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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Intergradation</span></span>
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<p>In <a href="Zoology" title="Zoology">zoology</a>, <b>intergradation</b> is the way in which two distinct <a href="Subspecies" title="Subspecies">subspecies</a> are connected via areas where <a href="Populations" class="mw-redirect" title="Populations">populations</a> are found that have the characteristics of both. There are two types of intergradation: primary and secondary intergradation.
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<div class="mw-heading mw-heading2"><h2 id="Primary_intergradation">Primary intergradation</h2></div>
<p>This occurs in cases where two subspecies are connected via one or more intermediate populations, each of which is in turn intermediate to its adjacent populations and exhibits more or less the same amount of <a href="Genetic_variability" title="Genetic variability">variability</a> as any other population within the <a href="Species" title="Species">species</a>. Adjacent populations and subspecies are subject to <a href="Cline_(population_genetics)" class="mw-redirect" title="Cline (population genetics)">cline</a> intergradation, and in these situations it is usually taken for granted that the clines are causally related (by <a href="Natural_selection" title="Natural selection">natural selection</a>) to <a href="Environmental_gradient" title="Environmental gradient">environmental gradients</a>.<sup id="cite_ref-M&A91_1-0" class="reference"><a href="#cite_note-M&A91-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
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<div class="mw-heading mw-heading2"><h2 id="Secondary_intergradation">Secondary intergradation</h2></div>
<p>When contact between a geographically isolated subspecies is reestablished with the main body of the species or with another isolate subspecies, interbreeding takes place as long as the isolate has not yet evolved an effective set of isolating mechanisms. Consequently, a relatively distinct zone or belt of <a href="Hybrid_(biology)" title="Hybrid (biology)">hybridization</a> will develop depending on the degree of <a href="Genetics" title="Genetics">genetic</a> and <a href="Phenotypic" class="mw-redirect" title="Phenotypic">phenotypic</a> difference that was achieved by the previously isolated <a href="Subspecies" title="Subspecies">subspecies</a>.<sup id="cite_ref-M&A91_1-1" class="reference"><a href="#cite_note-M&A91-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>
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<div class="mw-heading mw-heading2"><h2 id="See_also">See also</h2></div>
<ul><li><a href="Ring_species" title="Ring species">Ring species</a></li></ul>
<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>
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<li id="cite_note-M&A91-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-M&A91_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-M&A91_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text">Mayr E, Ashlock PD (1991). <i>Principles of Systematic Zoology</i>. Second edition. McGraw-Hill. <style data-mw-deduplicate="TemplateStyles:r1238218222">
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</style><a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>0-07-041144-1</bdi>.</span>
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