Download Teacher Materials - Scope, Sequence, and Coordination

SCOPE,
SEQUENCE,
COORDINATION
and
A National Curriculum Project for High School Science Education
This project was funded in part by the National Science
Foundation. Opinions expressed are those of the authors
and not necessarily those of the Foundation. The SS&C
Project encourages reproduction of these materials for
distribution in the classroom. For permission for any other
use, please contact SS&C, National Science Teachers
Association, 1840 Wilson Blvd., Arlington, VA 22201-3000.
Copyright 1996 National ScienceTeachers Association.
SCOPE, SEQUENCE,
and
COORDINATION
SS&C Research and Development Center
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Erma M. Anderson, Project Director
Nancy Erwin, Project Editor
Rick McGolerick, Project Coordinator
Arlington, Va., 703.312.9256
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North Scott H.S., Mike Brown
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Evaluation Center
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East Carolina University, 919.328.6172
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University of Minnesota, 612.625.2046
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and Coordination Center
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University of Houston-Downtown, 713.221.8583
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University of Puerto Rico, 809.765.5170
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Lee H.S., Thomas Ivy
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UPR Lab H.S.
* * * * * * * * * * * *
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Project Associates
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University of Buffalo
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Indiana University
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for the Advancement of Science
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Technology Education Association
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Science and Industry
Stephen D. Druger
Northwestern University
George Miller
University of California-Irvine
National Science Education Standard—Life Science
The Molecular Basis of Heredity
Most of the cells in a human contain two copies of each of 22 different chromosomes. In addition, there is a pair of chromosomes that determines sex: a
female contains two X chromosomes and a male contains one X and one Y
chromosome. Transmission of genetic information to offspring occurs through
egg and sperm cells that contain only one representative from each chromosome pair. An egg and a sperm unite to form a new individual. The fact that the
human body is formed form cells that contain two copies of each chromosome—and therefore two copies of each gene—explains many features of human heredity, such as how variations that are hidden in one generation can be
expressed in the next.
Teacher Materials
Learning Sequence Item:
1004
In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four
kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in
genes (as a string of molecular “letters”) and replicated (by a templating
mechanism). Each DNA molecule in a cell forms a single chromosome.
Changes in DNA (mutations) occur spontaneously at low rates. Some of these
changes make no difference to the organism, whereas others can change cells
and organisms. Only mutations in germ cells can create the variation that
changes an organisms’ offspring.
Inferred Generalization
Recombinations and crossing over are also factors affecting mutation rates.
The Human Genotype
May 1996
Adapted by: Lois Range and Godrej Sethna
Heredity, Traits, Genes, Chromosomes, and DNA. At this level, students can distinguish the autosomes from the
sex chromosomes. They should examine the human genotype and chromosomal abnormalities associated with human
genetic disease (autosomal), such as Down’s syndrome. Students should identify the sex cells, comparing and contrasting
their production and characteristics in males and females. Due to unique genetic combinations, the male gamete
determines the ultimate gender of the human embryo. Chromosomal abnormalities (linked to the sex chromosomes),
such as Turner’s and Klinefelter’s syndromes, can be used to demonstrate problems with variations in the number of
sex chromosomes. (Biology, A Framework for High School Science Education, p. 104.)
Contents
Matrix
Suggested Sequence of Events
Lab Activities
1. Karyotyping Human Chromosomes
2. The Right to Know and Not to Know
3. Little Left-handed Finger
4. Heads or Tails?
5. Good Cells, Bad Cells
6. Hemophilia vs. Color Blindness
Assessments
1. Color Blind, I
2. Color Blind, II
3. Genetic Disorder
This micro-unit was adapted by Lois M. Range (Jefferson Davis H.S., Houston, Texas), and
Godrej Sethna (Baylor College
3 of Medicine, Houston)
1004
Learning Sequence
Science as Inquiry
Heredity, Traits, Genes, Chromosomes, and DNA. At this level, students can distinguish the autosomes from the sex
chromosomes. They should examine the human genotype and chromosomal abnormalities associated with human genetic
disease (autosomal), such as Down’s syndrome. Students should identify the sex cells, comparing and contrasting their
production and characteristics in males and females. Due to unique genetic combinations, the male gamete determines
the ultimate gender of the human embryo. Chromosomal abnormalities (linked to the sex chromosomes), such as Turner’s
and Klinefelter’s syndromes, can be used to demonstrate problems with variations in the number of sex chromosomes.
