Supergene

A supergene is a chromosomal region encompassing multiple neighboring genes that are inherited together because of close genetic linkage, i.e. much less recombination than would normally be expected.

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.

The earliest use of the term "supergene" may be in an article by A. Ernst (1936) in the journal Archiv der Julius Klaus-Stiftung für Vererbungsforschung, Sozialanthropologie und Rassenhygiene.

[6] Classically, supergenes were hypothesized to have evolved from less tightly-linked genes coming together via chromosomal rearrangement or reduced crossing over, due to selection for particular multilocus phenotypes.

For instance, in Batesian mimicry supergenes in species such as Papilio memnon, genes are required to affect hind-wing, fore-wing, and body colour, and also the presence or absence of long projections (the "tails" of swallowtail butterflies).

Furthermore, in Paratettix texanus there appears to be complete suppression of crossing-over among 24 out of 25 of the colour-pattern genes, which can be distinguished by comparing their effects with those found in other species.

Analysis of Nabour's data by Darlington & Mather concluded that the genes responsible for the morphs of Paratettix texanus have been gradually aggregated into a group which acts as a single switch-mechanism.

That crossing-over can be suppressed by selection has been known for many years; Detlefsen and Roberts were able to reduce recombination between the loci for white eyes (w) and miniature wings (m) in Drosophila melanogaster from the normal 36% to 6% in one line and 0.6% in another.