(upbeat music)
- Hey, welcome back again for
8th grade natural selection.
This is Ms. Jarnagan again
and we're gonna be starting
to dive into chapter three,
doing lessons 3.1 and the
first bit of lesson 3.2 today.
So what you're gonna need for this lesson.
A pencil or pen, some lined
or blank pieces of paper,
and optional, but encouraged,
a family member or friend
you can check in with
and a copy of the "Mutations:
"Not Just for Superheroes" article.
So let's go ahead and
start off with lesson 3.1,
Introduction to Mutations.
So here's a letter from Dr. Alex Young.
Thank you for working so
carefully to explain this mystery.
Your explanations are great so far.
However, I'm curious about
a new piece of evidence
we just received and how it
fits in your explanation.
My colleague sent this histogram
that describes the
rough-skinned newt population,
using historical data.
The evidence shows the
distribution of poison-level traits
among individuals living
200 generations ago.
She said that most poisonous newts today
in the population could be so poisonous
because of a mutation.
Please research mutations
to determine whether
that's what's happening here.
I look forward to reading your reports.
Analyze the histogram sent
by Dr. Young's colleague.
So the question really is here,
how did the distribution of
the poison-level traits change
from 200 generations ago
to 50 generations ago?
And what could explain this change?
I'll help you out with
at least the first part.
When I'm looking at the population
between 200 generations
ago and 50 generations ago,
it actually seems like a good amount
of it is pretty much the same.
Like, if you look here for
traits one through nine,
pretty identical between the two.
However, there is something special.
Here, 200 generations ago,
we did not have any
level 10 poison traits.
But 50 generations ago, that did appear.
So kinda keep that sudden appearance
in the back of your head
while we're kinda considering,
well, what's causing all of this?
So we can kinda summarize
it as there were no newts
with a Poison Level 10
200 generations ago,
but there were poison newts
with Level 10 50 generations ago.
So we're gonna start
learning about mutations.
And we're gonna start by
reading a couple of articles.
The first one is "Mutations:
Not Just for Superheroes."
So either have a piece of paper out
or someone nearby to talk
to about any key ideas,
new learnings, or
questions you might have.
So in movies and comic books,
mutations make people into
superheroes, like Wolverine.
In the real world, though,
mutations often have no
visible affect at all.
- [Narrator] Movie mutations.
In movies, mutations are always exciting.
They might give someone
special powers or extra limbs.
However, real mutations
can be very boring.
They might not have any
noticeable effect at all.
What is a mutation, anyway?
The answer has to do with genes
and the way they are passed
down when organisms reproduce.
Genes are instructions for
making protein molecules,
and those protein molecules
determine an organism's traits.
When organisms reproduce,
they pass down copies
of their genes to their offspring.
However, the copies aren't always perfect.
As genes are duplicated,
changes can occur.
These changes are called mutations,
and they can be passed
from parent to offspring
when organisms reproduce.
Most of the changes are minor
and don't affect traits at all.
But every once in a while,
mutated genes give instructions
to take a new new protein molecule
that leads to a new
trait in the offspring.
The new traits that arise
from mutations may be adaptive
or non-adaptive, or
they may have no effect
on survival and reproduction.
It all depends on the
organisms' environment.
If a new trait makes organisms less likely
to survive and reproduce
in their environment,
the trait is non-adaptive.
Environment with that trait
don't have a very good chance
of surviving long enough to reproduce
and pass their mutated genes down
to the next generation.
If they don't pass the mutated genes down,
they don't pass the new trait down either.
Mutated traits that are non-adaptive
usually remain uncommon in the population.
On the other hand, mutated
genes sometimes result
in a new trait that
turns out to be adaptive.
Adaptive traits help organisms survive
and reproduce in their environments.
If a mutation results
in an adaptive trait,
organisms with that trait are more likely
to reproduce and pass
on their mutated genes
in the next generation.
Through natural selection,
adaptive traits become
more and more common
in the population over time.
A trait that is adaptive
in one environment
may be non-adaptive in another,
and that's what makes
mutations so important.
Environments don't stay the same forever.
