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PROTEIN SYNTHESIS: TRANSCRIPTION AND TRANSLATION ACTIVITY 7

13. Compare the amino acid sequence that resulted from each mutation to
the original DNA sequence. Based on your work, what can you say
about the effect of DNA mutations on the production of amino acid
sequences and proteins? Summarize your ideas in your science
notebook.

Part C: Modeling Genetic Modification

14. In your group, discuss what happens during protein synthesis in a
genetically modified organism:

• What processes take place in cells to generate proteins that result in

a trait?

• Do these processes change when a gene is modified?
• Does the protein that is generated change?

Be sure to include what you know about the link between DNA and
traits in your discussion.

15. Look over Student Sheet 7.2, “Modeling Genetic Modification,” which
shows a basic diagram of a plant’s cell, including the nucleus and
chromosomes in the nucleus. Add your initial ideas to the diagram to
model what is happening inside the plant’s cells when a genetic
modification is introduced.

16. Label your model, and add any notes that will help you understand the
relationship between the elements you added. For example, if you add
a modified gene, label the gene and describe its function. Do this for
all aspects of your model.

17. Share your ideas with the class, according to your teacher’s
instructions.

Build Understanding

1. Construct an explanation of protein synthesis in cells. Be sure to
include the following information in your explanation:

• The role of transcription
• The role of translation
• The role of DNA, mRNA, and amino acids

2. Think about the possible results for a two-base insertion or deletion to
a strand of DNA that codes for a protein. How might these results be
different from a three-base insertion or deletion?

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3. What is the difference between a mutation and a genetic modification?
4. Do you think it’s likely that the superweeds in Farmer Green’s fields are

the result of a spontaneous mutation? Explain your reasoning.
KEY SCIENTIFIC TERMS
amino acid
DNA
mRNA
mutation
protein
protein synthesis
RNA
transcription
translation
tRNA

Extension

Scientists have been studying RNA for decades, but it wasn’t until 2020 that
mRNA started making news headlines—as mRNA is the key ingredient in
several vaccines developed for COVID-19. These types of vaccines are not
new; research on using mRNA in the development of safe, effective
vaccines for certain types of cancer, AIDS, rabies, and other diseases has
been underway for years. Visit the SEPUP SGI Third Edition page of the
SEPUP website at www.sepuplhs.org/high/sgi-third-edition to read more
about mRNA vaccines, the engineering behind them, and how they work.

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8 Cell Differentiation and Gene Expression

every living organism’s cells contain genetic information that

codes for proteins. These proteins help organisms’ cells, tissues, and
systems function and bring about observable traits. The genotype of nearly
all of an organism’s cells is the same, but the phenotype—what is
expressed—depends on a cell’s interaction with the environment around it.
Not every cell expresses the same genes and makes the same proteins.
Proteins must be made at the right time and in the right place. For
example, a plant’s root cells have the genes needed to make the proteins
required for photosynthesis, but those genes are only expressed in the cells
used for that function (such as stems and leaves). Genetically modified
crops often rely on the plant expressing a new protein—sometimes in all
cells, and sometimes in specific cells.
In the last activity, you learned that genes are transcribed to produce RNA and
that this RNA is in turn translated to produce proteins. Some proteins are
made by almost every cell because they are needed for basic cell functions.
Other proteins are made by only one type of cell or small groups of cells. Cells
can turn many genes off and on, depending on what is going on in their
environment. In this activity, you will investigate how and why cells express
certain genes at different times. You will investigate cells and gene expression
in a human, but the same types of mechanisms are found in all organisms.

a b
FIGURE 8.1: Although the two human cells shown have the same genes in their nuclei, they are specialized
to make different proteins. The skeletal muscle cells (a) are specialized for voluntary muscle movement,
whereas the thyroid cell (b) makes large amounts of thyroid hormone.

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Guiding Question

If all cells in the same organism have the same genes, why
don’t they all make the same proteins?

Materials

FOR EACH GROUP OF FOUR STUDENTS

set of 14 Cellular Events cards

FOR EACH PAIR OF STUDENTS

3 colored pencils (blue, brown, and orange)

FOR EACH STUDENT

Student Sheet 8.1, “Chromosome Map”
Student Sheet 8.2, “Differentiation Model”
4 silver binder clips
7 red paper clips
7 green paper clips
model of human chromosome 2
model of human chromosome 11

Procedure

Part A: Gene Expression in Differentiated Cells

1. In your group, discuss why you think cells express different proteins
even though they all have the same DNA. Be prepared to share your
ideas and questions with the class.

2. In Figure 8.2, identify the two human
chromosomes that you will investigate today:
chromosome 2 and chromosome 11. You will
look at a small number of genes on these
chromosomes.

3. Look over Table 8.1 and Table 8.2. You will
investigate the expression of only 11 of the
approximately 25,000 human genes. Review the
proteins that these 11 genes produce and their
functions, which are listed in these tables.

FIGURE 8.2: Human male karyotype
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CELL DIFFERENTIATION AND GENE EXPRESSION ACTIVITY 8

TABLE 8.1: Selected Genes on Human Chromosome 2

PROTEIN PRODUCED BY THE GENE FUNCTION
Actin, smooth muscle type Produced by most cells for cell
movement and cell division;
AGA enzyme muscle cells produce large
Cellular respiration enzyme amounts of specific types of actin
Lactase enzyme for muscle contraction
Protein synthesis initiator Breaks down fats and some toxic
Ribosome protein S7 substances
Catalyzes reactions for aerobic
respiration in the mitochondria
Required for digestion of lactose,
the sugar in milk
Controls the beginning of protein
synthesis
Needed by ribosomes, which are
essential for protein synthesis

TABLE 8.2: Selected Genes on Human Chromosome 11

PROTEIN PRODUCED BY THE GENE FUNCTION
Cell growth controller Prevents cells from dividing unless
more cells are needed; helps
DNA repair prevent certain types of cancer
Fat and protein breakdown enzyme Repairs damage to DNA; helps
prevent certain types of cancer
Hemoglobin B Catalyzes one step in the
Insulin breakdown of proteins and fats in
the diet so they can be used for
energy
Carries oxygen to the cells
throughout the body
A hormone that regulates the
metabolism of sugars and fats

4. Look over Table 8.3, which lists the four kinds of specialized cells you
will work with in this activity. In Cells: Improving Global Health, you
learned about a variety of specialized cells and their different
functions. Each member of your group will look at gene activity in one
of the cells in Table 8.3. Decide as a group what kind of cell each of you
will investigate.

TABLE 8.3: Cell Type

Beta cell in the pancreas
Developing red blood cell
Intestinal lining cell
Smooth muscle cell in the digestive system

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5. Review Table 8.4, which shows which of the 11 genes on chromosomes
2 and 11 are expressed in your cell.

TABLE 8.4: Genes Expressed in Four Types of Human Cells

PROTEIN PRODUCED BETA CELL IN DEVELOPING INTESTINAL SMOOTH
BY THE GENE PANCREAS RED BLOOD LINING CELL MUSCLE CELL IN
Actin, smooth muscle CELL THE DIGESTIVE
type – – SYSTEM
AGA enzyme – –
– – + +
+ + –
Cell growth controller + + + +
+ + +
Cellular respiration + + – +
enzyme + + – +
DNA repair protein – + –
– + –
Fat and protein + + + –
breakdown enzyme – + +
Hemoglobin B +

Insulin +

Lactase –

Protein synthesis +
initiator +
Ribosome protein S7

Key: + = active gene, – = repressed gene

6. Use the information in Table 8.4 to do the following:
a. On Student Sheet 8.1, “Chromosome Map,” find the chromosomes
for your cell. Draw a single thick brown line in the position of each
gene that is not expressed in your cell type. These genes are still
present, but they are never expressed in your cell; they are
permanently turned off, or repressed. Your teacher will help you
with the first example.
b. On your Student Sheet, draw a single thick blue line in the position
of any gene that is expressed only in your cell type. These are just
some of a number of genes that produce specialized proteins that
help your cell perform its role in the human body.
c. On your Student Sheet, draw a single thick orange line in the
position of any gene that is expressed in all four cell types. These
genes produce proteins that nearly all cells need in order to function.

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CELL DIFFERENTIATION AND GENE EXPRESSION ACTIVITY 8

d. Compare the chromosomes for your cell with the others in your
group. Copy the information from their chromosomes onto your
Student Sheet to have a full set of chromosome diagrams for each
cell type.

7. Obtain a model of chromosomes 2 and 11. Place a silver binder clip over
each gene that is permanently repressed in your cell type. The silver
binder clip represents a specific transcription factor, a molecule that
controls the transcription of DNA into RNA. This transcription factor is
a repressor; it permanently turns off genes that your cell does not need.

