variation. The primary vehicle is a class inventory of human traits that
highlights similarities and differences. Although variation, both phenotypic
and genotypic, is the central focus of all five lessons, this concept is less
explicit in subsequent lessons than it is in this one.
One goal of the Human Genome Project was to provide the complete
sequence of the human genome. Another goal was to illuminate the extent
of human genetic variation by providing a detailed picture of human
similarities and differences at the molecular level. Research indicates that
any two individuals are 99.9 percent identical at the level of their DNA.
The 0.1 percent where we vary from one another (about 1 out of 1,000
DNA bases) is clearly very important. It is within this small fraction of
the genome that we find clues to the molecular basis for the phenotypic
differences that distinguish each one of us from all others.
In this lesson, students are introduced to the notion that although we are
very similar to one another, we are also very different and our differences
reflect a complex interplay between genetic and environmental factors.
This understanding sets the stage for subsequent lessons in the module in
which students learn about the molecular differences that help explain our
phenotypic differences and also consider some of the medical and ethical
implications of scientists’ growing understanding of these differences.
Web-Based Activities
In Advance
None.
Materials and Preparation
Photocopies and Transparencies
Equipment and Materials
• 1 copy of Master 1.1 for
• plant, fish, prepared slide of
each student
bacteria
• 1 copy of Master 1.2 for
• masking tape for labeled axes
each student
on the board or wall in which
students can enter data
• 120 3 × 5 cards (4 per student;
required only if the axes are on
the wall)
• tape measure (1 per pair of
students)
Construct four sets of axes on the board or the classroom wall (use masking
tape). Label the axes as shown in Figure 7.
64
Figure 7. Construct the four sets of axes shown here on the board or on a wall of your classroom.
1. Begin the lesson by telling the class something like, “If a visitor from
Procedure
another planet walked into this classroom, he might easily conclude
that humans all look very much alike.” If students complain that this
is not true, answer with something like, “You certainly are more like
one another than you are like this plant [point to the plant]. Or this
fish [point to the fish]. And for sure, you are more alike than any one
of you is like the bacteria on this slide [wave the prepared slide of
bacteria in the air]. Humans— Homo sapiens—have a set of traits that
define us as a species, just like all other species have a set of traits
that define them.”
2. Continue the lesson by saying, “Let’s see just how similar you are.”
Give one copy of Master 1.1, An Inventory of a Few Human Traits,
to each student and ask students to work in pairs to complete it.
If students are unfamiliar with the following terms, provide the
definitions below.
detached earlobes: Earlobes hang free, forming a distinct lobe.
hitchhiker’s thumb: Most distal joint of thumb can form almost a
90-degree angle with the next most proximal joint.
middigital hair: Hair is present on digits distal to knuckles.
cross left thumb over right: Natural tendency is to cross left thumb
over right when clasping hands together.
65
Student Lesson 1
Human Genetic Variation
3. As students complete the inventory, direct their attention to the four
sets of labeled axes you prepared. Ask students to enter their data at
the appropriate place on each set of axes.
If you constructed the axes on the board, students can use chalk to
record their data. If you used masking tape to construct the axes on the
wall, ask students to record their data by taping one 3 × 5 card in the
appropriate place on each set of axes.
Tip from the field test: You may wish to give males one color of chalk or
3 × 5 card to use in recording their data and females a different color.
This strategy will allow the class to determine whether any of the three
characteristics other than sex (for example, height) shows differences
related to sex.
4. After the students have finished collecting and recording their data,
ask them to look at the four histograms they built and identify what
evidence they see in those data that they share many traits with other
members of their class.
Students may answer that all people have only one nose, and all people
are only one sex or the other.
5. Continue the lesson by saying, “But now that I look around the room,
it is clear that you are different. What evidence do you see in these
data that people are different?”
Students should recognize that not everyone is the same height and not
everyone has the same hair color.
As students look at the data, you may wish to ask them to compare the
shapes of the histograms for sex and height. The sex histogram has two
distinct peaks because there are only two categories of individuals—
female and male. That is, sex is a discontinuous trait. In contrast, height
is a continuous trait that has many categories of individuals, ranging
from very short to very tall. The shape of the height histogram may
begin to approach a bell curve, or normal distribution. It may also have
two peaks—a bimodal distribution—with one peak representing the
female students and the other representing the males.
