CHAPTER 2 – NATURAL SELECTION AND REPRODUCTION
2.2.1: WARM-UP
1. What do you notice about the traits of the offspring
compared to the parents?
2. Where do organisms get their traits?
The traits of the offspring are similar to the parents.
Genes are passed on from parent to offspring. Genes
are instructions for making protein molecules. Protein
molecules are what give organisms their traits.
Share your observations of the offspring compared with the
parents.
• The traits of the offspring are similar, but not identical, to
those of the parents.
We will further investigate where individuals in populations
get their traits using a spider simulation.
We are going to begin our lesson today looking at another kind of organism and explore a
model of how individuals in a population get their traits. We will be focusing on the feature of
stripe color in a population of spiders.
Yesterday we read about glowing jellies
and the protein molecule that leads to
that trait.
2.2.1: WARM-UP
Project the Traits and Reproduction SIM
Let’s focus on and identify Otis and Ruby’s traits
• Otis is brown with a blue stripe and a little bristle
(hair),
• Ruby is yellow with a black stripe and a lot of bristle
(hair)
We will look at their genes for stripe color and how they lead to protein molecules and
therefore traits.
Then we will look at their offspring to see how the traits were passed down.
2.2.1: WARM-UP
Investigate Otis and
Ruby’s genes and protein
molecules.
Select stripe color on the
top menu and then press
on Otis to show his cells.
Let’s look at Otis. This is a
model of his cells.
2.2.1: WARM-UP
These pink shapes are
protein molecules.
Notice that they fit together
with other molecules in the
cell and together they
produce blue pigment.
This is how protein
molecules lead to the blue
stripe trait.
2.2.1: WARM-UP
Genes are found on chromosomes
and there are two copies of every
gene.
These copies can be the same
version or different versions.
Otis has two of the same version,
T2.
This version of the gene gives the
cells the instructions to make the
protein molecules that lead to the
blue pigment.
2.2.1: WARM-UP
Press the X in the top right
corner and then press on Ruby.
Let’s look at Ruby.
On her chromosomes she also has
two copies of the gene for stripe
color, but her copies are not the
same.
She has two different versions, T2
and T3.
Different versions of a gene are also
called alleles.
2.2.1: WARM-UP
Notice that she has one version of
the gene that is the same as Otis.
The T2 gene gives the cells
instructions to make the protein
molecule that leads to blue pigment.
That is the protein molecule with a
rounded shape.
Ruby also has another version of the
gene, T3.
This is still the gene for stripe color, but the protein molecule that is produced is a different
shape, it is pointy instead of round. Because of its different shape it fits together with a different
molecule and produces black pigment instead. Black pigment mixed with blue pigment produces
a black color, so her stripe is black.
2.2.1: WARM-UP
Press the X in the top right corner and
then press on Otis again.
This simulation will allows us to change the
genes of Otis and see what happens to his
protein molecules.
In real life organisms cannot just change their
genes, but this is a model that can help us see
what happens when we change the genes.
What do you think will happen if I change one of his gene copies to T3, the same version that
Ruby had?
His cells will start to produce the pointy protein molecule and he will produce
black pigment and his stripe will turn black
2.2.1: WARM-UP
Change one of the genes to T3.
The cell now makes the rounded and pointy
protein molecules and therefore blue and
black pigment.
Now Otis’s stripe is black.
Change the genes back to T2 and T2.
Note that you are putting his gene back
the way they were.
Press the X in the top right corner to return to the starting screen.
2.2.1: WARM-UP
Drag Ruby and Otis together
If Otis and Ruby have offspring, what color
stripes do you think they will have?
• some blue and some black
Press SKIP TO OFFSPRING on the
bottom right. Some spiders have black
stripes and some have blue stripes.
2.2.1: WARM-UP
Press a spider with a blue stripe. Point out that this spider has two copies of the T2
version of the gene. One came from Otis and one came from Ruby.
Organisms get genes from their parents. Notice the protein molecules in the cell.
Genes are instructions for making protein molecules and that protein molecules lead to traits.
Press the X in the top right corner.
2.2.1: WARM-UP
Press a spider with a black stripe.
The spider has two different versions of the gene, T2 and T3.
T2 came from Otis and T3 came from Ruby.
The cell has instructions to make both protein molecules, so the cell produces black and blue
pigment. The stripe color is black.
2.2.1: WARM-UP
Summarize where individuals in population get their traits.
Organisms get their genes from their parents and the genes are instructions for making protein
molecules which lead to traits.
2.2.1: WARM-UP
Crosscutting concept of Structure and Function.
