BigIdea
Genetics and Information Transfer
3
INVESTIGATION 8
BIOTECHNOLOGY:
BACTERIAL
TRANSFORMATION*
How can we use genetic engineering techniques to
manipulate heritable information?
■ BACKGROUND
Are genetically modified foods safe? There is ongoing debate about whether it is safe
to eat fruit and vegetables that are genetically modified to contain toxins that ward off
pests. For instance, biotechnologists have succeeded in inserting a gene (Bt) from the
bacterium Bacillus thuringiensis into the corn genome. When expressed, the Bt toxin
kills caterpillars and controls earworms that damage corn, but is the corn safe for
human consumption?
Genetic information passed from parent to offspring via DNA provides for
continuity of life. In order for information in DNA to direct cellular activities, it must
be transcribed into RNA. Some of the RNAs are used immediately for ribosomes or
to control other cellular processes. Other RNAs are translated into proteins that have
important roles in determining metabolism and development, i.e., cellular activities
and phenotypes (traits). When the DNA of a cell changes, the RNAs and proteins they
produce often change, which in turn changes how that cell functions.
DNA inside a cell can change several ways. It can be mutated, either spontaneously
or after the DNA replication machinery makes an error. Biotechnologists may cause an
intentional mutation in a cell’s own DNA as a way to change how that cell behaves. The
most powerful tool biotechnologists have, though, is the ability to transfer DNA from
one organism to another and make it function there. With this tool, they can make cells
produce novel protein products the cells did not make previously.
Examples of this powerful tool are all around us. Insulin that people take to control
their blood sugar levels is often made from engineered bacteria. Some vaccines, as
well as enzymes used for manufacturing denim jeans, are also made using engineered
cells. In the near future, engineered bacteria and other cells being developed could help
clean up spilled oil or chemicals, produce fuel for cars and trucks, and even store excess
carbon dioxide to help slow global climate change. Can you think of other possible
applications of genetic engineering? However, biotechnology and human manipulation
of DNA raise several ethical, social, and medical issues, such as the safety of genetically
modified foods. Can you think of other issues to consider?
* Transitioned from the AP Biology Lab Manual (2001)
Investigation 8 S97
This biotechnology depends on plasmids, small circles of DNA that were found first
in bacteria. Plasmids allow molecular biologists to manipulate genetic information in
a laboratory setting to understand more fully how DNA operates. Plasmids also let us
move DNA from one bacterium to another easily.
In this investigation, you will learn how to transform Escherichia coli (E. coli) bacteria
with DNA it has not possessed before so that it expresses new genetic information.
Bacterial cells that are able to take up exogenous (external) genetic material are
said to be “competent” and are capable of being transformed. You also will calculate
transformation efficiency to find out how well the E. coli took up the “foreign”
DNA. Using these techniques, you will have the opportunity to explore the field of
biotechnology further. You might want to explore the following questions:
• What causes mutations in bacteria? Can mutations affect plasmids?
• What is the function of plasmids in bacteria?
• Do cells take up more plasmids in some conditions and less in others?
By learning and applying these fundamental skills, you will acquire the tools to
conduct more sophisticated biotechnology investigations, including designing your own
experiments to manipulate DNA.
This investigation also provides you with the opportunity to review, connect, and
apply concepts that you have studied previously, including cell structure of bacteria;
structure and function of cell membranes, enzymes, and DNA and RNA; transcription
and translation; the operon model of the regulation of gene expression; evolution and
natural selection; and interactions between organisms and their environment.
Interspersed within each investigation are supplemental activities designed to
keep you on track and to provide opportunities for you to take a deeper dive into the
concepts. Your teacher may assign these activities for homework or ask that you do
them as you work through each investigation.
■ Learning Objectives
• To demonstrate the universality of DNA and its expression
• To explore the concept of phenotype expression in organisms
• To explore how genetic information can be transferred from one organism to another
• To investigate how horizontal gene transfer is a mechanism by which genetic
variation is increased in organisms
• To explore the relationship between environmental factors and gene expression
• To investigate the connection between the regulation of gene expression and
observed differences between individuals in a population of organisms
S98 Investigation 8
BIG IDEA 3: GENETICS AND INFORMATION TRANSFER
■ General Safety Precautions
Basic Sterile Technique
When working with and culturing bacteria, it is important not to introduce
contaminating bacteria or fungi into the experiment. Because these microorganisms are
ubiquitous, i.e., you can find them everywhere — on fingertips, bench tops, lab tables,
etc. — you must avoid these contaminating surfaces. When working with inoculation
loops, bulb pipettes, micropipettes, and agar plates, do not touch the tips of them (or,
in the case of agar, the surface itself) or place them directly onto contaminating surfaces.
