---
_id: '4262'
abstract:
- lang: eng
  text: Natural populations are structured spatially into local populations and genetically
    into diverse ‘genetic backgrounds’ defined by different combinations of selected
    alleles. If selection maintains genetic backgrounds at constant frequency then
    neutral diversity is enhanced. By contrast, if background frequencies fluctuate
    then diversity is reduced. Provided that the population size of each background
    is large enough, these effects can be described by the structured coalescent process.
    Almost all the extant results based on the coalescent deal with a single selected
    locus. Yet we know that very large numbers of genes are under selection and that
    any substantial effects are likely to be due to the cumulative effects of many
    loci. Here, we set up a general framework for the extension of the coalescent
    to multilocus scenarios and we use it to study the simplest model, where strong
    balancing selection acting on a set of n loci maintains 2n backgrounds at constant
    frequencies and at linkage equilibrium. Analytical results show that the expected
    linked neutral diversity increases exponentially with the number of selected loci
    and can become extremely large. However, simulation results reveal that the structured
    coalescent approach breaks down when the number of backgrounds approaches the
    population size, because of stochastic fluctuations in background frequencies.
    A new method is needed to extend the structured coalescent to cases with large
    numbers of backgrounds.
acknowledgement: "We thank B. Charlesworth, D. Charlesworth and F. Depaulis for valuable
  discussion and criticism. We are also\r\ngrateful to an anonymous reviewer, who
  pointed out an imprecision in the original manuscript. This work was\r\nsupported
  by the BBSRC."
article_processing_charge: No
article_type: original
author:
- first_name: Nicholas H
  full_name: Barton, Nicholas H
  id: 4880FE40-F248-11E8-B48F-1D18A9856A87
  last_name: Barton
  orcid: 0000-0002-8548-5240
- first_name: Arcadio
  full_name: Navarro, Arcadio
  last_name: Navarro
citation:
  ama: 'Barton NH, Navarro A. Extending the coalescent to multilocus systems: the
    case of balancing selection. <i>Genetical Research</i>. 2002;79(2):129-139. doi:<a
    href="https://doi.org/10.1017/S0016672301005493">10.1017/S0016672301005493</a>'
  apa: 'Barton, N. H., &#38; Navarro, A. (2002). Extending the coalescent to multilocus
    systems: the case of balancing selection. <i>Genetical Research</i>. Cambridge
    University Press. <a href="https://doi.org/10.1017/S0016672301005493">https://doi.org/10.1017/S0016672301005493</a>'
  chicago: 'Barton, Nicholas H, and Arcadio Navarro. “Extending the Coalescent to
    Multilocus Systems: The Case of Balancing Selection.” <i>Genetical Research</i>.
    Cambridge University Press, 2002. <a href="https://doi.org/10.1017/S0016672301005493">https://doi.org/10.1017/S0016672301005493</a>.'
  ieee: 'N. H. Barton and A. Navarro, “Extending the coalescent to multilocus systems:
    the case of balancing selection,” <i>Genetical Research</i>, vol. 79, no. 2. Cambridge
    University Press, pp. 129–139, 2002.'
  ista: 'Barton NH, Navarro A. 2002. Extending the coalescent to multilocus systems:
    the case of balancing selection. Genetical Research. 79(2), 129–139.'
  mla: 'Barton, Nicholas H., and Arcadio Navarro. “Extending the Coalescent to Multilocus
    Systems: The Case of Balancing Selection.” <i>Genetical Research</i>, vol. 79,
    no. 2, Cambridge University Press, 2002, pp. 129–39, doi:<a href="https://doi.org/10.1017/S0016672301005493">10.1017/S0016672301005493</a>.'
  short: N.H. Barton, A. Navarro, Genetical Research 79 (2002) 129–139.
date_created: 2018-12-11T12:07:55Z
date_published: 2002-05-23T00:00:00Z
date_updated: 2023-06-06T11:23:19Z
day: '23'
doi: 10.1017/S0016672301005493
extern: '1'
external_id:
  pmid:
  - '12073551'
intvolume: '        79'
issue: '2'
language:
- iso: eng
month: '05'
oa_version: None
page: 129 - 139
pmid: 1
publication: Genetical Research
publication_identifier:
  issn:
  - 0016-6723
publication_status: published
publisher: Cambridge University Press
publist_id: '1832'
quality_controlled: '1'
scopus_import: '1'
status: public
title: 'Extending the coalescent to multilocus systems: the case of balancing selection'
type: journal_article
user_id: ea97e931-d5af-11eb-85d4-e6957dddbf17
volume: 79
year: '2002'
...