--- _id: '4328' abstract: - lang: eng text: The hybrid zone which forms when two partially incompatible populations meet acts as a barrier to gene flow. We discuss electrophoretic and theoretical evidence on the strength of such barriers. Hybrid zones generally involve considerable electrophoretic divergence. The enzyme clines are consistent in position and width; in some cases, they show consistently asymmetric patterns of introgression. This consistency suggests that the clines are maintained primarily by the indirect effects of selection at linked loci, rather than by the effect of each individual locus on fitness. A cline at a single locus will present some barrier, regardless of the selective mechanism which maintains it. However, unless the locus induces virtually complete assortment or hybrid unfitness, the barrier will be weak. Spreading the same selection over more clines gives a stronger barrier. If the clines are staggered, this barrier is still unlikely to be significant; if they coincide, and if selection is stronger than recombination, then the barrier will be very strong; its strength and asymmetry will be consistent over different loci. Thus, the taxonomic status of divergent populations cannot be inferred just from the total amount of pre- or post-mating isolation; the number of genetic differences, and the interactions between them are equally important in determining rates of gene flow. alternative_title: - Systematics Association Special Volume article_processing_charge: No 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: Godfrey full_name: Hewitt, Godfrey last_name: Hewitt citation: ama: 'Barton NH, Hewitt G. Hybrid zones as barriers to gene flow. In: Oxford G, Rollinson D, eds. Protein Polymorphism: Adaptive and Taxonomic Significance. Vol 24. Academic Press; 1983:341-359.' apa: 'Barton, N. H., & Hewitt, G. (1983). Hybrid zones as barriers to gene flow. In G. Oxford & D. Rollinson (Eds.), Protein polymorphism: Adaptive and taxonomic significance (Vol. 24, pp. 341–359). University of York, United Kingdom: Academic Press.' chicago: 'Barton, Nicholas H, and Godfrey Hewitt. “Hybrid Zones as Barriers to Gene Flow.” In Protein Polymorphism: Adaptive and Taxonomic Significance, edited by Geoffrey Oxford and David Rollinson, 24:341–59. Academic Press, 1983.' ieee: 'N. H. Barton and G. Hewitt, “Hybrid zones as barriers to gene flow,” in Protein polymorphism: Adaptive and taxonomic significance, vol. 24, G. Oxford and D. Rollinson, Eds. Academic Press, 1983, pp. 341–359.' ista: 'Barton NH, Hewitt G. 1983.Hybrid zones as barriers to gene flow. In: Protein polymorphism: Adaptive and taxonomic significance. Systematics Association Special Volume, vol. 24, 341–359.' mla: 'Barton, Nicholas H., and Godfrey Hewitt. “Hybrid Zones as Barriers to Gene Flow.” Protein Polymorphism: Adaptive and Taxonomic Significance, edited by Geoffrey Oxford and David Rollinson, vol. 24, Academic Press, 1983, pp. 341–59.' short: 'N.H. Barton, G. Hewitt, in:, G. Oxford, D. Rollinson (Eds.), Protein Polymorphism: Adaptive and Taxonomic Significance, Academic Press, 1983, pp. 341–359.' conference: end_date: 1982-07-15 location: University of York, United Kingdom name: 'SystAss: Systematics Association' start_date: 1982-07-13 date_created: 2018-12-11T12:08:17Z date_published: 1983-01-01T00:00:00Z date_updated: 2022-01-24T11:05:31Z day: '01' editor: - first_name: Geoffrey full_name: Oxford, Geoffrey last_name: Oxford - first_name: David full_name: Rollinson, David last_name: Rollinson extern: '1' intvolume: ' 24' keyword: - chemotaxonomy language: - iso: eng month: '01' oa_version: None page: 341 - 359 publication: 'Protein polymorphism: Adaptive and taxonomic significance' publication_identifier: isbn: - 978-0-1253-1780-1 issn: - 0309-2593 publication_status: published publisher: Academic Press publist_id: '1710' quality_controlled: '1' status: public title: Hybrid zones as barriers to gene flow type: book_chapter user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9 volume: 24 year: '1983' ...