(Biology, A Framework for High School Science Education, p. 104.)
Science in Personal
and Social Perspectives
Science and Technology
Karyotyping Human
Chromosomes
Activity 1
The Right to Know and
Not to Know
Activity 2
Little Left-handed Finger
Activity 3
Good Cells, Bad Cells
Activity 5
Heads or Tails?
Activity 4
Hemophilia vs.
Color Blindness
Activity 6
Color Blind, I
Assessment 1
Color Blind, II
Assessment 2
Genetic Disorder
Assessment 3
4
History and Nature
of Science
Suggested Sequence of Events
Event #1
Lab Activity
1. Karyotyping Human Chromosomes (45 minutes)
Event #2
Lab Activity
2. The Right to Know and Not to Know (45 minutes)
Additional or Alternative Activity
3. Little Left-handed Finger (45 minutes)
Event #3
Lab Activity
4. Heads or Tails? (45 minutes)
Event #4
Lab Activity
5. Good Cells, Bad Cells (45 minutes)
Event #5
Lab Activity
6. Hemophilia vs. Color Blindness (45 minutes)
Event #6
Readings from Science as Inquiry, Science and Technology, Science in Personal
and Social Perspectives, and History and Nature of Science
Suggested readings:
Grady, Denise, “Just Who is a Female Athlete?” Discover Magazine, The Walt Disney
Company, June 1992, pp. 78–82.
Levine, Joe, “Do They Really Want to Know?”, [Medicine], Time Magazine, Oct. 20,
1986, p. 80.
Weiss, Rick, “The Genetic Gender Gap,” Science News, Vol. 135, May 20, 1989, pp.
312–315.
Assessment items are at the back of this volume.
5
Assessment Recommendations
This teacher materials packet contains a few items suggested for classroom assessment. Often, three
types of items are included. Some have been tested and reviewed, but not all.
1. Multiple-choice questions accompanied by short essays, called justification, that allow teachers to
find out if students really understand their selections on the multiple choice.
2. Open-ended questions asking for essay responses.
3. Suggestions for performance tasks, usually including laboratory work, questions to be answered,
data to be graphed and processed, and inferences to be made. Some tasks include proposals for
student design of such tasks. These may sometimes closely resemble a good laboratory task, since
the best types of laboratories are assessing student skills and performance at all times. Special
assessment tasks will not be needed if measures such as questions, tabulations, graphs, calculations,
etc., are incorporated into regular lab activities.
Teachers are encouraged to make changes in these items to suit their own classroom situations and to
develop further items of their own, hopefully finding inspiration in the models we have provided. We
hope you may consider adding your best items to our pool. We also will be very pleased to hear of
proposed revisions to our items when you think they are needed.
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1004
Activity 1
Teacher Sheet
Science as Inquiry
Karyotyping Human Chromosomes
How can we diagnose genetic abnormalities?
Overview:
Students will observe, prepare and classify human chromosomes into karyotypes. This activity
focuses on the value of karyotyping in the diagnosis of chromosomal abnormalities. Idiographs are used
to represent each chromosome.
Materials:
Per lab group:
copy of Plates 1 & 2
scissors
tape, transparent (glue, or removable glue)
ruler
Procedure:
Introduce this procedure by having
students examine the completed
karotype shown in Diagram 1. Al1
2
3
4
5
though actual photographs are used in
the procedure, these diagrams use
idiograms or caricatures of the chromosomes. Ask the students how the
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7
8
9
10
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12
chromosomes were grouped as shown.
Without much effort they should be
able to point out differences in size,
banding, and position of center (or
centromere). All of these things serve
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14
15
16
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18
as basis for all karotyping. Take the
time for students to determine the
number of chromosomes (46) and that
odd 23rd pair (the sex chromosomes).
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20
21
22
23
Provide each group (or student)
with Plate 1 (unnumbered version) and
Diagram 1 (Normal)
ask them to produce a karotype. The
sex chromosomes have been labeled.
