supergene

A supergene is a cluster of neighboring genes on a chromosome that are inherited together as a unit because recombination between the loci is suppressed in heterozygotes. This suppression of recombination enables multiple loci to act in a coordinated way to control a complex phenotype, producing discrete, coadapted phenotypic states rather than a continuous range of forms. Supergenes can arise when a structural rearrangement, such as a chromosomal inversion, reduces or eliminates recombination within the region, though other mechanisms that limit crossing over can also contribute.

Formation and maintenance of a supergene often involve selection for favorable combinations of alleles across several genes. When a rearrangement captures such alleles, the resulting haplotypes become maintained as distinct variants, or morphs, within a population. Because the genes within a supergene interact, breaking up the combination by recombination can reduce fitness, reinforcing the maintenance of the linkage block.

Examples of known supergenes include the social chromosome of the red imported fire ant (Solenopsis invicta), where a large region on chromosome 16 influences colony structure and queen number; the P supergene in some Heliconius butterfly species, which governs mimicry patterning and includes multiple patterning genes within an inverted segment; the rubbing of the mating strategies in the ruff (Calidris pugnax), which is controlled by a large inversion on chromosome 11; and the plumage and mating behaviors of the white-throated sparrow (Zonotrichia albicollis), associated with a large inversion on chromosome 2.

Supergenes illustrate how recombination suppression can maintain complex adaptive trait architectures as single inherited units, with implications for ecology, evolution, and speciation.