Introduction to Genetics and Evolution is a college-level class being offered simultaneously to new students at Duke University. The course gives interested people a very basic overview of some principles behind these very fundamental areas of biology. We often hear about new "genome sequences," commercial kits that can tell you about your ancestry (including pre-human) from your DNA or disease predispositions, debates about the truth of evolution, why animals behave the way they do, and how people found "genetic evidence for natural selection." This course provides the basic biology you need to understand all of these issues better, tries to clarify some misconceptions, and tries to prepare students for future, more advanced coursework in Biology (and especially evolutionary genetics). No prior coursework is assumed.
Genetic Scales (S)
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来自 Duke University 的课程
遗传学与进化导论
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从本节课中
Genetics I
An introduction to basic transmission genetics and inheritance. This module reflects what is often covered in high school biology courses in the USA.
与讲师见面
Dr. Mohamed NoorEarl D. McLean Professor and Chair,
Biology
Hello. Welcome back to Introduction to
Genetics and Evolution.
I decided to add this extra, short video because several people expressed that
they didn't know a little bit about the scales organization of genetic data.
Now, we talk about genes, and we talk about how they affect the phenotype,
and we talk about how they are hereditary, we mentioned DNA but
we never really said anything about how is it
that the DNA sequence encoded in genes actually affects phenotypes.
That could easily be the topic for an entire course.
In fact it is a topic for many courses.
But others introduce just some very basic concepts just to help you understand
the context of the class that we're doing right now on genetics and evolution.
And how is genetic information translated into phenotype?
Now we've already talked about how DNA is the primary hereditary material.
That is the material that is organizing chromosomes that is passed
from parents to offspring that is allowing this mechanism for heredity.
Now there are sections within chromosomes that have specific instructions and
these sections are referred to as genes.
This is a term that you hear all the time.
Now the question that I'm posing to you know is what, or
how does this impact the phenotype?
How is it that the DNA sequence that's present in these different genes
actually changes your hair color?
Or your eye color or your personality or your IQ.
Well a lot of this, not all it, a lot of this is done through protein.
Now you hear the term proteins all the time in the context of your diet.
You know, are you getting enough protein, this kind of food is high in protein.
And in fact, proteins are vitally important to many many aspects of your
health, well being and development.
Some proteins are structural.
They're basically putting you together.
Some are mechanical.
They're essential proteins in various, your muscles for example.
Some of them are biochemical.
The enzymes that you use for digesting your food for
example are largely protein based.
And they can even affect things like cell signaling.
So your hormones for example have protein components.
You know, the central dogma of molecular biology.
This is a fundamental principle.
And this is an oversimplification, I should stress ahead of time.
But, it is nonetheless a fundamental principle of molecular biology,
is that there are three primary levels of genetic information.
They are also interrelated to each other.
Now DNA, as we talked about, is that hereditary material that is passed to
offspring but it also replicates itself, both inside your body and
in the context of transmitting this genetic information to your offspring.
So DNA replicates itself.
DNA also produces RNAs.
And we'll focus on one particular kind of RNA here, referred to as messenger RNA.
Messenger RNA is an intermediate between DNA and protein.
There are some forms of RNA that are directly functional but
again we'll be emphasizing it in this video the messenger RNA.
Those ones which are actually putting together the protein sequence.
These messenger RNA's are translated into protein.
Now, the structure and content of these proteins are what directly
impacts your phenotype or how you look, how you feel, how you act.
Now, proteins are actually composed of chains of amino acids.
Again, you've probably heard the term amino acids in the context of things you
wanna get particular kinds of in your diet but
if you look over here on the right we have a string of amino acids.
Now this would be part of a protein.
If we zoom in on some and
we see a particular amino acid that you've heard of.
I know alanine, leucine, serime, et cetera.
Now how is it we get from DNA to these proteins?
Aside from having this RNA intermediate.
Let's talk about each step just very briefly.
So, the first step is DNA forming this RNA, specifically this messenger RNA.
Well, the formation of messenger RNA from DNA is referred to as transcription.
Now, as you may remember from other courses,
DNA is double stranded and you have this, you have this complimentary pairing So
for DNA to DNA you always have these four different types.
A C G and T.
These are the four different nucleotides of DNA.
A always binds with T.
C always binds with G.
G always binds to C.
And T always binds to A.
And we see that right here.
So here's DNA to DNA.
A to T.
A to T.
T to A.
C to G. G to C.
Now when you're producing the messenger RNA you have the same sort of
complementary relationship, except in this case the T is replaced with a U.
So this is a uracil.
So in addition to being a different sort of compound.
A DNA is deoxyribonucleic acid.
RNA is just ribonucleic acid.
It doesn't have the deoxy facet to it.
You see it has the same sort of complimentary pairing.
So we have a double strand of DNA has been separated out and
we have this RNA transcript that's being produced in the middle and
you have this same sort of relationship with nucleotides.
So you're essentially making a copy of the DNA as RNA.
You know, the sequence here of this RNA transcript,
exactly matches the one here at the bottom.
