Clone Probability Calculator
Calculate probability of finding a correct clone from a library. Uses Poisson distribution: P(at least 1) = 1 - e^(-N/F) where N = clones screened and F = library complexity. For molecular cloning.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Clone Probability Calculator | — | P = 1 - e^(-N/F) | probability |
Step-by-Step Examples
After ligation of insert into vector, 500 white colonies plated (on X-gal). Assume 10% have insert.
- N=500, F=500 (total), correct=50 clones expected
- P = 1 - e^(-50/500 x 500) = 1 - e^-50 ≈ 100%
- Actually: screen 5 to have 99% confidence of finding 1 correct
Screen 10,000 plaques from library of 10^6. One desired clone per library.
- N=10000, F=10^6, correct=1
- P = 1 - e^(-10000/10^6) = 0.00995 = 1%
- Need N=4600 for 99% confidence
5000 colonies from 10^5 library, 100 putative hits.
- P = 1-e^(-5000x100/10^5) = 1-e^-5 = 99.3%
- Very high probability of finding at least one correct clone
- Could reduce to 2303 for 90% confidence
Real-World Applications
Common Mistakes to Avoid
Screen more clones than statistically required. Biological variability means library complexity estimates are often optimistic.
Some sequences are toxic to E. coli and underrepresented. High-complexity libraries may have poor coverage of certain sequences.
Colony PCR confirms insert presence but not sequence. Sequence at least 3 positive clones to find one without mutations.