Be sure to wash your hands before beginning the procedure and after — and cover your
sneezes. Do not eat, drink, apply cosmetics, or use personal electronic devices in the work
area.
Working with E. coli
The host E. coli used in this investigation, plasmids, and the subsequent transformants
created by their combination are not pathogenic (disease-causing) bacteria like the
E. coli O157:H7 strain that has been in the news. However, handling E. coli requires
appropriate microbiological and safety procedures. Your teacher will provide
instructions, but these practices include, but are not limited to, the following:
• Decontaminating work surfaces once a day and after any spill of viable material with
a 10% household bleach solution
• Decontaminating all contaminated liquid or solid wastes before disposal [This can be
done in an autoclave (20 minutes at 121°C) or in a 10% bleach solution (soaked for
20 minutes).]
• Washing your hands after handling organisms containing recombinant DNA and
before leaving the lab
• Wearing protective eyewear and disposable gloves
• Not eating, drinking, applying cosmetics, or using personal electronic devices, such
as iPods and cell phones, in the work area
Investigation 8 S99
■ THE INVESTIGATIONS
■ Getting Started
DNA provides the instructions necessary for the survival, growth, and reproduction of
an organism. When genetic information changes, either through natural processes or
genetic engineering, the results may be observable in the organism. These changes may
be advantageous for the long-term survival and evolution of a species, but it also may be
disadvantageous to the individuals who possess the different genetic information.
In bacteria, genetic variation does not happen by mutation alone. It also can be
introduced through the lateral (horizontal) transfer of genetic material between cells.
Some bacteria undergo conjugation, which is direct cell-to-cell transfer. Other bacteria
acquire DNA by transduction (viral transmission of genetic information). The third
route is transformation, which is uptake of “naked” DNA from the environment outside
the cell.
(You may have previously studied transformation in a different context. In an
experiment conducted in 1928, Frederick Griffith, seeking a vaccine against a virulent
strain of pneumonia, suggested that bacteria are capable of transferring genetic
information through transformation. Little did Griffith know that his work would
provide a foundation for genetic engineering and recombinant DNA technology in the
21st century.)
The concept of cell transformation raises the following questions, among others:
• To transform an organism to express new genetic information, do you need to insert
the new gene into every cell in a multicellular organism or just one? Which organism
is best suited for total genetic transformation — one composed of many cells or one
composed of a single cell?
• Can a genetically transformed organism pass its new traits on to its offspring? To
get this information, which would be a better candidate for your investigation — an
organism in which each new generation develops and reproduces quickly or one that
does this more slowly?
• Based on how you answered the first two sets of questions, what organism would be a
good choice for investigating genetic transformation — a bacterium, earthworm, fish,
or mouse?
If your answer to the last question is “bacterium,” you are on the right track. Genetic
transformation of bacteria most often occurs when bacteria take up plasmids from
their environment. Plasmids are not part of the main DNA of a bacterium. They are
small, circular pieces of DNA that usually contain genes for one or more traits that
may be beneficial to survival. Many plasmids contain genes that code for resistance to
antibiotics like ampicillin and tetracycline. [Antibiotic-resistant bacteria are responsible
for a number of human health concerns, such as methicillin-resistant Staphylococcus
aureas (MRSA) infections.] Other plasmids code for an enzyme, toxin, or other protein
that gives bacteria with that plasmid some survival advantage. In nature, bacteria may
swap these beneficial plasmids from time to time. This process increases the variation
S100 Investigation 8
BIG IDEA 3: GENETICS AND INFORMATION TRANSFER
between bacteria — variation that natural selection can act on. In the laboratory,
scientists use plasmids to insert “genes of interest” into an organism to change the
organism’s phenotype, thus “transforming” the recipient cell. Using restriction enzymes,
genes can be cut out of human, animal, or plant DNA and, using plasmids as vectors
(carriers of genetic information), inserted into bacteria. If transformation is successful,
the recipient bacteria will express the newly acquired genetic information in its
phenotype (Figure 1).