Encourage them to try measuring the
length of the chromosomes and determining banding patterns. have them order them as in the example
form largest to smallest with the last pair being the sex chromosomes. Glue, tape and the reusable glue
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Activity 1
1
2
6
7
13
19
3
4
8
14
20
9
15
10
16
21
22
5
1
2
7
11
12
6
17
18
13
23
19
3
4
8
14
9
15
10
16
20
21
5
11
12
17
18
22
23
Diagram 3 (Turner’s Syndrome—XO)
Diagram 2 (Kleinfelter’s Syndrome—XXY)
surfaces can be used for this procedure. Plate I has the chromosomes of a normal male (XY). A numbered Plate 1 is provided for your use. Discuss with the students the ease or difficulty in completing the
process. The exactness of the karotype is unimportant for students but rather that they understand the
process and what it reveals.
Repeat the process using Plate II. This karotype should reveal a female with an extra #21 chromosome (a total of three #21 chromosomes). This type of chromosomal abnormality is referred to as Down
Syndrome.
Discuss with the students problems of
having too many, too few, or a few modified
A
B
structures of chromosomes. In each instance
it causes problems that may result in death.
Diagram 2 is the karotype of an individual
with Kleinfelter’s Syndrome (XXY), and
C
Diagram 3 is a karotype of an individual with
Turner’s Syndrome (XO). In both of these
syndromes, the sex chromosomes have
D
E
aberrations.
1
2
3
6
7
8
13
14
15
4
9
5
10
11
12
16
17
18
X
Y
Background:
F
Karyotyping is used to identify chromosome abnormalities in fetuses and infants
with abnormal features. The initial procedure begins by photographing a white blood
cell during the metaphase stage of mitosis.
In this stage, all chromosomes are double
19
G
20
21
22
Sequencing of Chromosomes
Diagram 4
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Activity 1
stranded, attached by a centromere, and are visible under a microscope. When the cells begin to divide,
colchicine is added to the culture to stop cell division. The cells are then placed in a solution that
ruptures their membranes, freeing the chromosomes. Then the chromosomes are stained and photographed using a microscope. The resulting photograph is enlarged and cut into pieces (one chromosome per piece) and arranged as homologous (matching) pairs according to shape, size or length, and
staining bands. The last pair of chromosomes which are unmatched in males (sex chromosomes) are
kept separate at the end of the karyotype (Diagram 4). In normal females, there will be two X chromosomes; in males, one X and one shorter Y chromosome.
Rules for karotyping have been established by a scientific convention referred to as the Paris Convention. They are arranged according to size, position of centromere, and banding. Next, they are numbered
from 1 (for the largest) to 22 (for the smallest). Numbers 1 through 22 are referred to as autosomes. The
final pair (#23) are the sex chromosomes. All cells have a pair of sex chromosomes—XX for females and
XY for males. The X-chromosome was one of the first to have a specific disease-causing gene identified
on it. It seems to hold a great deal of information. The Y-chromosome does not reflect this same richness
of genetic information, but obviously determines maleness.
Chromosomal abnormalities occur more often during the meiosis and mitosis processes. Apparently
in the sorting that occurs, some chromosomes are not correctly sorted and the cell possesses more or less
than the normal number (referred to as nondisjunction). In other cases, pieces of one chromosome may
become attached to another (referred to as translocation). In all of these cases, abnormalities result. This
sorting process will be discussed in Micro-Unit 1005 (which should be completed prior to 1004). Most
abnormalities were named after the scientists who first described the condition.
A discussion of common genetic abnormalities may be appropriate. The most commonly known is
Down Syndrome. It has been studied more than any other due to its frequency (0.69–1.44 per 1,000
newborns). Latest research indicates that with proper early developmental education these individuals
exceed previously predicted levels of intelligence. More recently, some are even actors and actresses.
Other common chromosomal abnormalities include: Patau Syndrome (extra #13), Turner Syndrome
(XO), Klinefelter Syndrome (XXY, XXXY, XXYY).
Variations:
Have students examine karyotypes for nine genetic disorders: triploidy, tetraploidy, Patau Syndrome,
Edward’s Syndrome, Down’s Syndrome, Turner’s Syndrome, Klinefelter’s Syndrome, and XXX syndrome. They will compare a normal karyotype with the abnormal karyotypes and chart the difference,
including causes, current research and resulting effects.