Mutations can introduce new traits,
increasing the chance
that one of those traits
might help make a population better able
to adopt to a changing environment.
- [Ms. Jarnagan] Okay, so
this is your chance to pause.
Any key ideas from the article?
Any questions you have?
So now we're gonna learn
more about mutations
in a specific organism, the cane toad.
Again, have a piece of paper out
or someone next to you
to talk about key ideas,
new learnings, and questions you may have.
So, on the left is a cane toad.
Cane toads like this one can
grow up to be 22 centimeters
or about nine inches long
and weigh up to 1.8
kilograms, or four pounds.
- [Narrator] Huge poisonous
toads have invaded Australia.
Humans brought cane toads
from Asia to Australia
in the 1930s, hoping the
toads would eat beetles
that were destroying crops.
Unfortunately, the toads
didn't eat many beetles.
They ate almost anything else
that could fit into their mouths, however.
The big toads grow up to 22
centimeters, nine inches long,
and weigh up to 1.8
kilograms, four pounds.
Cane toads are extremely poisonous,
and no Australian predators
can survive eating them.
Without predators in
their new environment,
the cane toad population
began growing and spreading.
Today, cane toads are common
in areas more than 1500
kilometers, 932 miles,
from the place where they were
first introduced to Australia.
Because there are so many
cane toads in Australia,
they compete with each other for food.
The cane toads are eating
everything in sight,
so food becomes scarce in
any area where they live.
To survive, cane toads have to keep moving
into new areas with more food sources.
The first toads to reach
new territory get to eat
all the food they want.
Slower toads are stuck
with whatever is left.
Recently, Australian scientists
have been finding cane toads
with bigger, more muscular legs.
These bigger legs can be traced back
to mutations that
changed the toads' genes.
Scientists compared the big-legged toads
to ordinary cane toads.
They identified several gene mutations
that gave the cells instructions
to make protein molecules
that were different
from the protein molecules
that other toads could make.
Protein molecules affected
the cane toads' legs,
increasing the leg size and strength.
Having bigger legs is an adaptive trait
that helps cane toads survive
in an environment where there
isn't much food to go around.
Bigger, stronger legs
help these toads outrun
other cane toads and be the first ones
to get to the food in new areas.
With better chances of getting food,
big-legged toads are more
likely to survive and reproduce.
Because of this, they are also more likely
to pass on their mutated
genes to their offspring.
Along with these mutated genes,
they pass on their adaptive traits.
When humans introduced
cane toads to Australia,
the cane toads' environment changed.
With no predators hunting
them in their new environment,
there were more cane toads,
and therefore much less food available.
However, mutations led to a
new trait in the population
that turned out to be adaptive
in the new environment.
The mutated trait for
bigger legs was adaptive
for cane toads in an
environment with scarce food
because it helped them
get more food and survive.
Through the process of natural selection,
big-legged cane toads are becoming more
and more common in the
cane toad population.
These stronger, faster toads
are spreading across Australia,
invading new areas all the time.
- [Ms. Jarnagan] Okay, it's
time to write or discuss.
What are some key ideas from the article
and what questions do you have?
When you're done with
this, keep these notes
on the side, because we're gonna come back
in just a little bit to think more
in detail about the cane toads.
Time on natural selection,
how do mutations become
more common in a population?
So you'll find that out.
Natural selection part eight.
That's gonna be 3.2 part two, and 3.3.
So from Ms. Jarnagan here in my fortress
of science in Seattle, Washington
and from the cat as well,
you guys have a great
day and see you soon.
Kitty, no!
Bye.
Okay, so we've been using
the word mutation a lot,
let's go ahead and define it now.
A mutation is a random change
to a gene that sometimes
results in a new trait.
I just wanna emphasize this word.
Sometimes results in a new trait.
Sometimes.
And with this picture that
you're looking at here,
this is a diagram of
something called a chromosome,
which is basically a big piece of DNA
that contains many genes.
The gene that's labeled in
red is one noting a mutation
that may lead to a new trait.
Maybe.
And we're gonna do an
activity really working more
with this idea of mutations
by predicting changes in
ostrilope populations.
