Biology Vista
Mechanisms of Genetics
NOTES
Overview
Students use simulations and technology to examine the inheritance of traits;
the replication, transcription, and translation of DNA and RNA; and the
significance of mutations in human populations.
General Time Frame
12–13 lessons (50 minutes each)
Background Information for the Vista
Organisms experience constancy and change. DNA serves as the mechanism
for the transmission of genetic information from one generation to the next.
The processes of DNA replication ensure constancy in the genetic makeup of
cells. However, changes can and do occur through mutation of DNA, directly
affecting the traits shown in the gametes or in the body cells of an individual.
Over the years researchers, and most recently the members of the Human
Genome Project, have extensively examined the human genome. The Human
Genome Project began in 1990 when the National Institutes of Health,
the Department of Energy, and international partners joined together to
decipher the massive amounts of genetic information of selected organisms.
One of the many benefits of the Human Genome Project has been a greater
understanding of how genetic variation leads to changes in humans.
Materials
Printed Materials Included in this Vista:
Mechanisms of Genetics Vista TEKS Correlation Chart
Fundamentally Genetics investigation pages
Insect Chromosomes Drawings
Dominant Fly investigation pages
Insect Parts Drawings
DNA, mRNA, and Protein Synthesis (computer simulation) investigation
pages
DNA, mRNA, and Protein Synthesis (paper/pencil) investigation pages
DNA Strands
mRNA Genetic Code Wheel
mRNA Genetic Code Chart
Protein Synthesis: Like a Banana Split investigation pages
Line drawings of banana split ingredients
The Human Genome investigation pages
Inheritance of Sickle-Cell Anemia Assessment Task pages
The Charles A. Dana Center at UT Austin
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Materials for the Teacher to Gather:
NOTES
2
Each learning experience has a list of necessary equipment and materials.
However, it is not the intention of TEXTEAMS to dictate the types and
quantities of materials/equipment to use for the learning experiences. All the
materials/equipment that are listed in the learning experiences are suggestions.
Teacher’s notes give specific instructions for areas where the author has
experienced the need for a specific item. Substitutions for materials/
equipment should be based on local budgets, availability, and facilities.
Biology Institute 2004
The Charles A. Dana Center at UT Austin
3
Biology
Inheritance of Sickle Cell Anemia
Inheritance of Sickle Cell Anemia
4
TEXTEAMS BIology Institute 2004
Biology
Inheritance of Sickle Cell Anemia
Fundamentally Genetics
NOTES
Learning Experience 1
Description:
Students practice the protocol used for describing genetic traits. As noted in
the chart below, students have prior knowledge of genetics from grades 6, 7,
and 8.
Grade 6
Grade 7
Grade 8
Biology
6.11 (C)
7.10 (C)
8.11(C)
6 (D)
Time Frame:
50 minutes
Materials:
Tasting paper, such as PTC or sodium benzoate (1 per student)
Fundamentally Genetics investigation pages (included in the Student Blackline
Masters at the end of this vista)
Advance Preparation:
Prepare a copy of the Fundamentally Genetics investigation pages for each
student.
Background Information for the Teacher:
Why study genetics? One of the most obvious answers is that it is a way to
achieve a better understanding of ourselves. However, this interest in actuality
can be extended well beyond the realm of the human species and applied to
the genetics of other living things as well.
Another reason to study genetics is its practical application to the welfare
of humans. As we study human genetic variation, we discover and describe
its roles in human diseases such as cancer, heart disease, and diabetes. One
has only to look at the large number of organizations involved in raising
significant funds for research to realize how important this area is to many
people.
A third reason to study genetics is that it provides us with data that can
be used to describe human evolution. Today we have the ability to trace
evolutionary history at the molecular level that expands upon the traditional
physical anthropology used in the past.
The Charles A. Dana Center at UT Austin
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NOTES
One of the steps used to study how traits are inherited is to design a key using
upper and lower case letters to represent dominant and recessive forms of a
trait, respectively. For example, the letter P might be used to represent the
dominant form of polydactyly, while p represents the recessive form of this
trait.
In most cases, there are two alleles (alternate forms of a gene) that control the
expressions of a trait.
However, many human traits result from multiple gene interactions. Alleles
are sections of DNA that are located on the different chromosomes of a
homologous pair. Humans have 46 chromosomes, 22 homologous pairs
(similar shape and size, and code for similar genetic traits) and one pair of sex
chromosomes.
A dominant trait occurs when an allele masters or controls the alternate allele.
For example, an individual with even one dominant allele from either parent
would exhibit polydactyly and have six fingers.
A widow’s peak hairline is also a dominant trait. The letter W could be used
to symbolize the allele for widow’s peak hairline. Since the most simple
inheritance patterns involve the transmission of one trait from the mom and
one trait from the dad, all WW and Ww individuals would have a widow’s
peak.
Any allele that is not expressed is called recessive. Since a straight hairline
is a recessive, the allele would be assigned a lowercase w. The only letter
combination that would represent a straight hairline would be ww. This would
mean that both parents contributed one w allele in the fertilization process.
The combination of alleles inherited from your parents is called a genotype.
When a person shows a dominant trait, they do not know exactly what
their genotype is. The alleles could be identical. For example, a person could
receive an unattached earlobe allele from both parents and produce an
offspring with unattached earlobes. Since unattached earlobes are a dominant
trait, the genotype would be EE. This combination of alleles is referred to as
homozygous from the Latin words homo meaning same, and zygote, which is
a cell formed at conception.
Sometimes the alleles inherited from your parents differ. For example, you
could receive an attached earlobe allele from your mother, but not your father.
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Biology Institute 2004
In this case, your genotype would be Ee. This combination of alleles is referred
to as heterozygous from the Latin words hetero meaning different, and zygote,
which is a cell formed at conception.
NOTES
In a simple inheritance pattern involving only two alleles, the person who
shows the recessive trait always knows his or her genotype because no
dominant traits are present. So, an individual who has attached earlobes would
have the genotype ee.
A physical attribute, that is if a person exhibits attached ear lobes or earlobes
that hang down, is called a phenotype. A phenotype is what you look like.
In this learning experience, the student uses a key to engage in the process of
linking letters to their own characteristics.
Procedures:
Teacher note: Emphasize to students that in this investigation we are
assuming that human traits are an expression of a pair of alleles. In reality, most
human traits are controlled by more than two alleles.
1.
Have students complete the Fundamentally Genetics investigation
pages.
Teacher note: At this time, use the terms dominant, recessive, genotype,
phenotype, homozygous, heterozygous, allele, and gene as you assist students.
You may want to have examples of the genetic traits listed in the Fundamentally
Genetics investigation pages to show students.
2. Have students report their results and construct charts or graphs of the
frequencies of the dominant and recessive traits in the class.
Formative Assessment: Monitor and redirect students as needed as they
record their responses to the Fundamentally Genetics investigation pages.
Answers will vary depending on the phenotype of individual students.
The Charles A. Dana Center at UT Austin
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Fundamentally Genetics
Looking at Your Traits
Are you dominant or recessive for the following traits? You and your group will have to look at each other
to figure this out. Record your responses in the appropriate blanks.
1. Tasting Paper—Taste the paper. It contains a harmless chemical that some people can taste and
others cannot. The ability to taste the chemical is a dominant trait. People who cannot taste this
chemical are recessive for the trait.
_____________________________
Dominant or Recessive
2. Tongue Rolling—Some people can roll their tongues into a taco- or U-shape. This is a dominant
trait. If you cannot roll your tongue into a taco- or U-shape, you are recessive for this trait.
_____________________________
Dominant or Recessive
3. Earlobes—It is a dominant trait to have earlobes that hang down. People who have earlobes
attached directly to the side of their heads are recessive for this trait.
_____________________________
Dominant or Recessive
4. Earbump—Some people have a bump on the inside rim of the upper part of the ear ridge called
Darwin’s ear point. The bump is due to the presence of a dominant allele. If you are lacking the
bump, you are recessive for this trait.
_____________________________
Dominant or Recessive
5. Widow’s Peak—If you have a hairline that comes to a point in the middle of your forehead,
you possess a dominant allele for widow’s peak. A straight or even hairline indicates that you are
recessive for this trait.
_____________________________
Dominant or Recessive
6. Hitchhiker’s Thumb—People who can bend the last joint of their thumbs back to a 90-degree
angle are dominant for hitchhiker’s thumb. People who lack this ability are recessive for this trait.
_____________________________
Dominant or Recessive
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TEXTEAMS BIology Institute 2004
7. Polydactyly—People born with six fingers or toes possess the dominant trait for polydactyly.
Having five fingers and toes is a recessive trait. In the U.S., people with extra toes or fingers usually
have them removed shortly after birth.
_____________________________
Dominant or Recessive
8. Syndactyly—Having webbed fingers and toes is a dominant trait. Sometimes only a pair of fingers
or toes are webbed. If you have fingers and toes that separate, then you are recessive for this trait.
_____________________________
Dominant or Recessive
9. Cleft Chin—If you have a chin that has a split in the middle like John Travolta’s, you have a cleft
chin. This is a recessive trait. The absence of a cleft chin is a dominant feature.
_____________________________
Dominant or Recessive
10. Hair Whorl—Have someone in your group look at the back of your head to determine if
your hair whorls to the right (clockwise) or to the left (counterclockwise). If you use hairspray or
gels on your hair, this activity may be a hard one to do. A clockwise whorl is dominant over the
recessive trait of a counterclockwise whorl.
_____________________________
Dominant or Recessive
The Charles A. Dana Center at UT Austin
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Describing Your Traits
Now that you know the traits you exhibit—your phenotype—how do you describe them? The
protocol is to use letters to describe genetic traits—your genotype. For example, an uppercase
T can represent the dominant trait for tasting the tasting papers and a lowercase t the recessive
trait for not tasting the tasting papers. In this learning experience, two letters are used to
represent the traits because one comes from your mother and one from your father; however,
traits sometimes are represented by more than two letters because more than two alleles are
involved. The ABO alleles for blood type are an example of such a combination. Two letters also
represent the gene, or DNA strand, for each of the 10 traits. So Tt also represents the gene for
the ability to taste the tasting papers. Each letter represents an allele for each version of the
gene—T for the version of being able to taste the tasting papers and t for the version of not
being able to taste the tasting papers.
An individual who receives a TT from their parents is described as homozygous for the ability
to taste the tasting papers. An individual who receives Tt from their parents is described as
heterozygous for the ability to taste the tasting papers. The heterozygous individual has two
different letters, Tt, as compared with the homozygous individual who has two letters that are
identical, TT.
When you have a recessive trait, such as not being able to taste the tasting papers, your
genotype is certain. The two pieces of genetic information you got from your parents are
recessive and recessive. So the genotype will be two lowercase letters, tt.
When you have a dominant trait, such as being able to taste the tasting papers, your genotype is
not certain. The pieces of genetic information you got from your parents could be dominant and
dominant, or dominant and recessive. So the genotype could be two uppercase letters, TT, or
one uppercase and one lowercase letter, Tt.
Use the following key to describe your phenotype and all your possible genotypes for each of
the 10 traits. Record your responses in the appropriate blanks.