Part B: Differentiated Cells at Work

8. Prepare a table like this in your science notebook, with at least eight
rows to record your data.

Gene Expression
My Cell Type: ____________________________________

Cellular Event Affected Gene and Result

9. Have one group member shuffle the deck of Cellular Events cards and
place it in the middle of your table. Put your models of chromosome 2
and chromosome 11 nearby.

10. Decide which group member will go first. That person should draw a
card from the top of the deck and read it aloud to the group. Each card
represents an event that is happening in a part of the human body where
your cells are located. Listen carefully to the description of the event.

11. Use the information on the card to determine which genes in your cell
are activated to make proteins at this time and which genes in your cell
are repressed at this time.

Note: Some events will affect all cell types, and others will affect only
some cell types.

Follow the directions on the card to place transcription factors that
determine whether the genes are expressed or temporarily repressed.
These transcription factors include both activators (green paper clips)
and repressors (red paper clips) that bind to portions of the DNA that
regulate the gene. Place the paper clips on the appropriate gene on
your model chromosomes.

Key: transcription activator = green paper clip;
transcription repressor = red paper clip

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12. If your cell type was affected by the event in Step 11, record the event,
the affected gene, and the result for your cell type in the table in your
science notebook.

13. Moving clockwise around your group, have the next person select a
card from the top of the deck. Repeat Steps 10–12.

14. Continue selecting cards and determining which genes are affected
until your teacher tells you to stop.

15. Compare your cell’s chromosome 2 to your group members’
chromosome 2. Discuss any similarities and differences you observe in
the genes that are expressed and repressed, and record your
observations in your science notebook.

16. Compare your cell’s chromosome 11 to your group members’
chromosome 11. Discuss any similarities and differences you observe
in the genes that are expressed and repressed, and record your
observations in your science notebook.

17. With your group, discuss the role of each transcription factor
(represented by the paper clips) and the types of changes in the cell or
its environment that led to the need to turn the genes on and off.

Part C: Making Differentiated Cells

18. With your partner, read “Stem Cell Differentiation.”

Stem Cell Differentiation

Organisms are made of many kinds of specialized cells. In plants, some
examples are root cells and leaf cells. In humans and other mammals, there
are red blood cells, pancreas cells, stomach lining cells, nerve cells, muscle
cells, and more. Each specialized cell performs a function in the organism.
Many of these cells form tissues and organs and contribute to maintaining
homeostasis in the organism.

Every cell in an organism is the offspring of another cell and has the same
genetic material as the fertilized egg (or equivalent) from which it
developed. It is amazing that the many different types of cells all arise from a
single fertilized cell—yet that is what happens during embryo development,
whether in a human or a plant. Initially, all cells in the embryo are alike. But
as they divide, they become more specialized and produce their own
characteristic proteins. Cells that have the ability to produce a variety of
types of specialized cells are called stem cells. The process by which stem
cells produce specialized cells is called differentiation. As differentiation
progresses, segments of the genetic material are either expressed or
repressed, in much the same way as in fully developed cells.

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CELL DIFFERENTIATION AND GENE EXPRESSION ACTIVITY 8

hematopoeitic blood
stem cells cells

fertilized stem cells blastocyst neural cells of nervous
egg stem cells system

mesenchymal connective tissue,
stem cells bones, cartilage, etc.

FIG33U7R7ESE8P.3U:PTShGeI dCeelvleSlBopment of specialized cells from stem cells in a human

Figure: 3377CellSB 14_01

AWgeinthdianMaeddCeovnedlo9p/9ing embryo, specific proteins or chemical factors direct
the differentiation of its cells. Examine Figure 8.3, which illustrates some
of the pathways that stem cell differentiation can take in humans.

Starting with the fertilized egg, the cells undergo mitosis to create more
identical cells. Once there are enough cells to form a blastocyst,
differentiation begins. At first, a cell will become a more specialized stem
cell. Then it will further differentiate into the types of adult cells you have
learned about (such as blood cells and nerve cells), which are still
genetically identical but have particular structures and functions and
produce specific proteins. Scientists are still learning about this complex
process, but they do know that it involves a combination of internal signals
from the cell’s genes and external signals that can come from neighboring
cells or from the environment directly surrounding the cells. These signals
activate or repress the cell’s genes, eventually leading to a fully developed
cell with a specific function. The cellular mechanisms of gene expression
and repression are the same as those in fully formed cells, but the results
are quite different!

Build Understanding

1. Compare the following in your group’s four cell types:
a. Chromosomes
b. Genes
c. Expression of the genes to produce proteins

2. What kinds of genes were permanently repressed in some cells? Why
were these genes repressed?

3. Explain why some proteins are made by nearly all cells and how they
support essential processes in cells. Give at least two examples.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

4. In this activity, you modeled gene expression in human cells. What
would you expect to be the same in a model that showed gene
expression in plant cells? What would you expect to differ? Explain
your reasoning.

5. The model on Student Sheet 8.2, “Differentiation Model,” has three
labeled stages: A, B, and C. On the model, label the process or
processes occurring at each stage. Below the model, explain what is
happening at each stage, being sure to discuss the following:

• How mitosis, differentiation, and/or gene expression are involved
• How the cells are similar and/or different

KEY SCIENTIFIC TERMS

chromosome
differentiation
DNA
expressed (gene)
gene expression
repressed (gene)
stem cells
transcription factor

Extension

The cells in organisms are affected by both their genes and the environment
around them. The study of how genes respond to different signals is called
epigenetics. Visit the SEPUP SGI Third Edition page of the SEPUP website
at www.sepuplhs.org/high/sgi-third-edition to learn more about what
scientists are discovering about these complex interactions.

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9 E xplaining Herbicide
Resistanc e in Weeds

farmer green thinks it’s possible that genes from a herbicide

resistant crop plant were transferred into weeds, resulting in the
superweeds in his corn fields. Farmer Green wondered if the same thing
happened to the other farmers in neighboring counties with superweeds in
their fields. He wants to know how the herbicide resistance gene could
move from one type of plant to another. In this activity, you will use what
you’ve learned about protein synthesis, gene expression, and cell
differentiation to try to answer Farmer Green’s question.

FIGURE 9.1: A farmer checks a corn crop before it is time for harvesting.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

What happens to cause a weed to produce offspring with the
gene for herbicide resistance?

Materials

FOR EACH STUDENT

partially completed Student Sheet 7.2, “Modeling Genetic Modification,”
from Activity 7

Procedure

1. Read “Acquiring New Genes.”

Acquiring New Genes

Cases of transgene migration have been well-documented since the 1990s,
when genetically modified crops were first introduced and used
commercially. Transgene migration occurs when a modified gene is
passed from a genetically engineered plant to its wild relative through
sexual reproduction. In many cases, a genetically modified crop plant
reproduced with a wild relative through cross-pollination. Cross-
pollination occurs when the pollen from one plant transfers to another
plant to produce offspring. This normally happens with plants of the same
species, but it can also happen with closely related species. For example,
the canola plant (Brassica napus) is an important agricultural crop whose
seeds are used to make canola oil for cooking and biodiesel production.
Canola is grown extensively in the United States, Canada, Australia, and
China. Research demonstrated that canola, which had been genetically
modified for herbicide resistance, cross-pollinated with its weedy relative,
common field mustard (Brassica rapa). Some of the resulting offspring of
the mustard plant carried the gene for herbicide resistance. Today, this
hardy herbicide resistant weed can be found growing among crop fields in
many countries worldwide, with the same gene for herbicide resistance as
its relative canola.

Transgene migration has been documented in a number of other
instances where genetically modified crops have reproduced with wild
relatives. These cases demonstrate how easily genetically modified plants
can pass on their genes to their wild relatives.

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EXPLAINING HERBICIDE RESISTANCE IN WEEDS ACTIVITY 9

Plants can also become
herbicide resistant without
cross-pollinating with a
genetically modified relative.
Farmers first discovered in
2006 that there was a herbicide
resistant variety of pigweed
(Palmer amaranth), a weedy
relative of the crop plant
amaranth. In 2018, scientists at
Kansas State University
discovered that pigweed was
resistant to herbicides as a
result of random mutations in
its DNA. This mutation led to a FIGURE 9.2: Herbicide resistant pigweed
herbicide resistance gene that is growing among crop plants
different from the gene found in
pigweed’s genetically modified relatives. Pigweed plants that had this
mutation were able to reproduce and generate offspring with the same
mutation. As farmers sprayed herbicides on their fields of herbicide
resistant crops, the pigweed plants with the herbicide resistant mutation
were unharmed and continued to grow. Herbicide resistant pigweed
continues to spread throughout the southern United States and into the
midwest. Pigweed is particularly problematic in its herbicide resistant
form since it can grow up to seven feet high and shade out shorter crops,
such as cotton and soy.

