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What do you think of when you think of the word mutation? Do you think about X-men
and some really awesome ability? Or...the ninja turtles?
We loved the ninja turtles when we were little!
We might be showing our age a little bit...
But mutations are really not that glamorous. Most people understand that a mutation is a change of genetic material---more
specifically a nucleic acid. RNA and DNA are both types of nucleic acids.
So how does a change happen? Remember that in DNA, the base adenine (A) goes with thymine (T). And the
base Cytosine (C) goes with Guanine (G). And that’s all good, but what happens if the
wrong base matches up? Many things can cause an error like that----external factors like
chemicals and radiation…or internal things like something goes wrong during DNA replication
in interphase, which is a stage that prepares cells to divide during mitosis. Now while
these things can increase the chance that a mutation is going to happen, it is important to understand that
mutations are random. If a mutation is going to be a helpful thing for an organism---which
is rare, as very few are helpful---- it can’t just “will” itself the get that mutation. An organism can't just "will" itself to get this.
It's definitely not like X-men either. More about that in natural selection.
Many mutations are actually neutral in their effect.
Meaning they neither help nor harm an organism.
And some mutations are harmful.
So we're going to talk about the different kinds of mutations.First we're going to talk about gene mutations.
So DNA makes up genes.
And genes code for proteins that influence different traits. So when DNA has changes----aka a mutation----then
different proteins can be produced and this can affect an organism’s traits.
So let's look at the gene mutations.
So first, substitution.That means you have the wrong base matched.
So instead of A with T...you can have A with G. Scandalous.
You can have an insertion, which means an extra base (or bases) are added in.
You can have a deletion, which means a base is removed.
Insertions and deletions have the potential to be especially dangerous because remember
in protein synthesis, we talked about how bases are read in threes? Well if you add
a base or remove a base, suddenly the number of bases total has changed, right? So if you read
in threes---depending on where it happened---- everything that is read afterwards could get
really messed up. We call this a frameshift. Now these were all types of gene mutations,
but we also have something called chromosome mutations. Remember that chromosomes are made
up of DNA and protein----highly organized---and they have lots of genes on them. All of the
body cells in your body each have 46 chromosomes.
Human sperm and egg cells have 23 chromosomes.
Well changes can occur at that large chromosome scale too.
So let's talk about these chromosome mutations.
Just like insertion in a gene mutation---where bases can get added-----you have something
called duplication in chromosomes. These are mutations where extra copies of genes
are generated. So extra copies of that chromosome are generated.
There is deletion, where some of the genetic material from the chromosome breaks off.
Inversion---when a broken chromosome segment gets inversed (which means reversed) and put back on the
chromosome. Or translocation (we weren’t kidding back when we said there are a lot
of “trans” words in biology)---that’s when a fragment from one chromosome breaks
off and attaches to another chromosome. There’s more mutations than what we covered
but the idea is that there are many kinds of different changes that can happen.
If a mutation is going to happen, there are vulnerable times like when DNA replication happens
during interphase and also other times too…like meiosis.
In humans, meiosis produces sperm and egg cells
that have 23 chromosomes.
But sometimes those chromosomes, when they're separating, don't separate completely.
We call this nondisjunction. This results in an egg or sperm that has too many or too few
chromosomes…and that can cause a genetic disorder depending on which chromosome we’re
talking about. Different chromosomes contain different genes so the specific chromosome
that is affected does make a difference in the result.
Let’s talk about some real life examples of mutations. Remember, we said that a lot
of times, mutations can have a neutral effect. Not all of your DNA codes for a direct protein
and other genes in your body can influence whether genes will even be turned on or turned off.
Let’s talk about sickle cell anemia. First- a little background. Hemoglobin is a protein
in your red blood cells that helps you carry oxygen. Well in the disorder sickle cell anemia,
the gene that codes for hemoglobin is mutated. If you inherit two copies of this mutated gene (one
from each parent), you can have this disorder. This disorder can make it difficult for your
red blood cells to carry oxygen because the shape of the red blood cell is affected from
this mutated hemoglobin protein. This can lead to anemia and other problems.
But get this---if you inherit one copy of the mutated gene
from one parent, you are a carrier but you don’t officially have the disease. Usually
you do not have symptoms. But those that are carriers appear to have a protective factor
against malaria. Malaria is a disease caused by a protist that can be transmitted by mosquitoes.
These individuals can still get malaria, but usually their symptoms are less severe.
So, in a way, this one copy of a mutation can be an advantage if you happen
to live in an area where malaria is really present.
Studying mutations and genetic disorders
is a huge field right now.
If this kind of thing interests you, there are a lot of careers to look into.
In fact, there's a career known as a genetic counselor.
They work to help families that may be at risk or affected by genetic disorders.
They do a lot of good in the world.
Well that's it for the amoeba sisters and we remind you to stay curious!