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64
i n ut e s
e ss
io
RY
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1–2
50 -m
ACTIVIT Y OVERVIEW
LA
O
40
to
ns
Nature and Nurture
BO RA
T
SUMMARY
Students design an experiment to investigate the effect of the environment on the
development of the green color trait in Nicotiana seedlings. This introduces the interplay of hereditary (nature) and environmental (nurture) factors in the development
of an organism’s traits.
KEY CONCEPTS AND PROCESS SKILLS
1.
Hypotheses are based on evidence and can be revised in light of new evidence.
2.
Experimental results do not give ratios that perfectly match theoretical
predictions.
3.
Organisms that reproduce rapidly are useful in studying genetics.
4.
A larger sample improves the reliability of experimental results.
5.
Genes are the units of information for inherited traits that parents transmit to
their offspring.
6.
Both heredity and the environment play roles in determining the traits of an
organism.
7.
Unfavorable environments can negate the positive effects of adaptive genes.
KEY VOCABULARY
allele
hypothesis
gene
inherit/heredity
heterozygous
“nature vs. nurture”
homozygous
trait
Teacher’s Guide
D-121
Activity 64 • Nature and Nurture
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
1
Transparency 55.1, “Parent and Grandparent Plants”
1
Transparency 64.1, “Seedling Colors in Light vs. Dark”
1
Transparency 64.2, “Elements of Good Experimental Design”
1
overhead projector
For each group of four students
12 Nicotiana seeds
1
clear plastic divided petri dish
1
black plastic divided petri dish
2
pieces of germinating paper
1
dropper
1
cup
*
*
access to sinks with running water
1
permanent-ink marker
*
masking tape
*
scissors
*Not supplied in kit
The usable shelf life of Nicotiana seeds is about 2 years. If your seeds are more than
1-1/2 years old, or if you do not know their age, it is recommended that you order
fresh ones. The shelf life of the seeds can be extended if they are refrigerated.
Each vial should still contain about 40-50 seeds. Plan to carefully monitor the use of
the seeds, so that enough will be left for all of your classes. Plan to have a space near
a window where students can leave the dishes with the germinating seeds for 7–10
days. (Note that since students have had experience distinguishing the seedling colors, they may be able to work with slightly less mature seedlings than they needed in
Activity 62, “Analyzing Genetic Data.”) Avoid placing the seeds in south-facing windows during hot weather.
Decide whether you will require all students to investigate the effect of environmental light or if you will let some investigate other variables. It is important that at least
four groups in each class investigate light vs. dark conditions to gather enough data
to be convincing. Allow about 1/2 period to set up the seeds for germination and
another 1 period 7–10 days later for students to obtain and discuss their results.
I Teacher’s Note: This activity has a number of assessment options, including an opportunity for a full lab report that you can assess for all elements of the D ESIGNING
AND
C ONDUCTING I NVESTIGATIONS (DCI) and C OMMUNICATING S CIENTIFIC I NFORMATION
D-122
Science and Life Issues
Nature and Nurture • Activity 64
(CM) variables. Alternatively, you can choose to assess any of the individual elements
of the DCI variable as described specifically in the teaching steps. Decide in advance
which of these assessments you will use.
TEACHING SUMMARY
Getting Started
1.
Introduce the idea that environmental factors, as well as genes, can influence
traits.
Doing the Activity
2.
Students plan and set up their experiments and allow them to continue for
7–10 days.
3.
The class analyzes the results.
Follow-Up
4.
5.
The class discusses the Analysis Questions.
The class further discusses the roles of heredity and environment (nature vs.
nurture) in the development of human traits.
Extension
Students post their results on the SALI page of the SEPUP website and compare their
results to results from other classes.
BACKGROUND INFORMATION
The Nicotiana Albino Mutation
Students may ask how the homozygous recessive grandparents could be crossed with
the homozygous dominant grandparents to produce the heterozygous parents if the
homozygous recessive seedlings fail to thrive. In fact, the albino mutation in Nicotiana
inhibits the production of the green photosynthetic pigment chlorophyll for only a
short time. Many of the young albino seedlings eventually produce some chlorophyll
and grow to maturity. They can then be bred with homozygous green plants to produce the parents that provide the seeds used in the students’ experiments.