Adapted from:
Holt, Rinehart and Winston, Modern Biology, Harcourt, Brace, Jovanovich, Inc., 1991.
Merrill, “An Everyday Experience Worksheet,” Biology, Macmillan/McGraw-Hill, Glencoe Division,
1992.
Seashore, M., and R. Wappner, Genetics in Primary Care and Clinical Medicine, Appleton & Lange,
1996.
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Activity 1
Plate 1. Numbered
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Activity 1
Plate 1. Sex Chromosomes are Labeled.
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Activity 1
Plate 2. Numbered
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Activity 1
Plate 2. Sex Chromosomes are Labeled.
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Activity 2
Teacher Sheet
Science in Personal and Social Perspectives
The Right to Know and Not to Know
What is your family’s profile?
Overview:
Students will be able to observe a variety of human traits, and construct a family pedigree. See
Micro-unit 902, Activity 3, for previous work with pedigrees. In this activity, students examine the
human genotype. Genotypes may be determined in some cases by analyzing the pattern of inheritance
shown in a pedigree chart.
Materials:
paper
pencil
PTC paper
Procedure:
Students conduct a survey using their family members, constructing a pedigree and numbering the
generations, according to each trait described below.
Ear lobe shape Students record whether the subject has “free” ear lobes or attached ear lobes.
Dimples. Students record whether the subject has dimples.
Freckles. Students record whether the subject has freckles.
PTC tasting. The ability to taste a harmless chemical (PTC) is a genetic trait. Students give subject a
1st generation
2nd generation
Sample Pedigree Chart
3rd generation
Symbol
Meaning
female without trait
female with trait
male without trait
male with trait
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Activity 2
piece of PTC paper, ask them to place it in their mouths and chew for a few seconds. If they can taste
PTC, they will notice a distinct bitter taste. Students record data.
Eye color. Although eye color is controlled by several genes, a single pair is responsible for blue eye color
(recessive trait). All non-blue eyes result from the dominant B gene. Students record subject’s eye color.
Background:
Show dogs and race horses are not the only animals that have a pedigree. A pedigree is nothing more
than a family tree that traces the inheritance of a particular genetic trait. This chart is a visual representation
showing the phenotypes of related individuals, and provides a basis for attempting to determine their
genotypes. The sample pedigree chart represents three generations of a family. Each symbol represents a
specific individual, as explained in the key. Genotypes may be determined, in some cases, by analyzing the
pattern of inheritance shown in a pedigree chart. In the sample, suppose the trait being analyzed was a
recessive trait inherited by a single pair of alleles (dominant = T, recessive = t). In order for an individual to
actually express a recessive trait, that person must be homozygous recessive, or have a tt genotype. In order
for an individual to not possess the trait, that person must have at least one dominant allele, such as TT or
Tt. By examining a pedigree chart, it may be possible to determine the specific genotype of dominant
individuals by looking at their offspring. In the sample, the first generation couple does not have the trait
(TT or Tt), but two of their children do (tt). This is the only genotype possible so that they both show the
dominant phenotype, but still each pass on a recessive allele to their offspring.
Variations:
Students design a pedigree chart using the following traits: hair on the middle joint of fingers,
straight little fingers, cleft chin, direction of hair whorl. They apply all appropriate symbols and labels,
with the possible genotypes of each subject. They compare the pedigrees they have constructed and
discuss similarities and differences.
Adapted from:
Holt, Rinehart and Winston, Modern Biology, Harcourt, Brace, Jovanovich, Inc., 1977.
Newman, Barbara, Biology Research Activities, Annapolis, Maryland: Alpha Publishing Co., 1991.
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1004
Activity 3
an alternative activity for Event 2
Teacher Sheet
Science as Inquiry
Little Left-handed Finger
Why is variation important?
Overview:
In this activity, students will predict the variations that occur in human traits and then graph those variations.
By doing so, students examine the human genotype.