Aside from the switch from T to U.
See TACTGCC, UACUGCC.
Et cetera.
So this how the DNA is making its copy as messenger RNA.
Now what happens is this RNA copy of the gene sequence will leave the cell,
I'm sorry, leave the cell nucleus, it will enter the cytoplasm and
that's where it directs the formation of these amino acid.
So here this messenger RNA, when it comes out.
has to produce these amino acid chains.
The term for
this translation from messenger RNA to amino acid chains is translation.
This says we are taking this messenger RNA sequence and
we are making it into a very specific string of amino acids.
It's not just any amino acids but it's very specific.
And again we have a code, just like the code we saw before.
Now this code for translation uses three nucleotides at a time or
three bases at a time.
So this is a triplet code.
So what happens, it's looking at the messenger RNA here at the bottom.
We have an AUG.
That is associated with one particular amino acid.
ACG, this is associated with another amino acid, GUA,
it's associated with another amino acid, et cetera.
So it's going in this triplet code.
Three nucleotides at a time.
From messenger RNA to the resulting string of amino acides, okay.
This will continue, until it gets to what's referred to as a stop codon.
There are three diffeent stop codons, this is one of them.
UAA.
UAA is not associated with an amino acid,
and it terminates the production of the string of amino acids.
So continue adding these on until you get to a stop codon, and then boom, done.
We have completed the process.
So let me show you how you actually identify these.
There are tables, these are referred to as codon tables,
that show you what AUG stands for, what UAA stands for, in terms of amino acids.
But here is a standard genetic code table.
Here's AUG, as you saw before, as.
That is correct, according to this table.
UAA was the stock code on, as you saw before, as well.
But you see all the different combinations; there's 64 different
combinations.
That's because it's 4 since there's 4 nucleotides to the 3rd power cause
it's a triplet code.
So 4 to the 3rd is 64 and that's the size of this table.
There's 64 possibilities here of which 61 are associated with amino acids.
3 of them are not.
There's three stop codons.
They are not associated with amino acid but we can immediately translate.
CCC will give you a Proline.
An AAA in the message line will give you a Lysine amino acid.
So we have this perfect genetic code for putting these things together.
Now, before closing may introduce some areas of the genome, because
I'll be using these terms occasionally and I want you to be familiar with them.
Again, as I mentioned before,
genes are these areas that have amino acid coding segments.
Not all of the gene, however, codes for an amino acid.
There are some segments of genes that don't.
And one example of a segment of a gene that does not so is the intron.
Introns are areas within genes that are actually spliced out of the messenger RNA.
So, an RNA is produced from large segment of the gene, but then these intron regions
just essentially get cut out of the final messenger RNAs that's put together.
As a result of that, they do not affect the final amino acid sequence.
[INAUDIBLE] That's a very important point.
So, intron sequences do not affect the final amino acid sequence.
The other region I'll introduce to you is what's referred to as intergenic regions.
These are the areas that are found between genes.
Now, just because it's not found in a protein coding gene does not mean it's not
important.
Does not mean that it does not have a function.
In fact, a lot of these intergenic regions are functional.
Several of them regulate how much messenger RNA is produced.
Especially from neighboring genes but not exclusively and some times the intergenic
regions even produce other types of RNAs that we've talked about here.
So let me give you a fictitious example, these are three real genes but
I've diagrammed them not how they truly are.
So let's say there's the check two gene.
Check two you may have heard of, because there is mutations in it
that are associated with a fivefold greater risk of breast cancer.
I have another gene here I refer to as NF2.
Another gene here, I refer to as Sox3.
I've depicted them again, fictitiously, so
that they're not actually right next to each other, like this.
So check to as I predicted here would have this.
Also codes for a messenger RNA.
And ultimately that is really to amino acid sequence.
But maybe a segment here, this is the intergenic region.
This segment right here may actually affect,
depending on the DNA sequence that is found here,
may affect how much of this check two messenger RNA is actually produced.
So this segment is actually vitally important and
it effects how much of is produced, which will then also potentially effect
how much of the protein is ultimately produced.
It does have a function, but
its sequence does not affect the amino acid sequence of this check to protein.
Nf2's expect two has large regions that are associated with amino acid sequence,
but also has an intron.
So the messenger RNA is ultimately produced from Nf2 in this
fictitious example.
But it has sequence attached to this sequence, but
the middle part would not be present.
Even though is there in the gene itself, it is not found in the messenger RNA.
Sox10 similarly has this large coding segment,
this protein coding segment, this protein coding segment but as two introns.
Again, those two introns would not be found in the final protein.
And again, both of these may have other sections here in the intergenic DNA that
are regulating.
How much of the messenger is produced of those two genes as well.
This was a i just wanna introduce some of these terms to you.
Code, i want you to understand the central DNA,
makes messenger RNA, which affects amino acids sequence of proteins and
I want you to notice that the genes these particular areas referred to as introns
that do not affect the final amino acid sequence of protein.
I hope that was helpful and I hope it was interesting.
Thank you for joining.