Heredity and the Environment
Most human traits are the result of complex interactions both among hereditary factors
and between these factors and the environment. In the case of most traits, the relative
extents of hereditary and environmental influence are not understood. One of the most
interesting and hotly debated questions is the role of heredity vs. the environment in
complex human traits such as intelligence and behavior. Yet even less complex traits are
Teacher’s Guide
D-123
Activity 64 • Nature and Nurture
difficult to understand completely. Why, for example, are the symptoms of the
Marfan syndrome so varied, even within a family where all affected individuals
carry exactly the same mutation in the same gene? First, the effects of different
genes interact, so the effect of the Marfan gene is influenced by other genes that
affect the biochemistry and physiology of the individual. In addition, there is an
interaction between the action of genes and environmental effects. Environmental factors can include nutrition, family environment, health care, medication,
drugs such as alcohol and cigarettes, and the uterine environment of the developing fetus, as well as many other factors that may be more difficult to measure
or describe.
The relative influence of genes and the environment in determining complex
human traits such as intelligence and behavior is a complex and sensitive issue.
Aspects of intelligence, behavior, or personality may be researched for their
genetic bases without passing moral judgments. It is important to avoid words
such as good and bad when referring to genes or to people with genetic or other
conditions. Biologists often use the term adaptive to refer to traits (such as green
color in Nicotiana) that better suit an organism for survival. Though genetic conditions, such as the Marfan syndrome, are considered unfortunate, people born
with them are no less “good” than people without the condition.
Some environmental effects on traits are shown in the photos in the Introduction to the activity on page D-55 in the Student Book. The growth of the cypress
trees is affected by wind. On the Siamese cat, temperature affects the development of the dark color—only the cooler tips of the extremities develop the darker color. The color of hydrangeas is affected by soil acidity.
Environment and the Nicotiana Seedlings
Environmental light is necessary for the development of the green color trait.
Without light, all of the seedlings appear like the albino mutants and are pale
yellow in color. They are also longer and more spindly in appearance. Other
environmental factors, such as water level, will affect other characteristics of
the seedlings.
The black dishes provided can be used to investigate the effect of light on development of the seedlings. The seedlings provided do not develop green color in
the black dishes, providing a clear example of the dual importance of environmental factors (in this case light) and genetic factors in determining one characteristic (color) of the seedlings. Other variables such as the amount of water
will affect the seedlings, but will not specifically affect the color traits that students investigated in Activities 55, “Plants Have Genes, Too!” and 62, “Analyzing Genetic Data.”
D-124
Science and Life Issues
Nature and Nurture • Activity 64
TEACHING SUGGESTIONS
GETTING STARTED
1.
Introduce the idea that environmental
factors, as well as genes, can influence
traits.
that they used in Activity 55, “Plants Have Genes,
Too!” and Activity 62, “Analyzing Genetic Data.”
Ask students, What environmental factors do you
think are important for seeds to sprout and grow?
Their suggestions are likely to include water, light,
nutrients, and other factors. Then ask, What factors
do you think are important for seedlings to devel-
Ask students how important they think genes are in
op the green color trait you observed in Activity 62?
determining a person’s traits, including behavior.
They are likely to suggest light and other factors.
Allow them to express their ideas about environ-
Explain that each group of four students will test
mental factors. Develop a list on the board of some
one environmental variable—light. They will
of the factors they suggest, which might include
design and conduct an experiment to test the effect
education, exercise, family, friends, personal expe-
of this one variable upon the development of the
riences, health care, nutrition, use of medication,
green color trait.
use of drugs (cigarettes, alcohol, etc.), exposure to
n Teacher’s Note: If you have enough seeds, you
pollutants, or the uterine environment.
can allow some students to investigate other vari-
Tell students that for many traits, the balance dur-
ables. However, at least four groups within each
ing development between the influence of heredity
class should investigate light so that sufficient data
and the influence of the environment is not yet
are obtained. Alternatively, students can explore
understood. Explain that the debate about the role
other variables as a follow-up project.
of heredity vs. the environment in determining
DOING THE ACTIVIT Y
traits is often referred to as “nature vs. nurture.”
