During electrophoresis, gels that are run with DNA samples should always have the following:?

Question

During electrophoresis, gels that are run with DNA samples should always have the following:
(1) an unamplified control lane (i.e., a reaction tube without any DNA sample); AND

(2) a lane with a DNA ladder.

a. What would be present in the unamplified control lane? What would you expect to see in that lane after the gel is run? Explain.


b. What is a DNA ladder? What would you expect to see in that lane after the gel is run? Explain.


c. Why would these two extra lanes be helpful when analyzing your gel?

Answer 1

Since there's no DNA in the control lane, ideally you won't see ANYTHING there. As for what happens when it's not ideal... that goes in part c of your question.

The DNA 'ladder' is a bunch of segments of DNA cut to known lengths. Ideally, they're fairly equally spaced, so they stretch out like the rungs of a ladder.

Having a control is a pretty good idea just in case something went a little wacky. If you're solution WITHOUT DNA makes a band that you can see on your electrophoresis, you want to know about it so you don't confuse it for stuff you're really looking for!

And since there isn't really a good way to make a 'standard' gel with a 'standard' current that's run for a 'standard' time such that you can just get a ruler and figure out the lengths of the bands you see, the ladder does the same kind of thing. With a ladder, you can look at your unknown bands and get some information about them by comparing them to the known bands in the ladder.

Handy!