2. In your group, discuss what you think might be causing weeds to
produce offspring with DNA that makes them herbicide resistant.
Include what you know about the link between DNA and traits. Some
question you might want to discuss are:

• What is the role of transcription and translation in a cell?
• What role might proteins play in herbicide resistance?
• How could a genetic modification cause herbicide resistance?

3. On your copy of Student Sheet 7.2, “Modeling Genetic Modification,”
from Activity 7, revise your model to include information about the
role of protein synthesis and gene expression in herbicide resistance.
Be sure to label your drawing. Add notes to help you show the
relationship between the elements you added to your model. Be
prepared to share your revisions with the class.

4. Share your ideas with the class, according to your teacher’s
instructions.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Build Understanding

1. Describe two ways that herbicide resistance can occur in weeds.
2. Imagine that a herbicide resistant crop plant cross-pollinates with a

weedy relative and that 50% of the offspring are herbicide resistant
weeds. Describe a situation where the herbicide resistant offspring
would be more likely to survive than the non-herbicide resistant
offspring.
3. Issue connection: Farmer Green has been relying on genetically
modified crops, but it now seems that this technology will no longer be
as effective because of the superweeds spreading in his fields. How
might Farmer Green’s concerns relate on a larger scale to the global
food supply and sustainability? Discuss all three pillars of
sustainability (social, economic, and environmental) in your response.
KEY SCIENTIFIC TERMS
DNA
gene
transgene migration

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10 M ofoHleecrubliacirdMeeRcehsaisntiasnmcse

when farmer green began growing herbicide resistant corn, he
noticed how well the corn plants survived when he applied herbicide and
how quickly the weeds in the field died. Now that he has superweeds in his
field that don’t respond to the herbicide, Farmer Green is wondering how
herbicide resistance works inside the plant cells. He uses a popular
commercial herbicide called glyphosate, which targets the protein EPSPS.
Plants normally use the EPSPS protein to make the amino acids they need
in order to grow. Glyphosate prevents the EPSPS from functioning
properly, so the plant can’t build the amino acids and therefore the proteins
that it needs.
Farmer Green knows that mutations in the gene for a protein can change
its structure and function. He wonders if a change in the EPSPS gene of a
plant could make the plant herbicide resistant. Is this what’s happened to
the superweeds in his field?

FIGURE 10.1: Farmers use large machinery to spray herbicides, such as
glyphosate, on their crops.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

How does a change in a plant’s DNA make the offspring of
that plant herbicide resistant?

Materials

FOR EACH PAIR OF STUDENTS

10 red chenille stems
10 blue chenille stems
5 white chenille stems
5 green chenille stems
a meter of coated wire

FOR EACH STUDENT

partially completed Student Sheet 7.2, “Modeling Genetic Modification,”
from Activities 7 and 9
Student Sheet 10.1, “Converting DNA to Proteins”

Procedure

Part A: Protein Structure

1. With your partner, read the information in Figure 10.2 about how a
DNA sequence codes for a protein sequence.

FIGURE 10.2: DNA and protein sequences
A gene is a long sequence of DNA subunits. The letters below (A,T, C, and G) represent the
four DNA subunits.

AGTCCCGT TGAACGA

A DNA sequence is read in three-subunit codes. The brackets below show the codes in
this piece of DNA.

AGTCCCGT TGAACGA

Each code speci es a protein subunit in a protein sequence. The blue, red, green, and
white circles below represent the four types of protein subunits.

AGTCCCGT TGAACGA

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LabAids SEPUP IAPS Repro 3e

MOLECULAR MECHANISMS OF HERBICIDE RESISTANCE ACTIVITY 10

2. Review Student Sheet 10.1, “Converting DNA to Proteins.” The DNA
sequence for the EPSPS gene is spaced into three-subunit codes,
similar to the codes in Figure 10.2. Each code has been entered in the
“EPSPS DNA Sequence” column on Student Sheet 10.1. Find this
information on the Student Sheet.

3. Use the Subunit Key at the top of the sheet to fill in the “Protein
Subunit” column.
a. Start with the first DNA subunit code for EPSPS.
b. Find the corresponding DNA code in the Subunit Key to see what
protein subunit (color) it corresponds to.
c. Write the color for the protein subunit in the “Protein Subunit”
column.
d. Repeat Steps 3a–3c for the entire EPSPS DNA sequence.

4. With your partner, read “Enzymes and Herbicides” to learn about how
enzymes work and the structure and function of EPSPS in plants.

Enzymes and Herbicides

Enzymes are a type of protein that speed up chemical reactions in the cells
of all organisms, including plants. There are over 5,000 different enzymes.
Like all proteins, for an enzyme to function, it must first fold into a specific
shape. This folding depends on how the four kinds of enzyme subunits
interact with one another and with water in
the cell. Some subunits repel each other and
water, and other subunits attract each other
and water. These interactions cause the
protein—in this case, an enzyme—to fold
into a unique shape.

How do enzymes work? SGI Genetics

Enzymes attach to molecules called FIGURE 10.3:Figure: Genetics SB 10_03 This enzyme is
substrates. Substrates bind to the part of the folded into a unique shape.
enzyme that physically matches its unique
shape, which is called the active site. When
an enzyme and substrate bind, the enzyme
changes shape to make a snug fit with the
substrate. The substrate undergoes a
chemical reaction, resulting in a product (or
products), which then releases from the
enzyme. The enzymes can then repeat the
process with new substrates.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY Products

Substrate
Active site

FIGURE 10.4: Enzymes speed up chemical reactions between substrates to form
products.

Environmental factors such as temperature and pH can affect the rate at
which an aecntzivyemseitweSuoabnrskdtsrb.aMtloecokletchuelessucbasltlreadtei.nIhnihbiitboirtos rcsacnabninaldsowbitihnPdtrhoeducts
enzyme’s
somewhere elseAocntivaenseitnezyme and change its shape so that the substrate
can no longer bind to the active site.

The EPSPS enzyme and glyphosate
Many herbicides target a specific enzyme or a set of enzymes that plants
need in order to grow. EPSPS is an example of an enzyme found in plants,
fungi, and bacteria that supports growth. In Procedure Step 2, you looked
at the order of the protein subunits in a portion of EPSPS. The order of
these protein subunits distinguishes EPSPS from other proteins.
seGuvlebynuptnhuMSFioiGagtyIssurlGiraaleeoydt:nPGeferkeot,tinicShtelsehtlemiscesibEtSohhBPlde1eS0/r_1pPb044liSacneidnt.ezythmaet Farmer Green uses, binds to the protein
to prevent it from functioning, which

Scientists discovered a mutated gene for the EPSPS enzyme in bacteria.
The mutation changes the structure of the EPSPS enzyme so that it can no
longer bind with herbicide molecules, but the enzyme can still support plant
growth. To make herbicide resistant plants, scientists modified the plant’s
normal EPSPS gene by replacing it with the mutated version from bacteria.

5. With your partner, use the EPSPS protein subunit sequence you
analyzed in Step 2 to model the structure of the EPSPS enzyme. Model
your enzyme as follows:
a. Use the coated wire to represent the backbone of your enzyme
chain.
b. Use colored chenille stems to represent the four kinds of subunits
of the enzyme.
c. Lay out all of your chenille stems along the length of the coated
wire to evenly space them before attaching any to make sure that
you use the entire length of the coated wire.

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MOLECULAR MECHANISMS OF HERBICIDE RESISTANCE ACTIVITY 10

d. Loop one end around the coated wire so that the remaining part of
the chenille stem extends away from the coated wire, and give just
one twist to hold the chenille stem in place. Your subunits do not
need to point in the same direction away from the coated wire.

6. Use the information in Table 10.1 to determine the orientation of each
subunit in the EPSPS enzyme. The colors of the protein subunits
indicate what type of subunit they are. This information indicates
where each subunit should be positioned when the protein is folded.
Some subunits are hydrophilic (attracted to water) and some are
hydrophobic (repelled by water). Record this for each subunit in the
“Type of Subunit” column on Student Sheet 10.1.

TABLE 10.1: Orientation of Protein Subunits

COLOR TYPE OF SUBUNIT ORIENTATION OF SUBUNIT
Blue Hydrophilic Tends to be on the surface of the folded protein
Red Hydrophobic Tends to be buried inside the folded protein, away from
any water
White Positive Attracted to negative (green); on or near the surface of
the folded protein
Green Negative Attracted to positive (white); on or near the surface of
the folded protein

7. Fold your enzyme so the chenille stems face the correct direction.

Hint: Since the red hydrophobic subunits prefer to be on the inside, start
by folding your coated wire so that the red subunits are all together to
form a center that the rest of your enzyme might fold around.

