GC Skew Calculator

Analyze GC skew to identify replication origins and termini in bacterial genomes using sliding window and cumulative analysis

What is GC Skew?

GC skew is a measure of DNA strand asymmetry calculated as (G-C)/(G+C), where G and C are the frequencies of guanine and cytosine. It reveals compositional bias between leading and lagging strands in bacterial genomes, helping identify replication origins (minimum cumulative skew) and termini (maximum cumulative skew).

How to Use This GC Skew Calculator

  1. Paste your DNA sequence (FASTA or plain text)
  2. Adjust window and step sizes for analysis resolution
  3. View skew plots and statistics automatically generated
  4. Identify potential origin/terminus from cumulative plot extrema

When to Use

This tool is useful when you need to:

  • Identify replication origins in bacterial genomes
  • Locate replication termini positions
  • Analyze strand compositional bias
  • Study genome organization and evolution

Example Input

Circular bacterial genome segment:

GCGCGCGCGCATATATATAGCGCGCGCGC...

Try with the Example button for a demonstration sequence.

Example Output

GC skew analysis results:

Position 1000: GC Skew = 0.125
Position 2000: GC Skew = -0.087
Cumulative minimum at: 45000 bp

FAQ

Q: What do the cumulative skew extrema indicate?
A: Minimum indicates likely replication origin; maximum indicates terminus.

Q: What window size should I use?
A: For bacterial genomes, 10kb windows with 1kb steps work well. Adjust based on genome size.