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TEXTEAMS BIology Institute 2004
Key
T—TASTING PAPER TASTER
H—HITCHHIKER’S THUMB PRESENT
t—nontasting paper taster
h—hitchhiker’s thumb not present
R—TONGUE ROLLER
P—SIX FINGERS OR TOES
r—nontongue roller
p—five fingers or toes
E—UNATTACHED EARLOBES
S—WEBBED FINGERS OR TOES
e—attached earlobes
s—nonwebbed fingers or toes
D—DARWIN’S EAR POINT PRESENT
C—NON CLEFT CHIN
d—Darwin’s ear point not present
c—cleft chin
W—WIDOW’S PEAK PRESENT
L—CLOCKWISE HAIR WHORL
w—widow’s peak not present
l—counterclockwise hair whorl
1. Tasting Paper—Taste the paper. It contains a harmless chemical that some people can taste
and others cannot. The ability to taste the chemical is a dominant trait. People who cannot taste
this chemical are recessive for the trait.
_________________________ ________________________
Phenotype
Genotype
2. Tongue Rolling—Some people can roll their tongues into a taco- or U-shape. This is a
dominant trait. If you cannot roll your tongue into a taco- or U-shape, you are recessive for this
trait.
_________________________ ________________________
Phenotype
Genotype
3. Earlobes—It is a dominant trait to have earlobes that hang down. People that have earlobes
attached directly to the side of their heads are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
The Charles A. Dana Center at UT Austin
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4. Earbump—Some people have a bump on the inside rim of the upper part of the ear ridge. It is
called Darwin’s ear point. If you have the bump, it is due to the presence of a dominant allele. If you
are lacking the bump, you are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
5. Widow’s Peak—If you have a hairline that comes to a point in the middle of your forehead, you
possess a dominant allele for widow’s peak. A straight or even hairline indicates you are recessive
for this trait.
_________________________ ________________________
Phenotype
Genotype
6. Hitchhiker’s Thumb—People who can bend the last joint of their thumbs back to a 90-degree
angle are dominant for hitchhiker’s thumb. People who lack this ability are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
7. Polydactyly—People born with six fingers or toes possess the dominant trait for polydactyly.
Having five fingers and toes is a recessive trait. In the U.S., people with extra toes or fingers usually
have them removed shortly after birth.
_________________________ ________________________
Phenotype
Genotype
8. Syndactyly—Having webbed fingers and toes is a dominant trait. Sometimes only a pair of fingers
or toes are webbed. If you have fingers and toes that separate, then you are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
9. Cleft Chin—If you have a chin that has a split in the middle, like John Travolta’s, you have a cleft
chin. This is a recessive trait. The absence of a cleft chin is a dominant feature.
_________________________ ________________________
Phenotype
Genotype
10. Hair Whorl—Have someone in your group look at the back of your head to determine if
your hair whorls to the right (clockwise) or to the left (counterclockwise). If you use hairspray or
gels on your hair, this activity may be a hard one to do. A clockwise whorl is dominant over the
recessive trait of a counterclockwise whorl.
_________________________ ________________________
Phenotype
Genotype
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TEXTEAMS BIology Institute 2004
Dominant Fly
NOTES
Learning Experience 2
Description:
Students determine the genotype and phenotype of fruit fly offspring. As
noted in the chart below, students have prior knowledge of genetics from
grades 6, 7, and 8.
Grade 6
Grade 7
Grade 8
Biology
6.11 (C)
7.10 (C)
8.11 (C)
6 (D)
Time Frame:
2 lessons (50 minutes each)
Materials:
Plastic twist-apart eggs (1 large and 1 small per student group)
Ribbon strip, 10 cm (1 per student group)
Hot glue gun (1 per class)
Colored pencils (1 set per student group)
White, unlined paper (1 sheet per student group)
Insect Chromosomes Drawings (included in the Teacher Blackline Masters
at the end of this vista)
Dominant Fly investigation pages (included in the Student Blackline
Masters at the end of this vista)
Insect Parts Drawings (included in the Student Blackline Masters at the
end of this vista)
Advance Preparation:
1. Prepare a copy of the Dominant Fly investigation pages, the Insect
Chromosomes Drawings, and the Insect Parts Drawings for each
student group.
2. Prepare an egg and sperm for each student group by cutting apart
the Insect Chromosomes Drawings and placing a complete set
of father chromosomes in the smaller egg and a complete set of
mother chromosomes in the larger egg. (Make sure each egg has one
chromosome from the 4 pairs given in Insect Chromosomes Drawings
1-5. It will not matter which female or male egg the students receive.)
Close the eggs. Glue the ribbon strip to the smaller egg to represent
the tail of a sperm cell. There are five different combinations of
chromosomes.
The Charles A. Dana Center at UT Austin
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NOTES
Background Information for the Teacher:
Thomas Morgan and others conducted experiments with the fruit fly
Drosophila sp. that provided proof that genes are arranged linearly on
chromosomes. This learning experience combines Gregor Mendel’s postulates:
(1) individual factors that control gene traits occur in pairs, and (2) genes
exhibit dominance or recessiveness. When students pair up mother and father
insect genes, they learn how genes line up with each other.
Chromosomes are made of DNA and protein. They are found in the nucleus
of eukaryotic cells and are visible during mitosis and meiosis. Some students
may not understand that it takes more than a single pair of chromosomes to
make up a living organism—even a fruit fly has four pairs of chromosomes.
In the insect genetics simulation, it takes all eight chromosomes to make an
insect. Don’t be surprised if some students take a little time to realize that
they need all of the chromosomes to make an insect, not just one or two
chromosomes.
The chromosomes that determine the sex of an organism are not an exact pair.
Males are called hemizygous because they receive one X chromosome from
the mother and one Y chromosome from the father. The term hemizygous
refers to the condition of pairing two nonhomologous chromosomes together.
Normal males have XY sex chromosomes. A normal female possesses two
X chromosomes (XX). A normal female is homozygous with regard to sex
chromosomes.
Procedures:
Have students complete the Dominant Fly investigation pages and the
construction of the fly.
Formative Assessment: Monitor student responses to the investigation
pages, ensuring that they are correctly interpreting genotypes and phenotypes.
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Biology Institute 2004
Dominant Fly investigation pages (correct student responses).
Data Table 1
Trait
Genotype
Phenotype
Head Size
Hh
Large head
Eye Color
Ee
Red eye
Antennae
Pp
Antennae present
Data Table 2
Chromosome
pair 1
Chromosome
pair 2
Chromosome
pair 3
Chromosome
pair 4
Trait
Genotype
Homozygous
or
Heterozygous
Dominant or
Recessive
Phenotype
Head size
Hh
Heterozygous
Dominant
Large head
Eye color
Ee
Heterozygous
Dominant
Red eye
Antennae
Pp
Heterozygous
Dominant
Antennae present
Thorax size
tt
Homozygous
Recessive
Long thorax
Wing color
Oo
Heterozygous
Dominant
Orange wings
Wing length
WW
Homozygous
Dominant
Short wings
Leg length
ll
Homozygous
Recessive
Long legs
Body color
Bb
Heterozygous
Dominant
Black body
Abdomen size
Aa
Heterozygous
Dominant
Long abdomen
Sex
XY
Hemizygous
Not Applicable
Male
The Charles A. Dana Center at UT Austin
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Also monitor the accuracy of the insect drawing. An example is shown below.
NOTES
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Biology Institute 2004
Insect Chromosomes—1
NOTES
* Body color refers to antennae, head, thorax, abdomen, and legs.
Insect Chromosomes—2
* Body color refers to antennae, head, thorax, abdomen, and legs.
The Charles A. Dana Center at UT Austin
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NOTES
Insect Chromosomes—3
* Body color refers to antennae, head, thorax, abdomen, and legs.
Insect Chromosomes—4
* Body color refers to antennae, head, thorax, abdomen, and legs.
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Biology Institute 2004
Insect Chromosomes—5
NOTES
* Body color refers to antennae, head, thorax, abdomen, and legs.
The Charles A. Dana Center at UT Austin
19
Dominant Fly
Genes that determine traits are encoded and arranged linearly on structures called chromosomes found in the nuclei of
most cells. When organisms reproduce, the resulting offspring should receive an equal number of chromosomes from the
mother and the father.
Materials:
Egg, sperm, Insect Parts drawings, colored pencils, unlined paper
Procedures:
1. Use the chromosomes and the Insect Traits Key below to determine the genotype and phenotype of the
offspring. Record the information in Data Table 1.
Insect Traits Key
H — LARGE HEAD
E — RED EYE
h — small head
e — apricot eye
P — ANTENNAE
PRESENT
p — antennae absent
T — SHORT THORAX
O — ORANGE WING
W — SHORT WINGS
t — long thorax
o — green wings
w — long wings
A — SHORT
ABDOMEN
B — BLACK BODY*
L — SHORT LEGS
b — gray body*
l — long legs
a — long abdomen
X X — Female
X Y — Male
20
* Body color refers to antennae, head, thorax,
abdomen, and legs.
TEXTEAMS BIology Institute 2004
Data Table 1
Trait
Genotype
Phenotype
Head Size
Hh
Large head
Eye Color
Antennae
2. Open the egg and sperm and examine the chromosomes. Pair up the chromosomes by matching the traits on
them. Use the information on the chromosomes and in the Insect Traits Key to complete Data Table 2.
Data Table 2
Trait
Genotype
Homozygous
or
Heterozygous
Dominant or
Recessive
Hemizygous
Not Applicable
Phenotype
Head size
Chromosome
pair 1
Eye color
Antennae
Thorax size
Chromosome
pair 2
Wing color
Wing length
Leg length
Chromosome
pair 3
Body color*
Abdomen size
Chromosome
pair 4
Sex
* Body color refers to antennae, head, thorax, abdomen, and legs.
The Charles A. Dana Center at UT Austin
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Insect Parts
Now that you have the phenotype of your offspring, draw the fly by tracing and then coloring the correct Insect Parts
on the unlined paper.
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TEXTEAMS BIology Institute 2004
DNA, mRNA, and
Protein Synthesis
NOTES
Learning Experience 3
Description:
Students investigate the mechanics and structure of DNA, mRNA, and protein
synthesis. As noted in the chart below, students have prior knowledge of
genetics from grades 6.
Grade 6
Grade 7
Grade 8
6.11 (B)
Biology
6 (A)(B)
Time Frame:
3–4 lessons (50 minutes each)
Materials:
Computer (1 per student group)
Projection system (1 for the teacher)
DNA, mRNA, and Protein Synthesis computer simulation investigation
pages (included in the Student Blackline Masters at the end of this vista)
DNA, mRNA, and Protein Synthesis paper/pencil investigation pages
(included in the student Blackline Masters at the end of this vista)
Advance Preparation:
There are two ways students can do the Learning Experience 3 investigation:
using paper/pencil or using the computer (either PC or Apple platform
computer). Investigation pages for both methods are included in this Learning
Experience. Prepare a copy of the appropriate version of the DNA, mRNA,
and Protein Synthesis investigation pages for each student group.
Background Information for the Teacher:
DNA is composed of building blocks called nucleotides and is located in
the nucleus of most cells. A nucleotide is composed of a deoxyribose (D), a
phosphate (P), and a nitrogen base. The phosphate, deoxyribose, and nitrogen
base are all connected by covalent bonds. A nucleotide is shown in Figure 1.
