page_title: Supergene
section_title: Structure
hierarchical_section_title: Supergene / Structure
caption_attribution_description: English: An example of heterostyly: Pin (A) and thrumb (B) flowers of the common primrose (Primula vulgaris), a distylous species. Pin and thrum flowers are borne by different plants. This genetically controled polymorphism enhances allogamy. Legend: (1) corolla, (2) calix, (3) stamen, (4) pistil. Français&#160;: Un exemple d' hétérostylie: fleurs longuistylée (A) et brévistylée (B) de primevère commune Primula vulgaris, une espèce dystilique. Les fleurs loguistylées et brévistylées se forment sur des plants différents. Ce polymorphisme sous contrôle génétique favorise l'allogammie. Légende: (1) corole, (2) calice, (3) étamines, (4) pistil.
context_page_description: A supergene is a group of neighboring genes on a chromosome which are inherited together because of close genetic linkage and are functionally related in an evolutionary sense, although they are rarely co-regulated genetically.
context_section_description: Supergenes have cis-effects due to multiple loci (which may be within a gene, or within a single gene's regulatory region), and tight linkage.  They are classically polymorphic, and different elements code for different fitness effects which combine to form a coherent or epistatic whole. The two classic supergenes are (1) the Primula heterostyly locus, which controls "pin" and "thrum" types, and (2) the locus controlling Batesian mimetic polymorphism in Papilio memnon butterflies.  For example, pin and thrum morphs of Primula have effects on genetic compatibility (pin style x thrum pollen, or thrum style x pin pollen matings are successful, while pin x pin, and thrum x thrum matings are rarely successful due to pollen-style incompatibility), and have different style length, anther height in the corolla tube, pollen size, and papilla size on the stigma. Each of these effects is controlled by a different locus in the same supergene, but recombinants are occasionally found with traits combining those of "pin" and "thrum" morphs.
  Gene complexes, in contrast, are simply tightly linked groups of genes, often created via gene duplication (sometimes called tandem duplication if the duplicates remain side-by-side). Here, each gene has similar though slightly diverged function.  For example, the human major histocompatibility complex (MHC) region is a complex of tightly linked genes all acting in the immune system, but has no claim to be a supergene, even though the component genes very likely have epistatic effects and are in strong disequilibrium due in part to selection.
caption: Pin(A) and thrum (B) flowers of Primula vulgaris are controlled by a supergene.
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