Hello Guillaume,

basically it´s due to overloading. SybrGreen is at least 4 times more sensitive than EtBr. You could either pipette less DNA into the slots of your gel or you could dilute your stain further. Why not make 20.000, 40.000 or 50.000fold dilutions of SybrGreen and see if the problem is solved?

Best regards

Dirk

As Dirk mentioned, it could be due to overloading! Are you running the gel at a higher voltage?

I remember seeing something like this and it was because the undergrad was making the agarose gel in water instead of 1X TAE

Dear Grzych,

If you are using 1X TAE ,so try to shift to 1X TBE which is more suitable for small DNA and try to use freshly prepared buffer with adjusted pH to preferably 8.5. At what voltage and time are you running your gel? look to the current as well with the voltage you used currently

Hi,

few easy check points to consider!

-pH of buffer (what ever it is TBE/TAE) at ~8.5

-make sure, buffer used to prepare gel and poured in tanks for running are at same  strength (prepare same strength for both purposes) preferably 1X / 0.5X 

-thorough melting of agarose (see not to have moving undissolved agarose particles  before casting the gel)

-make sure gel formed evenly (keep the gel at RT for few more minutes to form firmly) but not to dry it at any case, dont leave your agarose out side after gel formation for longer, place it in gel tank.

-load the reduced volumes of ladders or DNA samples (or for ladders refer the product sheet given along with it for each load volume)

-do not exceed the voltage, always keep room at low temp while running gel, if this is not feasible keep a cool pak beneath the buffer tank while electrophoresing (higher voltage makes the gel melt due to produced heat in buffer/gel and your set up goes waste). For 2% gels in 1X TBE, use voltage not more than 140-150.

-do not incorporate any alcoholic liquids into yous samples (for loading into gel)

-for staining the gel, see the exact proportion recommended by SYBR dye product leaflet. dont exceed the dye volume as it causes the increased background. which makes your study difficult.

See that you store your reagents at recommended conditions. 

I guess your ladders (1kb/100bp) are degraded or digested, use fresh tips always to handle any reagent. dont open and keep the vials for longer periods, this may lead to get any airborne organisms trapped in the vials by chance.