8. Follow your teacher’s instructions to compare your folded EPSPS
enzyme molecule with your classmates’ or group members’ molecules.
Discuss what might be causing any differences in structure between
your models.

Part B: Modeling Herbicide Resistance

9. With your group, discuss how changes to the EPSPS enzyme relate to
the herbicide resistance trait found in the superweeds in Farmer
Green’s fields. Be sure to include what you know about the link
between DNA and traits as you discuss the following:

• How can an enzyme support plant growth?
• How can a mutation protect a plant from herbicide?
• If a gene is mutated, what can happen to the structure of the

resulting enzyme?

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

10. On Student Sheet 7.2, “Modeling Genetic Modification,” revise your
model to include information about the role of the EPSPS in herbicide
resistance. Be sure to label your drawing. Add notes to help you show
the relationship between the elements you added to your model. Be
prepared to share your revisions.

11. Follow your teacher’s instructions to share your revisions with the class.

Build Understanding

1. Issue connection: What are some trade-offs of using herbicides on
crop plants?

2. How can genetic modification be a beneficial tool when generating a
herbicide resistant plant?

3. Imagine a plant with a mutation that makes it herbicide resistant. What
determines the percentage of offspring of that mutated plant that will
inherit the mutation for herbicide resistance?

Hint: Use what you know about Punnett squares.
4. Using your revised model on Student Sheet 7.2, construct an explanation

for how genetic modification in the EPSPS gene can result in a protein
that leads to herbicide resistance in plants. In your explanation, be sure
to include the following:

• The role of DNA
• The role of protein
• The process of transcription
• The process of translation
• How protein synthesis is similar or different in normal vs.

modified cells

• How scientists can tell that the modification was successful

KEY SCIENTIFIC TERMS

DNA
enzymes

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11 Meiosis and Sexual Reproduction

in the last activity, you learned that a specific mutation in the

EPSPS enzyme can change the structure of the enzyme so that it doesn’t
bind with herbicide and can still support plant growth, which makes the
plant herbicide resistant. This modification explains how a plant like the
corn in Farmer Green’s fields becomes herbicide resistant. But how can a
modified gene be transferred from one type of plant to another? How did
the modified gene get into superweeds? Did it come from modified corn?

FIGURE 11.1: These Ascaris
(roundworm) cells are
producing gametes.

FIGURE 11.2: These onion
cells are in various stages
of producing gametes.
Some of their cellular
structures are visible.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

In this activity, you will investigate the process by which sexually
reproducing organisms pass their genetic information to their offspring.
You will explore how gametes—an organism’s sex cells, like sperm and
eggs—are formed, and what happens in their DNA during this process.
Understanding this mechanism is important for determining how
superweeds could have been generated.

Guiding Question

How do organisms pass their genetic information to their
offspring?

Materials

FOR EACH PAIR OF STUDENTS

pop-beads chromosome model set:
16 blue pop beads
16 green pop beads
2 orange pop beads
2 blue centromeres
2 green centromeres

colored pencils
computer with Internet access

FOR EACH STUDENT

Student Sheet 11.1, “Meiosis”

Procedure

1. Visit the SEPUP SGI Third Edition page of the SEPUP website at
www.sepuplhs.org/high/sgi-third-edition. Follow your teacher’s
instructions to watch the meiosis simulation. Meiosis is the process of
cell division that occurs in developing sex cells, such as sperm and egg
cells. Pay close attention to what happens to the genetic material of the
cell at each phase.

2. On Student Sheet 11.1, “Meiosis,” draw what happens to the
chromosomes during each phase shown. Next to each drawing, write a
description summarizing the key events of each stage of meiosis.

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MEIOSIS AND SEXUAL REPRODUCTION ACTIVITY 11

3. With your partner, use the pop beads to model chromosomes and to
show what happens when a cell with two chromosomes—one pair—
undergoes meiosis. To do this:

a. Make two strands of four blue pop beads, and attach each strand to
a blue centromere. Repeat this process for green. This represents
one pair of chromosomes.

b. Simulate the replication of each chromosome during prophase I.
To do this, repeat Step 3a. Use the centromeres to form the shape of
the replicated chromosome shown in Figure 11.3.

FIGURE 11.3: Replicated chromosome model

Note that the X shape is a replicated chromosome. This model
therefore demonstrates one pair of replicated chromosomes, with a
tot3Fai4g2lu2roeS:Ef3P4Uf2oP2GSuGernI SGBsei0ns3e_tti0ec2srSBchromatids.

Agenda MedCond 9/9

Working with Pop Beads

Pop beads may be difficult to put together and pull apart, particularly if
they’re new. If this is the case, try these tips:

• To remove pop beads from a chain, pull the beads straight apart.
• Do not bend the peg connecting the pop beads, or it may break.
• Try swapping one pop bead for another one in your set.
• To put beads together, wet the ball and peg with a small amount of water.
• As a last resort, ask your teacher to provide a tiny amount of mineral oil

or petroleum jelly, and rub it on the ball and peg of the beads.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

4. Review Figure 11.4. Crossing over is a phenomenon that can happen

during prophase in meiosis I. If crossing over occurs, homologous
chromosomes exchange portions, as shown in the figure.

maternal paternal

homologous crossing over
chromosomes
paired during
prophase I of
mesiosis I

FIGURE 11.4: Crossing over

3422 SEPUP SGI Genetics SB
Figure: 3422GenSB 13_03

5. WAigthentdhaeMpeodCpo-nbdea9/d9model, demonstrate crossing over between the
replicated chromosomes you built in Step 3b. In your science
notebook, sketch what happened and describe the process of crossing
over.

6. Move the chromosome models through each remaining phase of
meiosis to show what occurs as the chromosomes move through
prophase, metaphase, anaphase, and telophase of meiosis I and II, and
the cells that result. In your science notebook, use colored pencils to
sketch the chromosomes at each stage.

7. With your partner, examine the parent cell in Figure 11.5. What
possible allele combinations could form in gametes produced from
this cell? Sketch your answer in your science notebook.

_P p

_S s FIGURE 11.5: Parent cell

8. Repeat Steps 3–6, but with a modification: Model a chromosome in a
ctheLFliialsg,btuhrAreeaidp:t3slha4Sa2cE2sePGbUoeePnneeSSnBGsIg1eG3ge_enm0ne7eetnitcictasol3lfyeomneodchifrieodmtooscoomnetawinitah new gene. To do
an orange pop
beAagde.nWdaiMthedyCoounrdp9a/9rtner, work with your pop-bead chromosome
model and your understanding of meiosis to answer this question:
What is the probability that a daughter cell will receive a gene that was
inserted into one chromosome in a parent cell?

C-80

c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

Maps1 Maps2 Maps3 Maps4 Maps5

MEIOSIS AND SEXUAL REPRODUCTION ACTIVITY 11

As you and your partner work with your model and discuss this
question, describe the role of each of the following:

DNA daughter cell

chromosomes parent cell

genes

9. Share your model and your reasoning from Step 8 with the other pair
in your group. Discuss any differences in your ideas.

10. In your science notebook, write an answer to the question posed in
Step 8. Incorporate each term from the list in Step 8 in your writing.

11. Return to the computer simulation on the SEPUP SGI Third Edition page
of the SEPUP website at www.sepuplhs.org/high/sgi-third-edition.
Proceed to the page comparing mitosis and meiosis, and complete
the simulation.

12. In your science notebook, summarize the similarities and differences
between mitosis and meiosis.

13. With your group, discuss the differences in how the following
processes lead to genetic variation in organisms:

• mutations
• different allele combinations during meiosis
• crossing over during meiosis

Build Understanding

1. How do the daughter cells that result from meiosis compare to the
parent cell? How does that change if crossing over occurs?

Hint: Think about the number of chromosomes and about genetic
variation.

2. Plants, animals, and other multicellular organisms grow new cells
using mitosis, but they reproduce sexually, combining the genes of two
parents. If one plant with a modified gene reproduces sexually with an
unmodified plant, how likely do you think it is that its offspring will
inherit that modified gene?

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

3. Farmer Green is still not sure if the superweeds in his fields are
herbicide resistant because of a mutation or if they are the result of
transgene migration from herbicide resistant corn, like the corn he
grows, to a weedy relative. What question does Farmer Green need
answered to determine which scenario occurred? Use what you know
about DNA and genes leading to the formation of proteins to explain
how the answer to your question would help Farmer Green figure out
which scenario occurred.