Materials:
Per lab group:
metric ruler
paper
pencil
Procedure:
Ask students to make a list of 10 differences, (examples of variations within one species—humans),
that they can easily see among their classmates, such as skin color, height, weight, eye color, etc. Have
them consider subtle differences, such as the length of the first finger. Using a metric ruler, students
measure the length of the first finger (in centimeters) of their left hand. Next, students record how many
of each finger length (total fingers) occurs in their group. Collect the group results on the chalkboard and
compare with other groups. Have students create a data table and bar graph showing class data. Ask the
students what advantages a short- or long-fingered person might have.
Background:
Meiosis is a special kind of cell division that forms gametes. It not only assures that the right number and
kinds of chromosomes will be passed on to the next generation, but also provides for a wide variety of chromosome combinations to be passed on. Just as shuffling the deck in a card game provides new combinations
of chromosomes for each new organism, meiosis “shuffles” chromosomes and provides new combinations for
new organisms. So, although two peas in a pod may look alike, there are actually differences between them.
Variations:
Have students measure and chart the human heart rate. To find a pulse, students lightly press on their necks to
one side of the windpipe, just under their jaw. Caution students to not press too hard—to much pressure may
result in decreased blood flow to the brain and students may feel faint. Using a stop watch, students clock their
heart rates for one minute, record the rate, then repeat two more times. They then average the results. Students
record their average heart rate on the chalkboard and find the average heart rate for the entire class.
Adapted from:
Laboratory Manual for Experiences in Biology, 2nd ed., Laidlaw Brothers, Publishers, 1985.
Newman, Barbara, Biology Research Activities, Annapolis, Maryland: Alpha Publishing Co., 1991.
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Activity 4
Teacher Sheet
Science as Inquiry
Heads or Tails?
How do we know if things occur just by chance?
Overview:
Students are introduced to a statistical test, chi-square. Using data provided, they determine if the
results were due to just pure chance.
Materials:
chi-square values table
copy of lab activity 902
calculator
coins, 2 similar (optional)
peas, equal mix of yellow and green (optional)
Procedure:
Students use chi-square to find out if the data they are given (simulated from lab activity 902) are
within acceptable range (statistically significant) as compared to results that are expected under ideal
conditions.
Background:
This activity is designed to find out if the results portrayed in the data table are within acceptable
range as compared to results that are expected under ideal conditions. For example, in a corn seedling
activity, for every 100 seedlings counted there would be 75 green and 25 albino plants—a ratio of 3:1.
The actual count is likely to be different. A statistical technique called chi-square (X2) is used to find out
if this difference is within acceptable range for events that occur as a result of chance and is not being
influenced by other extraneous factors that are not being investigated. Go over the following example
with students before they attempt to analyze the data in the lab activity on their own.
Let us say that the corn seedling activity yielded a count of 77 green and 23 albino corn plants. Based
upon the process of meiosis and the resulting gamete production, and assuming that in corn the color
green is dominant, the expected count would be 75 green and 25 albino plants for every 100 seedlings. A
punnet square is often used to illustrate this point (Fig. 1). The calculation below illustrates how the chisquare formula is used to determine a value for this data set:
X2 = sum of [difference2/expected ratio]
Observed ratio = 77:23
Expected ratio = 75:25
Difference (observed-expected) = +2, -2
Difference2 (d 2) = 4, 4
Difference2/expected ratio
= 4/75
4/25
= 0.0530
0.160
2
Chi-square = Ý [d /exp.] = 0.053 + 0.160 = 0.213
GG = Green
Gg = Green
gg = yellow
G
g
G
GG
Gg
g
Gg
gg
Fig. 1
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Activity 4
At this point we need to look at a table of chi-square values and probabilities to determine if the chisquare value of 0.213 is likely to happen purely by chance. Before we look up the probability in the
table, we have to calculate the number of degrees of freedom which in this example is 1 (2 - 1 = 1).
Degrees of freedom is calculated by subtracting 1 from the number of categories or classes of objects
being studied. In our example, the corn seedlings can be either green or albino. If we count the albino,
the only other possibility is the chance of it being green. When using the table we first find the degrees
of freedom in the left column, which in our case is 1. Going across the row for 1 degree of freedom we
find that the chi-square of 0.213 lies in between probability values of 0.455 (50%) and 0.0642 (80%). We
can conclude that an observed ratio of 77:23 is acceptable in place of expected ratio of 75:25 for a total
of 100 seedlings counted. In other words, if this activity was replicated, there is a 50 to 80% probability
that a difference of this magnitude or greater is likely to be observed. Chi-square values that fall above
0.05 probability (5%) are considered as statistically insignificant which means that there is more than 5%
probability that this difference (discrepancy between expected and observed value) could be attributed to
chance alone. Conversely, values equal to or less than 0.05 are considered statistically significant. (Note:
A value of less than 5% would be desirable to show a significant effect due to an experimental manipulation or alteration of a variable.)
