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Hi. It's Mr. Andersen and welcome to biology essentials video 53. This is on
environmental genotype effects. In other words, how the environment can effect genotypes.
Now remember genotypes are the genes that you have. But how those are expressed is called
your phenotype. So what you physically look like is your phenotype. But the genotype are
the genes that lie behind that. In other words, that make those proteins. That make your physical
appearance. And so basically as the environment changes, you can either express genes or not.
And so this is the Himalayan rabbit or at least a cartoon version of a Himalayan rabbit.
Himalayan rabbits are all black. But if you look at the picture, it's not all black. And
so basically what a Himalayan rabbit is doing is it's expressing the gene to make melanin
which causes the coloration that's black. However since the core of the body of the
Himalayan rabbit is warm, it disrupts the expression of that genotype. So you can't
make the melanin. And so the areas on a Himalayan rabbit that are cooler, that are away from
that core are actually able to be that black phenotype. And so you might not buy it. And
so this is a cool study that was done with Himalayan rabbits. Basically you shave the
Himalayan rabbit's back. So you get rid of all the fur on the back. And then you add,
not ice, but an ice pack to the back of Himalayan rabbit. And then you let it sit on there as
the hair grows back in. And when the hair browns back in, what you'll have is a black
patch wherever you shaved. And so what happened was by adding that ice pack you're able to
cool the temperature down. And so the core of the body is not able to heat it up. And
you can make the melanin that would naturally be there. And so basically you can regulate
whether or not that genotype is going to be expressed. I've always thought it would be
cool to have a Himalayan rabbit. Then just kind of make my name in its back in black.
But that's a little weird. So let's get on to the podcast. What am I going to talk about.
Basically I'm going to talk about how traits can be expressed or not. In other words, how
the genotypes can be expressed due to changes in the environment. I'll talk about how that
occurs in animals. I've mentioned the Himalayan rabbit. But I'll also talk about where that
might actually apply in the arctic fox or in the arctic hare. I'll also talk about how
plants can change or vary their color due to changes in their environment, notably the
pH. And then finally how bacteria can change their expression of genotypes. I'm going to
talk about the operon, especially the lac operon. But also show you how in the lab we
can use color change in bacteria to see what color or what type of a bacteria you have.
So let's start with the animal side and seasonal melanin. So this is an arctic fox. But so
is this. And so basically an arctic fox will change its color due to the season. Which
totally makes sense. In the winter, when it's snow everywhere, you want them to be white
so you can blend in for camouflage. Then in the summer you also want to blend in with
your environment. So how do they do that? Well basically they have a pineal gland. The
pineal gland sits kind of right in the core of the brain. It's right behind the eyes.
And basically it secretes melatonin. Melatonin is a hormone that's created during times of
darkness. And so during the winter they're going to secrete more melatonin. As they secrete
that melatonin, it's going to trigger the cells in the body not to produce melanin and
so they're going to have this white appearance. Now when summer comes. We're going to have
a decrease in melatonin. They're going to increase the amount of melanin and they're
going to have a dark appearance. And so that's evolved over time. Responding to the environment,
those that were able to turn off that melanin during the winter were able to survive longer.
And so we're going to see that in the arctic fox. But also the arctic hare. As they change
the amount of melanin that they have. And so we're either expressing that gene and having
the dark color or we're not expressing the gene. We can also see that same thing in plants.
And if you think about plants you might say well, they're always green. And that's the
photosynthetic parts. So the leaves obviously are always going to be a green color. That's
based on the amount of chlorophyll. But the function of the flower is to attract an animal,
notably the insects. And so basically this is the same hydrangea, it's the same species
of plant, but it's able to get different colors of flowers. And it's doing that in response
to the environment. Notably the soil environment. And so basically these ones are cultivated
by humans, but they can vary the pH of the soil. And if you have a pH in the 6s, then
you get this pink hydrangea. If lower the pH into the 5s you can get this blue hydrangea.
Basically the blue is coming from aluminum that when the pH gets lower their able to
pick up and then express that. And so the genes that they're making are dependent upon
what building blocks they have. In this case in their environment, whether they can express
it or not. So it's not like they're turning it on or off. But they're able to vary the
amount of coloration. And so that's going to give them variation in their environment.
Last thing I want to talk about was bacteria. And how bacteria can either express genotypes
or not. And when I say express it or not, the one thing that should jump to mind is
operons in bacteria. Remember basically in bacteria they have a string of genes that
are right next to each other. They can turn it on or they can turn it off. In this case
there are three genes that help the breakdown of lactose. And so you basically have a promoter
where RNA polymerase can get on. You can either make those or not. Dependent upon the presence
of lactose. If this makes no sense, make sure you watch the podcast on gene regulation.
But if you have this, then you're called lac positive. If you have the lac operon you have
this whole thing. If you don't have it, then you're lac negative. And so you're a bacteria
that can't breakdown lactose. And so a good way to differentiate between those that are
lac positive and those that are lac negative is using somethingcalled MacConkey Agar. So
you're growing colonies of bacteria on it. Basically you grow the bacteria. They'll grow
on this. They'll feed on the agar. They'll multiply over time. So you know 24 hours later
you have all these bacteria. But in the MacConkey Agar it's innovative. What they do is they
put a chemical in here that can sense the pH. Because if you're lac positive you're
going to make acids that are going to change the pH in the agar. And so basically they
put an indicator, is the word I was thinking of, that once the pH goes below 6.8 then it's
going to have a pink coloration or pink appearance. And so if you grow bacteria on MacConkey Agar,
so you can see over here we have bacteria that a lac negative. Because they don't have
that lac operon. Over here we have e. coli that are lac positive. And since they're breaking
down that lactose that's also found in the agar then they're lowering the pH and now
the indicators going to give it that pink appearance. And so it's just an example of
how a gene is either expressed and we see a phenotype. In this case that phenotype that
we don't necessarily see in the lac open we can actually see in the agar. And so that's
basically how an environment can effect genotypes. Can effect what phenotypes we see. And I hope
that's helpful.
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基因表現 (Genotype Expression)

21 分類 收藏
winnielin0604 發佈於 2020 年 4 月 7 日
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