Recombinant
plasmid
E. coli host cell
Transformed cell
Figure 1. Transformation of Bacteria
In nature, the efficiency of transformation is low and limited to relatively few bacterial
strains. Also, bacteria can take up DNA only at the end of logarithmic growth; at this
time, the cells are said to be “competent.” In the lab, you have discovered several ways
to increase the rate of transformation. Now, rather than just a few bacteria taking up a
plasmid you want them to use, millions of bacteria can be transformed. The number of
bacteria that take up a plasmid successfully is called the “transformation efficiency.” This
is one of the values you will calculate in this lab unit.
In this investigation, you will use a predefined procedure to transform E. coli bacteria
with a plasmid carrying a foreignBio_S_Lab08_01
gene. There are several different plasmids your
instructor can choose from; you will be instructed about which one to work with for this
unit.
NOTE: Illustration requires less width than specified.
E. coli is an ideal organism for the molecular geneticist to manipulate because it
naturally inhabits the human colon and easily can be grown in a nutrient medium such
as LB broth.
But what is E. coli’s natural or pre-transformation phenotype?
• Observe the colonies of E. coli grown on the starter LB/agar plate provided by
your teacher to glean some information before you determine if any genetic
transformation has occurred. What traits do you observe in pre-transformed
bacteria? Record your observations in your laboratory notebook.
Investigation 8 S101
Student Manual
pGLO Transformation
Lesson 1 Introduction to Transformation
In this lab you will perform a procedure known as genetic transformation. Remember
that a gene is a piece of DNA which provides the instructions for making (codes for) a
protein. This protein gives an organism a particular trait. Genetic transformation literally
means “change caused by genes,” and involves the insertion of a gene into an organism
in order to change the organism’s trait. Genetic transformation is used in many areas of
biotechnology. In agriculture, genes coding for traits such as frost, pest, or spoilage
resistance can be genetically transformed into plants. In bioremediation, bacteria can be
genetically transformed with genes enabling them to digest oil spills. In medicine, diseases
caused by defective genes are beginning to be treated by gene therapy; that is, by genetically
transforming a sick person’s cells with healthy copies of the defective gene that causes
the disease.
You will use a procedure to transform bacteria with a gene that codes for Green
Fluorescent Protein (GFP). The real-life source of this gene is the bioluminescent jellyfish
Aequorea victoria. Green Fluorescent Protein causes the jellyfish to fluoresce and glow in
the dark. Following the transformation procedure, the bacteria express their newly acquired
jellyfish gene and produce the fluorescent protein, which causes them to glow a brilliant
green color under ultraviolet light.
In this activity, you will learn about the process of moving genes from one organism to
another with the aid of a plasmid. In addition to one large chromosome, bacteria naturally
contain one or more small circular pieces of DNA called plasmids. Plasmid DNA usually
contains genes for one or more traits that may be beneficial to bacterial survival. In nature,
bacteria can transfer plasmids back and forth allowing them to share these beneficial
genes. This natural mechanism allows bacteria to adapt to new environments. The recent
occurrence of bacterial resistance to antibiotics is due to the transmission of plasmids.
Bio-Rad’s unique pGLO plasmid encodes the gene for GFP and a gene for resistance to
the antibiotic ampicillin. pGLO also incorporates a special gene regulation system, which can
be used to control expression of the fluorescent protein in transformed cells. The gene for GFP
can be switched on in transformed cells by adding the sugar arabinose to the cells’ nutrient
medium. Selection for cells that have been transformed with pGLO DNA is accomplished by
growth on ampillicin plates. Transformed cells will appear white (wild-type phenotype) on
plates not containing arabinose, and fluorescent green under UV light when arabinose is
included in the nutrient agar medium.
You will be provided with the tools and a protocol for performing genetic transformation.
STUDENT MANUAL
LESSON 1
Your task will be to:
1. Do the genetic transformation.
2. Determine the degree of success in your efforts to genetically alter an organism.
32
Lesson 1 Focus Questions
There are many considerations that need to be thought through in the process of
planning a scientific laboratory investigation. Below are a few for you to ponder as you take
on the challenge of doing a genetic transformation.
Since scientific laboratory investigations are designed to get information about a
question, our first step might be to formulate a question for this investigation.
Consideration 1: Can I Genetically Transform an Organism? Which Organism?
