Ka/Ks Ratio Calculator

The Ka/Ks Ratio Calculator compares two protein-coding DNA sequences to measure the evolutionary pressure acting on a gene — whether natural selection is driving change, removing it, or letting mutations accumulate freely. Paste your Reference Sequence and Comparison Sequence, then select a Genetic Code and Calculation Method to get the Ka/Ks ratio (ω). Secondary outputs include the nonsynonymous rate (Ka), synonymous rate (Ks), Selection Pressure classification, and the counts of synonymous and nonsynonymous sites.

Protein-coding DNA sequence without gaps

Homologous protein-coding DNA sequence

Remove positions with gaps in either sequence

Results

Ka/Ks Ratio (ω)

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Ka (Nonsynonymous Rate)

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Ks (Synonymous Rate)

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Selection Pressure

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Synonymous Sites

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Nonsynonymous Sites

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Frequently Asked Questions

What does the Ka/Ks ratio tell us about selection pressure?

Ka/Ks ratio (ω) indicates the type of selection: ω < 1 suggests purifying selection (harmful mutations removed), ω = 1 indicates neutral evolution, and ω > 1 suggests positive selection (beneficial mutations favored).

What is the difference between Ka and Ks?

Ka is the rate of nonsynonymous substitutions that change amino acids, while Ks is the rate of synonymous substitutions that don't change amino acids. Their ratio helps measure selection pressure on protein function.

Which calculation method should I choose?

Nei-Gojobori (1986) is the most widely used and standard method. Li-Wu-Luo is good for closely related sequences, while Modified Nei-Gojobori corrects for multiple substitutions at the same site.

What input format is required for the sequences?

Input sequences should be protein-coding DNA sequences in FASTA format or raw nucleotide sequences. The sequences must be properly aligned and of the same length for accurate calculations.

How do I interpret a Ka/Ks ratio close to 1?

A Ka/Ks ratio near 1 suggests neutral evolution where both synonymous and nonsynonymous mutations are equally tolerated, indicating relaxed selection pressure on the protein.

Can I use this calculator for any type of DNA sequence?

This calculator is specifically designed for protein-coding sequences. Non-coding regions don't have synonymous and nonsynonymous sites, so Ka/Ks analysis is not applicable to them.

What does it mean when Ka/Ks is greater than 1?

Ka/Ks > 1 indicates positive selection, where nonsynonymous changes are favored over synonymous ones. This suggests the protein is evolving under selective pressure for functional changes.

Should I remove gaps from my sequence alignment?

Yes, it's recommended to remove positions with gaps as they can introduce artifacts in the calculation. Gaps represent insertions/deletions rather than substitutions and should be excluded from Ka/Ks analysis.