Have students suggest human characteristics that
they believe are due to genes (nature) and other
characteristics that they believe are due to the environment (nurture). Allow time for students to discuss some of their ideas. Students may realize that
they disagree about the roles of genes and the environment for many traits. Clarify the areas of disagreement and stress the need for evidence about
this issue.
Introduce the use of plant seedlings to investigate
environmental effects. Use Transparency 55.1, “Parent and Grandparent Plants,” to be sure students
realize that they will be using the same kind of seeds
2.
Students plan and set up their experiments
and allow them to continue for 7–10 days.
Review as a class the Challenge and Procedure on
pages D-56 to D-57 in the Student Book. Discuss
good experimental design. Display Transparency
64.2, “Elements of Good Experimental Design,” to
help students in planning their experiments.
Each group of four students should set up a control
and an experimental dish of seedlings. Allow students to work on their plans in their groups. Be certain students record their hypotheses (Step 2). You
may want to check students’ plans before allowing
them to proceed to Step 5. Students should realize
Teacher’s Guide
D-125
that the control and experimental conditions for
affect the results, however; color development
the controlled variables should be exactly identical.
depends mostly on light exposure.)
Typical plans are likely to include placing six seeds
in the clear dish and six in the black dish. You may
3.
The class analyzes the results.
need to prompt students to consider placing the
After 7 days, begin to check the seedlings in the
dishes next to one another so they are in the same
clear dishes. When you can determine the different
part of the room, to space the seeds similarly in the
colors of the seedlings, they are ready to be count-
dishes, and to maintain a similar level of water for
ed. (The ones in the clear dishes should show a near
both sets of seeds. Then have them set the seeds in
3:1 ratio of green to pale seedlings.)
the designated area (in the light) that you have
reserved for them.
Have students collect and report their data. Their
data tables can be assessed with the “Organizing
C ONDUCTING
Students’ experimental designs can be assessed by
Data” element of the D ESIGNING
using the “Recording and Designing Procedure” ele-
I NVESTIGATIONS (DCI) variable. A level 3 answer is
ment of the D E S I G N I N G
T I G AT I O N S
AND
CONDUCTING INVES-
(DCI) variable. You can collect their
designs at this time, or evaluate them as part of a
complete laboratory report at the end of the activity.
n Teacher’s Note: Be sure to have students check the
AND
provided in the table below.
Use Transparency 64.1, “Seedling Colors in Light
vs. Dark,” to display the class’s results for this variable. If students investigated other variables, prepare a similar transparency for each variable. Dis-
water level every day or two, especially before the
cuss the control and experimental conditions. In
weekend. Remind students not to drown their seeds,
this experiment, the light is the control condition,
but to just keep the germinating papers moist.
since students know from Activity 62 what is like-
n Teacher’s Note: Temperatures in the dishes are
ly to happen to the seeds in the light. The dark con-
likely to vary due to more heat absorption by the
black dishes. This variable is difficult to control,
especially if you are using natural light. Avoiding a
very sunny south- or west-facing window may help
to control this variable. (Temperature is unlikely to
dition is the experimental condition. Encourage
students to calculate the ratio of green to yellow
seedlings in the light and to check how well it conforms to the predicted 3:1 ratio. Assuming each
group of students placed six seeds in the light, you
should have results from about 48 seedlings in the
Seedling Results
# green
# pale
yellow
ratio of
green:yellow
seeds in light
(clear dish)
4
2
2:1
The seedlings looked just like the ones in
Activity 62. Some were green and some were pale
yellow.
seeds in dark
(black dish)
0
6
all yellow
All of the seedlings were pale yellow. They were
long and the leaves looked really small.
D-126
Science and Life Issues
other observations
Nature and Nurture • Activity 64
light. Approximately 1/4, or about 12, of the
that both genes and light are necessary for the
seedlings should remain pale, due to the homozy-
plants to develop green color.”
gous recessive mutation students investigated in
Activity 62. (Remind students that they determined
that the green parent plants of the seeds both have
a recessive allele for color. Review the results of
Activity 62 if necessary.) The rest of the seedlings
should develop the normal green seedling color.
However, the seedlings grown in the dark should
all remain pale.
Urge students to explain how they can infer that the
environmental light affects the seedling color.
