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Nature vs. Nature Benchmark Lab
Codoshia Gordon
3/26/10
4th
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Purpose:
The purpose of this experiment is to determine how light and dark affect the
phenotype of tobacco seeds.
Introduction:
In class we grew tobacco seeds and focused on the leaf’s color and gene in order
to see the role genes and the environment play in our life as we grow up. There are two
alleles for this gene, green leaves and albino leaves. If the seeds come out albino then that
means they would have a homozygous genotype because because both genotypes would
be a lower case letter, but if it has a heterozygous genotype then that means the leaf
would be green because the letters would either be both uppercase or lowercase and
uppercase.
Since we got the seeds from a science supply company we were only told the
genotypes and phenotypes of the grandparents. So to find out F2 genotype we had to use
a Punnett Square with what we got from the grandparents to figure out F1 and F2. After
everything was solved out we figured out that the genotypes were Gg,Gg for the kids and
the percentage could be 75% green and 25% albino.
G
g
G
GG
Gg
g
Gg
gg
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Hypothesis:
If I grow tobacco seeds under light and dark conditions, then I think the
phenotypes of the plants in the light will be 50% albino 50% green and the phenotypes of
the plants in the dark will be 50% green and 50% albino because in the light the sun will
make the plants lighter and when the plants are in the dark it will get darker, changing it
back or to a darker green because the plant will absorb the suns light.
Materials:
 2 Petri dishes
 2 pieces of filter paper
 About 100 tobacco seeds
 Pipet
 Water
 Tape
 Marker
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Methods:
 Using tape and a marker, label the bottom of one Petri dish “light” and the bottom
of another Petri dish “dark.” Also include your NAMES and BLOCK on these
labels.
 Place a piece of filter paper into the bottom half of each of the two Petri dishes. If
necessary, trim the paper with scissors so that the paper lays flat in the bottom of
the dishes.
 Using the pipet, place enough water on each piece of filter paper to completely
soak it.
 Pour off any excess water that is not absorbed into the filter paper into the sink.
 Sprinkle about 50 tobacco seeds evenly over the moistened filter paper in each of
the two Petri dishes. Be sure the seeds are spread out evenly in the dishes.
 Replace the covers on the two dishes.
 Place the dish labeled “light” in a well-lighted area.
 Place the dish labeled “dark” in a completely darkened area where it will receive
absolutely no light.
 Allow the seeds to germinate for one week. Let the dishes sit undisturbed except
to add water if the filter paper becomes dry.
 Observe the Petri dishes at the end of one week. When nearly all the seedlings
have germinated, count the number of green and albino seedlings in each dish.
Record these numbers on your data table.
 After counting the seeds of different phenotypes, reverse the locations of the
“light” and “dark” seedlings. In other words, place the “light” dish in the dark,
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and the “dark” dish in the light.
 After several days, observe the Petri dishes again and record the number of each
kind of seedling in your second data table.
 Clean up according to teacher instructions.
Results:
Number of sprouts
Percentage Of sprouts
Green
820
74.9%
Seeds in light
Albino
275
25.1%
Seeds in Dark
Green
0
0
Albino
569
100%
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Analysis:
HYpothesis Light
green
albino
hypothesis dark
green
albino
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Class Data in Light
green
albino
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Class Data in Dark
green
albino
Caption:
These four charts show the results of tobacco seeds growing in the light and dark.
The top two show my hypothesis and what I thought it was going to be, and the bottom
two show the class results and what the data shows and how the seeds prove the
experiment.
Conclusion:
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I thought that if I grew tobacco seeds under light and dark conditions then
phenotypes in light will be 50% albino and the phenotype in the dark will be 50% green
because the sun will make it lighter and the dark will make it darker changing it back or
to a darker green. The data refutes my hypothesis because instead of my results being
50% of each my results were 25% albino and 75% green, then the other on was 100%
albino. There could have been problems with my experiment that would make it were the
experiment did not come out right. My first source of error is that someone could have
walked by and moved my seeds causing to lose their place on the towel and the water that
they were drinking making it hard to grow because they could not drink water to grow.
My second error would be the weather changes while the plants growing. This is a big
effect because certain plants need a certain amount of sunlight to survive, but if they do
not get that they could grow slower or not grow at all. Then my last source of error would
be that we did not grow the seeds ourselves so they could have not been counted to the
exact seed because then it would effect the outcome percentages. I am 50% sure that my
data is valid because even though I gave all these errors that could have been made I feel
that they rarely happened and the seeds were well taken care of in the other room.
Connection:
The purpose of this experiment is to be to determine if you put tobacco seeds in
dark or light would it have the same effect as it did in the light or the dark. The plants that
grew in the light are more affected by the genes from their parents. Using, my data I saw
that the plants in the light were more affected by genes. At first my work on the Punnet
square said that according to the genes the plants would be 25% albino and 75% green.
The data came it showed that the Punnet Square was right. The environment affects the
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plants in the dark. When I looked at my data I saw that it was 100% albino instead of the
25% Albino and 75% green like the Punnet Square hypothesized. Since the experiment
did not come out the right way, it proves that the dark seeds were more affected by the
environment. For example, someone that likes to bungee jump does not get that from
their parents or grandparents. They know they like to bungee jump from living life and
experiencing it. Another example would be when someone is fat, they get that from their
parent/family's genes and also the environment. People get fat from there parents and
living life by walking down the street and from eating at fast food restaurants or when
they see food on billboards and commercials. Commercials and billboards are designed to
make you want them, to get hungry everytime you see them, or want to buy them.
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