The Charles A. Dana Center at UT Austin
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NOTES
Figure 1
The overall shape of the DNA molecule (see Figure 2) resembles a ladder
twisted into a helix shape. Each vertical side of the ladder is made of
alternating deoxyriboses (D) and phosphates (P). The left vertical side in Figure
2 begins with a phosphate and is called the 5’ (five prime) end. The right
vertical side in Figure 2 begins with a deoxyribose and is called the 3’ (three
prime) end. The rungs of the ladder consist of nitrogen bases connected to
each other by hydrogen bonds. Nitrogen bases are of four types: adenine (A),
thymine (T), cytosine (C), and guanine (G). Normally, because of its structure,
adenine will bond only with thymine, and cytosine with guanine. When two
nitrogen bases are joined together as complementary nucleotides, they are
referred to as a base pair. A single human cell is estimated to have 3-5 billion
base pairs! That’s approximately two meters of DNA.
Figure 2
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Biology Institute 2004
DNA Replication
The function of DNA is to store and transmit genetic information. The
genetic information stored in DNA functions as a blueprint for all cellular
processes that occur in the lifetime of a living organism. During DNA
replication, an exact copy of the original cell is made. Thus, skin cells are
replaced with skin cells and muscle cells are replaced with muscle cells.
NOTES
When DNA replication begins, the hydrogen bonds holding the nitrogen
bases together break, causing the helix to separate at various points along
the ladder. These original strands will act as a template to form more DNA.
Free-floating nucleotides come in and attach to the original strand. The
DNA continues to separate, and more nucleotides float in and attach to the
original strand. This process continues until each original strand has been
replicated. On the strand beginning with deoxyribose, nucleotides are added
one at a time from the 5’ to 3’ direction. However, the other strand waits until
about 1,000 nucleotides are exposed and then adds a prefabricated block of
nucleotides. Thus, one strand is built in a continuous manner while the other
is built in a discontinuous manner (see Figure 3).
Figure 3
Transcription
It is the function of another nucleic acid, called messenger RNA (mRNA),
to relay genetic information to the ribosomes. RNA is made when a strand
of DNA is used as a template. This process is called transcription. The
transcription process is basically the same as replication, except that nucleotides
have ribose (R) instead of deoxyribose (hence, RNA instead of DNA), and
the nitrogen base uracil (U) is substituted for thymine. The transfer of genetic
information is relayed out of the nucleus by messenger RNA (mRNA) (see
Figure 4). The RNA is modified to become a mRNA molecule.
The Charles A. Dana Center at UT Austin
25
NOTES
Translation
As soon as a copy of mRNA is made, the copy exits the nucleus, moving
through the cytoplasm to link up with a ribosome. The ribosome is a cellular
structure that orchestrates the construction of a protein such as hemoglobin.
The ribosome is composed of two subunits, one large and one small. As
mRNA moves between the subunits, the nitrogen bases are scanned in groups
of three. A group of three nitrogen bases is called a codon. When the start
codon is recognized, protein synthesis is initiated. Transfer RNA (tRNA)
brings the amino acids to the ribosome. The ribosome has docking space for
two tRNAs at a time. The base of the tRNA contains three exposed nitrogen
bases called an anticodon that matches up with a complementary codon of
the mRNA (see Figure 5). As the various tRNA anticodons match up with
the complementary codons of mRNA, a growing strand of amino acids (a
polypeptide) is formed. The polypeptide will eventually become a protein.
Figure 5
Procedures:
Have students complete the DNA, mRNA, and Protein Synthesis investigation
pages.
Formative Assessment: Monitor and redirect student as needed during the
construction of their drawings.
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Biology Institute 2004
DNA, mRNA, and Protein Synthesis
computer simulation
In this investigation, use the PC or Apple™ platform computer to draw DNA, mRNA, and tRNA, and simulate
protein synthesis. The instructions are the same for either platform; however, the toolbars will be in different locations.
Before beginning, you must activate the Drawing tool by pulling down the View menu in MicroSoft Word™,
highlighting “Toolbar,” and selecting “Drawing.” The Drawing Toolbar should appear on the computer screen (see
Figure 1).
Figure 1
DNA
DNA is composed of building blocks called nucleotides and is located in the nucleus of most cells. A nucleotide is
composed of a deoxyribose (D), a phosphate (P), and a nitrogen base. The phosphate, deoxyribose, and the nitrogen base
are all connected by covalent bonds. A nucleotide is shown in Figure 2.
The Charles A. Dana Center at UT Austin
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Figure 2
The overall shape of the DNA molecule resembles a ladder twisted into a helix shape. Each vertical side of the ladder is
made of alternating deoxyriboses (D) and phosphates (P). The rungs of the ladder consist of nitrogen bases connected
to each other by hydrogen bonds. Nitrogen bases are of four types: adenine (A), thymine (T), cytosine (C), and
guanine (G). Normally, because of its structure, adenine will bond only with thymine, and cytosine with guanine. Four
nucleotides are shown in Figure 3.
Figure 3
Drawing DNA
To draw DNA, you must select several shapes to represent the different parts of DNA: the four different nitrogen bases,
phosphate, and deoxyribose.
Nitrogen bases. Using the Drawing Toolbar, click on “AutoShapes,” select “block arrows,” then select the chevron to
represent adenine and the pentagon to represent thymine.
28
TEXTEAMS BIology Institute 2004
Click on “AutoShapes,” select “flowchart,” then select “flowchart delay” to represent cytosine and “flowchart data” to
represent guanine.
The Charles A. Dana Center at UT Austin
29
Phosphate. Using the Drawing Toolbar, click on “Basic Shapes,” select “oval” to represent phosphate. Place the mouse
arrow over the edge of the oval and then click and drag the edge toward the center of the oval to reduce its size and
reshape it to a circle.
Deoxyribose. Using the Drawing Toolbar, click on “AutoShapes,” and select “block arrows,” then select “pentagon” to
represent deoxyribose.
Nucleotide. Arrange one of the shapes for the nitrogen bases, a phosphate, and a deoxyribose to create a nucleotide.
Assemble the nucleotide according to Figure 4.
30
TEXTEAMS BIology Institute 2004
Figure 4
Lines. Click on the diagonal line in the Drawing Toolbar, which causes the cursor to be replaced by a cross. Place the
center of the cross where the line is to start and hold the mouse button down while dragging the line to its ending
point. If you are having trouble controlling the start or end point of the line and it extends into the object, click on
“Draw,” order, and send to back. This will hide the ends of the line behind the shape. To move the line in very small
increments, click on “Draw”, grid, and “click” to remove the check mark from snap objects to grid. Use the up and
down arrows on the keyboard to move the line in very small increments.
Figure 5
The Charles A. Dana Center at UT Austin
31
Changing the Appearance of a Shape. To select a fill color for the nucleotide components, click on the shape,
then click on the arrow to the right of the fill color paint bucket in the Drawing Toolbar and click on ONE of the
following choices:
32
•
A color box
•
Select “More Fill Colors” for additional color choices
•
Select “Fill Effects” and choose a texture or pattern
•
Combine color and “Fill Effects” for more possibilities. Select “Fill Effects” ® “Pattern” ® “foreground color”
and/or “background color”
TEXTEAMS BIology Institute 2004
Figure 6
Labeling the Shapes. After the color of the shape has been selected, the nucleotide can be labeled. To add text for
the first time, click the text box on the Drawing Toolbar, drag a text box into the desired area, and type in the text. To
change the size of the text, highlight the text and change the font size. Clicking on the font color icon and selecting a
new color changes the color of the letter. To make the box lines disappear, right click on one of the textbox lines, select
“format text box,” “then color” (no fill) and “line color” (no line). Click OK.
Figure 7
Grouping Shapes Together. When using the Drawing tool to construct a DNA or RNA molecule, it is helpful to
group the shapes and lines together. To group the shapes and lines, left click on the white arrow on the Toolbar. While
the left mouse button is depressed, drag a box around the items to be grouped. Left click on the “Draw” button and
select “Group.”
The Charles A. Dana Center at UT Austin
33
Copying the Nucleotide. Once the shapes and lines have been grouped together, the nucleotide can be
copied and pasted as many times as needed. To create additional nucleotides with different nitrogen bases,
simply ungroup an existing nucleotide and change the nitrogen base. The nucleotide can be ungrouped by
clicking “Ungroup”.
Base Pairing Arrangement of DNA. There are four nitrogen bases found in a DNA molecule: adenine,
thymine, cytosine, and guanine. The nitrogen bases are held together by hydrogen bonds. Adenine pairs with
thymine, and the two are held together by two hydrogen bonds. Guanine pairs with cytosine, and the two
are held together by three hydrogen bonds.
Use what you have learned to create a model of a DNA molecule. To add the hydrogen bonds shown by the
dotted lines, first use the line tool to draw the lines. While the line is still selected, click on the dash style tool
and select a dash pattern.
34
TEXTEAMS BIology Institute 2004
DNA Replication
The function of DNA is to store and transmit genetic information. The genetic information stored in DNA
functions as a blueprint for all cellular processes that occur in the lifetime of a living organism. During DNA
replication, an exact copy of the original cell is made. Thus, skin cells are replaced with skin cells, and muscle
cells are replaced with muscle cells.
When DNA replication begins, the hydrogen bonds holding the nitrogen bases together break, causing the
helix to separate at various points along the ladder. These original strands will act as a template to form more
DNA. Free-floating nucleotides come in and attach to the original strand. The DNA continues to separate,
and more nucleotides float in and attach to the original strand. This process continues until each original
strand has been replicated.
Draw a model of DNA using Figure 8 as a guide. Print it for the teacher.
Figure 8
DNA and mRNA Transcription
DNA remains in the nucleus, so the transfer of genetic information is relayed by another molecule,
messenger RNA (mRNA). This molecule is made when DNA is used as a template in a process called
transcription. The process is basically the same as replication, except that the nucleotides have ribose (R)
instead of deoxyribose (hence, RNA instead of DNA) and the nitrogen base uracil (U) is substituted for
thymine. To create an mRNA molecule showing transcription, copy the left side of the DNA molecule. To
do this, use the white arrow on the Toolbar to draw a box around the part of the molecule to be copied,
click on “Draw,” then group. While the objects are still selected, copy them. Paste the left side of the DNA
molecule in your selected location, then build the mRNA nucleotides. Use Figure 9 as a model. Print it.
The Charles A. Dana Center at UT Austin
35
Figure 9
Translation
While still in the nucleus, the RNA strand is processed and becomes a strand of mRNA. The mRNA leaves the
nucleus and travels to the cytoplasm where it links up with a ribosome. Molecules of tRNA will bring amino acids to
the ribosome, based on the mRNA code. The growing amino acid chain becomes a protein. Draw a model of protein
synthesis.
Figure 10
36
TEXTEAMS BIology Institute 2004
DNA, mRNA and
Protein Synthesis (paper/pencil)
Complete the model of DNA below by drawing the missing nitrogen bases in the nucleotides. Label the structures,
design an identification key, and then color the DNA structures based on the key.
The Charles A. Dana Center at UT Austin
37
DNA Replication
Use the same DNA sequence from the DNA model on the first page to simulate how DNA replicates itself. During
replication, the hydrogen bonds between the nitrogen bases are broken and the molecule splits apart at various points
along the ladder. Nucleotides attach to the complementary base of the original strand. This continues until all segments
of DNA have been copied. The result is two DNA molecules, each composed of an original strand and a newly formed
strand.
Complete the model of DNA replication below by drawing the missing nitrogen bases in the nucleotides. Show
covalent bonding between the phosphate and deoxyribose, and the deoxyribose and the base. Show hydrogen bonding
between the nitrogen bases. There are two hydrogen bonds between adenine and thymine, and three hydrogen bonds
between cytosine and guanine. Label and color each part of the DNA replication using the same identification key you
designed for the DNA model.
