Re: What DNA samples would be good ones to choose for preservation?

Dear teacher,

I should begin by telling you that DNA is said to be highly stable. There
is no difference between samples of DNA. All DNA molecules are the same
and the only difference of storage will be triggered by solvant (buffer)
in which the DNA is dissolved. I believe that you can readily store DNA at
4 degrees Celsius for a long time without fearing any degradation. As a
buffer, I would suggest a TE solution (10 mM Tris.HCl-1mM EDTA, pH 7.5).

In molecular biology, the integrity of DNA is often essential. And here,
we could mean many things for the word 'integrity'. First of all, you
should know that DNA molecules have their biological properties from their
sequences and/or structures (secondary and tertiary). So, in your case,
you should try to find out in what aspect you are interested. Assuming
that you're only interested in the chemical stability (no bother with
secondary or tertiary structure), I would suggest an electrophoresis
method (that is an agarose or acrylamide gel). The goal is to denature the
DNA so that the migration on the gel will be strictly based on the length
(charge) of the DNA. If all your DNA molecules have the same length, you
should see one band on your gel. If your DNA is degraded, you should see a
'smear'. However, you have to take care that your gel is really in
denaturing conditions so that the smear is not a population of different
conformations of DNA. However, if you are working with plasmids (like
99.5% DNA scientists do !), you will always get about three bands on an
agarose gel. This is because there is always a population of plasmids that
have a nick (a break) in the backbone somewhere. This is not a bad sign
for your DNA. It's just normal. Anyway, as I said in the beginning, there
should be no real problem in storing your DNA at 4 degrees Celsius.

Hope this helps,

Sincerely,

Daniel.