Hey. It's Mr. Andersen. And
today I'm going to give all of the levels
within the unit one. So this is basically
on natural selection. Before we talk about
natural selection we should define the following
term and that is evolution. And so when you
start biology you should start with evolution.
People are confused sometimes as far as what
evolution is. If we were to define evolution
at its most basic term it is simply changes
in the gene pool or changes in the allele
frequency within the gene pool. And so what
is the smallest unit in biology that can evolve?
That would be the population. In other words
individuals are going to survive or not, and
based on those that survive or not are populations
are going to change over time. So we call
that evolution.\
Now one of the mechanisms by which evolution
can occur is something called natural selection.
And so what is natural selection? The definition
I would like you to remember is differential
reproductive success. In other words organisms
are going to live or die and based on those
that are able to live and pass their genes
on then we form a new population. And so a
term that I just threw around is something
called fitness. If you are able to survive
and pass on offspring then your fit at least
in the biological perspective. And so let
me change colors here for just a second. Okay.
So the most, the quintessential example of
this is the peppered moths of Europe. And
so basically they come in two different types.
They have the recessive type, which is homozygous
recessive. It's going to be this light coloration.
An then the dark coloration is either going
to be homozygous dominant or heterozygous
dominant. So these are your two different
types that you could have. This is a picture
of them on a tree. And you can see right here
that the white one is going to fit in much
better than the dark one. And that's the way
it use to be in Europe. Something like 98%
of the individuals were of the light type.
But during the industrial revolution when
we were using a lot of coal to generate energy,
it got really, really dark and so this bark
started to get darker and darker and darker.
So the birds were able to target those that
were light in color. And so we saw a shift
from the light coloration to the dark coloration.
And so it is not like the individuals were
changing. It is since the birds were eating
more of the white ones then that population
was going to drop and we saw an increase in
the dark ones. And so now the population had
changed. And so there's a lot of things that
can cause evolution. So you could have a small
sample size for example or you could have
mutations. But natural selection is the only
of those mechanisms that is actually going
to lead to populations that are better adapted
for their local environment. Okay. So next
let's talk about the population genetics lab.
Remember in the population genetics lab we
took a cup, we put fifty beads of different
color in it, we shake it out, we pull out
forty pair and that sets the allele frequencies
for our next generation. And so if you look
at the three different types that we did,
so this would be Hardy-Weinberg equilibrium,
we found that the allele frequency stayed
essentially the same through all of those
generations. And the reason why, the reason
it stayed the same is that we didn't violate
any of those five constraints of Hardy-Weinberg
equilibrium. In other words we had a large
population size. There was random mating.
There was no mutations. There's no gene flow.
And there is no natural selection. And so
it stayed the same that whole time. But when
we started to do selection, in other words
in the selection part of the population genetics
lab, what we were doing remember is we pull
out forty pair and then we'd kill all those
that were homozygous recessive. And so now
we were selecting those. You can think of
those as having recessive disorder and they
die from that. Well what we established now
was a new Hardy-Weinberg equilibrium and so
it kind of leveled out. Now it was really
hard to eventually get rid of those recessive
traits because you had to have two of them
to get rid of it And so it kind of leveled
out around 9% of the allele frequency. That's
the selection. And then finally we did heterozygote
advantage. So in heterozygote advantage remember
we were killing all of those that are homozygous
recessive, that would be an example of sickle
cell anemia, if you have homozygous recessive
you are going to die as a result of the disease.
But we also removed a third of those that
were homozygous dominant because they didn't
have the sickle cell heterozygous gene so
they would have been targeted by malaria.
And so we established a similar kind of equilibrium
at this point. And so again what is the goal
of the population genetics lab? It's just
showing how the positive or the dominant allele,
that's p, and the recessive allele will eventually
stabilize as long as you can keep all 5 of
those the same. But if it varies then what
is occurring? Evolution. So we are getting
change in the allele frequency in the gene
pool and so evolution has occurred. Okay.
Next thing we talked about was examples of
natural selection. Two examples I gave you,
number one was the change in the flowering,
the time of flowering. And so with global
warming we're starting to have spring come
much sooner. And so if you were to flower
all the way out here as a plant, in let's
say July or let's say August, well, you're
going to die as a result of that because there's
a lot of other plants flowering much earlier.
And so what we have seen with increase in
temperature if we look at time down here and
then this is when they flower, the number
that are flowering, is that we are seeing
a push in this direction. Sso we call that
directional selection, because flowers that
are now able to flower in late May are surviving.
And so they are out competing those that flower
later in the year. And so when you see a bell
shaped curve like this move direction, the
tendency is to think the plants are making
this choice. And remember that's not true
at all. What's happening is that those that
choose here are dying and so that is pushing
the bell shaped curve over here. Just like
before, if you used to flower earlier then
you would die as a result of that. And so
now let's say the temperature starts to get
colder and colder and colder we would expect
to see directional selection moving it in
the other direction. Another example of natural
selection I've talked about is the sickle
celled genes. Sickle cell anemia creates,
it's a hemophilia, excuse me, a mutation in
the hemoglobin protein that is found inside
the blood. But basically what it does is if
your heterozygous for the trait it allows
you to survive a malarial infection. And so
this graph right here shows you where malaria
is found. And this shows you the allele frequency
of this sickle celled disease in people that
live there. And so you can see that those
that had that allele were able to survive.