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���������
�������
�������
��������
�������������
�������
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38
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���������������������
TEXTEAMS BIology Institute 2004
Transcription
It is the function of another nucleic acid, called messenger RNA (mRNA), to relay genetic information to the
ribosomes. RNA is made when a strand of DNA is used as a template. This process is called transcription. The
transcription process is basically the same as replication, except that nucleotides have ribose (R) instead of deoxyribose
(hence, RNA instead of DNA), and the nitrogen base uracil (U) is substituted for thymine. The transfer of genetic
information is relayed out of the nucleus by messenger RNA (mRNA). The RNA is modified to become an mRNA
molecule.
Complete the model of transcription below by drawing the missing nitrogen bases in the mRNA nucleotides. Show
hydrogen bonding between the nitrogen bases. There are two hydrogen bonds between adenine and uracil, and three
hydrogen bonds between cytosine and guanine. Label and color each part of the transcription process using the same
identification key you designed for the DNA model.
���
�����������
�������
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��
The Charles A. Dana Center at UT Austin
39
Translation
Once mRNA leaves the nucleus, it travels through the cytoplasm to a ribosome. The mRNA inserts itself between the
subunits of a ribosome and the ribosome reads the mRNA, three nitrogen bases at a time. Three nitrogen bases together
are referred to as a codon. At the same time, transfer RNA (tRNA) brings the amino acid specified by the mRNA
to the ribosome. When the start codon (AUG) is read, protein synthesis begins and continues until a stop codon is
read. The amino acids brought in by the tRNA are bonded together one at a time and continue until the process is
completed.
Copy the mRNA sequence from your transcription model onto the mRNA strand inside the box. Label and color
each part of the translation using the same identification key you designed for the DNA model.
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40
��
����
TEXTEAMS BIology Institute 2004
Protein Synthesis: Like a
Banana Split
NOTES
Learning Experience 4
Description:
Students analyze the relationships among DNA, mRNA, and protein synthesis
through a simulation. As noted in the chart below, students have prior
knowledge of genetics from grade 6.
Grade 6
Grade 7
6.11 (C)
Grade 8
Biology
6 (A)(B)
Time Frame:
50 minutes
Materials:
Banana split ingredients, i.e., bananas; vanilla, chocolate, and strawberry ice
cream; three different toppings; three different types of whipped cream;
and cherries (sufficient amounts for the number of students in the
class - OPTIONAL)
Bowls for the banana splits (enough for the number of students in the
class - OPTIONAL)
Line drawings of banana split ingredients (included in the Teacher
Blackline Masters at the end of this vista)
DNA Strands (included in the Teacher Blackline Masters at the end of this
vista)
mRNA Genetic Code Wheel (included in the Student Blackline Masters
at the end of this vista)
mRNA Genetic Code Chart (included in the Student Blackline Masters
at the end of this vista)
Protein Synthesis: Like a Banana Split investigation pages (included in the
Student Blackline Masters at the end of this vista)
Advance Preparation:
1. Prepare a copy of the Protein Synthesis: Like a Banana Split
investigation pages for each student group.
2. Purchase sufficient amounts of bowls; bananas; vanilla, chocolate, and
strawberry ice cream; three different toppings; three different types of
whipped cream; and cherries.
The Charles A. Dana Center at UT Austin
41
NOTES
3. Prepare a copy of the line drawings of the banana split ingredients and
attach them to the corresponding purchased ingredients. Display them
so that students can easily see them. Prepare a copy of the stop sign
and set it up at the end of the banana split ingredients.
Teacher note: Making actual banana splits is an optional part of this learning
experience. You can forego using food items, and simply use the line drawings of
banana split ingredients provided in the Teacher Blackline Masters.
4. Prepare a copy of one of the DNA strands for each student group.
Background Information for the Teacher:
A protein consists of a variety of amino acids linked together in an
arrangement that is specified by DNA. A banana split can be used as an
analogy for a protein in that it, too, consists of a number of ingredients placed
together in an arrangement specified by a recipe. Just as there are many types
of proteins, there are different types of banana splits.
Both a mRNA Genetic Code Chart and Wheel are included in this learning
experience. It is best if students are proficient in using both the chart and
wheel. To practice reading the Genetic Code Wheel, use the first mRNA
sequence, AGU, in Data Table 1 in the investigation pages. The first letter in
the sequence is “A,” so start in the center circle of the wheel with the letter
“A.” The second nitrogen base of the codon is “G,” so move out into the
second circle from the center into the area marked “G.” Next, move to the
third circle from the center into the “U” area. The name of the amino acid is
located in the outermost circle. In this case, it is serine (see the example below
the mRNA Genetic Code Wheel).
To practice reading the mRNA Codon Chart, use the mRNA codon, AGU,
in Data Table 1 in the investigation pages. On the left hand side of the chart
locate the letter “A”. Move to the top of the chart and locate the letter “G”.
Find the area where “A” row intersects the “G” column, notice the four letters
to the right of that section. Locate the letter “U” on the right hand side
next to the section where “A” and “G” intersected. The name of the amino
acid coded by AGU is serine. Make sure students understand that they read
the chart left to right. They should find where the left hand row intersects
with the top column and then move to the right to locate the last base in the
codon.
SAFETY: Use caution when foods are part of laboratory investigations. Food
allergies can be a problem with some students.
Procedures:
Have groups complete the steps on the Protein Synthesis: Like a Banana Split
investigation pages.
Formative Assessment: Monitor, and redirect as needed, student use of
the mRNA Genetic Code Chart or the mRNA Genetic Code Wheel and
responses to the investigation pages.
42
Biology Institute 2004
Protein Synthesis: Like a Banana Split (correct student
responses)
NOTES
Data Table 1 [student responses]
DNA
mRNA
AMINO ACID
1.
TCA
AGU
Serine
2.
CCC
GGG
Glycine
3.
TAC
AUG
Methionine
4.
GGA
CCU
Proline
5.
CTC
GAG
Glutamic acid
6.
TAA
AUU
Isoleucine
7.
ACC
UGG
Tryptophan
8.
CGC
GCG
Alanine
9.
CGT
GCA
Alanine
10.
ATT
UAA
Stop
11.
AAA
UUU
Phenylalanine
12.
TTA
AAU
Lysine
13.
CCA
GGU
Glycine
14.
TTT
AAA
Aspargine
2. Name five amino acids listed on the mRNA Genetic Code Chart or
the mRNA Genetic Code Wheel. [Answers will vary.]
3. Name five ingredients used in a banana split. [Answers will vary.]
4. Use the mRNA Genetic Code Chart or the mRNA Genetic Code
Wheel to list ALL possible mRNA sequences for the amino acids
shown in the segment of hemoglobin below.
The Charles A. Dana Center at UT Austin
43
Data Table 2
NOTES
Valine
Histidine
Leucine
Threonine
Proline
Glutamic
Acid
GUA
CAC
CUA
ACA
CCA
GAA
GUG
CAU
CUG
ACG
CCG
GAG
GUC
CUC
ACC
CCC
GUU
CUU
ACU
CCU
5. Examine the mRNA sequences for each amino acid recorded in Data
Table 2. What do you notice about them? [First two letters are the same,
but the third is different.]
6. Suggest reasons for the fact that there are several ways to produce
the amino acids that build hemoglobin. [This is an example of the
redundancy of the genetic code; this variation in the third position of the triplet
is a source of genetic variation.]
7. Using the DNA strand, decode the ingredients for a banana split
recipe. Apply your knowledge of DNA transcription, translation, and
the mRNA Genetic Code Table or the mRNA Genetic Code Wheel
to complete the table. Use Data Table 3. [Answers will vary.]
Data Table 3
DNA
44
mRNA
Amino Acid
tRNA
Banana Split
Ingredient
Biology Institute 2004
8. Build your own banana split recipe. Use your knowledge of DNA
transcription and translation and the mRNA Genetic Code Chart
or the mRNA Genetic Code Wheel to decode it. Use Data Table 4.
[Answers will vary.]
NOTES
Data Table 4
DNA
mRNA
Amino Acid
tRNA
Banana Split
Ingredient
NOTE: Prior to starting the activity list the tRNA anticodons and
corresponding banana split ingredients on the board. The following
list is provided an example. Your list will depend on the ingredients
you purchase
UAC-bowl; AUG – banana; UGG – Chocolate Ice Cream;
CAA – Vanilla Ice Cream; CCC – Chocolate Syrup;
CUA – Vanilla Whip Cream; UAU – cherry;
CGU – plain whip cream; ACC – chocolate whip cream;
AGA – caramel syrup; CAG – sprinkles; ACU - Stop
The Charles A. Dana Center at UT Austin
45
���������
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���
���
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��������
����
���
���
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���
���
NOTE:
These are tRNA anticodons.
46
TEXTEAMS BIology Institute 2004
DNA Strands
NOTES
TACC A A AGAC TATATAC T
TAC ATG C A A ACC TATAC T
TACC A ATG G CCCC G TAC T
TAC ATG TG G C AG C TA AC T
TACCAATGGCCCCTAACT
TAC ATG C A A ACC TATAC T
TACC A A AGA ACC TATAC T
TAC ATG TG G CCCC TA AC T
The Charles A. Dana Center at UT Austin
47
mRNA Genetic Code Wheel
48
TEXTEAMS BIology Institute 2004
mRNA Genetic Code Chart
2nd Base
U
U
A
G
A
G
Phenylalanine
Serine
Tyrosine
Cysteine
Phenylalanine
Serine
Tyrosine
Cysteine
Leucine
Serine
stop
stop
Leucine
Serine
stop
Tryptophan
Leucine
Proline
Histidine
Arginine
Leucine
Proline
Histidine
Arginine
Leucine
Proline
Glutamine
Arginine
Leucine
Proline
Glutamine
Arginine
Isoleucine
Threonine
Asparagine
Serine
Isoleucine
Threonine
Asparagine
Serine
Isoleucine
Threonine
Lysine
Arginine
Methionine
Threonine
Lysine
Arginine
Valine
Alanine
Aspartic Acid
Glycine
Valine
Alanine
Aspartic Acid
Glycine
Valine
Alanine
Glutamic Acid
Glycine
Valine
Alanine
Glutamic Acid
Glycine
The Charles A. Dana Center at UT Austin
U
C
A
G
U
C
A
G
U
C
A
G
3rd Base
1st Base
C
C
U
C
A
G
49
Protein Synthesis: Like a Banana Split
1. Complete Data Table 1 using your knowledge of DNA transcription and the mRNA Genetic Code Wheel or
chart.
Data Table 1
DNA
mRNA
AMINO ACID
TCA
AGU
Serine
CCC
Glycine
Methionine
GGA
CCU
GAG
TAA
Glutamic acid
Isoleucine
Tryptophan
CGC
GCG
CGT
GCA
ATT
AAA
UUU
TTA
Lysine
CCA
Glycine
TTT
2. Name five amino acids listed on the mRNA Genetic Code Chart or the mRNA Genetic Code Wheel.
3. Name five ingredients used in a banana split.
4. Use the mRNA Genetic Code Chart or the mRNA Genetic Code Wheel to list ALL possible mRNA
sequences for the amino acids shown in this segment of hemoglobin below.
50
TEXTEAMS BIology Institute 2004
Data Table 2
Valine
Histidine
Leucine
Threonine
Proline
Glutamic Acid
5. Examine the mRNA sequences for each amino acid recorded in Data Table 2. What do you notice about
them?
