Download a code for traits: dna structure and function

A CODE FOR TRAITS: DNA STRUCTURE AND FUNCTION
INTRODUCTION
Just as an architect uses a blueprint to construct a building, an organism’s DNA is a blueprint for
its traits. The blueprints for the White House are different from the blueprints for the
Washington Monument, making these two buildings different on a structural level. It makes
sense, therefore, that organisms with different traits must have different DNA; but how is their
DNA different? In today’s lab, you will investigate how differences in DNA can produce
differences in human red blood cells.
OBJECTIVE
After completing this investigation, you will be able to explain how a genetic trait is determined
by the code in a DNA molecule.
MATERIALS
12 nucleotides, either pink or blue
plain white paper
glue stick or tape
PROCEDURES
_____ 1. CUT out your 12 nucleotides along the solid lines.
_____ 2. WRITE “Gene From (Mother or Father)” at the top of the plain white paper. The
paper should have an 8.5 inch side at the top (portrait orientation). The mother’s
gene has pink nucleotides, the father’s gene has blue nucleotides.
_____ 3. FIND the numbered nucleotides – there should be six. GLUE or TAPE these
nucleotides in numerical order, beginning with number 1, down the left side of
your paper. The tab of one nucleotide should fit into the notch of the nucleotide
before it.
_____ 4. CONSTRUCT the complementary strand of DNA to complete your gene. This
step models the anti-parallel nature of a DNA molecule – one side is “right-sideup” on a molecular level while the other side is “upside-down.” Identify the 5’ and 3’
ends.
_____ 5. LABEL your gene as either “normal hemoglobin” or “sickle hemoglobin”
according to the key below. COMPARE your gene sequence to those in the key.
RECORD the label to the right of your gene or at the bottom of your paper.
Label your gene with one of the following:
G G C T T A = normal hemoglobin gene “N”
G G C A T A = sickle hemoglobin gene “S”
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_____ 6. DRAW and LABEL the product of your gene, according to the information below.
RECORD this information next to or below your gene label from Step 5.
The normal hemoglobin gene
produces a normal-shaped
hemoglobin protein that gives red
blood cells their characteristic disc
shape. Normal hemoglobin is
capable of transporting a maximum
amount of oxygen.
The sickle hemoglobin gene codes
for a misshapen protein that
produces sickle-shaped red blood
cells. These cells can get stuck
against capillary walls and do not
transport oxygen efficiently.
_____ 7. SIMULATE sexual reproduction by finding a partner whose nucleotides are
opposite from your color. COMPLETE the data table below.
MOTHER
FATHER
OFFSPRING
Gene(s)
(use N and/or S)
Type of red blood
cells (draw and label)
_____ 8. COMPLETE the Analysis Questions.
INFORMATION ABOUT SICKLE CELL ANEMIA
Sickle Cell Anemia (SCA) is a genetic disorder caused by a point mutation (single base
substitution) on the 11th chromosome. Only individuals with the genotype “SS” inherit sickle
cell disease, which can be fatal because not enough oxygen is transported to vital organs.
Individuals with the genotype NS (or SN) have sickle cell trait. These people are considered
healthy, although they may suffer some symptoms of SCA if their blood oxygen level becomes
too low. Ten percent of the African American population has sickle cell trait. In regions of the
world with a high incidence of malaria, the sickle cell trait offers resistance against the parasite.
The high percentage of sickle cell trait in the United States is a genetic “footprint” of our
population’s African heritage.
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ANALYSIS QUESTIONS
1. Describe the shape of a DNA molecule. Be as specific as possible. Include 5’ and 3’.
2. How many base pairs does your gene have?
3. If a DNA molecule has 8436 Ts, how many As will it have? Justify your answer.
4. Use the template DNA molecule below to construct its complementary strand.
template gene =
A T C G C G A T A A G G C T A G C T G A C
complement =
5. How many hemoglobin genes has your offspring inherited? Explain why this makes sense
according to your knowledge of meiosis and fertilization. Use vocabulary to enhance your
answer.
6. Will your fictitious child be healthy or have sickle cell anemia? Explain your answer using
information from your data table and incorporating your knowledge of how DNA is a code
for traits. You may refer to the information about sickle cell anemia at the end of the lab
procedure to help you answer this question.
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EXTENSION
While attending a family reunion, you overhear your grandmother wondering why people who are so closely related
can look so different. She comments that you have freckles, but your brother doesn’t. How can this be possible
when you have the same parents? Help your grandmother understand these differences in traits by using your
knowledge of DNA structure and function. In your response, be sure to include:
 a description of how siblings can inherit different DNA
 a brief description of DNA structure and how one person’s DNA is different from another’s
 a discussion of how DNA is a code for traits
 independent assortment and crossing over during meiosis
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NUCLEOTIDES FOR NORMAL HEMOGLOBIN
1
deoxyribose
adenine
phosphate
group
phosphate
group
adenine
guanine
phosphate
group
thymine
deoxyribose
phosphate
group
phosphate
group
adenine
guanine
3
guanine
deoxyribose
phosphate
group
phosphate
group
deoxyribose
phosphate
group
2
deoxyribose
deoxyribose
4
6
deoxyribose
thymine
deoxyribose
deoxyribose
cytosine
phosphate
group
5
deoxyribose
phosphate
group
thymine
cytosine
deoxyribose
deoxyribose
phosphate
group
phosphate
group
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cytosine
NUCLEOTIDES FOR SICKLE HEMOGLOBIN
1
4
deoxyribose
adenine
deoxyribose
thymine
phosphate
group
phosphate
group
deoxyribose
guanine
phosphate
group
6
deoxyribose
adenine
deoxyribose
thymine
phosphate
group
phosphate
group
adenine
3
deoxyribose
guanine
phosphate
group
phosphate
group
guanine
phosphate
group
2
deoxyribose
deoxyribose
deoxyribose
cytosine
phosphate
group
5
deoxyribose
phosphate
group
thymine
deoxyribose
phosphate
group
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cytosine
deoxyribose
phosphate
group
cytosine