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62
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ACTIVIT Y OVERVIEW
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40
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Analyzing Genetic Data
BO RA
T
SUMMARY
Students quantify the results of the seeds they germinated in Activity 55, “Plants Have
Genes, Too!” They then compare their results to Mendel’s results.
KEY CONCEPTS AND PROCESS SKILLS
1.
Experimental results do not give ratios that perfectly match theoretical
predictions.
2.
A larger sample improves the reliability of experimental results.
3.
Genetic results obtained from one organism can often be applied to others,
providing an example of the unity of life.
4.
The 3:1 ratio observed by Mendel for the offspring of a hybrid cross can be
observed for traits in other organisms.
KEY VOCABULARY
allele
mutation
dominant
recessive
heterozygous
traits
homozygous
MATERIALS AND ADVANCE PREPARATION
For the teacher
*
1
Transparency 62.1, “Class Results”
1
Transparency 55.1, “Parent and Grandparent Plants”
1
overhead projector
For each group of four students
1
petri dish of germinated plants from Activity 55, “Plants Have Genes, Too!”
*Not supplied in kit
Teacher’s Guide
D-105
Activity 62 • Analyzing Genetic Data
Check to be certain that the seeds have germinated and are ready for counting. They
are ready to count when they are large enough for you to clearly distinguish between
green seedlings and paler seedlings, which should account for 1/4 of the seedlings. If
the seeds are not ready, postpone this activity until after Activity 63, “Show Me the
Genes!” However, be sure to complete this activity before starting Activity 64, “Nature
and Nurture.”
TEACHING SUMMARY
Getting Started
1.
Review students’ predictions from Activity 55, “Plants Have Genes, Too!”
Doing the Activity
2.
Students count and report their seed data.
3.
Students analyze the class’s data.
Follow-Up
4.
The class discusses students’ results and reviews the genetic principles they
illustrate.
Extension
Students post their results on the SALI page of the SEPUP website and compare their
results with results from other classes.
D-106
Science and Life Issues
Analyzing Genetic Data • Activity 62
TEACHING SUGGESTIONS
GETTING STARTED
1.
they have just done to those of Mendel and to the
critter-breeding scenario. In each case, first-generation plants with two different traits for a characteristic produced offspring showing only one of the
Review students’ predictions from Activity
two traits. These second-generation plants pro-
55, “Plants Have Genes, Too!”
duced offspring in which approximately 1/4 of the
Remind students that seeds are the result of sexual
reproduction. Display Transparency 55.1, “Parent
and Grandparent Plants,” to remind students of the
crosses that produced the seeds they germinated. If
you wish, you can begin by having the class discuss
Procedure Step 1 of the activity, on page D-45 in the
Student Book, or allow students to discuss it in their
groups. Students’ experiences with the critters and
Mendel’s results may lead them to change their predictions. Circulate around the room and listen to
their discussions.
offspring display the trait that had disappeared in
their parents’ generation. Some students may
notice the approximately 3:1 ratio of green
seedlings:pale yellow seedlings, while others may
need to be prompted to notice it. Encourage them
to calculate the ratio from their results. Encourage
thorough analysis of the results to prepare students
for assessments on the “Analyzing Data” element of
the D E S I G N I N G
Students count and report their seed data.
Students can usually distinguish easily between the
green and pale yellow seedlings. Have each group
of four prepare a summary of their results, which
they should record in their science notebooks. They
should report to you the number of green and pale
yellow seedlings they observe. Use Transparency
62.1, “Class Results,” to display the class’s results.
Students should record the class’s totals in their science notebooks as well. Fast finishers can go on to
answer Analysis Question 1 while waiting for the
class results to be posted.
3.
Students analyze the class’s data.
Discuss the results the class obtained. Ask them to
C O N D U C T I N G I N V E S T I G AT I O N S
(DCI) variable later in the course and for writing a
lab report for Activity 64, “Nature and Nurture.”
FOLLOW-UP
DOING THE ACTIVIT Y
2.
AND
4.
The class discusses students’ results and
reviews the genetic principles they
illustrate.
Use Analysis Question 1 to discuss the concept of
dominant and recessive traits. The students’ predictions may have included the idea that the green
would be dominant because green is darker than
yellow. Remind them that the darker color isn’t
always dominant. Refer to the seed-color trait in
Activity 60, “Mendel, First Geneticist”; the yellow
trait is dominant over green in this case. Point out
that the plant characteristic the students are studying is similar to the ones that Mendel described, in
that the characteristic has only two traits. There are
no in-between, striped, or spotted colors.
summarize the results and suggest their conclu-
Display the results on Transparency 62.1 while the
sions. Encourage them to compare the experiment
class discusses Analysis Questions 2 and 3. Students
Teacher’s Guide
D-107
Activity 62 • Analyzing Genetic Data
may need help understanding Analysis Question 4.
