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Related Concept Videos

Frequency-dependent Selection01:21

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 Screens02:46

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 Selection01:46

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...
Position-effect Variegation02:32

Position-effect Variegation

In 1928, a German botanist Emil Heitz observed the moss nuclei with a DNA binding dye. He observed that while some chromatin regions decondense and spread out in the interphase nucleus, others do not. He termed them euchromatin and heterochromatin, respectively. He proposed that the heterochromatin regions reflect a functionally inactive state of the genome. It was later confirmed that heterochromatin is transcriptionally repressed, and euchromatin is transcriptionally active chromatin.
Cis-regulatory Sequences02:02

Cis-regulatory Sequences

Cis-regulatory sequences are short fragments of non-coding DNA that are present on the same chromosomes as the genes that they regulate. These fragments serve as binding sites for transcriptional regulators, proteins that are responsible for controlling gene transcription and differential gene expression across cell types in eukaryotes. Cis-regulatory sequences can be close to the gene of interest or thousands of bases away in the DNA sequence; however, those sequences that are further away are...
Exon Recombination02:32

Exon Recombination

The evolution of new genes is critical for speciation. Exon recombination, also known as exon shuffling or domain shuffling, is an important means of new gene formation. It is observed across vertebrates, invertebrates, and in some plants such as potatoes and sunflowers. During exon recombination, exons from the same or different genes recombine and produce new exon-intron combinations, which might evolve into new genes. 
Exon shuffling follows “splice frame rules.” Each exon has three reading...

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Updated: May 10, 2026

Maintenance of a Drosophila melanogaster Population Cage
08:03

Maintenance of a Drosophila melanogaster Population Cage

Published on: March 15, 2016

Strong purifying selection at synonymous sites in D. melanogaster.

David S Lawrie1, Philipp W Messer, Ruth Hershberg

  • 1Department of Genetics, Stanford University, Stanford, CA, USA. dlawrie@stanford.edu

Plos Genetics
|June 6, 2013
PubMed
Summary

Contrary to expectations, 22% of synonymous sites in Drosophila melanogaster show strong selective constraint, not weak. This suggests synonymous sites play a crucial role in functional variation and evolution, warranting reevaluation in disease and adaptation studies.

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Area of Science:

  • Evolutionary Biology
  • Genomics
  • Molecular Biology

Background:

  • Synonymous sites are often overlooked, assumed to have weak selective constraint.
  • This assumption neglects their potential role in functional genetic variation.

Purpose of the Study:

  • To investigate the selective constraint acting on synonymous sites using population sequencing data.
  • To determine the extent and functional implications of constraint on synonymous sites in Drosophila melanogaster.

Main Methods:

  • Analysis of site frequency spectra from deep population sequencing data.
  • Integration of polymorphism and divergence data.
  • Correlation analysis between synonymous site constraint and gene expression levels.

Main Results:

  • 22% of four-fold synonymous (4D) sites in Drosophila melanogaster exhibit strong selective constraint.
  • Stronger purifying selection correlates with slower evolutionary rates on the Drosophila phylogeny.
  • Synonymous site constraint is linked to gene expression, particularly during development, and functionally important genes.

Conclusions:

  • Synonymous sites are under significant selective constraint, challenging previous assumptions.
  • This constraint is functionally relevant, linked to gene expression and developmental pathways.
  • The role of synonymous sites in evolution, disease, and adaptation requires reevaluation across species.