Could they be certain based on only their group’s
results? Bring out the idea that the class data provide a sufficient sample size to ensure that at least
some of the seedlings planted in the dark have the
gene for green color. Ask students to suggest an
experimental approach that might verify this
The Analysis Questions guide the students step-by-
assumption. They may suggest moving some of the
step through the interpretation of their results and
seeds from the black dish to the clear dish and mov-
some generalizations based on the results. They are
ing some from the clear dish to the black dish. Some
appropriate for either group or class discussion, or
students may predict that the seedlings germinated
individual work. However, your students may be
in the black dish are already too damaged from lack
ready for a more open-ended and sophisticated
of exposure to light to develop green color, while
approach to thinking about their results. We sug-
others may suggest that exposure to light will allow
gest that before students answer the Analysis Ques-
the green color to develop.
tions, you allow them about five to ten minutes in
their groups to discuss and write their conclusions
from the results obtained. Their conclusions
should include
•
a statement that summarizes the results of
the experiment, and
•
If possible, allow students to reverse the light conditions of some of their seedlings. Switching the
dish covers is sufficient to expose the light-deprived
seedlings to light. The dish of seeds moved to the
dark will need to be wrapped with aluminum foil or
black paper. Maintain some of the plants in their
their ideas about the importance of genes and
original conditions as controls. The controls should
the environment in determining the color of
not change in color. About 3/4 of the seedlings
Nicotiana seedlings.
moved from dark to light environments should
You may wish to have each group write its conclusion on a transparency and present it to the class.
Guide students toward direct, clear conclusions,
such as “The results show that about 3/4 of the
plants grown in the light develop green color. This
tells me that if the green allele is present the
seedlings will be green in the light. Plants grown in
develop green color over a period of a few days, providing additional evidence that environmental factors can affect hereditary traits. Point out that not
all environmental effects are so easily reversible.
This is observed with the seeds germinated in the
light and then moved to the dark: they maintain
their green color for many days.
the dark do not develop green color. This tells me
Teacher’s Guide
D-127
Activity 64 • Nature and Nurture
Encourage students to consider traits—particularly
FOLLOW–UP
4.
The class discusses the Analysis Questions.
complex (and subjective) ones such as intelligence—as an outcome of both genes and environ-
You may wish to have students answer some of the
ment. Encourage them also to be open to evaluating
questions individually before or after the class dis-
new evidence as it is gathered on these questions in
cussion. Analysis Question 1 can be used as an
the future.
assessment for the “Analyzing and Interpreting
Data” element of the D E S I G N I N G
AND
CONDUCT-
The role of heredity and the environment in human
traits is quite difficult to study. One longstanding
ING
I N V E S T I G AT I O N S (DCI) variable.
5.
The class further discusses the roles of
of identical twins. The following questions can be
genes and environment (nature vs. nurture)
used to start a discussion of twins that follows up on
in the development of human traits.
this activity and Activity 63, “Show Me the Genes!”
direction of research in this area involves the study
Ask students how they think each of the following
•
known. Were those twins exactly identical to
is influenced by genes vs. the environment: eye
each other? Were their appearances,
color, tongue rolling, finger crossing (as in Activity
behaviors, and preferences alike?
54), PTC tasting, height, arm span, presence of
freckles, and musical ability. The Background Infor-
Consider a pair of identical twins you have
•
What, then, does identical twin mean? What
mation in Activity 54, provides more information
is identical about them? What is different
about most of these traits. Freckles and skin color
about them?
are determined partly by genes and partly by exposure to the sun. Musical ability is a complex trait
that is most likely influenced by a complicated
interplay of hereditary and environmental factors.
Help students establish the concept of a continuum—a scale with continuing variation between the
two extremes of nature and nurture, as shown in
Figure 1 below.
Very early on, they were in fact identical. A fertilized egg, or zygote, occasionally splits into two
identical embryos, each of which then develops
independently into a fetus in the uterus. Thus, the
genes of the identical twins are in fact the same—in
every cell of their bodies. This holds true throughout their lifetimes, except when random mutations
occur as cells divide (a process that contributes to
cancer development).
Figure 1
“Nature vs. Nurture”
nature
genes
only
D-128
nurture
↔
mostly
genes
Science and Life Issues
↔
both contribute
about equally
mostly
↔ environment
↔
environment
only
Nature and Nurture • Activity 64
Two level 3 answers follow:
Encourage students to suggest what causes the identical twins to develop into distinct human beings.
