Please enable JavaScript.
Coggle requires JavaScript to display documents.
Supergenes and their role in evolution - Coggle Diagram
Supergenes and their role in evolution
References
Thompson MJ, Jiggins CD. 2014. Supergenes and their role in evolution. Heredity. 113(1):1–8. doi:
https://doi.org/10.1038/hdy.2014.20
.
Introduction
The fitness of alleles can be enhanced by a genetic backbone that maintains favorable combinations of alleles and reduces the production of recombinant genotypes
Supergenes provide a mechanism where complex balanced polymorphisms can be maintained without the generation of maladaptive intermediates which greatly affects morphological adaption
Modelling the origins of a supergene
Selection can act to modify the recombination rate between two already linked loci
Rate of change in recombination is greatest when the modifier is already in strong linkage disequilibrium with the loci under selection
With this information, it was realized that a multilocus multiallelic polymorphism is unlikely to be stable without some initial degree of linkage
Using frequency-dependent disruptive selection it was demonstrated that the genetic architecture underlying polymorphism can evolve from an initially multilocus architecture towards genetic control by one or a few major effect loci
A new perspective from developmental genetics
The supergene hypothesis has been criticized by developmental biologists such as Nijhout
This theory helps explain how one locus can take control of a complex phenotype
Nijhout suggested that distinct phenotypes map to a single coding region, suggesting that switching of multiple phenotypes can be explained by a single transcription factor with complex downstream targets or by alternative splicing of a single gene
Similarly, West-Eberhard believed a single regulatory locus with complex downstream effects could act in the same way as the linked set of loci described in the classical theory of a supergene
Emerging evidence from empirical examples show that in many cases supergenes show high levels of linkage disequilibrium and chromosomal rearrangements which provides support for the classical theory of a supergene which involves multiple linked and co-adapted elements
A new definition
The newest definition of a supergene is a genetic architecture that involves multiple linked functional genetic elements that allow switching between discrete, complex phenotypes maintained in a stable local polymorphism
To qualify as a supergene, a biological system needs to indicate clear evidence of a complex phenotype of multiple co-adapted elements, with a pattern of inheritance practically identical to alternative alleles at a single locus, and maintained in a polymorphism in a single population
Mimicry
Mimicry often leads to negative frequency-dependent selection, creating a balanced polymorphism and the need for correlated expression of co-adapted characters
An example can be seen in the South American butterfly in H. numata
Mapping of the wing pattern locus of H. numata and genomic comparison with related species have show that high linkage disequilibrium in wild populations results from multiple chromosomal rearrangements that are associated with different wing patterns
Social polymorphism
The "green beard" hypothesis was originally accepted which stats that altruism could evolve if altruistic behavior were directed towards other carriers of the altruistic allele
An example of social polymorphism is seen in the Imported Red Fire Ant S. invicta where the odorant-binding protein gene Gp-9 and the linked gene pgm-3 influences worker behavior and queen reproductive strategies
Gp-9 is considered a "green beard" due to its association with the tolerance of multiple queens within a singular nest
Conclusion
Physical linkage reduces the probability that a particular trait combinations are rearranged by recombination to give offspring with novel combinations
These findings has the potential to offer insight into convergent evolution of particular architectures and the role that the genome structure can have in adaptation