Students will repeat this procedure using the data they are provided for soybean plants. It may be
necessary to remind the students that there are 2 degrees of freedom in the case of soybean plants.
Degrees of
freedom
1
2
3
4
5
6
7
8
9
10
P = 0.99
0.95
0.80
0.50
0.20
0.05
0.01
0.0000157
0.0201
0.115
0.297
0.554
0.872
1.239
1.646
2.088
2.558
0.00393
0.103
0.352
0.711
1.145
1.635
2.167
2.733
3.325
3.940
0.0642
0.446
1.005
1.649
2.343
3.070
3.822
4.594
5.380
6.179
0.455
1.386
2.366
3.357
4.351
5.348
6.346
7.344
8.343
9.342
1.642
3.219
4.642
5.989
7.289
8.558
9.830
11.030
12.242
13.442
3.841
5.991
7.815
9.488
11.070
12.592
14.067
15.507
16.919
18.307
6.635
9.210
11.341
13.277
15.086
16.812
18.475
20.090
21.666
23.209
Variations:
You may choose to do other activities such as the classic coin toss or picking out yellow and green
peas from a container, etc. as an introduction to the concept of probability. It is important to remind the
students that larger sample sizes tend to increase the probability of observed values getting closer to
expected values.
Adapted from:
Crow, L. W., and G. H. Sethna, Patterns, Houston: Texas Scope, Sequence, and Coordination Project,
1993.
Keeton, W., M. Dabney and R. Zollinhofer, Biology in the Laboratory, New York: W. W. Norton, 1970.
Morholt, E., and P. F. Brandewein, A Sourcebook for the Biological Sciences, Fort Worth, Texas:
Harcourt Brace Jovanovich College Publishers, 1986.
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Activity 5
Teacher Sheet
Science in Personal and Social Perspectives
Good Cells, Bad Cells
How do normal and sickled erythocytes compare?
Overview:
Using a microscope, students will compare and contrast under the microscope normal and sickled red
blood cells. There are two forms of the disorder, one in which only half of the red cells are sickled, and
another in which all the red blood cells are sickled. In this activity, students study human genetic disease
(autosomal) associated with chromosomal abnormalities.
Materials:
Blood Cell Comparison Diagram
Per lab group:
compound microscope
pencil, red
prepared slides of normal and
sickled red blood cells
Normal Red Cells
Sickled Red Cells
valine
histidine
leucine
threosine
proline
glutamic acid
glutamic acid
lysine
hemoglobin A
valine
histidine
leucine
threosine
proline
valine
glutamic acid
lysine
hemoglobin S
Procedure:
Have students examine normal red
blood cells under low power, then under
high power. Using a red pencil, they should
create a line drawing of what they see. They
also label the cell parts, i.e., cell membrane,
cytoplasm. Then students shade the parts of
the cell in which hemoglobin is found.
Next, have students examine a slide of
sickled red blood cells. Students draw these
cells and label any visible parts.
Background:
white
stained
Prepared slides are available from
cells
slide
biological supply houses or local hospitals.
microscopic-type
Normal red blood cells are round, have no
colchicine
view of cells and
photographic-type
added
chromosomes
view of cells and
nucleus, and are very pale pink in color.
chromosomes
Cells that appear dark blue in color are
stained white blood cells.
Sickle-cell anemia is a disorder in which red blood cells are sickle-shaped rather than round—
appearing as irregular shapes—pointed, jagged, and/or elongated in form. The disorder is genetic (inherited). Sickle-cells cannot carry as much oxygen as normal (round, large) red blood cells. As a result,
people with this disorder do not get enough oxygen to the rest of their body’s cells.
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Activity 5
People of African descent seem to suffer this
disorder most. In Africa, about 4% of the members of
certain tribes have sickle-cell anemia, while in the U. S.,
1 in 10 African Americans carry the abnormal allele.
