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Related Concept Videos

Types of Selection01:46

Types of Selection

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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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Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.
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Among the three main modes of HGT—transformation, conjugation, and transduction—transduction is unique in that it is mediated by bacteriophages, or bacterial viruses.Transduction occurs in two ways. Generalized transduction occurs during the lytic cycle of a bacteriophage infection. In this process, bacteriophages infect bacterial cells, replicate within them, and ultimately cause cell lysis, releasing newly assembled virions. Occasionally, random fragments of the bacterial genome...
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Natural selection is an evolutionary process in which individuals with survival-promoting traits reproduce at higher rates. These favorable traits become more common within a population or species. Naturally selected traits initially arise via random genetic mutations. In order for selection to occur, there must be variation within a population, the trait controlling the variation must be heritable, and there must be an evolutionary advantage for variation in the trait.
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Frequency-dependent Selection01:21

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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.
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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).
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Drosophila melanogaster Larva Injection Protocol
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Natural selection drives Drosophila immune system evolution.

Todd A Schlenke1, David J Begun

  • 1Section of Evolution and Ecology, Division of Biological Sciences, Storer Hall, University of California, Davis, CA 95616, USA. taschlenke@ucdavis.edu

Genetics
|August 22, 2003
PubMed
Summary
This summary is machine-generated.

Natural selection drives immune protein evolution in fruit flies. Unlike mammals, Drosophila immune genes show less diversity, possibly due to their general immune response.

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Area of Science:

  • Evolutionary biology
  • Population genetics
  • Immunology

Background:

  • Natural selection is implicated in the evolution of host immune system proteins.
  • Few studies have made population genetic inferences from multiple immune genes within a single species.

Purpose of the Study:

  • To investigate the role of selection in the evolution of immune system proteins.
  • To compare genetic diversity and divergence between immune and non-immune genes in Drosophila.

Main Methods:

  • Sequencing DNA polymorphism and divergence data from 34 innate immune genes and 28 non-immunity genes in Drosophila simulans.
  • Analyzing population genetic statistics such as K(A)/K(S) ratio, silent heterozygosity, and haplotype diversity.

Main Results:

  • Significant differences observed in genetic statistics between immune and non-immunity genes.
  • Evidence suggests directional selection plays a key role in immune protein evolution.
  • No strong evidence for selective maintenance of protein diversity in Drosophila immune proteins, unlike in mammals.

Conclusions:

  • Directional selection is a significant factor in the evolution of Drosophila's immune system proteins.
  • The generalized innate immune response in Drosophila may explain the lack of protein diversity maintenance.
  • Findings contribute to understanding the evolutionary pressures on immune system genes.