•
My hypothesis was correct. I predicted that
Do they—their bodies and brains—experience
fewer seedlings in the dark would be green. I
exactly the same things while they grow up? Obvi-
didn’t say how many I thought would be
ously not, although the extent of the differences
pale. What I found was that none of the
certainly can vary tremendously. In fact, the
seedlings in the dark turned green. The total
research technique of “twin study” in psychology
class results showed that 47 out of 47
and biology relies upon the fact that identical twins
seedlings in the dark stayed pale. But many of
raised in separate households are an approximation
the seedlings in the light turned green, so
of a nature vs. nurture experiment. Even if a pair of
some of the seeds in the dark must have had
twins grows up together, slight differences in every-
the green allele.
thing they experience can affect their development.
•
No, my hypothesis was not correct. I predicted
the ratio would be the same, but the plants in
Extension
the black dish wouldn’t have as many plants
Students post their results on the SALI page of the
growing. Instead it affected color more than
SEPUP website and compare their results to
growth. All of my group’s plants in the black
results from other classes.
dish had yellow leaves and all sprouted and
grew. The plants in the clear dish also grew,
For a larger sample size, students can com-
but 5 out of 6 had green leaves.
bine their data with data gathered by
other classes from other schools.
For a level 4, students might comment on other
Go to the SALI page of the SEPUP
differences in the appearance of the seedlings
website for instructions.
that they failed to predict. For example, the
seedlings grown in the dark grow longer than
SUGGESTED ANSWERS
the ones grown in the light.
TO ANALYSIS QUESTIONS
2.
1.
Was your hypothesis correct? Explain.
DCI
aid
What effect did heredity have in determining the
color of the seedlings?
Answers will depend on the student’s
Genes determine whether the seedlings have
original hypothesis. Those students
the potential to develop green color. Homozy-
who predicted that their seedlings would not
gous recessive seeds do not have the potential
grow normally in the dark should state that
to develop green color under any conditions.
their hypothesis was correct. Those who pre-
Seeds with one or two alleles for the green color
dicted the dark would have no effect will state
trait can develop the green color only in the
their hypothesis was incorrect. Look for stu-
right environment.
dents to compare their hypotheses with the
actual data.
3.
What effect did the environment have in determining the color of the seedlings?
Teacher’s Guide
D-129
Activity 64 • Nature and Nurture
4.
It was necessary for the environment to include
The right environment alone is not enough to
light in order for the seedlings with an allele for
ensure an organism will grow and be healthy
the green color trait to be able to actually turn
(in this case seen as green color). Homozygous
green. Without an appropriate environment,
recessive plants will not develop green color,
the seedlings do not develop green color.
despite adequate light.
Can heredity alone ensure an organism will grow
well and be healthy? Explain.
This activity tells us that genes alone are not
enough for an organism to grow and be
5.
Reflection: What role do you think genes and
the environment play in human development and
health? Explain your thinking and give some
examples.
healthy. The organism must also have an envi-
Student answers will vary. Elicit their ideas. The
ronment that promotes growth and allows the
discussion from Step 5 of the Teaching Sugges-
genes to function.
tions in this activity expands on this question.
Can the environment alone ensure an organism will
grow well and be healthy? Explain.
D-130
6.
Science and Life Issues
Seedling Colors in Light vs. Dark
Germinated
in Light
Group
# Green
# Pale
Yellow
Germinated
in Dark
# Green
# Pale
Yellow
1
2
3
4
5
6
7
©2006 The Regents of the University of California
8
Totals
Science and Life Issues Transparency 64.1
D-131
Elements of Good Experimental Design
• Builds on previous research
• Describes all steps in procedure clearly and completely
• Describes all data to be collected
• Keeps all variables, except the one being tested, the same
• Includes a control for comparison
• Uses an appropriate group of subjects
• May include a large sample size
• May include multiple trials
• Can be reproduced by other investigators to give similar results
©2006 The Regents of the University of California
• Respects human and animal subjects
Elements may vary, depending on the problem being studied
Science and Life Issues Transparency 64.2
D-133