Name
Date
Gene Expression in Genetic Tobacco
I Background Information
An organism’s phenotype or physical appearance for a particular trait is the
result of both its genetic makeup and the environment. In many instances, an
organism may have genes for a particular phenotype, but they are turned-off by
environmental factors such as light or temperature. The ability of certain
genes to be turned-on or turned-off by environmental factors has evolved in
some species over many generations. The most likely reason this occurred is
because organisms that can turn genes off, when the proteins they produce are
not needed, are more energy efficient. This energy efficiency provided a
survival advantage for individuals possessing the characteristic.
Tobacco seeds will germinate and grow in as little as three days if they are kept
moist. The seeds contain an embryonic plant along with cotyledons that serve as
a food source for the embryonic plant before its leaves develop, produce
chlorophyll, and carry out photosynthesis. Tobacco seedlings that possess a
dominant allele for chlorophyll production will produce chlorophyll if
environmental conditions are correct. However, tobacco seedlings that possess
two recessive alleles are genetically programmed to be albino, and will not
possess chlorophyll. Therefore, photosynthesis cannot occur in albino plants.
II Problem
Will the presence of sunlight effect the expression of the genes for chlorophyll
production in tobacco seedlings?
III Hypothesis
IV Experiment
1. Set up two experimental petri dishes by arranging about 50 tobacco seeds on
a moistened filter paper in the bottom of a petri dish. Also, set up one control
petri dish, by placing 50 tobacco seeds on a dry filter paper in the bottom of a
petri dish. The seeds should be spread out on each of the papers. Use a
toothpick to move the tobacco seeds.
2. Put the covers over the dishes and label them (C, ED, and EL). Place one of
the experimental dishes and the control dish in the light on the plant stand.
Place the other experimental dish in a drawer in the dark. Record the appearance
of the seeds and starting date in your seed growth log.
3. Each day, check the seeds and record the progress they have made in regard
to growth and development. Record any changes in the seed growth log. Add
water to the experimental dishes if necessary to keep the filter paper moist.
4. It will take between 7 and 10 days for the seeds to grow sufficiently to see
their leaves. Once the seeds have grown sufficiently, examine the color of the
leaves and record data in tables. In addition, take photographs of the tobacco
seedlings using a digital camera and magnifying glass.
V Data Analysis
Growth Log
Date
Appearance of
Control Dish
Appearance of
Dark Dish
Appearance of
Light Dish
Data Tables and Photo Documentation
(Use the data from 4 classes to fill in the data tables below- scroll to bottom of this
page for data)
Control Dish
Chlorophyll Producing
Albino
# Of Seeds
% Of Seeds
Light Dish
Chlorophyll Producing
Albino
# Of Seeds
% Of Seeds
Dark Dish
Chlorophyll Producing
Albino
# Of Seeds
% Of Seeds
Dish kept in dark
exposed to Light for
24-48 hours
Chlorophyll Producing
Albino
# Of Seeds
% Of Seeds
Data Analysis Questions
1. Was the control dish in the experiment a positive or negative control?
_______
Explain why in the space below.
2. What are the phenotypes of the tobacco seedlings growing in the light at
the end of the experiment?
3. What are the phenotypes of the tobacco seedlings grown in the dark
(before they were exposed to light)?
4. What are the phenotypes of the tobacco seedlings grown in the dark but
then exposed to light for 24 hours?
5. From the data collected, what is the effect of light on the alleles for
chlorophyll production?
6. Explain why did some of the seedlings in the light dish failed to produce
chlorophyll and end up being albino?
7. Predict what will happen to the albino seedlings in the light dish by day 30
if growth was allowed to proceed. Explain your prediction.
8. Albino seedlings will not survive long enough to reproduce and pass their
alleles on to the next generation. If this is so, explain how were albino
seeds produced by the parent plants from which our seeds were
harvested?
9. Were all of the tobacco seedlings that grew in the dark albino? ________
Explain your answer in the space below.
10. Is it energy efficient for plants to produce chlorophyll only when sunlight
is present in the environment? ________ Explain your answer in the
space below.
VI Conclusion
The experiment supports/does not support the hypothesis.
________________________________________________
CLASS RESULTS:
Genetic Tobacco Results 2003
Dish Kept in Light
# Green Class A = 28
Class B = 67 Class C = 50
# Albino Class A = 15
Class B = 22
Class C = 15
Class D = 102
Total = 247
Class D = 16
Total = 68
Dish Kept in Dark
# Green Class A = 0
# Albino Class A= 59
Class B = 0
Class B =76
Class C = 0
Class D = 0
Total = 0
Class C =131
Class D = 91
Total = 359
Dish Kept in Dark and then Exposed to Light for 24 – 48 hours
# Green Class A =30
Class B =52
Class C =119
Class D =97
Total = 298
# Albino Class A= 16
Class B =15
Class C =29
Class D =25
Total = 85
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