Gene Conversion in Drosophila pseudoobscura

Genetic exchange either through cross overs or gene conversion events can homogenize nucleotide diversity between homologous chromosomes, although the two mechanisms differ in how much of the genome they affect. Genetic cross overs can exchange megabases of DNA between homologs while gene conversion may only exchange several hundred bases between chromosomes. In addition, crossing over reduces the association of linked genes. Genome rearrangements can alter the relative frequency of crossing over and gene conversion events where cross overs tend to be reduced leading to higher levels of association among allelic variation within the chromosome. For this reason, genome rearrangements have been proposed to arise to hold combinations of locally adapted alleles together in response to migration-selection balance. Drosophila pseudoobscura has over 30 different chromosomal arrangements on the third chromosome in natural population whose frequency varies with changes in environmental habitats. The pattern and organization of genetic diversity in the third chromosome in D. pseudoobscura is consistent with the evolution of locally adapted combinations of alleles prior to inversion mutation events. Genes involved in adaptation were identified by local clusters of fixed SNP differences in genes encoding fixed amino acid differences or that were differential expressed. Adaptive genes were separated by regions with inferred higher levels of gene exchange leading to shared polymorphism among arrangements. Here we tested whether the genetic exchange resulted from gene conversion among different gene arrangements. We find that gene conversion tracts occur away from adaptive genes suggesting that inversions captured adaptive alleles and that gene conversion has homogenized regions with non-adaptive alleles and been selected against in regions with adaptive alleles.

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Work Title Gene Conversion in Drosophila pseudoobscura
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Creators
  1. Stephen Schaeffer
License CC BY 4.0 (Attribution)
Work Type Article
Acknowledgments
  1. These data presented in this work was generated through support from the National Institutes of Health R01 GM 098478 to (S.W.S.). The funders had no role in study design, data collection, data analysis, the decision to publish, or preparation of the manuscript.
Publication Date July 19, 2022
Deposited July 19, 2022

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  • Updated Acknowledgments Show Changes
    Acknowledgments
    • These data presented in this work was generated through support from the National Institutes of Health R01 GM 098478 to (S.W.S.). The funders had no role in study design, data collection, data analysis, the decision to publish, or preparation of the manuscript.
  • Added Creator Stephen Schaeffer
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    Description
    • Genetic exchange either through cross overs or gene conversion events can homogenize nucleotide diversity between homologous chromosomes, although the two mechanisms differ in how much of the genome they affect. Genetic cross overs can exchange megabases of DNA between homologs while gene conversion may only exchange several hundred bases between chromosomes. In addition, crossing over reduces the association of linked genes. Genome rearrangements can alter the relative frequency of crossing over and gene conversion events where cross overs tend to be reduced leading to higher levels of association among allelic variation within the chromosome. For this reason, genome rearrangements have been proposed to arise to hold combinations of locally adapted alleles together in response to migration-selection balance. Drosophila pseudoobscura has over 30 different chromosomal arrangements on the third chromosome in natural population whose frequency varies with changes in environmental habitats. The pattern and organization of genetic diversity in the third chromosome in D. pseudoobscura is consistent with the evolution of locally adapted combinations of alleles prior to inversion mutation events. Genes involved in adaptation were identified by local clusters of fixed SNP differences in genes encoding fixed amino acid differences or that were differential expressed. Adaptive genes were separated by regions with inferred higher levels of gene exchange leading to shared polymorphism among arrangements. Here we tested whether the genetic exchange resulted from gene conversion among different gene arrangements. We find that gene conversion tracts occur away from adaptive genes suggesting that inversions captured adaptive alleles and that gene conversion has homogenized regions with non-adaptive alleles and been selected against in regions with adaptive alleles.
    Publication Date
    • 2022-07-19
    License
    • https://creativecommons.org/licenses/by/4.0/
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