6. Suggest reasons for the fact that there are several ways to produce the amino acids that build hemoglobin.
7. Using the DNA strand, decode the ingredients for a banana split recipe. Apply your knowledge of DNA
transcription, translation, and the mRNA Genetic Code Chart or the mRNA Genetic Code Wheel to
complete the table. Use Data Table 3.
Data Table 3
DNA
mRNA
The Charles A. Dana Center at UT Austin
Amino Acid
tRNA
Banana Split
Ingredient
51
8. Build your own banana split recipe. Use your knowledge of DNA transcription and translation and the mRNA
Genetic Code Table or the mRNA Genetic Code Wheel to decode it. Use Data Table 4.
Data Table 4
DNA
52
mRNA
Amino Acid
tRNA
Banana Split Ingredient
TEXTEAMS BIology Institute 2004
The Human Genome
NOTES
Learning Experience 5
Description:
Students examine the distribution of alleles in human populations. As noted in
the chart below, students have prior knowledge of genetics from grades 6, 7,
and 8.
Grade 6
Grade 7
Grade 8
Biology
6.11 (A)
7.10 (B)
8.11 (A)(B)(C)
6 (C)(D)
Time Frame:
50 minutes
Materials:
The Human Genome investigation pages (included in the Student
Blackline Masters at the end of this vista) come from the National Human
Genome Research Institute and the National Institutes of Health. For more
information, visit http://www.nhgri.nih.gov/educationkit/
Advance Preparation:
Prepare a copy of The Human Genome investigation pages for each student
group.
Background Information for the Teacher:
In 1990, the National Institutes of Health and the Department of Energy
joined with international partners to begin a worldwide effort to map and
sequence the genome of humans and certain model organisms. This effort,
known as the Human Genome Project (HGP), was completed in 2003. As
genomic information was collected, it was placed into databases that are shared
within the research community. These databases are used to study cancer,
diabetes, and other common diseases. Hopefully, the information from the
Human Genome Project will lead to the development of new drug therapies,
gene therapy, and diagnosis and prevention of certain diseases. Other goals of
the HGP are to develop new technologies and software that make mapping
and sequencing of the genome more efficient and less expensive, and to study
the ethical, legal, and social implications of genetic research.
The Human Genome Project has also examined genetic variation in human
populations by analyzing the DNA of groups of people from around the
world. One example is the investigation of three different alleles for blood
protein, GC-1, HP-1, and FY-O. The GC-1 allele provides the code for a
protein that attaches to and regulates the distribution of vitamin D in the
The Charles A. Dana Center at UT Austin
53
NOTES
human body. The HP-1 allele provides the code for haptoglobin, a protein that
attaches itself to the hemoglobin released by red blood cells when they die a
natural death or are destroyed by a disease such as malaria.
The FY gene provides the code for a blood protein found on the surface of
red blood cells. This protein makes it easier for the malarial parasite Plasmodium
vivax to multiply in red blood cells and cause malaria. However, the FY-O
allele results in the absence of this protein, making it difficult for the parasite
to gain entry into the red blood cells to multiply. Therefore, the FY-O allele
provides a selective advantage in parts of the world where Plasmodium vivax
malaria is common. This advantage accounts for the high frequency of the FYO allele in those regions.
Procedures:
Have students complete The Human Genome investigation pages.
Formative Assessment: Monitor student responses to The Human Genome
investigation pages.
The Human Genome Investigation pages (correct student
responses)
Table 1
GC-1
HP-1
FY-O
Africa
88%
42%
96%
Asia &
Middle East
0%
40%
3%
Australia
83%
27%
0%
Europe
0%
38%
.3%
North
America
73%
32%
0%
South
America
76%
60%
.2%
1. What is the range of frequencies for each allele shown? [GC-1 is 0%–
88%, HP-1 is 27%–60%, FY-0 is 0%–96%.]
2. On a worldwide basis, which allele varies the most in frequency? [FY0]
3. On a worldwide basis, which allele varies the most in distribution
across the continents? [HP-1]
4. Examine Map 1 showing the occurrence of the malarial parasite
Plasmodium vivax. What inference can be made concerning the
occurrence of Plasmodium vivax and the variation in the frequency
of the FY-O allele in human populations? [The FY-0 allele provides a
protective advantage in areas where malaria is common.]
54
Biology Institute 2004
The Human Genome
In 1990, the National Institutes of Health and the Department of Energy joined with international partners to begin
a worldwide effort to map and sequence the genome of humans and certain model organisms. This effort, known as
the Human Genome Project (HGP), was completed in 2003. As genomic information was collected, it was placed
into databases and shared within the research community. These databases are used to study cancer, diabetes, and other
common diseases.
The Human Genome Project has also examined genetic variation in human populations by analyzing the DNA of
groups of people from around the world. One example is the investigation of three different alleles for blood protein,
GC-1, HP-1, and FY-O. The GC-1 allele provides the code for a protein that attaches to and regulates the distribution
of vitamin D in the human body. The HP-1 allele provides the code for haptoglobin, a protein that attaches itself to the
hemoglobin released by red blood cells when they die a natural death or are destroyed by a disease such as malaria.
The FY gene provides the code for a blood protein found on the surface of red blood cells. This protein makes it
easier for the malarial parasite Plasmodium vivax to multiply in red blood cells and cause malaria. However, the FY-O
allele results in the absence of this protein, making it difficult for the parasite to gain entry into the red blood cells to
multiply. Therefore, the FY-O allele provides a selective advantage in parts of the world where Plasmodium vivax malaria
is common. This advantage accounts for the high frequency of the FY-O allele in those regions.
Use the maps below to identify the genetic frequency (as a percent) of the three different alleles (GC-1, HP-1, and FYO) in the world’s populations. Record the frequency of each allele on each continent in Table 1.
Occurrence of GC-1 allele
73%
88%
76%
The Charles A. Dana Center at UT Austin
83%
55
Occurrence of HP-1 allele
38%
73%
32%
17%
42%
60%
27%
Occurrence of FY-O allele
.3%
0.2%
96%
3%
0%
From the National Human Genome Research Institute and the National Institutes of Health. For more information
visit http://www.nhgri.nih.gov/educationkit/
56
TEXTEAMS BIology Institute 2004
Table 1
GC-1
HP-1
FY-O
Africa
Asia &
Middle East
Australia
Europe
North
America
South
America
1. What is the range of frequencies for each allele shown?
2. On a worldwide basis, which allele varies the most in frequency?
3. On a worldwide basis, which allele varies the most in distribution across the continents?
4. Examine Map 1 showing the occurrence of the malarial parasite Plasmodium vivax. What inference can be made
concerning the occurrence of Plasmodium vivax and the variation in the frequency of the FY-O allele in human
populations?
Map 1 Occurrence of Malarial Parasite Plasmodium vivax
The Charles A. Dana Center at UT Austin
57
NOTES
Assessment Task:
Inheritance of Sickle-Cell
Anemia
Materials:
Paper strips depicting the two strands of a DNA molecule, 50 cm (2 per
student group)
Blank paper strips, 50 cm (3 per student group)
Markers or colored pencils (4 different colors per student group
mRNA Genetic Code Chart/Wheel (used in Learning Experience 4)
Inheritance of Sickle-Cell Anemia Assessment Task pages (included in the
Student Blackline Masters at the end of this vista)
Advance Preparation:
1. Collect materials as needed. Adding machine paper could be used for
the paper strips. Cut the strips of paper in lengths of 50cm each.
2. To illustrate a DNA molecule using two paper strips for each team,
you will use the following 5’ to 3’ strand of DNA to represent a
portion of the hemoglobin gene. On one strip, copy this side of the
base sequence using blue pencil or marker:
5’ TAC CAA GTA AAT TGA GGA CTC CTC TTT ACT 3’
3. On a second strip, copy the complentary base sequence using red
pencil or marker.
3’ATG GTT CAT TTA ACT CCT GAG GAG AAA TGA 5’
4. Prepare copies of the Inheritance of Sickle-Cell Anemia Assessment
Task pages.
Procedures:
Have students prepare copies of the Inheritance of Sickle-Cell Anemia
Assessment Task pages.
Inheritance of Sickle-Cell Anemia Assessment Task pages
(correct student responses):
Part 1
1. Your teacher will give you two strips of paper (one written in blue,
the other written in red) that represent a DNA molecule. This DNA
molecule represents a portion of the normal gene for the protein
hemoglobin. Why are two strips, not one, needed to represent DNA?
[Because DNA is double-stranded]
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Biology Institute 2004
2. Use these two strips to make an exact copy of the DNA molecule
given to you.
NOTES
(A) Describe what you just did to make a copy. [“Unzipped” the DNA
wrote one new strand to be complementary to one side of the original molecule,
wrote the other new strand to be complementary to the other side of the
original molecule, and matched up the two new sides to create an exact copy of
the original molecule.]
(B) What is this process called? [Replication]
3. What do the four letters on the DNA molecule represent? [Nitrogen
bases]
4. What is the significance of the 3’ to 5’ direction on each strand? [New
DNA is synthesized beginning at the 3’ end]
5. Select the 5’ to 3’ coding strand (the blue strand) of your DNA
molecule. Then, obtain one blank strip of paper from your teacher.
On the blank strip, write the mRNA base sequence in a third color.
(A) What is the mRNA coding sequence on your strip? [AUG GUU
CAU UUA ACU CCU GAG GAG AAA UGA]
(B) What does this base sequence represent? [The mRNA base sequence for
a portion of normal hemoglobin gene]
(C) What step of protein synthesis did you just perform? [Transcription]
(D) Why must the DNA message go through this step? [DNA cannot leave
the cell’s nucleus to direct protein synthesis, but mRNA can.]
(E) Name the two structural differences of DNA and mRNA. [In RNA,
uracil replaces thymine; DNA is double stranded, RNA is single stranded.]
6. Using your mRNA strip, demonstrate the process of converting the
information in mRNA to tRNA.
(A) Describe in detail what you just did in this process. [Attached the first
codon of the mRNA strand to the ribosome, found the anticodon that fit with
the mRNA codon, translated the mRNA codons to the correct amino acid, slid
the mRNA along the ribosome to the next codons and found the anticodons
that fit them, and constructed a chain of amino acids to make a protein.]
(B) What step of protein synthesis did you just complete? [Translation]
Part 2
1. Observe the drawings of normal human red blood cells (RBCs) and
sickle-shaped red blood cells (RBCs).
(A) Describe the differences between the two types of RBCs. [The
normal human red blood cells have a smooth, disc-shaped appearance. The
sickle-shaped red blood cells have an irregular appearance and are shaped like
crescents or half-moons.]
(B) What physiological functions might be affected by the shape of the
sickled cells? [The sickled cells cannot easily travel through narrow blood
capillaries.]
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NOTES
2. Hemoglobin consists of four polypeptide chains: two alpha chains and
two beta chains. Normal hemoglobin is called hemoglobin A. The
hemoglobin that produces sickle cells is called hemoglobin S. Since
the protein hemoglobin is made of two kinds of polypeptide chains,
how is it possible that there could be two forms of this protein? [The
“hemoglobin A” and “hemoglobin B” forms of hemoglobin must differ with
regard to the structure of one of the two different kinds of polypeptide chains.]