Hint: Think about what genes the superweeds would have in each
scenario and if the genes would produce the modified EPSPS enzyme
or a different type of protein.
KEY SCIENTIFIC TERMS
chromosome
crossing over
daughter cell
DNA
gametes
gene
meiosis
mitosis
parent cell

C-82

12 Genes and Chromosomes

as you have observed in the previous activities, the role of
chromosomes in cells helps to explain which genes are passed from one
generation to the next. Understanding the role of chromosomes is also
fundamental to learning how inserting genes into one organism might
affect the organism’s offspring. The reading in this activity will help you
gather evidence and information about genes and chromosomes to refine
your understanding of how herbicide resistance can be passed from a plant
to its offspring.

FIGURE 12.1: Humans all have the same number of chromosomes and the same
sequence of genes. Variations in the alleles for the same genes, along with
environmental factors, cause variation in human phenotypes.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

What happens to genes and chromosomes during meiosis
and sexual reproduction?

Materials

FOR EACH STUDENT

Student Sheet 12.1, “Three-Level Reading Guide: Genes and Chromosomes”

Procedure

1. Use Student Sheet 12.1, “Three-Level Reading Guide: Genes and
Chromosomes” to guide you as you complete the following reading.

Reading blood group protein
ichthyosis (a skin disease)
Chromosomes Carrying Genes ocular albinism
angiokeratoma (skin growths)
In each cell of a living organism, DNA
carries genetic information in the sequence a protein found in the blood
of its nitrogen bases. A gene is the section of deutan (a kind of red-green color-blindness)
DNA that contains information that G6PD (enzyme)
influences one or more traits. The DNA is protan (a kind of red-green color-blindness)
wrapped with proteins into structures called hemophilia A (failure of blood clotting)
chromosomes.
The number of chromosomes in each cell of FIGURE 12.2: This map of the human X
an organism depends on the species. chromosome shows the location of several
Bacteria, such as Escherichia coli (E. coli), s3p4e2c2ifSicEPgUePneSsGaI GndentehteictsraSBits they influence.
have one circular chromosome that Figure: 3422GenSB 14_01
contains about 4,500 genes. Some bacteria Agenda MedCond 9/9
also have one or more smaller plasmids that
carry a small number of genes. In
comparison, every human body cell except
for the sex cells contains the same set of 46
chromosomes, each of which carry
hundreds of genes—for a total of 20,000–
25,000 genes!

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GENES AND CHROMOSOMES ACTIVITY 12

In eukaryotes (organisms with a nucleus in FIGURE 12.3: This male karyotype shows the X chromosome
each cell), the chromosomes are present in and smaller Y chromosome present in male cells.
pairs. Each chromosome in a pair is
similar to its partner in size and the genes
it carries, except for the chromosome pair
that determines the organism’s sex. The
karyotype in Figure 12.3 illustrates the 23
pairs of chromosomes in the cell of a
human male. Notice that chromosomes in
pairs 1–22 are nearly identical in size and
shape. The two chromosomes of pair 23
are the sex chromosomes—they
determine the individual’s sex. In human
males, pair 23 has one X chromosome and
one Y chromosome. These two
chromosomes differ in size and shape. If
this were a karyotype for a human female,
pair 23 would contain two nearly identical
X chromosomes. If this were a karyotype
for a mouse, there would be 20 pairs of
chromosomes—and for a corn plant, there
would be 10 pairs.

Growth and Reproduction

For organisms to grow and reproduce, cells must divide to form offspring
cells, called daughter cells. As you know, during mitosis the chromosomes
are divided evenly between the two new cells to produce two daughter cells
that are identical to the parent cell. This occurs regularly for cell growth
and tissue repair in somatic cells (body cells, but not reproductive cells) in
multicellular organisms—such as humans, fish, and corn plants—and in
single-celled organisms, such as E. coli. In this way, cells in the body of a
multicellular organism (again, except for the sex cells) are the exact genetic
copies of the parent cell.

How and why are gametes different from the rest of the cells in an
organism? The answer lies in the processes of meiosis and sexual
reproduction. Sexual reproduction occurs when a male sperm fertilizes a
female egg. If these sex cells had a full set of chromosomes, each generation
would have twice the number of chromosomes as its parents. To prevent
this from happening, meiosis produces gametes (egg or sperm) that have
half as many chromosomes as other cells in the body.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

A gamete is haploid because it has one set of human body egg (n)
chromosomes. This is referred to as n cell (2n)

chromosomes. Human gametes contain 23 46 23
chromosomes (n = 23). A somatic
(nonreproductive) cell is diploid (it has 2n 46

chromosomes) because it has pairs of 23
chromosomes. When a human haploid egg and a
haploid sperm unite by fertilization, they form a sperm (n) fertilized egg
cell (2n)

diploid cell with 46 chromosomes (23 pairs). This same process occurs in FIGURE 12.4: Sex cells
and fertilization
all organisms that reproduce sexually. Only the number of ch3r4o2m2 oSEsPoUmPeSsGI Genetics SB
differs, as shown in Table 12.1.
Figure: 3422GenSB 14_03
Agenda MedCond 9/9

TABLE 12.1: Number of Chromosomes in Organisms

ORGANISM DIPLOID (2n) HAPLOID (n)
Human CHROMOSOMES FOUND CHROMOSOMES FOUND
Corn IN SOMATIC CELLS IN SEX CELLS
Rye plant 46 23
Common fruit fly 20 10
Garden snail 14 7
Gorilla 8 4
Elephant 54 27
48 24
56 28

Chromosomes and Genes

In Activity 5: Breeding Corn for Two Traits, you modeled the process of
crossing corn plants with such traits as purple or yellow kernels and
smooth or wrinkled kernels. This demonstrates independent assortment,
which means that it is equally likely for a PpSs corn plant to produce any of
four kinds of gametes: PS, Ps, pS, and ps.

Now that scientists have determined that genes are sections of
chromosomes, we know that genes on the same chromosome usually stay
together during meiosis. These are called linked genes, and they don’t
usually show independent assortment: The combination of traits that they
influence is passed on to the next generation together. For example, in fruit
flies, the genes for body color and eye color are found on the same
chromosome. Therefore, a parent with a gray body and yellow eyes would
pass on this combination of genes to its offspring.

Figure 12.5 shows fertilization and meiosis in two generations of a plant.
The red chromosomes represent those inherited from the female parent
plant, and the blue ones represent those inherited from the male parent
plant. As the chromosomes line up before division, the paternal and

C-86

GENES AND CHROMOSOMES ACTIVITY 12

BC d [continued from left]
A BC
parent D
sex cells E ae
before
fertilization

sperm egg CB BC BC BC
aa AA
fertilization dd
DD E
o spring cell E d ee
before meiosis C C E
B B CB BC
aa CB BC
ae A AA
D DD
dd
CB BCCB BC ee
a aA A EE

D Dd d
e eE E

CB BC BC CB BC CB
aA aa AA
Dd
eE DD dd

BC CB ee EE
aA
D D BC d BC d
Dd BC BC A A
eE
ae ae E E

daughter cells after meiosis

[continued at right] KEY
A/a = ower color gene
B/b = leaf shape gene
C/c = leaf color gene
D/d = height gene
E/e = number of blossoms gene

FIGURE 12.5: Chromosomes and meiosis C-87
LabAids SEPUP SGI Genetics 3e
Figure: Cells 3e SB 12.05
MyriadPro Reg 9.5/11

Maps1 Maps2 Maps3 Maps4 Maps5

c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

maternal chromosomes in the pair line up randomly and separate
independently of one another. This is called independent segregation of the
chromosomes, and it leads to increased genetic variation in the daughter
cells.

Sexual Reproduction and Variation

What happens in meiosis also helps explain why offspring of the same
parents are not identical. In Activity 11: Meiosis and Sexual Reproduction,
you observed the chromosomal variation in gametes produced by one
parent due to both independent segregation and crossing over of
chromosomes.

• Independent segregation of chromosomes means that a parent will

produce gametes with different combinations of traits. When two
parents reproduce, new combinations of chromosomes produce
offspring with a combination of traits from both parents. Notice that the
offspring formed by fertilization inherit one set of chromosomes from
each parent, which means that the offspring inherit only one allele for
each gene from each parent.

