Higher Percentage Agarose (e.g., 1-2%):
* Smaller pore size: This allows for better separation of smaller DNA fragments. The gel acts like a sieve, trapping smaller fragments for longer, causing them to migrate more slowly.
* Used for:
* Analyzing DNA fragments less than 1000 base pairs (bp)
* High-resolution separation of small fragments
* Restriction fragment length polymorphism (RFLP) analysis
Lower Percentage Agarose (e.g., 0.5-0.8%):
* Larger pore size: This allows for faster migration of larger DNA fragments.
* Used for:
* Separating larger DNA fragments (over 1000 bp)
* Analyzing genomic DNA
* Pulsed-field gel electrophoresis (PFGE) for very large DNA molecules
Key Considerations:
* Fragment Size: The size of the DNA fragments you are trying to separate is the primary factor in determining the gel percentage.
* Resolution: Higher percentage gels provide higher resolution for separating small fragments, while lower percentage gels are better for separating large fragments.
* Migration Time: Higher percentage gels slow down migration, requiring longer running times. Lower percentage gels allow for faster migration.
Example:
If you are analyzing the products of a restriction enzyme digest containing fragments ranging from 500 to 1000 bp, you would likely choose a 1% agarose gel. If you were analyzing genomic DNA with fragments ranging from 50,000 to 100,000 bp, a 0.7% agarose gel would be more appropriate.