6. Challenge students to try to describe just how different they are by
guessing how many traits they would have to consider to identify any
given student in the room as unique. Write the students’ predictions
on the board.
66
7. Conduct the game described below with several volunteers.
• Choose a volunteer to determine his or her “uniqueness” as
compared with the other students.
• Ask all students to stand.
• Invite the volunteer to begin to identify his or her phenotype for
each of the 13 human traits listed on Master 1.1, An Inventory
of a Few Human Traits. Begin with the first trait and proceed
sequentially. As the volunteer lists his or her phenotype for each
trait, direct the students who share the volunteer’s phenotype
for that trait to remain standing. Direct all other students to sit.
• Continue in this fashion until the volunteer is the only person
still standing. Count how many traits the class had to consider
to distinguish the volunteer from all other students in the class.
Compare this number with the students’ predictions.
• Repeat as desired with another volunteer.
8. Ask students to work in pairs to answer the questions on Master 1.2,
Thinking about Human Variation.
Question 1. Some human traits can be changed by human intervention,
Collect and review the
and some cannot. Provide examples of each of these types of traits.
students’ completed
Biological sex and blood type cannot be changed. Hair color, skin
Master 1.2 to assess their
color, and even height and mental abilities can be changed by human
understanding of the
intervention. Students also may suggest that body piercing alters
lesson’s major concepts.
human traits.
Question 2. You probably already know that some traits are genetic and
others are environmental. But most human traits reflect an interaction
between genetic and environmental factors. Name some traits that might
fall into this category and explain why you think they do.
Height, weight, intelligence, and artistic or athletic ability are examples
Increasing evidence
of traits that are influenced by genetic and environmental factors. Some
indicates that all human
students may mention disorders such as certain types of cancer or
diseases have genetic and
even psychiatric disorders. We know that these types of traits are
environmental
both genetic and environmental because we see evidence that they
run in families and because we know we can modify them by
components. Point out
changing the environment.
that diseases such as
cancer, heart disease, and
Question 3. Describe some of the benefits of human genetic variation.
diabetes are traits that
What are some of the potential problems that such variation can cause?
show an interaction
between genetic and
Students may mention a number of benefits, such as allowing people
to be distinguished from one another and increasing the diversity of
environmental factors.
abilities, interests, and perspectives among humans. Some students may
Students will consider
recognize that genetic variation also benefits the species because it is
this concept in Lesson 4,
the basis for evolution by natural selection. Students will consider this
Are You Susceptible?
aspect of variation in Lesson 2, The Meaning of Genetic Variation.
67
Student Lesson 1
Human Genetic Variation
Expect students to recognize that just as being different from one
another has advantages, it also has disadvantages. For example, genetic
variation makes successful tissue and organ transplants more difficult
to accomplish than if we were all genetically identical. Students also
may note that the existence of real (or perceived) differences among
members of a population can allow prejudice and discrimination to
exist.
You may wish to point out that research reveals that more variation
exists within populations than between them (Figure 4, page 22). As
noted in “Understanding Human Genetic Variation” (pages 19–29), an
examination of human proteins demonstrated that about 85 percent
of all variation occurred within populations, whereas only 15 percent
occurred between populations. That is, we are more “like” people with
other ethnic or geographic origins than we might think.
9. Invite students to summarize the lesson’s major concepts by asking,
“What has this lesson illustrated about how one human compares
with another human? What has it illustrated about human variation
in general?”
These open-ended
Expect students to recognize that humans share many traits. Students
questions invite students
may also note that there is a wide range of variation in human traits and
to step back from the
one does not have to consider very many traits before a given person’s
lesson’s details to consider
uniqueness is demonstrated. Students should point out that some traits
its broader implications.
can be changed by human intervention and some cannot and that
Another way to invite
although some traits are genetic and others are environmental, most
such refl ection is to ask
human traits reflect an interaction between genetic and environmental
students to identify the
factors (that is, most are multifactorial). You may wish to introduce the
term “multifactorial” at this point; students will study multifactorial
most important or the
traits in more detail in Lesson 4, Are You Susceptible?
most interesting idea they
learned as a result of
Be sure that students generalize their responses to focus on variation
completing the lesson.
in populations, not variation simply between themselves and their
partners. Point out that the concept of variation in populations will
reappear in different, but less obvious, ways in the other lessons in
this module.
