| Main mechanism | Expression in identical twins |
| Intrinsic |
|
| Gene expression noise | Discordanta |
| Stochastic switching in gene expression noise | Discordant |
| Germinal mutations/chromosome recombination and shuffling | Concordant |
| Random monoallelic expression (epigenetically-driven) | Discordanta |
| Stochastic epistasis | Concordant |
| Ecological |
|
| Non-shared environment | Discordant |