1. To genetically transform an entire organism, you must insert the new gene into every
cell in the organism. Which organism is better suited for total genetic transformation—
one composed of many cells, or one composed of a single cell?
2. Scientists often want to know if the genetically transformed organism can pass its new
traits on to its offspring and future generations. To get this information, which would be a
better candidate for your investigation, an organism in which each new generation
develops and reproduces quickly, or one which does this more slowly?
3. Safety is another important consideration in choosing an experimental organism. What
traits or characteristics should the organism have (or not have) to be sure it will not
harm you or the environment?
33
STUDENT MANUAL
LESSON 1
4. Based on the above considerations, which would be the best choice for a genetic
transformation: a bacterium, earthworm, fish, or mouse? Describe your reasoning.
Consideration 2: How Can I Tell if Cells Have Been Genetically Transformed?
Recall that the goal of genetic transformation is to change an organism’s traits,
also known as their phenotype. Before any change in the phenotype of an organism
can be detected, a thorough examination of its natural (pre-transformation) phenotype
must be made. Look at the colonies of E. coli on your starter plates. List all observable
traits or characteristics that can be described:
The following pre-transformation observations of E. coli might provide baseline data to
make reference to when attempting to determine if any genetic transformation has
occurred.
a) Number of colonies
b) Size of :
1) the largest colony
2) the smallest colony
3) the majority of colonies
c) Color of the colonies
d) Distribution of the colonies on the plate
e) Visible appearance when viewed with ultraviolet (UV) light
f)
The ability of the cells to live and reproduce in the presence of an antibiotic such as
ampicillin
1. Describe how you could use two LB/agar plates, some E. coli and some ampicillin to
determine how E. coli cells are affected by ampicillin.
STUDENT MANUAL
LESSON 1
2. What would you expect your experimental results to indicate about the effect of
ampicillin on the E. coli cells?
34
Consideration 3: The Genes
Genetic transformation involves the insertion of some new DNA into the E. coli
cells. In addition to one large chromosome, bacteria often contain one or more small
circular pieces of DNA called plasmids. Plasmid DNA usually contains genes for more
than one trait. Scientists use a process called genetic engineering to insert genes coding
for new traits into a plasmid. In this case, the pGLO plasmid has been genetically
engineered to carry the GFP gene which codes for the green fluorescent protein, GFP,
and a gene (bla) that codes for a protein that gives the bacteria resistance to an antibiotic.
The genetically engineered plasmid can then be used to genetically transform bacteria
to give them this new trait.
pGLO plasmid DNA
GFP
Cell
wall
Flagellum
Beta-lactamase
(antibiotic resistance)
Bacterial
chromosomal
DNA
Pore
Consideration 4: The Act of Transformation
This transformation procedure involves three main steps. These steps are intended to
introduce the plasmid DNA into the E. coli cells and provide an environment for the cells to
express their newly acquired genes.
To move the pGLO plasmid DNA through the cell membrane you will:
1. Use a transformation solution containing CaCl2 (calcium chloride).
2. Carry out a procedure referred to as heat shock.
3. Provide them with nutrients and a short incubation period to begin expressing their
newly acquired genes.
35
STUDENT MANUAL
LESSON 1
For transformed cells to grow in the presence of ampicillin you must:
STUDENT MANUAL
LESSON 2
Lesson 2 Transformation Laboratory
Workstation (✔) Checklist
Your workstation: Materials and supplies that should be present at your workstation prior
to beginning this lab are listed below.
Student workstation
Material
Quantity
E. coli starter plate
1
Poured agar plates (1 LB, 2 LB/amp, 1 LB/amp/ara)
4
Transformation solution
1
LB nutrient broth
1
Inoculation loops
7 (1 pk of 10)
Pipets
5
Foam microcentrifuge tube holder/float
1
Container (such as foam cup) full of crushed ice (not cubed ice)1
Marking pen
1
Copy of Quick Guide
1
Microcentrifuge tubes
2
(✔)
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
❏
Common workstation. A list of materials, supplies, and equipment that should be present
at a common location to be accessed by your team is also listed below.
Material
Rehydrated pGLO plasmid
42°C water bath and thermometer
UV Light
37°C incubator
(optional, see General Laboratory Skills–Incubation)
2–20 µl adjustable volume micropipets
2–20 µl micropipet tips
36
Quantity
1 vial
1
1
1
❏
❏
❏
❏
1
1
❏
❏
-pGLO
+pGLO
1. Label one closed micro test tube +pGLO and another -pGLO. Label both tubes with
your group’s name. Place them in the foam tube rack.
