Understanding Mutations: The Impact on Genetics and Evolution

Captions are on! Click CC at bottom right to turn off. Ever since I was a kid, I have been curious about mutations. I think certain movies may have had an impact; I used to imagine mutations with amazing abilities.

But, there was also a lot I didn’t understand. Let me explain. Many people understand that a mutation is a change of genetic material---more specifically

a change within a nucleic acid. RNA and DNA are both types of nucleic acids. Therefore, anything with RNA or DNA can have a mutation.

That means animals- and that definitely includes humans- also plants, fungi, protists, bacteria, Archeaa- they can all have mutations. Additionally, so can viruses.

Many mutations can be neutral in effect. You can see this codon codes for the amino acid leucine. But if it experiences this particular silent mutation, even though a base has been altered,

it still codes for leucine. It did not change the amino acid. Mutations can also be harmful or helpful.

But it’s important to understand that mutations are random. The organism can’t “will” itself to get a certain mutation. You can learn more about this in our natural selection video where we talk about how a

bacterium may already possess a helpful mutation that allows it to survive an antibiotic, but the bacterium didn’t “will” itself to mutate to get this certain mutation. Ok, so again, mutations are random.

But there can be factors that can make mutations more likely to occur. External factors like certain types of chemicals or excessive radiation or internal factors like an event that causes a problem with DNA replication in interphase.

During interphase, cells can replicate DNA before they divide. So let’s discuss some different types of mutations. We’ll start with gene mutations.

DNA makes up genes and genes can code for proteins that influence different traits. So when a mutation in DNA happens, which specifically means a change in one or more DNA bases, then different proteins can be produced which can affect an organism’s traits.

In this example, we have fruit fly DNA. Mutations could include substitution which means the wrong base is matched. Insertion, which means an extra base (or bases) are added in.

There is also deletion, which means a base is removed. Insertions and deletions have the potential to be especially dangerous. Why?

Remember in protein synthesis, how 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. And if you read the bases in threes---depending on where it happened---- everything that is

read afterwards could be affected. We call this a frameshift mutation. If you look at this frameshift example here where a single base has been inserted, you

can see now how the following codons---which have 3 bases each---are now all affected as the reading frame has been shifted. This example shows how it can lead to many amino acid changes.

There are also chromosomal mutations. Remember that chromosomes are made up of DNA and protein----highly organized---and they have lots of genes on them.

The human chromosome number is 46 with 23 from an egg cell and 23 from a sperm cell. This type of fruit fly here, however, has 8 chromosomes so 4 came from an egg cell and 4 came from a sperm cell.

Some examples of chromosomal mutations include duplication, where extra copies of genes are generated. Deletion, where some of the genetic material breaks off.

Inversion, when a broken chromosome segment gets inversed (which means reversed) and put back on the chromosome. Or translocation when a fragment from one chromosome breaks off and attaches to another

chromosome. There’s more mutations than what we covered of course, but the idea is that there are many different kinds of changes that can happen.

If a mutation is going to happen, we already mentioned that there are especially vulnerable times such as during DNA replication but also there are other times too…like meiosis. In fruit flies and other animals, meiosis makes sperm and egg cells that can have half

the number of chromosomes as the organism. However, sometimes those chromosomes don’t separate completely. We call this nondisjunction.

This can result in an egg or sperm cell that has too many or too few chromosomes. It’s possible for a mutation to be passed down to an offspring. Consider a protist with a mutation.

Many protists reproduce asexually, and when they divide, the daughter cell can inherit the same mutation. A fruit fly, which reproduces sexually, can pass a mutation to its offspring if that mutation

is found in the genetic material of the sperm or egg cell. You may wonder why we’ve been mentioning fruit flies so much? Well, they’re AWESOME.

But, also, it turns out that fruit fly mutations---and how they are inherited---are frequently studied. We have some links in the video description for more info. These studied mutations can also occur in humans, and we’ll give a gene mutation example

of a substitution in the case of sickle cell anemia. First- a little background. Hemoglobin is a protein in your red blood cells that helps you carry oxygen.

But in the disorder sickle cell anemia, the gene that codes for hemoglobin is mutated. If you inherit two copies of this 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. While unfortunately there is not a cure for this disorder yet, the good news is that treatment

for this disorder has greatly improved. Another thing to mention, if an individual only inherits one copy of the mutated gene from one parent, they are a carrier but they don’t officially have the disease.

Usually they 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 their symptoms are often less severe. We should mention that studying mutations and genetic disorders is a large and important field right now.

Genetic counselors work to help families that may be affected by genetic disorders. If you have an interest in learning more about careers related to this topic, please check out some of our further reading suggestions in the description below.

Well, that’s it for The Amoeba Sisters, and we remind you to stay curious.