• Crossing over of chromosomes only happens during meiosis I, when

chromosomes exchange segments at their ends, as shown in Figure 12.6.
Crossing over happens quite frequently, and it substantially increases the
genetic variation of the gametes that an individual can generate.

aA e eEE e Ee E
CB BC

Dd

eE

FIGURE 12.6: These two chromosomes have exchanged segments of their DNA
th34ro2u2gShEPtUheP pSGroIcGeesnseotficcsroSBssing over. Each chromosome now has DNA from the
mFiagtuerren:a3l4a2n2GdetnhSeBp1a4te_r0n5al parent.
Agenda MedCond 9/9

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GENES AND CHROMOSOMES ACTIVITY 12

Abnormal Meiosis

Meiosis does not always go perfectly. Errors during meiosis can lead to
abnormalities in chromosome number, shape, or size. Genetic specialists
use karyotypes to test for chromosome abnormalities. To make a karyotype
for a human, the white blood cells are separated from a sample of the
patient’s blood. These cells are placed in a solution with a substance that
causes them to divide. Another substance is then added to stop the cell
division in metaphase, when the chromosomes are at their most condensed
and easy to see. The cells are then spread on a microscope slide, stained
with a special dye, and photographed. Finally, the images of the
chromosomes are arranged in pairs according to size and shape.

One of the most common errors that occurs in meiosis is
nondisjunction—the failure of chromosomes to separate during cell
division. If this happens, a gamete can form with an extra chromosome or
a missing chromosome. Nondisjunctions often result in gametes that either
cannot participate in fertilization or produce zygotes that do not survive
past the initial stages of cell division. However, chromosomal abnormalities
can occasionally appear in an offspring. Some examples of this in humans
are described in Table 12.2.

TABLE 12.2: Chromosome-Related Syndromes in Humans

SYNDROME NAME CHROMOSOMAL COMMON EFFECTS
Down syndrome ABNORMALITY Delayed physical and mental development, heart
Three copies of defects
Klinefelter syndrome chromosome 21 (trisomy
Prader-Willi syndrome 21) Learning difficulties, sometimes sterility, higher risk
Turner syndrome Males have extra X for some forms of cancer and heart disease
chromosome (XXY) Reduced muscle tone, short stature, learning
Missing part of difficulties, chronic hunger
chromosome 15 Short stature, sometimes sterility, sometimes do
Females missing all or not enter or complete puberty
part of an X chromosome

The phenotypes produced by these conditions vary. For example, the
effects of Down syndrome, one of the most common chromosome
abnormalities, are usually mild to moderate but are sometimes severe.
Educational interventions and good health care often improve the outlook
for affected individuals. Today, most individuals with chromosomal
abnormalities live full and productive lives.
Nondisjunction does not always have negative effects. In many plant species,
and some animal species, nondisjunction leads to a condition known as
polyploidy, where normally diploid organisms have additional sets of
chromosomes. Many of these plants are more vigorous than their diploid
relatives. Polyploidy can lead to new species and is an important source of

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

variety for a number of agricultural crops. For example, you may have heard
of durum wheat, which is often used to make pasta. Durum wheat has four
sets of chromosomes. Its relative, bread wheat, has 6 sets, and some
strawberries have 10 sets! Without this type of abnormal meiosis, we would
not have many of the agricultural crops that people rely on for food.

Build Understanding

1. Describe the differences in how the independent segregation of
chromosomes and crossing over during meiosis increase human
variation.

2. Develop a model to show how a plant that is genetically modified to be
herbicide resistant is able to pass on a modified gene to its offspring.
Include labels and captions to help explain the roles of DNA and
chromosomes in this process.

Note: You do not need to show every stage of meiosis in your model.
3. What questions do you still have about plants and herbicide resistance?
4. Issue connection: Polyploidy is widespread among plant species,

including about 30% of plant types that are grown for food and other
agricultural uses. How might this be important for maintaining the
sustainability of the global food supply?

KEY SCIENTIFIC TERMS

chromosome
crossing over
diploid
gamete
gene
haploid
karyotype
meiosis
mitosis
nondisjunction
polyploidy
somatic cells

C-90

13 Which Plant is Genetically Modified?

a field biologist visited farmer Green to inspect the superweeds
in his fields. The biologist noted that the weeds looked similar to the
superweeds reported in neighboring counties. She told Farmer Green that
she suspects the superweeds are related to a crop of canola that had been
genetically modified with the same herbicide resistance gene that Farmer
Green’s corn plants have—and canola is grown by many farmers across the
state. Given that the superweeds were reported across three counties
within two growing seasons of each other, the biologist thinks the most
likely cause is transgene migration—the modified canola crop bred with a
weedy relative, resulting in the superweeds found in Farmer Green’s fields.
But she pointed out that it’s also possible that the continuous application of
herbicides left behind weeds with a natural mutation that makes them
resistant to herbicides. To determine if Farmer Green’s superweeds had the
same herbicide resistance gene as the canola, the biologist collected
samples from his fields and sent them for testing.

FIGURE 13.1: This scientist is investigating the possibility of transgene migration in crop plants.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Imagine that you work for the genetics laboratory that has been hired to
perform the genetic tests. Samples of superweeds from affected fields,
including Farmer Green’s, were sent to your laboratory. You also have a
sample of the genetically modified canola. Now your lab must determine
which of the superweeds, if any, have the same herbicide resistance gene as
the genetically modified crop of canola.

Guiding Question

Which weed samples contain the herbicide resistance gene?

Materials

FOR EVERY TWO GROUPS OF FOUR STUDENTS

electrophoresis chamber with lid and power supply
electrophoresis buffer solution
electrical outlet

FOR EACH GROUP OF FOUR STUDENTS

4 SEPUP stir sticks
4 pipettes
agar gel
bottles of DNA samples from each of the following:

sample A: Farmer Green’s weeds
sample B: Neighbor Farm #1 weeds
sample C: Neighbor Farm #2 weeds
bottle of DNA sample from genetically modified canola
Chemplate
bottle of glycerin
bottle of water
timer
cup of water
paper towels

FOR EACH STUDENT

chemical splash goggles

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WHICH PLANT IS GENETICALLY MODIFIED? ACTIVITY 13

SAFETY

Wear chemical splash goggles at all times during this lab. If
accidental spills occur, inform your teacher immediately, and follow
their instructions to clean up the spill. Do not plug in the power until
the chamber is securely closed, and keep the lid closed at all times
when the power supply is plugged in. Wash your hands after
completing the activity.

Procedure

Part A: DNA Fingerprinting

1. With your partner, read “DNA Fingerprinting.”

DNA Fingerprinting

If a gene does not affect the physical appearance of an organism, how do
we determine the presence of one gene or another? One method is
through DNA fingerprinting. While all organisms contain DNA, every
individual organism contains a unique pattern of DNA sequences called a
DNA fingerprint. DNA fingerprints, like those shown in Figure 13.2, allow
scientists to compare the DNA of one organism to another.

blood at crime scene suspect 1 suspect 2

FIGURE 13.2: Comparing the
DNA fingerprints of blood found
at a crime scene to blood samples
from two suspects allows
investigators to determine if the
blood of either suspect was found
at the crime scene.
To create a DNA fingerprint, scientists use enzymes to cut a sample of an
woregF3ii4agg2nhu2irtse,Sm:tE3hP’4srU2oDP2uGNSgGehAnI GSaiBenpn1troe8ot_iscc0mes1sSasBlcl aplileecdegsetlhealtecatrreotphheonresseisp.aTrhateeldig, hbatesredthoenDtNheAir,
theAgfuenrdthaeMreitdCwoinlldm9/o9ve through the gel in a fixed amount of time. Pieces of
the same size form a band in the gel. The more pieces of the same size, the
thicker the band will be. In people, only samples from the same individual

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

DNA Fingerprinting continued

(or identical twins) will have an
identical pattern of bands in their
DNA. Other organisms that
reproduce asexually can have DNA
fingerprints that are identical to
their offspring’s.

In this activity, you will use gel
electrophoresis to analyze DNA
samples from several farms. This
will allow you to determine which
weeds contain the gene for
herbicide resistance by comparing a
control sample with the gene for
herbicide resistance with samples
from weeds on Farmer Green’s farm
and two other neighboring farms.

FIGURE 13.3: The DNA in this gel has
been stained with a blue dye to make
the banding pattern easy to see.

Part B: Comparing Genes

2. Follow your teacher’s instructions for recording your notes during this
laboratory. Watch carefully as your teacher demonstrates how to set up
the electrophoresis chamber and run the samples in the agar gel.

3. Follow your teacher’s instructions to set up your electrophoresis
chamber, which you will share with another group.
a. Place your gel in the chamber.
b. Work with the other group to pour buffer solution against the
side of the electrophoresis chamber until the surfaces of the gels
are just covered.

4. With your group, prepare each of the four DNA samples to be loaded
into the gel (samples A, B, and C, and a control sample of DNA from
canola that is genetically modified for herbicide resistance). To prepare
the samples, do the following:
a. Place 2 drops of each DNA sample into their own cup in the
SEPUP Chemplate.
b. To each sample, add 2 drops of glycerin.

