Fixation dynamics of beneficial alleles in prokaryotic polyploid chromosomes and plasmids

Abstract Theoretical population genetics has been mostly developed for sexually reproducing diploid and for monoploid (haploid) organisms, focusing on eukaryotes. The evolution of bacteria and archaea is often studied by models for the allele dynamics in monoploid populations. However, many prokaryo...

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Bibliographic Details
Published in:Genetics (Austin) 2022-09, Vol.222 (2)
Main Authors: Santer, Mario, Kupczok, Anne, Dagan, Tal, Uecker, Hildegard
Format: Article
Language:English
Subjects:
Adaptation
Alleles
Archaea
Chromosomes
Copy number
Diploids
Environmental conditions
Eukaryotes
Fixation
Genetic diversity
Genetics
Genotypes
Heterozygosity
Investigation
Mathematical analysis
Mutation
Phenotypes
Phenotypic variations
Plasmids
Ploidy
Polyploidy
Population genetics
Populations
Prokaryotes
Reproduction (biology)
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Summary:Abstract Theoretical population genetics has been mostly developed for sexually reproducing diploid and for monoploid (haploid) organisms, focusing on eukaryotes. The evolution of bacteria and archaea is often studied by models for the allele dynamics in monoploid populations. However, many prokaryotic organisms harbor multicopy replicons—chromosomes and plasmids—and theory for the allele dynamics in populations of polyploid prokaryotes remains lacking. Here, we present a population genetics model for replicons with multiple copies in the cell. Using this model, we characterize the fixation process of a dominant beneficial mutation at 2 levels: the phenotype and the genotype. Our results show that depending on the mode of replication and segregation, the fixation of the mutant phenotype may precede genotypic fixation by many generations; we term this time interval the heterozygosity window. We furthermore derive concise analytical expressions for the occurrence and length of the heterozygosity window, showing that it emerges if the copy number is high and selection strong. Within the heterozygosity window, the population is phenotypically adapted, while both alleles persist in the population. Replicon ploidy thus allows for the maintenance of genetic variation following phenotypic adaptation and consequently for reversibility in adaptation to fluctuating environmental conditions.
ISSN:1943-2631
0016-6731
1943-2631
DOI:10.1093/genetics/iyac121