SUGGESTED ANSWERS
Use Transparency 55.1, “Parent and Grandparent
TO ANALYSIS QUESTIONS
Plants,” to help them think about this question.
The 3:1 ratio of green:pale yellow seedlings strong-
1.
Look back in your science notebook for the prediction you made in Activity 55. Was your predic-
ly suggests that the parents of the seedlings have
tion correct? Explain.
one yellow and one green allele. Analysis Question
4 can be used to assess students’ understanding of
Student answers will depend on both their pre-
what the results suggest about the alleles of the par-
dictions and their data. Look for the ability to
ent generation. Score responses with the U N D E R -
compare the actual data to their predictions. A
S TA N D I N G
possible example follows:
C O N C E P T S (UC) scoring guide.
Emphasize the idea that the students’ results from
My prediction was wrong. I predicted that some
one experiment suggest that the pale yellow color
of the offspring would have striped green and
trait of Nicotiana follows the Mendelian model for a
yellow leaves, but they were either yellow or
recessive trait, but do not provide absolute proof.
green. I thought the green and yellow traits
However, additional experiments have confirmed
would mix, but they did not.
that the pale yellow seedlings are the result of a single mutation and that the trait is recessive.
2.
Compare the class’s results for seedling color
to Mendel’s results for various pea plant
After discussing the students’ results, explain to
traits. Why are they similar? What do they suggest
them that every sexually reproducing organism
about the inheritance of the pale yellow and green
studied, including humans, displays traits that fol-
Nicotiana traits?
low Mendel’s model of inheritance. In Activity 65,
Many students will state that their results are
“Breeding Critters—More Traits,” they will simulate
similar to Mendel’s because their ratios of 3:1
some other, more complicated, patterns of inheri-
green: pale yellow seedlings are similar to
tance and how they relate to the basic Mendelian
Mendel’s results for pea plant traits. The disap-
model. They will learn more about human traits in
pearance of the pale yellow trait in the second
Activity 66, “Patterns in Pedigrees,” and some of the
generation and its reappearance in the third
following activities.
generation is similar to Mendel’s result for dom-
Extension
inant and recessive traits. These results suggest
that the pale yellow and green Nicotiana traits
Students post their results on the SALI page of the
are inherited in the same way as the pea traits
SEPUP website and compare their results with
Mendel studied. Results not fitting Mendel’s
results from other classes.
model (a ratio far from 3:1) may suggest that
D-108
This provides a larger sample size. Instruc-
the sample size was too small. You may wish to
tions for posting your classes’
combine data from several classes, as suggested
results are provided on the SALI
in the Extension. Another possible source of
page of the SEPUP website.
error is attempting to distinguish between
Science and Life Issues
Analyzing Genetic Data • Activity 62
green and pale seedlings before they have
This cross is similar to the one modeled in
grown enough for the colors to be obvious.
Activity 59 in that both of the parents in each
3.
cross had a recessive trait that appeared in a
Do each group’s results fit Mendel’s model?
fraction of their offspring. You can infer the
Explain.
4.
presence of the recessive trait from the reappa-
The groups’ results may fit Mendel’s model, but
rance of the pale yellow trait in the third gener-
many may not fit as well as the overall class’s
ation, similar to the reapparance of the orange
results. Many groups may get ratios that are not
tail trait in the third generation in the critters.
as close to 3:1. The larger the sample size, the
The near 3:1 ratio that should be observed in
greater the chance that the results will give a
the whole class data for seedlings is statistically
3:1 ratio.
and theoretically identical to the ratio obtained
in Activity 59.
When you first set out these seeds to germinate, you
were told that they were all the offspring of two
5.
Construct a Punnett square to show what will hap-
green parent plants. You were also told that each of
pen if one of the green parent-generation Nicotiana
the green parents had one green parent and one yel-
plants is crossed with a pale yellow plant. Explain
low parent.
the results.
a.
Based on the class’s results, what can you con-
Assuming students use G for the dominant
clude about the color alleles of each of UC
the green parents of your seedlings?
green trait and g for the recessive pale yellow
A level 3 answer follows:
trait, their squares should look like the one
below. The Punnett square shows that half of
the offspring will be green and half will be yel-
The appearance of the yellow trait in approxi-
low. If the green parents were homozygous,
mately 1/4 of the seedlings provides evidence
none of the offspring would be yellow.
that each of the parent plants had a recessive
g
G
allele for yellow color. This suggests that each
parent had one green and one yellow allele for
color. (A level 4 answer might include a Punnett
square or might add that the parent plants were
g
Gg
gg
g
Gg
gg
heterozygous, if you have stressed the terms heterozygous and homozygous.)
b.
How is this breeding cross similar to the one
you modeled in Activity 59, “Gene Combo”?
Explain.
Teacher’s Guide
D-109
Class Results
Germinating Plants Results
©2006 The Regents of the University of California
Student
Group
No. of Green
Seedlings
No. of Yellow
Seedlings
Totals
Science and Life Issues Transparency 62.1
D-111