However, this gene is a key cytokine-binding receptor in the immune system, so balancing selection related to the host response to pathogens cannot be excluded.
The pattern of genetic variability showed little evidence for maintenance of protein variation by balancing selection in A. gambiae immune system.
This observation is probably attributable to the fact that many of the genes in the immunity system evolve under balancing selection in human populations for a heterozygote advantage, which would reduce the level of population differentiation [ 17, 18].
Considering that there is evidence of balancing selection on male reproductive proteins in several systems [80] [83] it is not unreasonable to hypothesize that it might also be playing a role in HMS.
The first genome scan for signatures of balancing selection has also confirmed an enrichment of immune system and host-pathogen interaction related genes [ 1].
In categories of genes where H|H is a weak or negative predictor of eQTLs, such as innate immune system genes, this would be consistent with balancing selection acting on such eQTLs.
We have not identified genes that show increased polymorphism in high frequency, which would be expected under a scenario of balancing selection, which is expected for antigens under selection by the host immune system.
Furthermore, these results indicate that the olfactory receptors and the immune system (MHC genes) have most likely undergone a process of balancing selection both in the domestic European pig breeds and in the wild boar.
However, the underlying mechanisms of geographic clines in morph (or allele) frequency are little understood in real examples in the wild, probably because balancing selection among many fitness components has not been sufficiently tested in each polymorphic system.
But not all variation in nature arises from balancing selection.
Actually, small values correspond to positive selection and large values to balancing selection.