2. Open the tubes and, using a sterile transfer pipet, transfer 250 µl of transformation
solution (CaCl2) into each tube.
Transformation Solution
37
-pGLO
+pGLO
250 µl
STUDENT MANUAL
LESSON 2
Transformation Procedure
Ice
+pGLO
4. Use a sterile loop to pick up 2–4 large colonies of bacteria from your starter plate.
Select starter colonies that are "fat" (ie: 1–2 mm in diameter). It is important to take
individual colonies (not a swab of bacteria from the dense portion of the plate), since the
bacteria must be actively growing to achieve high transforation efficiency. Choose only
bacterial colonies that are uniformly circular with smooth edges. Pick up the +pGLO tube
and immerse the loop into the transformation solution at the bottom of the tube. Spin the
loop between your index finger and thumb until the entire colony is dispersed in the
transformation solution (with no floating chunks). Place the tube back in the tube rack in
the ice. Using a new sterile loop, repeat for the -pGLO tube.
(+pGLO)
(-pGLO)
5. Examine the pGLO DNA solution with the UV lamp. Note your observations. Immerse
a new sterile loop into the pGLO plasmid DNA stock tube. Withdraw a loopful. There
should be a film of plasmid solution across the ring. This is similar to seeing a soapy
film across a ring for blowing soap bubbles. Mix the loopful into the cell suspension of
the +pGLO tube. Optionally, pipet 10 µl of pGLO plasmid into the +pGLO tube & mix.
Do not add plasmid DNA to the -pGLO tube. Close both the +pGLO and -pGLO tubes
and return them to the rack on ice.
+pGLO
STUDENT MANUAL
LESSON 2
3. Place the tubes on ice.
pGLO Plasmid DNA
(+pGLO)
38
(-pGLO)
Rack
Ice
7. While the tubes are sitting on ice, label your four LB nutrient agar plates on the bottom
(not the lid) as follows:
•
Label one LB/amp plate:
+ pGLO
•
Label the LB/amp/ara plate:
+ pGLO
•
Label the other LB/amp plate:
- pGLO
•
Label the LB plate:
- pGLO
pGLO
pGLO
LB/
amp/ara
LB/amp
pGLO
pGLO
LB/amp
LB
8. Heat shock. Using the foam rack as a holder, transfer both the (+) pGLO and
(-) pGLO tubes into the water bath, set at 42oC, for exactly 50 sec. Make sure to
push the tubes all the way down in the rack so the bottom of the tubes stick out and
make contact with the warm water. Double-check the temperature of the water bath
with two thermometers to ensure accuracy.
When the 50 sec are done, place both tubes back on ice. For the best transformation
results, the transfer from the ice (0°C) to 42°C and then back to the ice must be rapid.
Incubate tubes on ice for 2 min.
Water bath
Ice
42°C for 50 sec
39
Ice
STUDENT MANUAL
LESSON 2
6. Incubate the tubes on ice for 10 min. Make sure to push the tubes all the way down in
the rack so the bottom of the tubes stick out and make contact with the ice.
-pGLO
+pGLO
250 µl
LB broth
-pGLO
+pGLO
10. Gently flick the closed tubes with your finger to mix and resuspend the bacteria. Using a
new sterile pipet for each tube, pipet 100 µl of the transformation and control suspensions
onto the appropriate nutrient agar plates.
100 µl
O
amp
+p
O
GL
LB/
GL
LB
/amp/ara
-p
O
+p
GL
LB/
-p
amp
40
GL
LB
Control plates
Transformation plates
O
STUDENT MANUAL
LESSON 2
9. Remove the rack containing the tubes from the ice and place on the bench top.
Open a tube and, using a new sterile pipet, add 250 µl of LB nutrient broth to the
tube and reclose it. Repeat with a new sterile pipet for the other tube. Incubate the
tubes for 10 min at room temperature.
O
amp
-p
O
LB/
+p
GL
LB
/amp/ara
O
GL
GL
LB/
amp
-p
O
+p
GL
LB
12. Stack up your plates and tape them together. Put your group name and class period
on the bottom of the stack and place the stack of plates upside down in the 37°C
incubator until the next day. The plates are inverted to prevent condensation on the
lid which may drip onto the culture and interfere with your results.
