Epistasis is the phenomenon whereby one polymorphism’s effect on a trait depends on other polymorphisms present in the genome(Hemani et al. 2014). Although it has been proved to shape genetic variation and contribute to differences within and between populations for long time, there is still lack of empirical evidence to show genomic footprint shaped by epistasis.
Here, Corbettdetig et al(2013) designed a simple approach to capture the genotype ratio distortion caused by epistasis using a large panel of Drosophila melanogaster. In brief, Corbettdetig and colleagues first create the Drosophila Synthetic Population Resource(DSPR) using strains original from diverse geographic location (Extended Data Fig.1). And the PCA analysis (Extended Data Fig.2) indicate there is no residual population structure.
In these DSPR population, the unfavourable allelic combinations will be under-represented if epistasis effect virtually exist. And the authors do found such under-representation which corresponding to genotype ratio distortion (GRD) in 22 pairs of interacting alleles(Fig. 1).
These genomic incompatible alleles were confirmed using extra cross experiment which indicate a significant decrease of reproductive fitness. Meanwhile, Corbettdetig and colleagues also screen for GRD in two additional plant species. 7 GRD instances in Arabidopsis and 5 in maize were detected using same method. So it could be concluded that fitness epistasis is widespread within natural population. More importantly, it indicates that the raw material to drive reproductive isolation is segregating contemporaneously within species and does not necessarily require the emergence of incompatible mutations independently derived and fixed in allopatry.
Reference:
Corbett-Detig, R., Zhou, J., Clark, A., Hartl, D., & Ayroles, J. (2013). Genetic incompatibilities are widespread within species Nature, 504 (7478), 135-137 DOI: 10.1038/nature12678
Hemani, G., Shakhbazov, K., Westra, H., Esko, T., Henders, A., McRae, A., Yang, J., Gibson, G., Martin, N., Metspalu, A., Franke, L., Montgomery, G., Visscher, P., & Powell, J. (2014). Detection and replication of epistasis influencing transcription in humans Nature, 508 (7495), 249-253 DOI: 10.1038/nature13005