Hi. It's Mr. Andersen and in this podcast I'm going to talk about mutations.
Mutations are simply changes in DNA. And why is changes in DNA bad? Well, DNA remember,
is going to be transcribed to make something called this, messenger RNA. And that's going
to be translated to make something called a protein. And that protein is going to make
you. And so if you have changes in the DNA that's going to cause changes in the messenger
RNA and that's eventually going to change the proteins. And it's eventually going to
change you. And so mutations we tend to think of as being bad. But mutations are also good.
In fact all life on our planet started with a change in the DNA that was selected for
or against creating the wonderful diversity that we have on our planet. And so when we're
thinking about mutations and how they effect the proteins, a good analogy is to think about
recipes. And so this is one of my favorite recipes. It's the Nestle Tollhouse Chocolate
Chip Cookie's recipe. And so basically what I'm going to do is I'm going to make a quick
mutation in this recipe. So if you look carefully see if you can spot the mutation. And if you
saw it. Let me go back. Now there's the mutation. So basically what we have is a point mutation
right here. So the word stiqks of butter has been changed to sticks of butter. I could
still read this recipe and I could make pretty good chocolate chip cookies. Now let's look
at another point mutation. So I'm going to change one thing in this recipe. I don't know
if you saw that. If I change it again. So what I've done is I've changed the number
of teaspoons from one to nine. Now what are the cookies going to taste like now? They're
probably going to taste awful. I'm going to have way too much baking soda inside there.
And they're going to taste awful. Kind of alkaline I would say. And so let's look at
another mutation then. Let's say we have this mutation. Again the first two are just changes
in one letter. Let's look at this mutation. I bet you probably caught that one. So again,
what are we doing? Well basically we're shifting this to turn on the oven to the end instead
of where it should be, which is right back here. Is that going to change our cookies?
For sure. We're going to end up with not cookies. We're going to end up with dough. And so if
you think about this, changes in the DNA is just like changes in the recipe. What causes
them, however, is not a typo. Basically there are two ways that you can get mutations. First
are what are called spontaneous mutations. That's when just something in the process
of replicating the DNA or forming the gametes goes wrong. And so a very common type, it's
not that common, but a common type is called strand slippage, where the two strands, the
parent strand and the daughter strand will slip past each other. And then you get bonding
that's not perfect. And so that would be an example of a spontaneous mutation. But a lot
of mutations are caused by our environment. And those are what are called induced mutations.
And so if radiation for example is causing skin cancer, that would be an induced mutation.
Or cigarettes. It's a chemical that's causing this mutation. And we didn't used to know
what was going on. We knew that cigarettes caused cancer but we didn't know exactly how
it worked. And so recent studies have shown that this chemical is just one of the mutagens
found within cigarette smoke. It's called benzo a pyrene. And basically if you look
at this chain right here, it's fitting right into the double helix. And it's causing a
mutation in the DNA. Now if it's in the area where there's no genes it may not be harmful.
But if it's an area, especially an area where we have cancer suppressing genes, that's just
going to lead to cancer. And it's a cause coming from the environment. And so basically
just like with the recipe in the cookies, we can have mutations just at one point. And
we call those point mutations. Or we can have larger mutations where big chunks of the chromosome
are being moved. And so let's look at the first type of point mutation. So if I go and
mutate, I don't know if you caught that. Let's try that again. This is called a substitution
mutation. So right here we've added a C instead of a T. And so you might think that's bad.
Well, we've got protection for that inside our cell. There are going to be proteins that
are going to cruise up and down our DNA. And we have A bonded to C. It's not going to quite
match up. And so we're going to know that there is something wrong and so basically
these enzymes could cut out the C and then they could put the T back in again. And that
would be no problem. But let's say they're cruising down and they see there's a C on
this. An A on this side, well they might think, not thinking, but they might realize that
we have to get rid of this A. And so they're going to put a G in here. And so 50% of the
time they're going to replace the wrong letter. And if that letter is not inside a gene it's
no big deal. But if it's inside a gene, where we're actually making amino acids to make
proteins, it can be a huge deal. That's a substitution. We could also have radiation
or chemicals that are causing the DNA to break apart like this. Well we have a number of
proteins that can fix that as well. But sometimes when they fix it they'll actually add a new
letter. And so this strand you can see is totally fine. But now we've added this new
letter here. When this cell replicates, when it makes a copy of itself, this strand is
now going to have an extra letter in it. And what that could do is that could shift all
the letters over. And that could screw up the whole protein. Or if we look at our DNA
again, what's another thing that could happen? Well maybe it's a chemical or radiation that
causes one of our nucleotides to be lost. So now we're missing that. And now when the
DNA tries to fix it, it will fold on itself. But we still have missing one letter on this
side. So we have a deletion. And so this side, if we copy the DNA, it's fine. But if we try
to make copies of this side we're going to miss big portions or at least one letter out
of that gene. Now we can also have major changes, or large scale changes. And so this could
occur during mitosis. It could occur during meiosis. But basically what we're doing is
instead of losing one letter, it could effect one gene. We could loose big portions of the
chromosome and all the genes that are found within that. And so this would be a deletion,
where we're missing this huge chunk of a chromosome which could be hundreds if not thousands of
genes. Or this could be a duplication. Where we're duplicating a portion of that during
the S phase. Or we could have an inversion where we're copying this but it's being flipped
upside down. We could also have an insertion where we're taking one chromosome and actually
inserting that into another chromosome. That might seem crazy. And it's like we could never
exist past that. But if you think about it, these genes have chromosomes. And so it doesn't
mean that individual is necessarily going to die. This could be during mitosis and so
it wouldn't be a very big deal at all. Or it could occur during meiosis. But we'd still
have these genes that we need. And so this would be an insertion. And then we could also
have a translocation where we're taking one chunk of this one over to here and this one
back again. And so there's a ton of different mutations that we can have in the chromosomes.
And that's probably how chromosomes came to be in the beginning. Some are good. Some are
bad. But they're all changes in the DNA. And I hope that's helpful.