What we're gonna do is
we're gonna consider
what can happen to a
population of ostrilopes
that are capable of mutations,
whose environment is changing to be cold.
Before we start, though,
let's consider two different situations.
This first one here is Population A.
Let's say Population A is
put into a cold environment,
but they're not able to mutate.
Do you think that they would survive?
Go ahead, pause, write,
and discuss on that.
Now look at this histogram thinking
about a change to a cold
environment and no mutations,
so no new traits can happen.
I can know a few things.
I know that traits number,
here we go, one sec, okay.
I know that traits number eight, nine,
and 10 would not appear
because there's no mutations.
That's terrible because
those are the traits
that would most likely
help in a cold environment.
And traits one, two, and three,
I would predict that those ones would die
because they don't have
enough fur to survive.
However, we do have these
middle ground traits,
between four, five, six,
and seven, that well,
there's at least a possibility
that maybe this Population A could survive
if its environment turned
cold and they couldn't mutate.
Okay, similar idea now.
Let's look at this Population B.
They are also now in a cold environment
and they can't mutate.
Do you expect that they would survive?
So let's go ahead and walk
through the same thinking.
The environment's becoming cold
and this population can't mutate.
If there's no mutations,
no new traits will happen,
so I know that these traits.
I know that the traits that are going
between right here with
three, four, five, six,
seven, eight, nine, 10, those won't appear
if there's no mutations, so
they're not even a possibility.
And if it got cold, well,
trait level one and two,
like I said before is almost hairless.
I would expect these to not even survive.
So Population B with no mutations
and it gets cold?
That's gonna equal not
so happy dying time.
But now, we're going to
actually think about mutations.
Population B would be dead
if it couldn't mutate in a
new environment that was cold.
But what if it could mutate?
Go ahead, write, pause,
do you think this
population would survive?
Okay, if you have access to Amplify,
please go to Lesson 3.1,
Introduction to Mutations, page four.
And try out these missions if you can.
So I'm gonna simulate what would happen
to that Population B if their
environment was set to cold
and they had mutations on.
So they started out in a
fairly warm environment.
I'm gonna set it to cold though.
And I'm gonna enable mutations.
Press run, and let's zoom
in to see what happens.
So as we're starting out, we
have these traits one and two
that are shivering.
They're finding mates, but
oh no, that little guy died.
Right, well this one is
looking around for food.
He's got some fur.
Oh, he's shivering now too.
Let's put this a little on fast forward.
This has only been a
couple of generations.
But oh, oh did you see
that little red dot?
Mutation happened.
That's your little note.
So they're still shivering,
but oh that one mutated and died.
Well it's not going too well for them.
But as we're watching,
they're not totally dying out.
And I just found a trait three.
Just found a trait number three.
That's a little different from before.
So gonna stop here for a moment.
Fast forward in time and
we're gonna take a look
at what happens after
70 generations of this.
This is an example histogram
of what could happen
to Population B if they were set
to a cold environment and
they had mutations enabled.
So pause real quick, write and discuss.
What fur trait was most
common after 70 generations?
And was that trait
present in generation one?
So the trait that became the most common
after 70 generations
is gonna be this trait
number nine right here.
And if we'd remember how
these histograms are written
for us, anything that's present
in the final generation we
recorded, like generation 70,
that would be in the blue bar and anything
that existed in the starting population,
well that would be in a hash-mark bar.
Trait level nine was not present
in the original population.
Now this one's just for you.
So, this population died out
when there were no mutations.
How did having mutations
allow the population
to survive the environmental
change to cold?
Go ahead and pause and think that through.
Okay, let's go on to Lesson
3.2, Mutations in a Population.
So these are the two situations
we considered earlier
about Population B being
put into a cold environment.
In one situation they could mutate,
in the other ones they couldn't.
So spend a second looking at them
and thinking how are
these histograms similar?
And how are they different?
Okay, so I'm gonna start
analyzing this with you.
Anything that's similar,
I'm gonna start by marking
in green highlight.
And anything that I see is different,
I'll put in a yellow highlight.
First few similarities I see is,
well they're both ostrilopes.