Malaria is a debilitating disease prevalent in parts
of Africa, but uncommon in the U. S. today. It is
caused by a unicellular organism that invades red
blood cells. Some types can be fatal if untreated.
People homozygous for normal hemoglobin are
susceptible to malaria. Those who are heterozygous or
homozygous for the sickle-cell hemoglobin are less
susceptible. Therefore, in parts of Africa where
malaria is prevalent, heterozygotes tend to live longer
than people having the other genotypes.
Unfortunately, those homozygous for sickle-cell
usually die quite young. The likelihood of two
heterozygotes producing children is great, and
genetics tells us that every 2 out of 4 of those
children will be heterozygotes, like their parents.
Thus, the incidence of the recessive allele in African
black populations remains high, even though such a
high incidence also results in many offspring having
sickle-cell anemia. Because malaria is uncommon in
the U. S., heterozygotes have no such advantage,
and over the years, the frequency of the recessive
allele has declined due to natural selection.
BLOOD SAMPLES
Color red
Cytoplasm
Cell membrane
Normal Cells
Sickled Cells
RR Normal
Variations:
Have students draw the sex chromosomes. Then, on the chromosomes, they should label the genes
for hemophilia. The dominant gene is H. The recessive gene is h.
Tay-Sachs disease is another example of a sex-linked disease that could be studied.
Adapted from:
Laboratory Manual for Experiences in Biology, 2nd ed., Laidlaw Brothers, Publishers, 1985.
Biological Science: Molecules to Man, Rev. Ed., Boston, Mass: Houghton Mifflin Co., 1968.
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Activity 6
Teacher Sheet
Science in Personal and Social Perspectives
Hemophilia vs. Color Blindness
How are traits inherited?
Overview:
Students will determine how hemophilia and color blindness are inherited in several families. In this
activity, students examine the human genotype in terms of chromosomal abnormalities linked to sex
chromosomes.
Materials:
Per lab group:
coins, 8
tape, masking
pen (or fine-tip marker)
Procedure:
Part A. Students will first test chances for inheriting hemophilia. Have students tape and label both
sides of the coins as shown in the diagrams. The labels (letters) represent the results that might appear in
Coin 1. Male
XH
Y
Coin 3. Male
Xh
Y
Coin 2. Female
XH
Xh
Coin 4. Female
XH
Xh
front
back
front
back
Coin 5. Male
Xb
Y
Coin 7. Male
XB
Y
Coin 6. Female
XB
XB
Coin 8. Female
XB
Xb
front
back
front
back
FAMILY 1
FAMILY 3
FAMILY 2
FAMILY 4
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Activity 6
Sample Table (partial list only)
offspring of these parents. Placing two
coins (in the combinations listed) in their
Gene
Offspring
cupped hands, students shake, then drop the
combinations
observed
coins on a table top. They create, then
record on a data table the results of the toss.
X hX h
Students repeat the process for a total of 40
throws, first for Family 1 (normal, mother is
X bX B
heterozygous), then for Family 2, (father is
hemophiliac, mother is heterozygous).
X BY
Part B. Students repeat the process as
above, except that the test is for color blindness in Family 3 (father is color blind, mother
has two dominant genes); then for Family 4 (normal, mother is heterozygous).
Total
5
Background:
Hemophilia is an inherited disorder in which the person’s blood will not clot. If a person has a
dominant H, they will have normal blood. If a person has only a recessive h gene, their blood will not
clot. Genes for hemophilia are located on the sex chromosomes. Females have two X chromosomes,
while males have one X and one Y chromosomes. Only the X chromosomes have the genes for hemophilia. A female can be X HXH, XHXh or XhXh for the clotting trait. A male can have XHY or XhY.
Color blindness is also a genetic disorder. In this disorder, a person does not see colors such as red
and green. Instead, the person sees gray instead of green and yellow instead of red. To see all colors, a
person must have at least one dominant C gene. Having only recessive genes determines whether a
person is color blind, such as XBXB, XBXb or X hXb for females and XBY or XbY for males.
In a rare form of color blindness, a person cannot distinguish the color blue. This abnormality affects
both males and females equally, and occurs because of an autosomal gene (red/green color blindness is
sex linked).