68
This lesson introduces students to several ideas that you may wish them to
Potential
explore in more depth. For example, assign students to use their textbooks
Extensions
to identify the biological mechanisms that lead to and maintain diversity
in populations.
Alternatively, ask students to list some of the advantages and disadvantages
of genetic variation in nonhuman populations. Invite them to locate and
report on cases where scientists are concerned that it may be diminishing
(for example, in domesticated crops and in populations of endangered
species being maintained in zoos and other protected settings).
Finally, to extend the discussion of the multifactorial nature of most human
traits, challenge students to suggest ways that scientists might investigate
the relative contributions that heredity and the environment make to such
traits (for example, twin studies or studies of adopted children in relation
to their adoptive and biological parents).
69
Student Lesson 1
Human Genetic Variation
Lesson 1 Organizer
Procedure
What the Teacher Does
Reference
Tell the class something like this: “If a visitor from another planet
Page 65
walked into this classroom, he might easily conclude that humans all Step 1
look very much alike.”
Ask, “Do you agree with this statement?” Use examples to help
students recognize that humans are more similar to each other than
they are to other species and that humans have a set of traits that
define us as a species.
Invite students to explore similarities among classmates. Give each
Page 65
student one copy of Master 1.1 and ask them to work in pairs to
Step 2
complete it.
Define terms (on page 65) if unfamiliar to students.
Ask students to enter data from their copy of Master 1.1 onto
Page 66
graphs you prepared on the board.
Step 3
Have class analyze data on graphs and identify evidence that
Page 66
supports the idea that students share many traits with other class
Step 4
members.
Continue by pointing out that you can see that individuals are
Page 66
different. Ask students, “What evidence supports that people are
Step 5
different?”
Ask students how many traits they would need to consider to
Page 66
identify a given student as unique. Write predictions on the board.
Step 6
Conduct the game described in Step 7 to determine uniqueness
Page 67
among class members.
Step 7
Give each student a copy of Master 1.2. Ask students to work in
Page 67
pairs to answer the questions. Discuss answers with the class (on
Step 8
pages 67 to 68).
Ask, “What has this lesson illustrated about how one human
Page 68
compares with another human? What has it illustrated about human Step 9
variation in general?” Ask students to summarize their ideas and
share with the class.
= Involves copying a master.
70
L E S S O N 2
Explore
The Meaning of
Genetic Variation
Focus
At a Glance
Students investigate variation in the beta globin gene by identifying
base changes that do and do not alter function, and by using several
Web- or print-based resources to consider the significance in different
environments of the base change associated with sickle cell disease.
Major Concept
The ultimate source of genetic variation is differences in DNA sequences.
Most of those genetic differences do not affect how individuals function.
Some genetic variation, however, is associated with disease, and some
improves the ability of the species to survive changes in the environment.
Genetic variation, therefore, is the basis for evolution by natural selection.
Objectives
After completing this lesson, students will
• recognize that the extent of molecular variation between two people
is only about 0.1 percent, but because of the large size of the human
genome, this translates to about 3 million base differences;
• understand that most human genetic variation does not appear to
affect function;
• be able to explain that some human genetic variation is related to
disease and provide an example; and
• be able to describe a benefit of human genetic variation and relate
this benefit to human evolution by natural selection.
Prerequisite Knowledge
Students should understand basic Mendelian patterns of inheritance,
especially autosomal-recessive inheritance; the basic structure of DNA;
the transcription of DNA to messenger RNA; and the translation of
messenger RNA to protein.
Basic Science–Health Connection
Although the idea is made explicit only in annotations to teachers, this
lesson illustrates how advances in science and technology have allowed us
to establish relationships between some genetic variations and particular
phenotypes. For example, our understanding of the relationship between
DNA and protein has allowed us to establish a relationship between a
71
Human Genetic Variation
change in a single base pair and the symptomology of sickle cell disease.
Similarly, our understanding of the basic biochemical mechanisms
underlying the symptoms associated with sickle cell disease has provided
important clues about possible strategies for clinical intervention. You
may wish to make some of these points with your students as they
complete the lesson.
As discussed in Understanding Human Genetic Variation (pages 19–29),