To acquire an understanding of the fundamental concepts of genomics and biotechnology, and their implications for human biology, evolution, medicine, social policy and individual life path choices in the 21st century.
Mutations
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来自 University of Maryland, College Park 的课程
基因与人类（从行为到生物技术）
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从本节课中
Introduction to Genetics
Module One provides a foundational overview of genetics tools and principles.
与讲师见面
Raymond J. St. LegerProfessor
Department of Entomology
Tammatha O'BrienLecturer
Department of Entomology
[MUSIC]
Hello, and welcome back.
So now that we're familiar with essential dogma of biology, we
understand the signifigance and key regions of our DNA and RNA.
And we know the various ways of
controlling gene expression without altering the sequence
of DNA, now we're going to enter the exciting DNA altering world of Mutations.
[SOUND]
Mutations are defined simply as a change. For DNA that means a change
in the Nucleotide sequence.Recall the four letters of DNA, G, A, T or C, Nucleotides.
Simply changing or having mutation of one or more of
these DNA Nucleotides can lead to a change in the mRNA.
In ultimately a change in the protein that's made.Some possible outcomes from
a DNA mutations are non functional protein.
A protein that has partial function.
A protein with a completely new or novel function, no protein at all or
interesting enough no noticeable change in protein
function even though there was a DNA mutation.
Mutations in genre may also affect timing or level of gene expression.
One of the fundamental properties of mutations is
that mutations just occur randomly.
When and if mutations occur is completely
unrelated to any advantage that mutation may provide.
We don't want to rise because an organism needs
them, and conversely, they don't arise to harm an organism.
They're spontaneous.
Natural selection plays a role in these mutations whether they will exist
in a population are not cause they can be selected for or against.
Now I want you to think about DNA and
RNA as sentences that code for genes, all the genes in the
sentence are composed of three letter words that we going to call codons.
In the same way three letters can make
a unique word, three Nucleotides make up unique codons.
The Nucleotides for making up DNA codons again are A,G,C and T for DNA.For
RNA, RNA uses the Nucleotides U instead of T so the
four Nucleotides of RNA are A,G,C and U.
Three letter codon corresponds to specific amino acids, and those amino
acids, to refresh your memory, are the building blocks to proteins.
In this way, the three letter codons determine which Amino acids are
going to be arranged in the proper order to synthesize the proper protein.
So, we can think of codons that make up
a gene as a sentence comprised of three letter words.
One example of a sentence comprised of three
letter words is, the red hat was big.
You'll notice that this analogy corresponds to a gene in
that we have a sentence composed of three letter words.
Again. The red hat was big.
Two types of mutations we're going to talk
about are insertion and mutations and deletion mutation.
And you can probably hypothesize from their names what happens in each mutation.
For insertion mutation, one
or more Nucleotides will be inserted.
A deletion mutation will have a deletion of one or more Nucleotides.
These mutations, insertions and deletion mutations, are called INDELs.
And they can lead to something called friendship mutations.
Consider our sentence. The red hat was big.
In the case of an insertion mutation, imagine we
insert a letter, say A, into the word red.
So now when you try to read the three letter words, it reads, the rea,
well, you'll notice that's not a word
and everything else in the sentence is gibberish.
What effect do you think that would have if we changed the co,
codons used as the template to make a protein in the same manner.
Now imagine the other type of mutation, the deletion mutation.
You have the same sets. The red hat was big but in this case
the D is removed. It's deleted.
We have the
[INAUDIBLE],
Wait, that doesn't make sense. Those three letter words don't mean much.
So, we have a frame shift mutation occurring
again, since RNA is read in three letter frames.
Once the word is altered, one word is
altered, the rest of the sentence is also shifted.
Another type of mutation that we'll talk about are called substitution mutations.
These don't change the reading frame of the sentence, we have the same sentence.
The red hat was big but
for a substitution mutation, we'll substitute, in this
example, an e in red with an a.
So now, we get a different sentence with a different meaning.
Rad hat was big.
I actually introduced this type of mutation
earlier to discuss the sickle cell trait.
In that case, one single codon is
changed by substituting one Nucleotide with another Nucleotide.
And you can see the dramatic effect it had on the shape of hemoglobin.
It altered not only the shape, but remember, form dictates function.
A change in the shape of hemoglobin changed how it functioned.
If we want to look at gene mutations, this is difficult to study in humans,
but because we never have control of a
human of a human's environment or life style.
And when we try to study DNA mutations in humans,
we also run across that pesky little issue of, ethics.
So fortunately, we have model
organisms that we can use to study mutations.
We'll see that nature's thrifty in that a lot of genes
do the same thing in flies, mice and even tiny bacteria.
One example of this similarity in different organisms can be
seen in people with the mutation called the tin man gene.
It's named after the tin man in The Wizard of
Oz, and people with this mutation often have congenital heart defects.
But this mutation was first observed in fruit flies
born without a functional heart, hence the name, tin man gene.
Based on the similarities in gene function and expression in flies and humans
you can see why some geneticists refer to flies as little humans with wings.
Flies drink alcohol when they're sexually rejected, they can become aggressive
so we can use them to study behavior, they're great models.
Because they have sleepless nights and they can be used to study insomnia.
They're a wonderful model
organism because we can study these traits much much more.
I want to drive home the connection between form and function.
So that you truly understand significantly how a little change
in our proteins can ultimately affect our overall bodies function.
So we talked about form and function.
Well let me give you a practical example of form and function.
Take this chair for example.
Very specific form of shape that relates to
its very specific function.
What if I change the shape of form ever so slightly?
So, just change where the seat is.
Has it affected the function? Well' let's see.
I can sit on it, it's asking for a mishap.
But I can still sit on it,
so a slightly different shape, slightly different function.
It's not going to work in the same way.
But let's look at it more dramatically.
What if there were a dramatic change in the shape of this chair?
So now I change
the shape.
All the elements are still here but is the function the same?
No, the function is not the same.
So what we're going to see with when we talk about proteins and mutations
is that different changes and shape can have different effects on the functions.
Some can be small or non consequential and other ones can be pretty extreme.
Now, imagine if I were to start this with a hammer, it's going
much more extreme effect on the shape and a much more extreme effect on it's form.
Although mutations are often thought of as harmful, they provide
a rich source of genetic diversity in the world around us.
Mutations can play a key role in why you don't look
exactly like your mother, or your father, sister or your brother.
Well, why you're uniquely you.
[SOUND]
