Supergene

About: Supergene is a research topic. Over the lifetime, 120 publications have been published within this topic receiving 3452 citations.

Evolution of supergene families associated with insecticide resistance.

Abstract: The emergence of insecticide resistance in the mosquito poses a serious threat to the efficacy of many malaria control programs. We have searched the Anopheles gambiae genome for members of the three major enzyme families-the carboxylesterases, glutathione transferases, and cytochrome P450s-that are primarily responsible for metabolic resistance to insecticides. A comparative genomic analysis with Drosophila melanogaster reveals that a considerable expansion of these supergene families has occurred in the mosquito. Low gene orthology and little chromosomal synteny paradoxically contrast the easily identified orthologous groups of genes presumably seeded by common ancestors. In A. gambiae, the independent expansion of paralogous genes is mainly a consequence of the formation of clusters among locally duplicated genes. These expansions may reflect the functional diversification of supergene families consistent with major differences in the life history and ecology of these organisms. These data provide a basis for identifying the resistance-associated enzymes within these families. This will enable the resistance status of mosquitoes, flies, and possibly other holometabolous insects to be monitored. The analyses also provide the means for identifying previously unknown molecules involved in fundamental biological processes such as development.

A supergene determines highly divergent male reproductive morphs in the ruff

Abstract: Three strikingly different alternative male mating morphs (aggressive 'independents', semicooperative 'satellites' and female-mimic 'faeders') coexist as a balanced polymorphism in the ruff, Philomachus pugnax, a lek-breeding wading bird. Major differences in body size, ornamentation, and aggressive and mating behaviors are inherited as an autosomal polymorphism. We show that development into satellites and faeders is determined by a supergene consisting of divergent alternative, dominant and non-recombining haplotypes of an inversion on chromosome 11, which contains 125 predicted genes. Independents are homozygous for the ancestral sequence. One breakpoint of the inversion disrupts the essential CENP-N gene (encoding centromere protein N), and pedigree analysis confirms the lethality of homozygosity for the inversion. We describe new differences in behavior, testis size and steroid metabolism among morphs and identify polymorphic genes within the inversion that are likely to contribute to the differences among morphs in reproductive traits.

Linkage disequilibrium due to random genetic drift in finite subdivided populations.

Abstract: In order to clarify the mechanisms responsible for the observed linkage disequilibrium, such as that found between markers in the major histocompatibility complex of man and mouse, linkage disequilibrium between two linked loci was studied for a finite population with a subdivided structure. The infinite allele model was used. In analogy with the subdivision of the inbreeding coefficient, the linkage disequilibrium coefficient was subdivided, and various variance components of disequilibrium were defined. It was found that the disequilibrium components may get very large when migration is limited if the correlation of alleles at the two loci within a colony is taken relative to that of the entire population. In other words, with limited migration, random genetic drift of gamete types prevails in each colony. A possible test in which the variance components of disequilibrium are compared is suggested; the test discriminates between epistatic natural selection and limited migration, showing the former as the main cause of the observed linkage disequilibrium. It is pointed out that the major histocompatibility complex polymorphism is in accord with the population genetics model of multigene families that incorporate gene conversion or double unequal crossing-over between the loci in the supergene family.

Supergenes and their role in evolution.

Abstract: Adaptation is commonly a multidimensional problem, with changes in multiple traits required to match a complex environment. This is epitomized by balanced polymorphisms in which multiple phenotypes co-exist and are maintained in a population by a balance of selective forces. Consideration of such polymorphisms led to the concept of the supergene, where alternative phenotypes in a balanced polymorphism segregate as if controlled by a single genetic locus, resulting from tight genetic linkage between multiple functional loci. Recently, the molecular basis for several supergenes has been resolved. Thus, major chromosomal inversions have been shown to be associated with polymorphisms in butterflies, ants and birds, offering a mechanism for localised reduction in recombination. In several examples of plant self-incompatibility, the functional role of multiple elements within the supergene architecture has been demonstrated, conclusively showing that balanced polymorphism can be maintained at multiple coadapted and tightly linked elements. Despite recent criticism, we argue that the supergene concept remains relevant and is more testable than ever with modern molecular methods.