# Epistasis

Epistasis is about interactions between mutations in an evolving systems.

• No epistasis corresponds to mutation effects “stacking” without any particular kind of interaction.
• Positive epistasis happens when the combined effect of the two mutations is more positive than the sum of their contributions.
• Negative epistasis is the same principle with negative effects.

Cancer is an example negative epistasis where the addition of a lot of mutations is needed to obtain a cancerous cell.

These interactions make the biological systems so complicated to study and understand.

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