And so we have seen natural selection, or
we've seen an increase in that allele frequency
in that population. Because it offers them
protection against malaria.\
\
The next thing we talked about was genetic
drift. Genetic drift remember is going to
be another thing that can actually cause evolution.
Genetic drift, when you see that word, what
I want you to think about is chance. So genetic
drift is when we decrease the population size.
And so this is a cool simulation. It's a computer
simulation over here where we have two thousand
in this one and then we've just got regular
Hardy-Weinberg equilibrium. And you see what
happens is the allele frequencies tend to
stay right around 0.5. But once we decrease
the number down to two hundred or even twenty,
what happens is chance takes over. And so
these start to move in odd directions or they
like to drift away from that equilibrium.
And what's causing that is simply just chance.
And so once we decrease the size of our population,
chance can take over. So if you look over
here. Let's say this is our original population.
It has an allele population of 0.5 for both.
But let's say I just grab a handful of those
randomly. What I am going to now have is allele
frequencies that are much different than that
original population. And so you can get a
founder population that's nothing like that
original population. And that's just due to
chance. Remember two specific examples of
that would be the bottle-neck effect where
you have a large population that gets squeezed
through a bottle-neck. And even though it
may make a comeback, it's going to have less
genetic diversity. Another one would be a
founding population. So why is it that we
only find finches on the Galapagos? It's because
those are the birds that were originally blown
there. And then they adaptively radiated to
the climates on each of the different islands.
An example of this would be the Northern Elephant
Seal. You will remember they were almost hunted
to extinction. Something like twenty left
on the planet. And so they were able to make
a comeback, but they had lost a lot of that
genetic diversity that they had before. Evidence
for evolution. Evidence for evolution, abounds
in biology. You look no further than antibiotic
resistance for example. As we take more and
more antibiotics, bacteria are simply becoming
resistant to those antibiotics. You'll find
the same thing in HIV. That as we develop
new drugs, they can quickly mutate and adapt
to that. There's other pieces of evidence
that we have that shows that evolution and
natural selection are occurring. This would
be different bone structures in different
animals. And so if you look at our arm and
that of a whale you will find that they have
the same exact bone structure. And so that
indicates that these are homologous. Homologous
means they come from the same origins. In
other words you could probably build a whale
flipper in a different way, but if you're
set with an ancestor with this bone structure,
that is how you are going to make the flipper.
Another example would be biogeography. So
these are all the different Galapagos tortoises
that we'd find in the Galapagos. Some are
adapted to areas where there is not much food,
so they have a longer neck and this kind of
saddle shaped shell. It's not that they somehow
reached out their neck and grabbed higher
fruit and that's how they got the long neck.
It's just that those that had a real short
neck weren't able to survive on al island
like this. Whereas if you were on an island
like Santa Cruz, where there's food everywhere,
to have a long neck would have made you more
susceptible to any kind of a predator when
you were growing up. And so where organisms
are also gives us evidence to evolution. But
the trump card would be DNA and RNA. It's
going to be the genetic material that we have.
So this is data from, in class we did that
viral infection where I sent this one code.
So that's the RNA of the original code and
then you passed it from person to person with
occasional mutations. And so there's thirty-seven
people in the class that have been infected
by that. But we see all these varying strains.
And so if you think of all life on our planet,
all life on our planet came from that first
organism, that had this genetic material,
this DNA. It's been mutated. It's adapted
to its climate, its local climates over time.
But we can look at the DNA, for example, of
these tortoises, and we can find how similar
it is. And we could also compare that to the
DNA of the tortoise in Ecuador that probably
floated to the Galapagos Islands. So we can
make these relationships. And so if Darwin
would have had genetic material available
and the type that we have today, there wouldn't
have been debate about whether natural selection
or evolution are real. The next thing we did
was the camouflage lab. Remember in the camouflage
lab there were two parts to that. You developed
an experiment where you were placing chads
on fabric. And then we were selecting those
and determining the allele frequencies over
time. And so we found that those that blended
in, their allele frequencies went up. And
those that stood out their allele frequencies
went down. We also did the great chad capture.
Remember where the chads were spread around
the room and if they showed up then you targeted
those. These would be the dark colors that
you targeted. And then the green and the white
fit in with the floor. And so if we were to
keep playing the great chad capture over and
over and over, we would see natural selection.
Eventually you would have so many of the white
and green that maybe the other ones would
have a chance or maybe they would go extinct.
So that's the camouflage lab. And then the
last thing that I wanted to talk about in
this first unit is the idea that all life
shares common ancestry. And so there are certain
things that are conserved. In other words,
all organisms use DNA for their genetic material.
All organisms take that DNA, make messenger
RNA, make proteins and make the organism itself.
So this whole central dogma is another thing
that's conserved in life. And then we also
conserve like ATP, the machinery that we use
to harness energy and release it from our
food or in photosynthesis. That's going to
be the same in all living things. And so since
all of these share the same things it makes
sense that they share a common ancestry. And
we also find, you know, glycolysis and parts
of the respiration are conserved throughout
all of life. And so that indicates that they
are used by this last universal common ancestor.
And so that's just the beginning to natural
selection and I hope that's helpful.}
