organism has a genome of some kind (be it RNA, or DNA), there is considerable variation in the sizes of these blueprints. One major factor that impacts genome size is whether the organism is prokaryotic or eukaryotic. In prokaryotes, the genome contains little to no non-coding sequence, such that genes are tightly clustered in groups or operons sequentially along the chromosome. Conversely, the genes in eukaryotes are punctuated by long stretches of non-coding sequence.

Transcription

Transcription

Overview
Transcription is the process of synthesizing RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene sequence. Additionally, many other proteins and regulatory sequences are involved in the proper synthesis of messenger RNA (mRNA). Regulation of transcription is responsible for the differentiation of all the different types of cells and often for the proper cellular response to environmental signals.
Transcription Can Produce Different Kinds...

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...

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...

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Related Experiment Video

Updated: Oct 30, 2025

Environmentally Induced Heritable Changes in Flax

Environmentally Induced Heritable Changes in Flax

Published on: January 26, 2011

Exploring environmental selection on genome size in angiosperms.

Lubna Faizullah¹, Joseph A Morton¹, Erika I Hersch-Green²

¹Character Evolution Team, Royal Botanic Gardens, Kew, Richmond, Surrey, UK; School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London, UK.

Trends in Plant Science

|July 5, 2021

Summary

Most flowering plants have small genomes, despite evolutionary pressures for larger ones. This study suggests larger genome sizes may incur costs related to cell size, nutrient demands, and photosynthesis, favoring smaller genomes under stress.

Keywords:

genome size diversity minimum cell size nutrients, stomata photosynthesis water-use efficiency

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Experimental Manipulation of Body Size to Estimate Morphological Scaling Relationships in Drosophila

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Published on: October 1, 2011

Area of Science:

Plant biology
Evolutionary biology
Genomics

Background:

Angiosperms exhibit wide genome size (GS) variation, with most species possessing small genomes.
Despite polyploidy and repeat amplification, selection for smaller GS is observed, suggesting costs associated with larger genomes.

Purpose of the Study:

To investigate the potential costs of increased genome size (GS) in angiosperms.
To explore how these costs might influence selection and evolutionary dynamics.

Main Methods:

Exploration of impacts of GS on minimum cell size.
Analysis of consequences for photosynthesis and water-use efficiency.
Assessment of nutrient (nitrogen, phosphorus) demands of the nucleus.

Main Results:

Larger GS may lead to smaller cell size, impacting photosynthesis and water-use efficiency.
Increased nuclear nutrient demands (N, P) create trade-offs with photosynthesis.
Nutrient, water, or CO2 stress may favor smaller genome sizes.

Conclusions:

Genome size reduction may be driven by physiological costs.
Environmental stress conditions could favor species with smaller genomes.
GS has implications for ecological and evolutionary trajectories of angiosperms.