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WHICH PLANT IS GENETICALLY MODIFIED? ACTIVITY 13

c. To each sample, add 2 drops of water.
d. Stir the contents of each cup with a clean SEPUP stir stick. Be sure

to use a fresh stir stick for each cup to prevent cross-contamination
of the samples. Rinse the stir stick in your cup of water
immediately after use.
5. Work with your group to transfer each DNA sample from the SEPUP
Chemplate into one of the middle four wells in the gel (place sample A
into well 2, sample B into well 3, and so on), using a clean pipette each
time. To do this, hold the pipette that contains the DNA sample
directly above the well. With both hands, slowly lower the tip of the
pipette into the buffer solution. Once the sample is loaded,
immediately rinse the pipette in your cup of water.
6. When both group’s gels are ready, carefully place the lid of the
electrophoresis chamber in place. Make sure to put the lid on the
chamber in the correct orientation, as shown by your teacher.
7. Without moving the chamber, check that the lid is on securely. Plug in
the power cord to start the flow of electricity.
8. Allow the gel to run for 30 minutes or until you see the samples
separate in the gel.
9. Disconnect the power. Carefully remove the lid of the electrophoresis
chamber and remove your group's gel as directed by your teacher.
10. Compare each lane of the gel to the lane that contains the control
sample of the herbicide resistant canola DNA. With your group,
discuss your results. Draw a sketch of your results in your science
notebook.
11. With your group, discuss the conclusions you might draw based on the
electrophoresis results. Be sure to support your conclusions with
evidence.

Build Understanding

1. Examine the following DNA electrophoresis results.

DNA band band band band
added AB C D
here

3422 SEPUP SGI Genetics SB C-95
Figure: 3422GenSB 18_08
Agenda MedCond 9/9

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

a. Which single labeled band represents the smallest pieces of DNA?
Explain how you can tell.

b. Which labeled band represents the most common-sized piece of
DNA in this sample? Explain how you can tell.

2. Farmer Green claims that the superweeds in his fields are herbicide
resistant as a result of transgene migration from weeds breeding with
genetically modified canola. Do you agree or disagree with his claim?
Develop an argument supported by evidence and reasoning.
KEY SCIENTIFIC TERMS
DNA
gel electrophoresis
gene
mutation
transgene migration

Extension

Gel electrophoresis is just one technique used to study genetics. As scientists
work to understand more about genetics, the techniques they use have
expanded and improved. One technique is PCR, or polymerase chain reaction,
which is used to make copies of segments of DNA. Sound familiar? It’s one
method that’s used in COVID-19 tests. Visit the SEPUP SGI Third Edition page
of the SEPUP website at www.sepuplhs.org/high/sgi-third-edition to learn
more about what this technique is, how it works, and why it’s used for
applications such as COVID-19 tests.

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14 G enetically Modified
Organisms and Biodiversity

Number of herbicide-resistant 20
weed species in the U.S.
genetic modification of crop plants provides an opportunity to
1in5 crease food production quickly and efficiently by introducing genes from
other organisms that produce a desired trait. About 90% of all major crops
in the U.S., including corn, soy, and wheat, are genetically modified. Many
1s0uccesses have resulted from genetic modification, such as Golden Rice
and pest-resistant corn, which you will learn more about in Activity 15:
Benefits and Trade-Offs of Genetically Modified Organisms. You have also
le5arned about the trade-offs that exist with genetically modified plants. For
example, transgene migration is well-documented and is difficult to
c0ontrol, as seen with ordinary weeds becoming herbicide resistant
supe1r9w90eeds1t9h92at ca1n99r4edu1c9e9c6rop1p99r8odu2c0t0io0n. 2002 2004 2006 2008 2010 2012 2014
Look at Figure 14.1. What do you notice aboYuetatrhe use of herbicides
compared to the presence of herbicide resistant weed species?

20

15

10

5

0 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 2012 2014
1990
Year

Number of herbicide resistant weed species in the US
Number of herbicides commonly applied in US

FIGURE 14.1: Increase in herbicide resistant weeds after herbicide resistant soy was first introduced in
the U.S. in 1996.

LabAids SEPUP SGI Genetics 3e C-97
Figure: Cells 3e SB 14_01
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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Transgene migration isn’t the only challenge posed by genetically modified
plants. These plants can also affect biodiversity—the variety of plant and
animal life present in a particular habitat or ecosystem—by outcompeting
native species. For example, plants that are modified to become drought-
tolerant may survive better in hot, dry climates than native plants. If the
modified plant outcompetes the native plants for resources, the native
plants may not produce as many offspring, leading to decreased or locally
extinct native plant populations.
And this may cause other related effects. If animals or insects rely on the
native plants for shelter and food, their numbers may decrease as well. In
turn, many crop plants rely on insects and other animals as pollinators.
Crops such as apples, nuts, oranges, and squash are directly dependent on
insect pollination. Other crops, such as alfalfa, sugar beets, carrots, and
onions, depend on insect pollinators to create seeds. If these populations
decline, it could dramatically affect food production.

Investigative Phenomenon

Farmer Green has heard reports from other found in other genetically modified crops,
farmers in his county that their fields are he was determined to learn more about
untouched by superweeds. Those farmers how the presence of these superweeds
are using alternative farming techniques would affect the future of his farm. He also
that do not include traditional herbicides wanted to know why some farmers were
and allow pollinators to thrive. Once Farmer not having any issues with superweeds.
Green knew that the weeds in his fields Could certain farming practices prevent
contained the herbicide resistance gene superweeds from spreading?

Guiding Question

How do superweeds affect biodiversity?

Materials

FOR EACH GROUP OF FOUR STUDENTS

set of 4 Superweed Data cards

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GENETICALLY MODIFIED ORGANISMS AND BIODIVERSITY ACTIVITY 14

Procedure

1. Read “Using Data,” and discuss the questions that follow with your
group.

Using Data 200

When scientists collect data, 160

part of their role as experts is kg corn/acre 120
to decide on the best
methods for analyzing the
data and presenting their 80

analysis to others. To do this, 40
scientists can use a number
of methods and concepts
from statistics and 0 2020
2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

probability. Graphs A and B Year

show the same data FIGURE 14.2: Corn production Graph A
presented in two ways.
Though these graphs show
the same data, Graph B 200SEPUP SGI 3e Genetics SB
Figure: 3422GenSB 14_02a

includes what is called a 160

best-fit line, which helps to
show if there are linear trends 120kg corn/acre
in the data over time.
When might a best fit-line
80

be helpful for analyzing data?
When would it not be helpful?
40

Graph C uses a best-fit line
to show a different set of data.
Compare Graph C to Graph 0 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019
B. What do you notice?
c7 m0 y0 k9 c0 m42 y92 k0 c100 m0 y20 k70 c25 m0 y15 k90

Maps1 Maps2 Maps3 Maps4 Maps5 Year

FIGURE 14.3: Corn production Graph Bc0m30y70k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko c15 m90 y90 k0

c60 m30 y100 k0 c50 m20 y75 k0 c15 m90 y90 k0 c90 m55 y40 k0 c39 m7 y12 k0

200 SEPUP SGI 3e Genetics SB c15 m10 y0 k85 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6 c25 m0 y15 k90
Figure: 3422GenSB 14_02b

160

kg corn/acre 120

80

40

0 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

Maps1 Maps5 c7 m0 y0 k9 Yearc0 m42 y92 k0c100 m0 y20 k70c25 m0 y15 k90 C-99

Maps2 Maps3 Maps4

FIGURE 14.4: Corn production Graph Cc60m30y100k0 c50m20y75k0 c15m90y90k0 c90m55y40k0
c0 m30 y70 k0 c0 m43 y94 k0 c15 m10 y0 k85 c95 m50 y30 ko c15 m90 y90 k0

c39 m7 y12 k0

SEPUP SGI 3e Genetics SB c15 m10 y0 k85 c80 m0 y0 k55 c12 m7 y0 k0 c0 m0 y0 k6 c25 m0 y15 k90
Figure: 3422GenSB 14_02c

GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

2. Review the Superweed Data cards with your group. Based on what you
see in the data, discuss how you think superweeds are affecting
biodiversity.

3. Pair up with a student from a group other than your own, and take
turns sharing your group’s thoughts from Step 2. After you’ve each
shared your thinking, discuss the similarities and differences between
your ideas. Be prepared to share your thinking with the class.

4. Follow your teacher’s instructions to share one idea from your
discussion. Be sure to include whether your partner agreed or
disagreed with your idea, and why.

5. Write the guiding question in your science notebook: How do
superweeds affect biodiversity? With your group, discuss any new
evidence from the card set and any questions you still have about how
superweeds became herbicide resistant. Record the new evidence and
your questions in your science notebook. You will revisit this
information in the next activities.