And they both had the
same starting populations
with traits one and two.
And in the end, neither of
them had trait three either.
And though it's not on the histogram,
I do also know another similarity
is they were both put
into a cold environment.
Now let's think about what's different.
One thing that's different
between the two is this population
with no mutations turned
on only survived 25 generations
before they're just died out.
Whereas the one that
has mutations survived
for 70 generations.
There's also the straight point here
that this population could
mutate, this one could not.
And finally, for the
population that mutated,
they had traits four through 10 appear,
whereas the population
that could not mutate
didn't have these.
Overall, things that are similar.
Both of them are ostrilopes.
They're at the same distribution
of traits in the starting population,
and they have the same
change to their environment.
Things that are different.
One could mutate while
the other wasn't able to.
The population with mutations
survived 70 generations.
The population without mutations
died after 25 generations.
And new traits appeared in
the mutation population.
Okay, so we're gonna back to thinking
about the cane toad invaders
article from earlier
and how mutations
affected their population.
If you still have your
annotations from before,
go ahead and bring those notes back out.
What you're going to be doing is,
you'll be posed a question
and then re-read a segment
of the article to answer that question.
The first question to write or listen
for is what was the change
to the cane toad environment?
- [Narrator] Huge poisonous
toads have invaded Australia.
Humans brought cane toads from Asia
to Australia in the 1930s,
hoping the toads would eat beetles
that were destroying crops.
Unfortunately, the toads
didn't eat many beetles.
They ate almost anything else
that could fit into their mouths, however.
The big toads grow up to 22
centimeters, nine inches long.
And weigh up to 1.8
kilograms, four pounds.
Cane toads are extremely poisonous,
and no Australian predators
can survive eating them.
Without predators in
their new environment,
the cane toad population
began growing and spreading.
- [Ms. Jarnagan] Okay,
so what was the change
to the cane toad environment?
The change was they moved
from their native environment
in Asia to Australia.
They had many new food
sources in the beginning
and no predators to eat them.
Your next question to listen for.
How did the environment
change affect survival?
- [Narrator] Because there
are so many cane toads
in Australia, they compete
with each other for food.
The cane toads are eating
everything in sight,
so food becomes scarce in
any area where they live.
To survive, cane toads have
to keep moving into new areas
with more food sources.
The first toads to reach new territory get
to eat all the food they want.
Slower toads are stuck
with whatever is left.
- [Ms. Jarnagan] Time
to write and discuss.
How did the environment
change affect survival?
When the environment changed,
there wasn't enough food for
all of the toads after a while,
so the toads began to
starve and die without food.
So for your next question,
write or listen for what
caused stronger legs
in the cane toad population?
- [Narrator] Recently,
Australian scientists
have been finding cane toads
with bigger, more muscular legs.
These bigger legs can be
traced back to mutations
that changed the toads' genes.
Scientist compared the big-legged toads
to ordinary cane toads.
They identified several gene mutations
that gave the cells instructions
to make protein molecules
that were different
from the protein molecules
that other toads could make.
These new protein molecules
affected the cane toads' legs,
increasing the leg size and strength.
- [Ms. Jarnagan] So,
what caused stronger legs
in the cane toad population?
Mutations to the toads' genes caused them
to make different proteins.
This led to a new trait, stronger legs.
So, write or listen for next.
What was the effect of stronger legs
in the cane toad population?
- [Narrator] Having bigger
legs is an adaptive trait
that helps cane toads
survive in an environment
where there isn't much food to go around.
Bigger, stronger legs
help these toads outrun
other cane toads and be the first ones
to get to the food in new areas.
With better chances of getting food,
big-legged toads are more
likely to survive and reproduce.
Because of this, they are also more likely
to pass on their mutated
genes to their offspring.
Along with these mutated genes,
they pass on their adaptive traits.
- [Ms. Jarnagan] What was
the effect of stronger legs
in the cane toad population?
The stronger leg is an adaptive trait
because frogs with stronger
legs are more likely
to eat food, survive,
and pass on the mutated strong
leg trait to their offspring.
(upbeat music)