Point out that microscopic structures can be modeled to show how their
function depends on their shapes.
As we saw in the Sim, the structure—or shape—of the protein molecule
determines its function, or what that protein molecule does.
The rounded protein molecule only fit together with a certain molecule,
which lead to the production of blue pigment.
The pointy protein molecule only fit together with a different molecule,
which lead to the production of black pigment.
2.2.1: WARM-UP
Chapter 2 Question:
How did the trait for increased poison level become more common in the newt population?
Now that we know where individuals in populations get their traits, we can continue to think
about how the trait for poison level became more common in the newt population.
2.2.2: SIM
At the end of chapter 1 the class agreed that the newt population became more poisonous because the
snakes in this environment caused poison to be an adaptive trait, but now some park visitors are
offering additions to the claim.
Some park visitors have offered two competing ideas.
• Some park visitors have suggested that Poison Level 10 is the most common because
newts with this trait live longer than other newts.
• Others think that Poison Level 10 is the most common because newts with this trait
reproduce more than other newts.
Each of these ideas builds on the claim we decided to support at the end of Chapter 1, but
now we need to figure out which one is best supported by evidence.
2.2.2: SIM
Discuss the claim additions…
Do you agree or disagree with the claims - share your ideas with your partner.
2.2.2: SIM
Investigation Question
How do some traits become more common over many generations while others
become less common?
To be able to support one of these claims we
need to understand why traits become more
common in a population.
In previous activities, we looked at how
offspring get genes from their parents when
organisms reproduce.
Genes are instructions for making protein
molecules that determine an individual’s traits.
2.2.2: SIM
How is it possible then that some traits can
become more common over many generations
while others become less common over many
generations?
Shouldn’t each generation match the generation
before it?
Discuss your ideas about the investigation
question with a partner.
The next activity will provide evidence to help
you better answer this investigation question.
Investigation Question
How do some traits become more common over many generations while others
become less common?
2.2.2: SIM
Some organisms reproduce more than
others.
Let’s review possible answers to the Investigation
Question.
• Some organisms can have more offspring than
others.
• Some organisms will not survive in the
environment long enough to reproduce.
If yellow ostrilopes from one generation had
more offspring than green ostrilopes, would the
next generation have more yellow ostrilopes
than green ostrilopes?
YES
2.2.2: SIM
Introduce the Sim activity.
You will use the Sim to gather evidence about whether ostrilopes with adaptive traits have
more offspring than ostrilopes with non-adaptive traits.
Let’s establish which traits are adaptive.
The environment color for this Sim activity is
Yellow 7 and there will be carnithons present
in the environment.
Which color trait is most adaptive in this
environment?
Yellow 7
2.2.2: SIM
Our Sim mimics the natural world, which is
very complex.
Like the natural world, random events can
occur in the Sim world that could make it
difficult to draw conclusions if we don’t collect
enough data.
For example, some ostrilopes might randomly
have more opportunities to reproduce than
others.
2.2.2: SIM
By collecting enough data, we’ll be able to
determine if the data shows a pattern that
is not due to random events.
So, we are each going to collect data and then
use all of it in a class data set.
By averaging all our data, we might be able to
find a pattern to show us which ostrilopes tend
to have the most opportunities to reproduce.
2.2.2: SIM
Using the Reproduction Claims mode let’s zoom in and demonstrate locating an ostrilope
with a color trait from the data table on your screen (Blue 1, Blue 4, Yellow 7, Yellow 10).
Let’s Project the Natural Selection Simulation and demonstrate collecting data
and resetting the Sim.
2.2.2: SIM
In previous Sim activities, we were
looking for changes over time, so we
watched a whole population for many
generations.
In this Sim activity, we are looking at
individuals.
When the individual you are following
dies, you will need to reset the Sim and
choose another individual to observe
from the beginning.
2.2.2: SIM
Select that ostrilope and press RUN.
Count the number of times that ostrilope reproduces, and record that number in the data
table. Reset the Sim to collect data for a different ostrilope color.
Let’s Project the Natural Selection Simulation and demonstrate collecting data
and resetting the Sim.
Record the number of
times the ostrilope
Reproduces
Reset SIM after each ostrilope dies.
2.2.2: SIM
2.2.2: SIM
We gathered information about the number
of offspring for each color trait in the data
table.
But, following just a few ostrilopes before
they die is not enough for us to identify a
pattern at the scale of the population.
To do this, we need to compare
observations from the whole class and
come to a group conclusion about what we
see.
We’ll need to collect data from each group
and average it.
