Classification By Fitness or Trait Value
Two-locus epistatic interactions can be either synergistic (enhancing the effectiveness) or antagonistic (reducing the activity). In the example of a haploid organism with genotypes (at two loci) AB, Ab, aB or ab, we can think of the following trait values where higher values suggest greater expression of the characteristic (the exact values are simply given as examples):
| AB | Ab | aB | ab | |
| No epistasis (additive across loci) | 2 | 1 | 1 | 0 |
| Synergistic epistasis | 3 | 1 | 1 | 0 |
| Antagonistic epistasis | 1 | 1 | 1 | 0 |
Hence, we can classify thus:
| Trait values | Type of epistasis |
| AB = Ab + aB − ab | No epistasis, additive inheritance |
| AB > Ab + aB − ab | Synergistic epistasis |
| AB < Ab + aB − ab | Antagonistic epistasis |
Understanding whether the majority of genetic interactions are synergistic or antagonistic will help solve such problems as the evolution of sex.
Read more about this topic: Epistasis
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