6. Share some of the new items you added to your science notebook with
the class.

Build Understanding

1. Issue connection: Why might biodiversity be important for
sustainable food production?

2. How can changes in biodiversity affect food production?
3. How can transgene migration affect biodiversity in a particular

habitat?
4. Farmer Green believes that his income will continue to decrease if

superweeds continue to grow in his fields. What do you think he could
do to change this outcome?

KEY SCIENTIFIC TERMS

biodiversity

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15 Benefits and Trade-Offs of
Genetically Modified Organisms

so far in this unit, you have learned about different reasons that

scientists develop genetically modified organisms to help address
sustainability problems. For example, you’ve learned that genetically
modified plants can improve farmers’ crop yields. To make a decision
about whether to use genetically modified organisms, people collect
evidence about the organism and weigh the trade-offs of its use.
In this activity, you will evaluate the potential benefits and trade-offs of using
genetically modified organisms to try to solve different sustainability issues.

FIGURE 15.1: The growth and harvest of genetically modified organisms has been
proposed as a potential solution for many sustainability issues, such as overfishing.
However, some people believe that the benefits are not worth the potential risks.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Guiding Question

What are some of the benefits and trade-offs of using genetically
modified organisms?

Materials

FOR EACH STUDENT

partially completed Student Sheet 2.3, “Genetics Case Study Comparison,”
from Activities 2 and 5
Student Sheet 15.1, “Genetically Modified Organisms”
3–5 sticky notes

Procedure

Part A: Case Studies

1. With your group, make a list of the concerns often associated with
genetically modified organisms. To help you generate ideas, refer to
your copy of Student Sheet 2.3, “Genetics Case Study Comparison.”

2. Discuss your ideas with the class, as directed by your teacher.
3. With the class, list the questions that should be answered if a

community is to responsibly evaluate the environmental, social, and
economic effects of using a genetically modified organism.
4. Follow your teacher’s instructions to move into case study reading
groups. Your group will read one of four case studies.
5. Individually read your assigned case study, using the Read, Think, and
Take Note strategy. To do this:
a. Stop at least three times during the reading to mark on a sticky

note your thoughts or questions about the reading. Use the “ Read,
Think, and Take Note Guidelines” to start your thinking.
b. After writing a thought or question on a sticky note, place it next to
the paragraph in the reading that prompted your note.

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BENEFITS AND TRADE-OFFS OF GENETICALLY MODIFIED ORGANISMS ACTIVITY 15

Read, Think, and Take Note Guidelines

As you read, use a sticky note from time to time to:

• Explain a thought or reaction to something you read
• Note something in the reading that is confusing or unfamiliar
• List a word from the reading that you do not know
• Describe a connection to something you’ve learned or read previously
• Make a statement about the reading
• Pose a question about the reading
• Draw a diagram or picture of an idea of connection

6. When you’ve finished reading, place your sticky notes on the table in
front of you. Share your thinking with your group. Look for
connections between your notes and those of others in your group.

Hint: Did any of you have similar questions? Were people unfamiliar
with the same words? Did people react differently to statements in the
reading?

7. Place your sticky notes in your science notebook. Below them, write a
short summary of what your group discussed and any conclusions the
group came to. Record the appropriate information from your case
study on Student Sheet 2.3.

8. Return to your original group to share the information from your case
study. As each group member shares about the case study they read,
record the appropriate information on Student Sheet 2.3.

9. With your group, review the list of questions from Step 3. Which
questions were answered for the genetically modified organisms you
read about? What questions do you still have about these organisms
and their possible environmental, social, and economic effects?

Part B: Genetically Modified Organism Benefits and Trade-Offs

10. Discuss with your group the general benefits and trade-offs of using
genetically modified organisms. Consider what you have learned in
this activity and in other activities in this unit. Use this information
to fill in the columns on Student Sheet 15.1, “Genetically Modified
Organisms.”

11. Follow your teacher’s directions to share your ideas with the class. Add
any new ideas to Student Sheet 15.1.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

Readings

CASE STUDY 1

Golden Rice

it is estimated that 250 million children To combat vitamin A deficiency, experts in
under age 5 suffer from vitamin A deficiency biotechnology have developed a way to deliver
and that 250,000 to 500,000 children experience vitamin A to more people through rice. For
blindness every year as a result. Some more than 3 billion people, white rice is their
geneticists claim to have found a solution, but main food. Geneticists have inserted genes from
others argue that what those geneticists are plants with high levels of beta-carotene into the
doing is more problematic than helpful. gene sequence of rice plants. These genes cause
the plants to produce beta-carotene, and the
Vitamin A is essential for the human body to hope is that the rice will now produce beta-
function. Proper functioning of the immune carotene. In their first attempts to genetically
system, vision, gene transcription, and bone modify the rice, geneticists inserted a daffodil
metabolism all rely on vitamin A. The human gene. This modification, however, did not
body converts beta-carotene—a pigment found produce enough beta-carotene in the rice to
in carrots, leafy green vegetables, sweet potatoes, meet a human body’s daily needs.
and many other foods—into vitamin A.
In their second attempt, geneticists used a
Vitamin A deficiency is a complex disorder maize (corn) gene. The resulting strain of
that results from a number of socioeconomic and genetically modified rice, called Golden Rice 2,
environmental issues. Factors such as limited may succeed in reducing the numbers of people
access to a varied diet accompanied by fats, social with vitamin A deficiency. Golden Rice 2
issues such as poverty, occurence of parasitic contains enough beta-carotene to meet half the
infections, and the rate of famine all play a role in daily value of vitamin A in one serving of
the development of vitamin A deficiency.

FIGURE 15.2: Vitamin A deficiency
prevalence worldwide

clinical mild
severe no data: problem likely
moderate problem under control

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BENEFITS AND TRADE-OFFS OF GENETICALLY MODIFIED ORGANISMS ACTIVITY 15

FIGURE 15.3: White rice
and Golden Rice

cooked rice. However, human bodies also need Another objection to farming Golden Rice 2
protein and fat in their diets to convert beta- is the potential for cross-pollination with
carotene to vitamin A, and malnourished existing crops. Transgene migration is
people often do not have access to foods considered inevitable by scientists. The results
containing protein and fat. can be damaging to biodiversity and the
sustainability of food production. In addition,
Some groups object to the possible use of many rice farmers—particularly in areas where
Golden Rice 2 to address vitamin A deficiency. vitamin A deficiency is high—save and then
They argue that people with vitamin A plant their rice’s seed from one season to the
deficiency would be better treated by next instead of buying new seed. But since
supporting access to a varied diet to improve genetically engineered plants like Golden Rice 2
overall nutrient consumption, improving are patented, farmers must purchase a license to
access to health care, and developing grow the plants. Currently, the company that
educational programs. Eating more leafy engineered Golden Rice 2 is providing free
greens, sweet potatoes, and other beta- licenses to farmers in the southern hemisphere
carotene-rich foods would alleviate vitamin A whose annual income is less than $10,000.
deficiency, but most people who depend on However, other farmers still struggle to
rice as a primary food source have difficulty purchase licenses and new seed every year and
accessing other beta-carotene-rich foods generate a profit.
year-round.

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GENETICS SCIENCE & GLOBAL ISSUES: BIOLOGY

CASE STUDY 2

Disease-Resistant Rice

there are over 7 billion people living on that is resistant to pests, disease, changes in
Earth today, and that number is expected to weather, and poor soil conditions.
reach nearly 10 billion by 2050. With an
increasing population, providing enough Rice blast fungus is the most destructive rice
resources, such as food, is a growing concern. disease in the world. It kills 10%–30% of all rice
Producing more food could require more land, crops produced every year—enough rice to feed
more water, and more people to grow the food. 60 million people. One standard method for
Another way to increase the amount of food is dealing with this disease is spraying fungicide.
to make it easier to grow, and this could include However, fungicides can have negative effects
producing crops that grow faster, use fewer on the environment and can harm other
resources, or resist disease or environmental organisms in the environment. In addition,
changes, such as droughts. blast fungus can become immune to the
fungicide over time, forcing scientists to create
Rice is a critical food source for more than 3 new fungicides.
billion people worldwide, with rice consumption
reaching nearly 500 million tons in 2018. It is Another method for combating the blast
projected that 650 million tons of rice will be fungus is to create strains of rice that are
needed in 2050 to feed the increasing world resistant to it. If rice plants have the gene for
population. Yet, just as the need for rice is blast fungus resistance, fungicide would not
increasing, rice yield has been declining due to need to be used.
pests and plant diseases, climate change, and
other environmental issues. Scientists are Before genetic modification was developed,
researching a variety of methods to produce rice selective breeding was used to cross rice plants
to develop rice varieties with desired traits, and
this process could take years to achieve results.

FIGURE 15.4: Rice growing in the
field ready for harvest

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