Download The Genetics of Garden Peas

The Genetics
of Garden Peas
Topic
Students simulate Gregor Mendel’s work on the inheritance of traits in
garden peas.
Introduction
Inheritance of genes explains all of the traits expressed in organisms,
from the colors in pea plant flowers to patterns of baldness in adult
humans. The work of Gregor Mendel (1822–1884) paved the way toward
understanding dominant and recessive traits, and helped geneticists
analyze the influence of genes on health, appearance, and sex.
Time Required
60 minutes
Materials
✒ 8 index cards
✒ black markers
Safety Note
Please review and follow the safety guidelines.
Procedure
1.
In this lab, you will play the role of a plant breeder. Index cards will
represent your plants. Divide the index cards into two stacks of four
cards each. Each stack of cards represents a pure-breeding stock of
plants. Pure-breeding plants consistently breed true for the trait
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THE GENETICS OF GARDEN PEAS
2
being studied. The two stacks will serve as your parental generation,
or the original mother and father of the family line.
2. Write P on each of the four cards in one stack. This letter
represents a dominant gene from a pure-breeding, purple-flowering
pea plant.
3. Write p on each of the four cards in the other stack. The p stands
for a recessive gene from a pure-breeding, white-flowering pea plant.
Be sure that you can tell your P from your p (Figure 1).
index cards
p
p
p
p
P
P
P
P
Figure 1
4. Turn both stacks of cards face down.
5. Draw one card from each stack and set the pair aside, face down.
6. Continue drawing one card from each stack, pairing them up and
placing them face down in separate stacks, until you have paired up
all of the cards.
7. These four new stacks of cards represent the offspring of the
parent plants. These offspring are called the F1 (first filial)
generation. Turn over one pair of F1 cards. On the first column of
the data table, record the combination of letters on these two
cards. In the second column, write down the color this pair of letters
represents. (P is a dominant trait for purple, and p is a recessive
trait for white. If your cards show PP or Pp, the flowers will be
purple. If your cards show pp, the flowers will be white.)
8. Repeat step 8 for the other pairs of cards.
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THE GENETICS OF GARDEN PEAS
3
Pick up all eight cards and separate them into two new stacks, each
of which contains two P cards and two p cards. Turn one stack face
down and shuffle it. Then turn the other stack face down and
shuffle it.
10. Without looking at the letters on the cards, draw one card from each
stack. Pair these cards and set them aside, face down. Do the
same for the rest of the cards in the two stacks. These four new
stacks represent plants of the F2 (second filial) generation.
11. One at a time, turn over each stack of cards. Record the letters on
each pair of cards in the third column of the data table. In the
fourth column, write the colors represented by each set of letters.
9.
Data
Table:
Combination
index
cards
Data
Table:
Combination of
of index
cards
Pairs
of cards
Combination of
letters in F1
generation
Colors of flowers Combination of
in F1 generation letters in F2
generation
Colors of flowers
in F2 generation
1st
2nd
3rd
4th
Analysis
In the F1 generation, what percentage of the plants expressed the
dominant (P) gene? in the F2 generation?
2. If you wanted to raise all purple flowers for several generations,
what breeding stock would you use? Why?
3. What breeding stock would produce white flowers for several
generations? Why?
4. Besides color of flowers, there are thousands of other genetic traits
in plants, including height of stem, shape of fruit, and color of fruit.
What are some of the genetic traits in humans?
1.
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THE GENETICS OF GARDEN PEAS
4
What’s Going On?
In this activity, P represents the gene for purple flowers, a
dominant trait in pea plants; and p represents the gene for
white flowers, a recessive trait. You created one stack of
cards with all P genes (purple flowers) and another stack
with all p genes (white flowers).
When you paired one card from each stack, you modeled
breeding the two groups of plants, creating the F1
generation. All of these offspring had one dominant gene for
purple flowers and one recessive gene for white flowers. All
of the F1 generation plants produced purple flowers.
The next two new stacks, each with two Ps and two ps,
represented two individuals in the F1 generation. By pairing
cards from these two stacks, you modeled breeding two F1
plants. When you laid out the cards in pairs, you created the
F2 generation, the offspring of the F1 plants. Three-fourths of
the F2 plants were purple and one-quarter were white.
Mendel found exactly the same kind of results in the actual
crosses he did with white and purple pea plants.
Want to Know More?
See Our Findings.
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OUR FINDINGS
THE GENETICS OF GARDEN PEAS
Analysis
1. 100%; 50%
2. PP; If “p” (white flower) genes are present, they will begin appearing
after two or three generations.
3. pp; any P (purple flower) genes would mask the white flowers genes.
4. Answers will vary; students might mention hair color, height, color of
eyes, freckles, and attached or free earlobes.
