Before you start

Reagents and materials

Totals are for 1 gels (+10% extra). Per-gel (50 mL) amounts are in the middle column.

Reagent	Per gel (50 mL)	Total
1× TAE or TBE bufferfor the gel; more for running buffer	50 mL	50 mL
Agarose (1% gel)	0.5 g	0.5 g
DNA stain (e.g. SYBR Safe 1:10,000)	5 µL	5 µL
6× loading dye	10 µL	10 µL
DNA ladder	5 µL	5 µL

Dilute to 1× (40 mM Tris-acetate, 1 mM EDTA) for gels and running buffer.

Use at 0.5× or 1×. TBE resolves small fragments (< 1 kb) more sharply; TAE is better for gel extraction.

Tick steps as you go (saved in this browser). Steps with a clock have a built-in timer.

Dissolve agarose
Add agarose to 1× buffer and microwave in short bursts with swirling until completely clear.
Cool and add stain
Cool to about 55–60 °C (you can hold the flask), add the stain and swirl without bubbles.
Cast
Pour into the tray with the comb and let set 20–30 min at room temperature.
Load
Place the gel in the tank, cover with 1× buffer, remove the comb and load samples mixed with loading dye and a ladder.
Run
Run at 5–8 V/cm (about 100–120 V for a mini gel) toward the positive (red) electrode until the dye front has moved far enough.
Image
Image on a blue-light or UV transilluminator; minimise UV exposure if you will extract DNA.

Problem	What to check or change
Smeared bands	Load less DNA, lower the voltage, use fresh buffer, check for degraded samples.
Wavy or distorted bands	Remove the comb carefully, avoid salt-heavy samples, ensure the gel is fully set.
Faint bands	Load more, check the stain, image with longer exposure.

Ethidium bromide is a mutagen; prefer safer stains. Protect eyes and skin from UV. Hot agarose can boil over.