3. In Part 1, you found the mRNA coding sequence for the first nine
amino acids that code for hemoglobin. Here is the sequence for the
first nine amino acids found in the mutated form of hemoglobin that
causes sickle-cell anemia:
start
meth—val—his—leu—thr—pro—val—glu—lys
What is a mutation? [A mutation is a change in DNA or in a chromosome.]
4. Locate the difference(s) between the normal hemoglobin DNA
sequence and the mutated sickle-cell hemoglobin. Use the figure
below to see how the mutation occurred and to find the mutation on
the DNA molecule.
start
meth val
his
leu
thr
pro
glu
glu lys
AUG GUU CAU UUA ACU CCU GAG GAG AAA — normal mRNA
TAC CAA GTA AAT TGA GGA CTC CTC TTT — normal DNA
start
meth
AUG
TAC
val
his
leu
thr
pro
val
glu
lys
GUU CAU UUA ACU CCU GUG GAG AAA — mutated mRNA
CAA GTA AAT TGA GGA CAC CTC TTT — mutated DNA
Describe in detail what you just did in this process. [In normal hemoglobin, the
normal amino acid is glutamine. In sickle-cell hemoglobin, the mutated amino acid is
valine. Using the Genetic Coding Chart or wheel to determine which DNA codon(s)
code for valine, it shows that the DNA codons CAA, CAG, CAT, or CAC code for
valine. Using the Chart/Wheel also makes it possible to determine that the mRNA
codons GUA, GUC, GUG, or GUU code for valine. The DNA codons GTT and
GTC code for glutamine, as do the mRNA codons GAA or GAG.]
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Biology Institute 2004
Assessment Task: Inheritance of Sickle
Cell Anemia
Your team has received the following letter:
Dear DNA Team:
My name is Dr. Ilene Martin and I specialize in obstetrics. While I have much experience at helping my patients and their husbands
through a pregnancy, I am not an expert in many of the genetic concerns that couples have before they get pregnant. I am aware that
people on your DNA Team have a broad and thorough understanding of how the DNA molecule works and can explain those
workings to people in everyday language that they can understand.
George and Beatrice Jackson are patients of mine who are considering starting a family. Both George and Beatrice have family
members with sickle-cell anemia, so you can see their concern.They want to become fully informed regarding how DNA works and
how it codes to make the normal form of the protein hemoglobin.They also would like a full explanation of what goes wrong with the
DNA to cause a person to have sickle-cell anemia.
I would like for your DNA team to explain the workings of DNA and how sickle-cell anemia gets passed on to future generations.
Please let me know if this is possible.
Thank you,
Dr. Ilene Martin
Your task is to develop models and clear explanations to help Dr. Martin’s patients learn how DNA works, how it codes
to make normal hemoglobin, and what can go wrong with the DNA to cause sickle-cell anemia.
Safety precautions
None required.
The Charles A. Dana Center at UT Austin
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Part 1
1. Your teacher will give you two strips of paper (one written in blue, the other written in red) that represent a
DNA molecule. This DNA molecule represents a portion of the normal gene for the protein hemoglobin. Why
are two strips, not one, needed to represent DNA?
2. Use these two strips to make an exact copy of the DNA molecule given to you.
(A) Describe what you just did to make a copy.
(B) What is this process called?
3. What do the four letters on the DNA molecule represent?
4. What is the significance of the 3’ to 5’ direction on each strand?
5. Select the 5’ to 3’ coding strand (the blue strand) of your DNA molecule. Then, obtain one blank strip of
paper from your teacher. On the blank strip, write the mRNA base sequence in a third color.
(A) What is the mRNA coding sequence on your strip?
(B) What does this base sequence represent?
(C) What step of protein synthesis did you just perform?
(D) Why must the DNA message go through this step?
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TEXTEAMS BIology Institute 2004
(E) Name the two structural differences of DNA and mRNA.
6. Using your mRNA strip, demonstrate the process of converting the information in mRNA to tRNA.
(A) Describe in detail what you just did in this process.
(B) What step of protein synthesis did you just complete?
Part 2
1. Observe the drawings of a normal human red blood cells (RBCs) and a sickle-shaped red blood cells (RBCs).
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(A) Describe the differences between the two types of RBCs.
(B) What physiological functions might be affected by the shape of the sickled cells?
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2. Hemoglobin consists of four polypeptide chains: two alpha chains and two beta chains. Normal hemoglobin
is called hemoglobin A. The hemoglobin that produces sickle cells is called hemoglobin S. Since the protein
hemoglobin is made of two kinds of polypeptide chains, how is it possible that there could be two forms of
this protein?
3. In Part 1, you found the mRNA coding sequence for the first nine amino acids that code for hemoglobin.
Here is the sequence for the first nine amino acids found in the mutated form of hemoglobin that causes
sickle-cell anemia:
start
meth—val—his—leu—thr—pro—val—glu—lys
What is a mutation?
4. Locate the difference(s) between the normal hemoglobin DNA sequence and the mutated sickle-cell
hemoglobin. Use the figure below to see how the mutation occurred and to find the mutation on the DNA
molecule.
start
meth val
his
leu
thr
pro
glu
glu lys
AUG GUU CAU UUA ACU CCU GAG GAG AAA — normal mRNA
TAC CAA GTA AAT TGA GGA CTC CTC TTT — normal DNA
start
meth
AUG
TAC
val
his
leu
thr
pro
val
glu
lys
GUU CAU UUA ACU CCU GUG GAG AAA — mutated mRNA
CAA GTA AAT TGA GGA CAC CTC TTT — mutated DNA
Describe in detail what you just did in this process.
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TEXTEAMS BIology Institute 2004
Mechanisms of Genetics
Teacher Blackline Masters
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Insect Chromosomes—1
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TEXTEAMS BIology Institute 2004
Insect Chromosomes—2
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Insect Chromosomes—3
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Insect Chromosomes—4
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Insect Chromosomes—5
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TEXTEAMS BIology Institute 2004
Insect Parts:
Now that you have the phenotype of your offspring, draw the fly by tracing and then coloring the correct
Insect Parts on the unlined paper.
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mRNA Genetic Code Wheel
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TEXTEAMS BIology Institute 2004
mRNA Genetic Code Chart
2nd Base
U
U
A
G
A
G
Phenylalanine
Serine
Tyrosine
Cysteine
Phenylalanine
Serine
Tyrosine
Cysteine
Leucine
Serine
stop
stop
Leucine
Serine
stop
Tryptophan
Leucine
Proline
Histidine
Arginine
Leucine
Proline
Histidine
Arginine
Leucine
Proline
Glutamine
Arginine
Leucine
Proline
Glutamine
Arginine
Isoleucine
Threonine
Asparagine
Serine
Isoleucine
Threonine
Asparagine
Serine
Isoleucine
Threonine
Lysine
Arginine
Methionine
Threonine
Lysine
Arginine
Valine
Alanine
Aspartic Acid
Glycine
Valine
Alanine
Aspartic Acid
Glycine
Valine
Alanine
Glutamic Acid
Glycine
Valine
Alanine
Glutamic Acid
Glycine
The Charles A. Dana Center at UT Austin
U
C
A
G
U
C
A
G
U
C
A
G
3rd Base
1st Base
C
C
U
C
A
G
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TEXTEAMS BIology Institute 2004
The Charles A. Dana Center at UT Austin
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TEXTEAMS BIology Institute 2004
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TEXTEAMS BIology Institute 2004
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TEXTEAMS BIology Institute 2004
DNA Strands
TA C C A A A G A C TATATA C T
TA C AT G C A A A C C TATA C T
TA C C A AT G G C C C C G TA C T
TA C AT G T G G C A G C TA A C T
TA C C A AT G G C A U C TA A C T
TA C AT G C A A A C C TATA C T
TA C C A A A G A A C C TATA C T
TA C AT G T G G C C C C TA A C T
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TEXTEAMS BIology Institute 2004
Mechanisms of Genetics
Student Blackline Masters
The Charles A. Dana Center at UT Austin
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Fundamentally Genetics
Looking at Your Traits
Are you dominant or recessive for the following traits? You and your group will have to look at each other
to figure this out. Record your responses in the appropriate blanks.
1. Tasting Paper—Taste the paper. It contains a harmless chemical that some people can taste and
others cannot. The ability to taste the chemical is a dominant trait. People who cannot taste this
chemical are recessive for the trait.
_____________________________
Dominant or Recessive
2. Tongue Rolling—Some people can roll their tongues into a taco- or U-shape. This is a dominant
trait. If you cannot roll your tongue into a taco- or U-shape, you are recessive for this trait.
_____________________________
Dominant or Recessive
3. Earlobes—It is a dominant trait to have earlobes that hang down. People who have earlobes
attached directly to the side of their heads are recessive for this trait.
_____________________________
Dominant or Recessive
4. Earbump—Some people have a bump on the inside rim of the upper part of the ear ridge called
Darwin’s ear point. The bump is due to the presence of a dominant allele. If you are lacking the
bump, you are recessive for this trait.
_____________________________
Dominant or Recessive
5. Widow’s Peak—If you have a hairline that comes to a point in the middle of your forehead,
you possess a dominant allele for widow’s peak. A straight or even hairline indicates that you are
recessive for this trait.
_____________________________
Dominant or Recessive
6. Hitchhiker’s Thumb—People who can bend the last joint of their thumbs back to a 90-degree
angle are dominant for hitchhiker’s thumb. People who lack this ability are recessive for this trait.
_____________________________
Dominant or Recessive
7. Polydactyly—People born with six fingers or toes possess the dominant trait for polydactyly.
Having five fingers and toes is a recessive trait. In the U.S., people with extra toes or fingers usually
have them removed shortly after birth.
_____________________________
Dominant or Recessive
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TEXTEAMS BIology Institute 2004
8. Syndactyly—Having webbed fingers and toes is a dominant trait. Sometimes only a pair of fingers
or toes are webbed. If you have fingers and toes that separate, then you are recessive for this trait.
_____________________________
Dominant or Recessive
9. Cleft Chin—If you have a chin that has a split in the middle, like John Travolta, you have a cleft chin.
This is a recessive trait. The absence of a cleft chin is a dominant feature.
_____________________________
Dominant or Recessive
10. Hair Whorl—Have someone in your group look at the back of your head to determine if
your hair whorls to the right (clockwise) or to the left (counterclockwise). If you use hairspray or
gels on your hair, this activity may be a hard one to do. A clockwise whorl is dominant over the
recessive trait of a counterclockwise whorl.
_____________________________
Dominant or Recessive
Describing Your Traits
Now that you know the traits you exhibit—your phenotype—how do you describe them? The protocol
is to use letters to describe genetic traits—your genotype. For example, an uppercase T can represent
the dominant trait for tasting the tasting papers and a lowercase t the recessive trait for not tasting the
tasting papers. In this learning experience, two letters are used to represent the traits because one comes
from your mother and one from your father; however, traits sometimes are represented by more than
two letters because more than two alleles are involved. The ABO alleles for blood type are an example of
such a combination. Two letters also represent the gene, or DNA strand, for each of the 10 traits. So Tt
also represents the gene for the ability to taste the tasting papers. Each letter represents an allele for each
version of the gene—T for the version of being able to taste the tasting papers and t for the version of not
being able to taste the tasting papers.
An individual who receives a TT from their parents is described as homozygous for the ability to taste the
tasting papers. An individual who receives Tt from their parents is described as heterozygous for the ability
to taste the tasting papers. The heterozygous individual has two different letters, Tt, as compared with the
homozygous individual who has two letters that are identical, TT or tt.
