Download Genetics Long-term Lab 2014

Genetics Long-Term Lab
Background:
This lab will involve Genetics, classification, and plants. 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. Each group of students will have two Petri dishes one for dark and one for light
conditions. After roughly two weeks the conditions will be switched for two more weeks and groups will state observations of
changes.
Procedures:
Day 1 set up
 The teacher will set up one light and one dark control for all classes.
 Get in groups of three or four. Every group will choose a representative to be the secretary to write down data. (The data
will be kept with the teacher)
 Get two sterile Petri dishes and put group # and Block light or dark with a wax pencil.
 Then ask teacher for 25 tobacco seeds for each dish. These are to be arranged on a moistened filter paper in the bottom of
the dish. (50 total) Make sure the top is on the dish.
 1st Block will go in Room 217 to put the “light” Petri dish near the window and 4th Block will go in Room 215 to do the same.
 The “dark” ones will go in draws in Room 219.
 Write Hypothesis around amount of green vs. albino in the light vs. the dark, whether or not the dark will grow initially,
whether or not the dark will grow once put in the light, whether or not the light plants will die or continue to grow when
put in the dark.
For roughly 2 weeks
 Every day the groups will check them and write down observations. Afterwards return to class and check the dark one and
do the same as for the light. Then give the observations/data back to the teacher. (A couple of drops of water will be
added when needed.)
 When well developed leaves form the class will examine the color of the leaves and record how many green vs. albino
(white) there are of each with their cell phone magnifying glass app or school magnifying glasses.
For roughly the next two weeks
 Change the Petri dish labels to reverse the process. (Light to dark and dark to light.) Then check for changes as the groups
did the previous two weeks.
At the end write a lab report to include the following: Purpose, Hypotheses, materials used, and Raw data, Observations, Results:
charts and graphs (see examples of charts below), Analysis (see questions below), and Conclusion –Worth a Quiz grade
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Growth Log
Date
Appearance of
Control Dish
Appearance of Dark
Dish
Appearance of Light
Dish
Light Dish
Chlorophyll Producing
Albino
# Of Seeds
% Of Seeds
Dark Dish
Chlorophyll Producing
Albino
# Of Seeds
% Of Seeds
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Analysis Questions
What are the phenotypes of the tobacco seedlings grown in the light (1st two weeks only)?
What are the phenotypes of the tobacco seedlings grown in the dark (before they were exposed to light)?
What happened to the light tobacco seedlings when they were put in darkness?
What happened to the dark tobacco seedlings when they were exposed to light?
From the data collected, what is the effect of light on the alleles for chlorophyll production?
Explain why did some of the seedlings in the light dish failed to produce chlorophyll and end up being albino?
Is it energy efficient for plants to produce chlorophyll only when sunlight is present in the environment? Explain your
answer in the space below.
8. Look up the Classification of tobacco in general and then state the changes found for green tobacco and albino tobacco.
9. Use the Hardy-Weinberg equation to determine the number of albino tobacco in a population of 1000 green tobacco
plants planted in Virginia.
10. Based on the experiment what characteristics of plants did your group discover?
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Conclusion
The experiment supports/does not support the hypotheses. Explain each hypothesis separately.
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