Collecting whole class data using the DATA TOOL
2.2.2: SIM
Let’s share what you notice from the
data tool
Observe the following:
• Not all ostrilopes reproduced the same
amount.
• Ostrilopes with adaptive traits (Yellow
Color 7) reproduced more on average
(because they were the most likely to
survive).
• Ostrilopes with non-adaptive traits
(Levels 1, 4, and 10) reproduced less on
average (because they were less likely to
survive as long).
2.2.2: SIM
Discuss with your table how this averaged data from the class helps to answer the
Investigation Question
2.2.2: SIM
1. What pattern describes the relationship between how long an ostrilope lived and how many offspring it had?
2. Which ostrilopes became more common over time, and why?
3. Which ostrilopes became less common over time, and why?
4. If the color of the environment became blue, which ostrilopes do you think would become more or less
common, and why?
Ostrilopes that lived longer had more offspring.
Ostrilopes with Yellow Color 7 became more common because they survived longer, so they had more
opportunities to reproduce and have offspring.
Ostrilopes with colors that didn’t blend into the environment, like Blue Color 1, 4, and Yellow Color 10, became less
common because they were more likely to be eaten by predators before they could have many offspring.
Ostrilopes with blue-color traits would become more common because they’d be camouflaged and survive longer, so
they could have more offspring. Ostrilopes with green and yellow colors would be more likely to be eaten by
carnithons before they could have many offspring.
2.2.2: SIM
Answer the poll by selecting your choice at the bottom of .
Supports: ostrilopes with Yellow Color 7
had a higher average then the others.
VIEW POLLING DATA
2.2.2: SIM
2.2.3: MODELING TOOL
You will create a model to explain how different organisms’ survival and
reproduction rates lead to traits becoming more or less common over time.GOAL
You will be using the Modeling Tool
to respond to Sherman.
Scientists often explain their
thinking in writing and by making
visual models.
You are going to return to
the Sherman’s Story from the
previous lesson and explain your
thinking by writing a response and
making a visual model.
You will create a model to explain how different organisms’ survival and
reproduction rates lead to traits becoming more or less common over time.GOAL
Reread the Sherman’s
Story independently.
This is the same story you saw in
the Warm-Up in Lesson 2.1, but
this time there is some new text in
the last panel.
2.2.3: MODELING TOOL
NEW TRAIT
LABELS
You will make a
model of how the
distribution of beak-
strength traits
changed.
This model will help
you write your
responses to
Sherman.
You can add more
than one Trait label
to a single trait.
Add trait
labels
Predict
Histogram
2.2.3: MODELING TOOL
Respond to Prompt after creating
your visual model.
1 2
3
2.2.3: MODELING TOOL
Modeling Tool Response:
A proficient model is shown below. You should group the Trait labels together as shown in Histogram 1 (+S
with +O, -S with -O). Proficient models should include at least two traits labeled in Histogram 1 but might
include all traits labeled. Predictions about Histogram 2 will vary significantly. Correct responses should show a
shift in distribution of traits toward stronger beak strength and should only include traits that were present in
Histogram 1.
TIME
2.2.3: MODELING TOOL
WHY DO THESE BIRDS HAVE STRONGER BEAKS
TIME
Individuals get their traits from their parents.
The birds with stronger beaks
were able to crack open more
seeds and eat more, which
means they lived longer and
reproduced more, passing on
their strong-beak trait.
What may have happened is birds with weak beaks couldn’t crack enough seeds to have enough to eat to survive,
and so they died before they could reproduce, which means they did not pass on their weak-beak trait.
Over many generations, the
distribution of traits changed
so that the population had
more and more individuals
with the strong-beak trait.
2.2.3: MODELING TOOL
Let’s share your responses to Sherman’s Story.
Connecting Sherman’s Story to the old claim that individual newts became more
poisonous because they wanted to.
In the Warm-Up, you read and thought about the claims regarding the newt mystery.
Based on Sherman’s Story that you just read, what else can we say to people who
think that the newts in Oregon State Park became more poisonous because they
wanted to?
That’s impossible. Traits are determined by protein
molecules that are determined by genes that are inherited
from an individual’s parents. Individuals cannot choose their
traits.
2.2.3: MODELING TOOL
Example:
• We have been investigating how populations change over many generations.
• Most of these changes are in response to environmental changes.
• This is connected to what you learned about in the Microbiome unit.
• When one part of the body system changes, such as an increase in the number of harmful gut
bacteria, other body systems are affected.
• As a result, the other helpful bacteria in the intestines cannot survive, which makes people sick.
Think creatively!
Challenge yourself to connect a very
different science topic to our current topic.