When you have a recessive trait, such as not being able to taste the tasting papers, your genotype is
certain. The two pieces of genetic information you got from your parents are recessive and recessive. So
the genotype will be two lowercase letters, tt.
When you have a dominant trait, such as being able to taste the tasting papers, your genotype is not
certain. The pieces of genetic information you got from your parents could be dominant and dominant, or
dominant and recessive. So the genotype could be two uppercase letters, TT, or one uppercase and one
lowercase letter, Tt.
Use the following key to describe your phenotype and all your possible genotypes for each of the 10 traits.
Record your responses in the appropriate blanks.
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Key
T—TASTING PAPER TASTER
H—HITCHHIKER’S THUMB PRESENT
t—nontasting paper taster
h—hitchhiker’s thumb not present
R—TONGUE ROLLER
P—SIX FINGERS OR TOES
r—nontongue roller
p—five fingers or toes
E—UNATTACHED EARLOBES
S—WEBBED FINGERS OR TOES
e—attached earlobes
s—nonwebbed fingers or toes
D—DARWIN’S EAR POINT PRESENT
C—NON CLEFT CHIN
d—Darwin’s ear point not present
c—cleft chin
W—WIDOW’S PEAK PRESENT
L—CLOCKWISE HAIR WHORL
w—widow’s peak not present
l—counterclockwise hair whorl
1. Tasting Paper—Taste the paper. It contains a harmless chemical that some people can taste and
others cannot. The ability to taste the chemical is a dominant trait. People who cannot taste this
chemical are recessive for the trait.
_________________________ ________________________
Phenotype
Genotype
2. Tongue Rolling—Some people can roll their tongues into a taco- or U-shape. This is a dominant
trait. If you cannot roll your tongue into a taco- or U-shape you are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
3. Earlobes—It is a dominant trait to have earlobes that hang down. People that have earlobes
attached directly to the side of their heads are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
4. Earbump—Some people have a bump on the inside rim of the upper part of the ear ridge. It is
called Darwin’s ear point. If you have the bump, it is due to the presence of a dominant allele. If you
are lacking the bump, you are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
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TEXTEAMS BIology Institute 2004
5. Widow’s Peak—If you have a hairline that comes to a point in the middle of your forehead, you
possess a dominant allele for widow’s peak. A straight or even hairline indicates you are recessive
for this trait.
_________________________ ________________________
Phenotype
Genotype
6. Hitchhiker’s Thumb—People who can bend the last joint of their thumbs back to a 90-degree
angle are dominant for hitchhiker’s thumb. People who lack this ability are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
7. Polydactyly—People born with six fingers or toes possess the dominant trait for polydactyly.
Having five fingers and toes is a recessive trait. In the U.S., people with extra toes or fingers usually
have them removed shortly after birth.
_________________________ ________________________
Phenotype
Genotype
8. Syndactyly—Having webbed fingers and toes is a dominant trait. Sometimes only a pair of fingers
or toes are webbed. If you have fingers and toes that separate, then you are recessive for this trait.
_________________________ ________________________
Phenotype
Genotype
9. Cleft Chin—If you have a chin that has a split in the middle, like John Travolta, you have a cleft chin.
This is a recessive trait. The absence of a cleft chin is a dominant feature.
_________________________ ________________________
Phenotype
Genotype
10. Hair Whorl—Have someone in your group look at the back of your head to determine if
your hair whorls to the right (clockwise) or to the left (counterclockwise). If you use hairspray or
gels on your hair, this activity may be a hard one to do. A clockwise whorl is dominant over the
recessive trait of a counterclockwise whorl.
_________________________ ________________________
Phenotype
Genotype
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Dominant Fly
Genes that determine traits are encoded and arranged linearly on structures called chromosomes found in
the nuclei of most cells. When organisms reproduce, the resulting offspring should receive an equal number
of chromosomes from the mother and the father.
Materials:
Egg, sperm, Insect Parts drawings, colored pencils, unlined paper
Procedures:
1. Use the chromosomes and the Insect Traits Key below to determine the genotype and phenotype
of the offspring. Record the information in Data Table 1.
Insect Traits Key
H — LARGE HEAD
E — RED EYE
P — ANTENNAE PRESENT
h — small head
e — apricot eye
p — antennae absent
T — SHORT THORAX
O — ORANGE WING
W — SHORT WINGS
t — long thorax
o — green wings
w — long wings
A — SHORT ABDOMEN
B — BLACK BODY*
L — SHORT LEGS
a — long abdomen
b — gray body*
l — long legs
X X — Female
* Body color refers to antennae, head, thorax, abdomen, and
legs.
X Y — Male
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TEXTEAMS BIology Institute 2004
Data Table 1
Trait
Genotype
Phenotype
Head Size
Hh
Large head
Eye Color
Antennae
2. Open the egg and sperm and examine the chromosomes. Pair up the chromosomes by matching
the numbers on them. Use the information on the chromosomes and in the Insect Traits Key to
complete Data Table 2.
Data Table 2
Trait
Genotype
Homozygous or
Heterozygous
Dominant or
Recessive
Hemizygous
Not Applicable
Phenotype
Head size
Chromosome
pair 1
Eye color
Antennae
Thorax size
Chromosome
pair 2
Wing color
Wing length
Leg length
Chromosome
pair 3
Body color*
Abdomen
size
Chromosome
pair 4
Sex
* Body color refers to antennae, head, thorax, abdomen, and legs.
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DNA, mRNA, and Protein Synthesis
(Computer Simulation)
In this investigation, use the PC or Apple™ platform computer to draw DNA, mRNA, and tRNA and
simulate protein synthesis. The instructions are the same for either platform; however the toolbars will be
in different locations.
Before beginning, you must activate the Drawing tool by pulling down the View menu in MicroSoft Word™,
highlighting “Toolbars,” and selecting “Drawing.” The Drawing Toolbar should appear on the computer
screen (see Figure 1).
Figure 1
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TEXTEAMS BIology Institute 2004
DNA
DNA is composed of building blocks called nucleotides and is located in the nucleus of most cells.
A nucleotide is composed of a deoxyribose (D), a phosphate (P), and a nitrogen base. The phosphate,
deoxyribose, and the nitrogen base are all connected by covalent bonds. A nucleotide is shown in Figure 2.
Figure 2
The overall shape of the DNA molecule resembles a ladder twisted into a helix shape. Each vertical side of
the ladder is made of alternating deoxyriboses (D) and phosphates (P). The rungs of the ladder consist of
nitrogen bases connected to each other by hydrogen bonds. Nitrogen bases are of four types: adenine (A),
thymine (T), cytosine (C), and guanine (G). Normally, because of its structure, adenine will bond only with
thymine, and cytosine with guanine. Four nucleotides are shown in Figure 3.
Figure 3
Drawing DNA
To draw DNA, you must select several shapes to represent the different parts of DNA: the four different
nitrogen bases, phosphate, and deoxyribose.
Nitrogen bases. Using the Drawing Toolbar, click on “AutoShapes,” select “block arrows,” then select
the chevron to represent adenine and the pentagon to represent thymine.
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Click on “AutoShapes,” select “flowchart,” then select “flowchart delay” to represent cytosine and
“flowchart data” to represent guanine.
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TEXTEAMS BIology Institute 2004
Phosphate. Using the Drawing Toolbar, click on “Basic Shapes,” select “oval” to represent phosphate. Place the
mouse arrow over the edge of the oval and then click and drag the edge toward the center of the oval to reduce its
size and reshape it to a circle.
Deoxyribose. Using the Drawing Toolbar, click on “AutoShapes,” and select “block arrows,” then select “pentagon”
to represent deoxyribose.
Nucleotide. Arrange one of the shapes for the nitrogen bases, a phosphate, and a deoxyribose to create a
nucleotide. Assemble the nucleotide according to Figure 4.
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Figure 4
Lines. Click on the diagonal line in the Drawing Toolbar, which causes the cursor to be replaced by a cross. Place
the center of the cross where the line is to start and hold the mouse button down while dragging the line to its
ending point. If you are having trouble controlling the start or end point of the line and it extends into the object,
click on “Draw,” order, and send to back. This will hide the ends of the line behind the shape. To move the line in very
small increments, click on “Draw”, grid, and “click” to remove the check mark from snap objects to grid. Use the up
and down arrows on the keyboard to move the line in very small increments.
Figure 5
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TEXTEAMS BIology Institute 2004
Changing the Appearance of a Shape. To select a fill color for the nucleotide components, click on the
shape, then click on the arrow to the right of the fill color paint bucket in the Drawing Toolbar and click on ONE of
the following choices:
•
A color box
•
Select “More Fill Colors” for additional color choices
•
Select “Fill Effects” and choose a texture or pattern
•
Combine color and “Fill Effects” for more possibilities. Select “Fill Effects” ® “Pattern” ® “foreground color”
and/or “background color”
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Figure 6
Labeling the Shapes. After the color of the shape has been selected, the nucleotide can be labeled. To add text
for the first time, click the text box on the Drawing Toolbar, drag a text box into the desired area, and type in the
text. To change the size of the text, highlight the text and change the font size. Clicking on the font color icon and
selecting a new color changes the color of the letter. To make the box lines disappear, right click on one of the
textbox lines, select “format text box,” “then color” (no fill) and “line color” (no line). Click OK.
Figure 7
Grouping Shapes Together. When using the Drawing tool to construct a DNA or RNA molecule, it is helpful
to group the shapes and lines together. To group the shapes and lines, left click on the white arrow on the Toolbar.
While the left mouse button is depressed, drag a box around the items to be grouped. Left click on the “Draw”
button and select “Group.”
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Copying the Nucleotide. Once the shapes and lines have been grouped together, the nucleotide can be copied
and pasted as many times as needed. To create additional nucleotides with different nitrogen bases, simply ungroup
an existing nucleotide and change the nitrogen base. The nucleotide can be ungrouped by clicking “Ungroup”.
Base Pairing Arrangement of DNA. There are four nitrogen bases found in a DNA molecule: adenine,
thymine, cytosine, and guanine. The nitrogen bases are held together by hydrogen bonds. Adenine pairs with thymine,
and the two are held together by two hydrogen bonds. Guanine pairs with cytosine, and the two are held together
by three hydrogen bonds.
Use what you have learned to create a model of a DNA molecule. To add the hydrogen bonds shown by the dotted
lines, first use the line tool to draw the lines. While the line is still selected, click on the dash style tool and select a
dash pattern.
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DNA Replication
The function of DNA is to store and transmit genetic information. The genetic information stored in DNA functions
as a blueprint for all cellular processes that occur in the lifetime of a living organism. During DNA replication, an
exact copy of the original cell is made. Thus, skin cells are replaced with skin cells, and muscle cells are replaced with
muscle cells.
When DNA replication begins, the hydrogen bonds holding the nitrogen bases together break, causing the helix to
separate at various points along the ladder. These original strands will act as a template to form more DNA. Freefloating nucleotides come in and attach to the original strand. The DNA continues to separate, and more nucleotides
float in and attach to the original strand. This process continues until each original strand has been replicated.
Draw a model of DNA using Figure 8 as a guide. Print it for the teacher.