Variations:
Have students design an experiment that investigates the idea that snoring is genetically based. They
should use separate and control variables, and consider parts of the mouth and throat that might be
involved in snoring.
Adapted from:
Merrill, “An Everyday Experience Worksheet,” Biology, Macmillan/McGraw-Hill, Glencoe Division,
1992.
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Assessment 1
Science in Personal and
Social Perspectives
Color Blind, I
Item:
A couple’s daughter is color blind. Does the father have normal color vision, or is he color blind?
Explain your answer. Draw pedigrees that show the possible phenotypes of parents and a color blind
daughter.
Answer:
The father is color blind, with the genotype XcY. The daughter received a copy of her father’s X
chromosome (or she would not be female). The mother carried at least one recessive allele, which the
daughter inherited.
Father
color-blind
Mother
"normal"
heterozygous
X cY
X cX
gametes X c Y
Xc X
X cX c
Daughter
recessive trait
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1004
Assessment 2
Science in Personal and
Social Perspectives
Color Blind, II
Item:
In a rare form of color blindness, a person cannot distinguish the color blue. This abnormality, when
it does occur, affects both males and females in equal numbers. Explain this pattern of inheritance and
compare it to that involved in red/green color blindness.
Answer:
This form of color blindness is due to an autosomal gene—whereas the red/green color blindness is
sex linked.
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Assessment 3
Science in Personal and
Social Perspectives
Genetic Disorder
Item:
Males having Klinefelter syndrome are found to have two X chromosomes and one Y chromosome.
What is the genetic basis of that chromosome abnormality? In other words, how could such a thing
happen?
Answer:
The chromosome abnormality results from nondisjunction of the sex chromosomes. This results in a
male with a genotype which includes the configuration XXY at the location of the 23rd (sex) pair of
chromosomes.
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Unit Materials/References
Consumables
Item
Quantity (per lab group)
Chi-square values table
1
coins, similar (optional)
2
coins
8
copy of Lab Activity 902
1
copy of Plate 1
2
copy of Plate 2
2
tape, masking
—
tape, transparent (or glue)
—
peas, equal mix of yellow and green (optional)
—
pen (or fine-tip marker)
1
pencil
1
pencil, red
1
paper
—
PTC paper
1
Activity
4
4
6
4
1
1
6
1
4
6
2
5
2
2
Nonconsumables
Item
Quantity (per lab group)
calculator
1
compound microscope
1
prepared slides of normal and sickled blood cells
1
scissors
1
metric ruler
1
Activity
4
5
5
1
2, 3*
*indicates alternative or additional activity
Key to activities:
1. Karyotyping Human Chromosomes
2. The Right to Know and Not to Know
3. Little Left-handed Finger
4. Heads or Tails?
5. Good Cells, Bad Cells
6. Hemophilia vs. Color Blindness
Activity Sources
Biological Science: Molecules to Man, Rev. Ed., Boston, Mass: Houghton Mifflin Co., 1968.
Crow, L. W., and G. H. Sethna, Patterns, Houston: Texas Scope, Sequence, and Coordination Project, 1993.
Holt, Rinehart and Winston, Modern Biology, Harcourt, Brace, Jovanovich, Inc., 1991.
(continued)
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1004
Unit Materials/References
Holt, Rinehart and Winston, Modern Biology, Harcourt, Brace, Jovanovich, Inc., 1977.
Keeton, W., M. Dabney and R. Zollinhofer, Biology in the Laboratory, New York: W. W. Norton, 1970.
Laboratory Manual for Experiences in Biology, 2nd ed., Laidlaw Brothers, Publishers, 1985.
Merrill, “An Everyday Experience Worksheet,” Biology, Macmillan/McGraw-Hill, Glencoe Division,
1992.
Morholt, E., and P. F. Brandewein, A Sourcebook for the Biological Sciences, Ft. Worth, Texas: Harcourt
Brace Jovanovich College Publishers, 1986.
Newman, Barbara, Biology Research Activities, Annapolis, Maryland: Alpha Publishing Co., 1991.
Seashore, M., and R. Wappner, Genetics in Primary Care and Clinical Medicine, Appleton & Lange,
1996.
27