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SAFETY PRECAUTIONS
Review Before Starting Any Experiment
Each experiment includes special safety precautions that are relevant
to that particular project. These do not include all the basic safety
precautions that are necessary whenever you are working on a
scientific experiment. For this reason, it is necessary that you read
and remain mindful of the General Safety Precautions that follow.
Experimental science can be dangerous, and good laboratory
procedure always includes carefully following basic safety rules. Things
can happen very quickly while you are performing an experiment.
Materials can spill, break, or even catch fire. There will be no time after
the fact to protect yourself. Always prepare for unexpected dangers by
following the basic safety guidelines during the entire experiment,
whether or not something seems dangerous to you at a given moment.
We have been quite sparing in prescribing safety precautions for the
individual experiments. For one reason, we want you to take very
seriously every safety precaution that is printed in this book. If you
see it written here, you can be sure that it is here because it is
absolutely critical.
Read the safety precautions here and at the beginning of each
experiment before performing each activity. It is difficult to remember a
long set of general rules. By rereading these general precautions every
time you set up an experiment, you will be reminding yourself that lab
safety is critically important. In addition, use your good judgment and
pay close attention when performing potentially dangerous procedures.
Just because the text does not say “be careful with hot liquids” or
“don’t cut yourself with a knife” does not mean that you can be
careless when boiling water or punching holes in plastic bottles. Notes
in the text are special precautions to which you must pay special
attention.
GENERAL SAFETY PRECAUTIONS
Accidents caused by carelessness, haste, insufficient knowledge,
or taking an unnecessary risk can be avoided by practicing safety
procedures and being alert while conducting experiments. Be sure to
check the individual experiments in this book for additional safety
regulations and adult supervision requirements. If you will be working
in a lab, do not work alone. When you are working off site, keep in
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SAFETY PRECAUTIONS
2
groups with a minimum of three students per group, and follow school
rules and state legal requirements for the number of supervisors
required. Ask an adult supervisor with basic training in first aid to carry
a small first-aid kit. Make sure everyone knows where this person will
be during the experiment.
PREPARING
• Clear all surfaces before beginning experiments.
• Read the instructions before you start.
• Know the hazards of the experiments and anticipate dangers.
PROTECTING YOURSELF
• Follow the directions step-by-step.
• Do only one experiment at a time.
exits, fire blanket and extinguisher, master gas and
• Locate
electricity shut-offs, eyewash, and first-aid kit.
• Make sure there is adequate ventilation.
• Do not horseplay.
• Keep floor and workspace neat, clean, and dry.
• Clean up spills immediately.
• If glassware breaks, do not clean it up; ask for teacher assistance.
• Tie back long hair.
• Never eat, drink, or smoke in the laboratory or workspace.
not eat or drink any substances tested unless expressly
• Do
permitted to do so by a knowledgeable adult.
USING EQUIPMENT WITH CARE
• Set up apparatus far from the edge of the desk.
• Use knives or other sharp-pointed instruments with care.
• Pull plugs, not cords, when removing electrical plugs.
• Clean glassware before and after use.
• Check glassware for scratches, cracks, and sharp edges.
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SAFETY PRECAUTIONS
3
• Clean up broken glassware immediately.
• Do not use reflected sunlight to illuminate your microscope.
• Do not touch metal conductors.
• Use alcohol-filled thermometers, not mercury-filled thermometers.
USING CHEMICALS
• Never taste or inhale chemicals
• Label all bottles and apparatus containing chemicals
• Read labels carefully.
chemical contact with skin and eyes (wear safety glasses, lab
• Avoid
apron, and gloves).
• Do not touch chemical solutions.
• Wash hands before and after using solutions.
• Wipe up spills thoroughly.
HEATING SUBSTANCES
• Wear safety glasses, apron, and gloves when boiling water.
• Keep your face away from test tubes and beakers.
test tubes, beakers, and other glassware made of Pyrex™
• Use
glass.
• Never leave apparatus unattended.
• Use safety tongs and heat-resistant gloves.
your laboratory does not have heat-proof workbenches, put your
• IfBunsen
burner on a heat-proof mat before lighting it.
care when lighting your Bunsen burner; light it with the airhole
• Take
closed, and use a Bunsen burner lighter in preference to wooden
matches.
• Turn off hot plates, Bunsen burners, and gas when you are done.
flammable substances away from flames and other sources
• Keep
of heat.
• Have a fire extinguisher on hand.
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SAFETY PRECAUTIONS
4
FINISHING UP
• Thoroughly clean your work area and any glassware used.
• Wash your hands.
careful not to return chemicals or contaminated reagents to the
• Be
wrong containers.
• Do not dispose of materials in the sink unless instructed to do so.
up all residues and put them in proper containers for
• Clean
disposal.
of all chemicals according to all local, state, and federal
• Dispose
laws.
BE SAFETY CONSCIOUS AT ALL TIMES!
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