Figure 8
DNA and mRNA Transcription
DNA remains in the nucleus, so the transfer of genetic information is relayed by another molecule, messenger RNA
(mRNA). This molecule is made when DNA is used as a template in a process called transcription. The process is
basically the same as replication, except that the nucleotides have ribose (R) instead of deoxyribose (hence, RNA
instead of DNA) and the nitrogen base uracil (U) is substituted for thymine. To create an mRNA molecule showing
transcription, copy the left side of the DNA molecule. To do this, use the white arrow on the Toolbar to draw a box
around the part of the molecule to be copied, click on “Draw,” then group. While the objects are still selected, copy
them. Paste the left side of the DNA molecule in your selected location, then build the mRNA nucleotides. Use
Figure 9 as a model. Print it.
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Figure 9
Translation
While still in the nucleus, the RNA strand is processed and becomes a strand of mRNA. The mRNA leaves the
nucleus and travels to the cytoplasm where it links up with a ribosome. Molecules of tRNA will bring amino acids to
the ribosome, based on the mRNA code. The growing amino acid chain becomes a protein. Draw a model of protein
synthesis.
Figure 10
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TEXTEAMS BIology Institute 2004
DNA, mRNA, and Protein Synthesis
(Paper/Pencil)
Complete the model of DNA below by drawing the missing nitrogen bases and the nucleotides. Label the structures,
design an identification key, and color the DNA structures based on the key.
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DNA Replication
Use the same DNA sequence from the DNA model on the first page to simulate how DNA replicates itself. During
replication, the hydrogen bonds between the nitrogen bases are broken and the molecule splits apart at various
points along the ladder. Nucleotides attach to the complementary base of the original strand. This continues until all
segments of DNA have been copied. The result is two DNA molecules, each composed of an original strand and a
newly formed strand.
Complete the model of DNA replication below by drawing the missing nitrogen bases in the nucleotides. Show
covalent bonding between the phosphate and deoxyribose, and the deoxyribose and the base. Show hydrogen
bonding between the nitrogen bases. There are two hydrogen bonds between adenine and thymine, and three
hydrogen bonds between cytosine and guanine. Label and color each part of the DNA replication using the same
identification key you designed for the DNA model.
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TEXTEAMS BIology Institute 2004
Transcription
It is the function of another nucleic acid, called messenger RNA (mRNA), to relay genetic information to the
ribosomes. RNA is made when a strand of DNA is used as a template. This process is called transcription. The
transcription process is basically the same as replication, except that nucleotides have ribose (R) instead of
deoxyribose (hence, RNA instead of DNA), and the nitrogen base uracil (U) is substituted for thymine. The transfer
of genetic information is relayed out of the nucleus by messenger RNA (mRNA). The RNA is modified to become an
mRNA molecule.
Complete the model of transcription below by drawing the missing nitrogen bases in the mRNA nucleotides. Show
hydrogen bonding between the nitrogen bases. There are two hydrogen bonds between adenine and uracil, and three
hydrogen bonds between cytosine and guanine. Label and color each part of the transcription process using the
same identification key you designed for the DNA model.
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Translation
Once mRNA leaves the nucleus, it travels through the cytoplasm to a ribosome. The mRNA inserts itself between
the subunits of a ribosome and the ribosome reads the mRNA, three nitrogen bases at a time. Three nitrogen bases
together are referred to as a codon. At the same time, transfer RNA (tRNA) brings the amino acid specified by the
mRNA to the ribosome. When the start codon (AUG) is read, protein synthesis begins and continues until a stop
codon is read. The amino acids brought in by the tRNA are bonded together one at a time and continue until the
process is completed.
Copy the mRNA sequence from your transcription model onto the mRNA strand inside the box. Label and color
each part of the translation using the same identification key you designed for the DNA model.
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TEXTEAMS BIology Institute 2004
Protein Synthesis:
Like a Banana Split
1. Complete Data Table 1 using your knowledge of DNA transcription and the mRNA Genetic Code
Wheel or Chart.
Data Table 1
DNA
mRNA
AMINO ACID
TCA
AGU
Serine
CCC
Glycine
Methionine
GGA
CCU
GAG
TAA
Glutamic acid
Isoleucine
Tryptophan
CGC
GCG
CGT
GCA
ATT
AAA
UUU
TTA
Asparagine
CCA
Glycine
TTT
2. Name five amino acids listed on the mRNA Genetic Code Chart or the mRNA Genetic Code Wheel.
3. Name five ingredients used in a banana split.
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4. Use the mRNA Genetic Code Chart or the mRNA Genetic Code Wheel to list ALL possible mRNA
sequences for the amino acids shown in this segment of hemoglobin.
Data Table 2
Valine
Histidine
Leucine
Threonine
Proline
Glutamic Acid
5. Examine the mRNA sequences for each amino acid recorded in Data Table 2. What do you notice about
them?
6. Suggest reasons for the fact that there are several ways to produce the amino acids that build hemoglobin.
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7. Using the DNA strand, decode the ingredients for a banana split recipe. Apply your knowledge of DNA
transcription, translation, and the mRNA Genetic Code Chart or the mRNA Genetic Code Wheel to
complete the table. Use Data Table 3.
Data Table 3
DNA
mRNA
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Amino Acid
tRNA
Banana Split
Ingredient
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8. Build your own banana split recipe. Use your knowledge of DNA transcription and translation and the mRNA
Genetic Code Table or the mRNA Genetic Code Chart to decode it. Use Data Table 4.
Data Table 4
DNA
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mRNA
Amino Acid
tRNA
Banana Split Ingredient
TEXTEAMS BIology Institute 2004
The Human Genome
In 1990, the National Institutes of Health and the Department of Energy joined with international partners to begin
a worldwide effort to map and sequence the genome of humans and certain model organisms. This effort, known
as the Human Genome Project (HGP), was completed in 2003. As genomic information was collected, it was placed
into databases and shared within the research community. These databases are used to study cancer, diabetes, and
other common diseases.
The Human Genome Project has also examined genetic variation in human populations by analyzing the DNA
of groups of people from around the world. One example is the investigation of three different alleles for blood
protein, GC-1, HP-1, and FY-O. The GC-1 allele provides the code for a protein that attaches to and regulates the
distribution of vitamin D in the human body. The HP-1 allele provides the code for haptoglobin, a protein that
attaches itself to the hemoglobin released by red blood cells when they die a natural death or are destroyed by a
disease such as malaria.
The FY gene provides the code for a blood protein found on the surface of red blood cells. This protein makes it
easier for the malarial parasite Plasmodium vivax to multiply in red blood cells and cause malaria. However, the FY-O
allele results in the absence of this protein, making it difficult for the parasite to gain entry into the red blood cells
to multiply. Therefore, the FY-O allele provides a selective advantage in parts of the world where Plasmodium vivax
malaria is common. This advantage accounts for the high frequency of the FY-O allele in those regions.
Use the maps below to identify the genetic frequency (as a percent) of the three different alleles (GC-1, HP-1, and
FY-O) in the world’s populations. Record the frequency of each allele on each continent in Table 1.
Occurrence of GC-1 allele
73%
88%
76%
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83%
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Occurrence of HP-1 allele
38%
73%
32%
17%
42%
60%
27%
Occurrence of FY-O allele
.3%
0.2%
96%
3%
0%
From the National Human Genome Research Institute and the National Institutes of Health. For more information
visit http://www.nhgri.nih.gov/educationkit/
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Table 1
GC-1
HP-1
FY-O
Africa
Asia &
Middle East
Australia
Europe
North
America
South
America
1. What is the range of frequencies for each allele shown?
2. On a worldwide basis, which allele varies the most in frequency?
3. On a worldwide basis, which allele varies the most in distribution across the continents?
4. Examine Map 1 showing the occurrence of the malarial parasite Plasmodium vivax. What inference can be
made concerning the occurrence of Plasmodium vivax and the variation in the frequency of the FY-O allele in
human populations?
Map 1 Occurrence of Malarial Parasite Plasmodium vivax
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Assessment Task: Inheritance of Sickle
Cell Anemia
Your team has received the following letter:
Dear DNA Team:
My name is Dr. Ilene Martin and I specialize in obstetrics. Although I have much experience at helping my patients and their
husbands through a pregnancy, I am not an expert in many of the genetic concerns that couples have before they get pregnant. I am
aware that people on your DNA Team have a broad and thorough understanding of how the DNA molecule works and can explain
those workings to people in everyday language that they can understand.
George and Beatrice Jackson are patients of mine who are considering starting a family. Both George and Beatrice have family
members with sickle-cell anemia, so you can see their concern.They want to become fully informed regarding how DNA works and
how it codes to make the normal form of the protein hemoglobin.They also would like a full explanation of what goes wrong with the
DNA to cause a person to have sickle-cell anemia.
I would like for your DNA team to explain the workings of DNA and how sickle-cell anemia gets passed on to future generations.
Please let me know if this is possible.
Thank you,
Dr. Ilene Martin
Your task is to develop models and clear explanations to help Dr. Martin’s patients learn how DNA works, how it codes
to make normal hemoglobin, and what can go wrong with the DNA to cause sickle-cell anemia.
Safety precautions:
None required.
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Part 1
1. Your teacher will give you two strips of paper (one written in blue, the other written in red) that represent a
DNA molecule. This DNA molecule represents a portion of the normal gene for the protein hemoglobin. Why
are two strips, not one, needed to represent DNA?
2. Use these two strips to make an exact copy of the DNA molecule given to you.
(A) Describe what you just did to make a copy.
(B) What is this process called?
3. What do the four letters on the DNA molecule represent?
4. What is the significance of the 3’ to 5’ direction on each strand?
5. Select the 5’ to 3’ coding strand (the blue strand) of your DNA molecule. Then, obtain one blank strip of
paper from your teacher. On the blank strip, write the mRNA base sequence in a third color.
(A) What is the mRNA coding sequence on your strip?
(B) What does this base sequence represent?
(C) What step of protein synthesis did you just perform?
(D) Why must the DNA message go through this step?
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(E) Name the two structural differences of DNA and mRNA.
6. Using your mRNA strip, demonstrate the process of converting the information in mRNA to tRNA.
(A) Describe in detail what you just did in this process.
(B) What step of protein synthesis did you just complete?
Part 2
1. Observe the drawings of normal human red blood cells (RBCs) and sickle-shaped red blood cells (RBCs).
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(A) Describe the differences between the two types of RBCs.
(B) What physiological functions might be affected by the shape of the sickled cells?
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2. Hemoglobin consists of four polypeptide chains: two alpha chains and two beta chains. Normal hemoglobin
is called hemoglobin A. The hemoglobin that produces sickle cells is called hemoglobin S. Since the protein
hemoglobin is made of two kinds of polypeptide chains, how is it possible that there could be two forms of
this protein?
3. In Part 1, you found the mRNA coding sequence for the first nine amino acids that code for hemoglobin.
Here is the sequence for the first nine amino acids found in the mutated form of hemoglobin that causes
sickle-cell anemia:
start
meth—val—his—leu—thr—pro—val—glu—lys
What is a mutation?
4. Locate the difference(s) between the normal hemoglobin DNA sequence and the mutated sickle-cell
hemoglobin. Use the figure below to see how the mutation occurred and to find the mutation on the DNA
molecule.
start
meth val
his
leu
thr
pro
glu
glu lys
AUG GUU CAU UUA ACU CCU GAG GAG AAA — normal mRNA
TAC CAA GTA AAT TGA GGA CTC CTC TTT — normal DNA
start
meth
AUG
TAC
val
his
leu
thr
pro
val
glu
lys
GUU CAU UUA ACU CCU GUG GAG AAA — mutated mRNA
CAA GTA AAT TGA GGA CAC CTC TTT — mutated DNA
Describe in detail what you just did in this process.
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