- [Neil] An Internal Control is it's a type of control that occurs
within every like biological sample that you have, you know, you might
have one group of samples that you designate a control group, and you
have another group of samples that you designate a treatment group.
But independent of those two categorizations, There is also some
quality of them, that you are keeping track of across all the samples
that you haven't expected result for. That, to me, is an internal
control.

So one example of an internal control actually, is used quite
frequently when you are looking at things like gene expression. So
let's say you have some new drug treatment that you are examining, and
you have two sets of samples. One you give the drug treatment and one
you give a placebo, so something that should not have any effect. And
you want to see what the effect of this drug is, on expression of some
interesting gene that you really care about. So in one set of samples,
you might expect the gene to come on the other set of samples, you
expect the gene to not turn on. But across all of the samples, you
should also have certain housekeeping genes. So to say that you're
also keeping track of so regardless of what the drug treatment is, you
have a set of genes that you keep track of, and all the samples where
you expect to have pretty consistent levels of expression. That's a
type of internal control.

So the nice thing about the agar sandwich is that it has a couple of
different internal controls. So within each biological sample for each
seedling, there are specific observations that I'm expecting to occur
in each seedling and from my own research, looking at the agar
sandwich, every sample has an internal negative control so between the
two blocks of agar media there is that air gap in between. And we knew
from previous observations that exposure to air should have no
inductive effect on root branch production. So the fact that there's a
lack of induction indicates that that is a negative control Within my
experiment with the agar sandwich within every sample, you always have
the root in contact with unaltered regular standard media and that
should induce root branching. So that's the type of positive control
to show that the root is capable of producing branches at all.