Risco off-target
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
Homologia × (1-MM/5)
About this calculator
The off-target risk calculator estimates the likelihood of CRISPR acting on unintended genomic sites. It uses sequence homology between the target and other genomic regions multiplied by a factor accounting for mismatch numbers (MM). Higher homology and fewer mismatches increase off-target risk.
The formula Homology × (1-MM/5) is a simplified model. Homology measures sequence similarity (0 to 1), while (1-MM/5) adjusts for mismatch impact. For example, 5 mismatches yield a 0.8 factor, lowering the calculated risk.
Use this tool in gene-editing projects to prioritize low-risk targets. It helps guide target selection but cannot replace deeper analyses like sequence mapping or experimental testing. Always combine it with other methods for safety.
Note: The calculator ignores factors like epigenetic context or cell activity. Results require caution, especially in human therapies. Consult experts before applying genetic edits in clinical settings.
Frequently asked questions
How does the calculator estimate off-target risk?
It combines similarity between target and other sequences (homology) with mismatch count using the formula Homology × (1-MM/5).
What is the purpose of the (1-MM/5) factor?
This factor reduces calculated risk as mismatches increase, reflecting lower enzyme activation probability in divergent sequences.
Is the tool accurate enough for clinical use?
No. It is a simplified model. Results must be validated with sequencing or in vitro tests.
Which CRISPR systems is the calculation valid for?
It works for sequence-homology-based systems like classic CRISPR-Cas9, but not for variants using modified guide RNAs.
How can results improve editing accuracy?
Prioritize sequences with low calculated risk and combine with DNA secondary structure analysis and epigenetic context evaluation.