41
STUDENT MANUAL
LESSON 2
11. Use a new sterile loop for each plate. Spread the suspensions evenly around the
surface of the LB nutrient agar by quickly skating the flat surface of a new sterile loop
back and forth across the plate surface. DO NOT PRESS TOO DEEP INTO THE AGAR.
Uncover one plate at a time and re-cover immediately after spreading the suspension of
cells. This will minimize contamination.
STUDENT MANUAL
LESSON 2
Lesson 2 Review Questions
Name ___________________
Before collecting data and analyzing your results answer the following questions.
1. On which of the plates would you expect to find bacteria most like the original
non-transformed E. coli colonies you initially observed? Explain your predictions.
2. If there are any genetically transformed bacterial cells, on which plate(s) would they
most likely be located? Explain your predictions.
3. Which plates should be compared to determine if any genetic transformation has
occurred? Why?
4. What is meant by a control plate? What purpose does a control serve?
42
Lesson 3 Data Collection and Analysis
A. Data Collection
Observe the results you obtained from the transformation lab under normal room lighting.
Then turn out the lights and hold the ultraviolet light over the plates. Alternatively the protocol
can incorporate digital documentation of the plates with Vernier’s Blue Digital BioImaging
System (Appendix E).
2. How much bacterial growth do you see on each plate, relatively speaking?
3. What color are the bacteria?
4. How many bacterial colonies are on each plate (count the spots you see).
Observations
Transformation plates
+pGLO
LB/amp
+pGLO
LB/amp/ara
Observations
Control plates
-pGLO
LB/amp
-pGLO
LB
43
STUDENT MANUAL
LESSON 3
1. Carefully observe and draw what you see on each of the four plates. Put your drawings
in the data table below. Record your data to allow you to compare observations of the
“+ pGLO” cells with your observations for the non-transformed E. coli. Write down the
following observations for each plate.
B. Analysis of Results
The goal of data analysis for this investigation is to determine if genetic transformation
has occurred.
1. Which of the traits that you originally observed for E. coli did not seem to become
altered? In the space below list these untransformed traits and how you arrived at this
analysis for each trait listed.
Original trait
Analysis of observations
STUDENT MANUAL
LESSON 3
2. Of the E. coli traits you originally noted, which seem now to be significantly different
after performing the transformation procedure? List those traits below and describe the
changes that you observed.
New trait
Observed change
3. If the genetically transformed cells have acquired the ability to live in the presence of the
antibiotic ampicillin, then what might be inferred about the other genes on the plasmid that
you used in your transformation procedure?
4. From the results that you obtained, how could you prove that the changes that occurred
were due to the procedure that you performed?
44
Lesson 3 Review Questions
Name _____________________
What’s Glowing?
If a fluorescent green color is observed in the E. coli colonies then a new question
might well be raised, “What are the two possible sources of fluorescence within the
colonies when exposed to UV light?”
1. Recall what you observed when you shined the UV light onto a sample of original
pGLO plasmid DNA and describe your observations.
2. Which of the two possible sources of the fluorescence can now be eliminated?
3. What does this observation indicate about the source of the fluorescence?
4. Describe the evidence that indicates whether your attempt at performing a genetic
transformation was successful or not successful.
45
STUDENT MANUAL
LESSON 3
Explain:
Lesson 3 Review Questions
Name ____________________
The Interaction between Genes and Environment
Look again at your four plates. Do you observe some E. coli growing on the LB plate that
does not contain ampicillin or arabinose?
STUDENT MANUAL
LESSON 3
1. From your results, can you tell if these bacteria are ampicillin resistant by looking at
them on the LB plate? Explain your answer.
2. How would you change the bacteria’s environment—the plate they are growing on—to
best tell if they are ampicillin resistant?
3. Very often an organism’s traits are caused by a combination of its genes and its environment.
Think about the green color you saw in the genetically transformed bacteria:
a.
What two factors must be present in the bacteria’s environment for you to see the
green color? (Hint: one factor is in the plate and the other factor is in how you look
at the bacteria).
b.
What do you think each of the two environmental factors you listed above are
doing to cause the genetically transformed bacteria to turn green?
c.
What advantage would there be for an organism to be able to turn on or off particular
genes in response to certain conditions?
46