DNA Substitution Rate Calculator
Calculate dN (nonsynonymous) and dS (synonymous) substitution rates. dN/dS (omega) reveals selection: >1 positive, <1 purifying, ≈1 neutral. Core tool of molecular evolution.
🧬 Molecular Evolution📐 omega = dN/dS🧬 Biology
Synonymous substitutions Ks
Synonymous sites SS
Nonsynonymous substitutions Ka
Nonsynonymous sites NS
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| DNA Substitution Rate Calculator | — | omega = dN/dS | substitutions/site |
Step-by-Step Examples
Example 1
Housekeeping Gene
30 Ks over 200 SS; 3 Ka over 600 NS.
- dS=0.15, dN=0.005
- omega=0.005/0.15=0.033
- Strong purifying selection — highly conserved function
✓ omega=0.033 — strong purifying selection
Example 2
Immune Gene
40 Ks/150 SS; 50 Ka/300 NS.
- dS=0.267, dN=0.167
- omega=0.167/0.267=0.625
- Moderate purifying selection — some positive sites possible
✓ omega=0.625 — moderate
Example 3
Venom Protein
10 Ks/100 SS; 25 Ka/200 NS.
- dS=0.100, dN=0.125
- omega=0.125/0.100=1.25
- Positive selection — gene evolving adaptively
✓ omega=1.25 — positive selection detected
Real-World Applications
Comparative Genomics
Genome-wide dN/dS scans identify positively selected genes.
Host-Pathogen Coevolution
Arms race genes show high omega in surface proteins.
Molecular Evolution
Estimate selective constraints on protein evolution.
Drug Targets
Low dN/dS indicates conserved function — good drug targets.
Common Mistakes to Avoid
⚠️
Saturation at high divergence
dS>1 indicates multiple substitutions at same site. Use Jukes-Cantor correction.
⚠️
Average omega misses site-specific selection
Use PAML site models to detect positively selected codons within conserved proteins.
⚠️
Assuming synonymous = neutral
Some synonymous codons affect splicing, codon usage, mRNA stability — not fully neutral.
Frequently Asked Questions
What is dN/dS? ▾
Ratio of nonsynonymous (amino acid-changing) to synonymous (silent) substitution rates. Synonymous used as neutral reference.
What does dN/dS > 1 mean? ▾
More amino acid changes than expected under neutrality — positive (adaptive) selection driving protein evolution.
What is purifying selection? ▾
Negative selection removing deleterious mutations. Most proteins show omega 0.01-0.5 reflecting strong conservation.
What is PAML? ▾
Phylogenetic Analysis by Maximum Likelihood — software for calculating dN/dS and detecting positive selection at specific codons.
What are typical omega values? ▾
Housekeeping genes: 0.01-0.1. Average protein: 0.1-0.3. Immune genes: 0.3-0.8. Positively selected: >1.