Download 14.3 Studying the Human Genome

Name
Class
Date
14.3 Studying the Human Genome
Lesson Objectives
Summarize the methods of DNA analysis.
State the goals of the Human Genome Project and explain what we have learned so far.
Lesson Summary
Manipulating DNA Since the 1970s, techniques have been developed that allow scientists
to cut, separate, and replicate DNA base-by-base. Using these tools, scientists can read the
base sequences in DNA from any cell.
▶ Restriction enzymes cut DNA into smaller pieces, called restriction fragments, which are
several hundred bases in length. Each restriction enzyme cuts DNA at a different sequence
of bases.
▶ Gel electrophoresis separates different-sized DNA fragments by placing them at one end
of a porous gel, then applying an electrical voltage. The electrical charge moves the DNA.
▶ Using dye-labeled nucleotides, scientists can stop replication at any point along a single
DNA strand. The fragments can then be separated by size using gel electrophoresis and
“read,” base-by-base.
The Human Genome Project was a 13-year international effort to sequence all 3 billion
base pairs in human DNA and identify all human genes. The project was completed in 2003.
▶ The researchers identified markers in widely separated strands of DNA.
▶ They used “shotgun sequencing,” which uses a computer to match DNA base sequences.
▶ To identify genes, they found promoters, exons, and other sites on the DNA molecule.
▶ To locate and identify as many haplotypes (collections of linked single-base differences) in
the human population as possible, the International HapMap Project began in 2002.
▶ The Human Genome Project identified genes associated with many diseases and
disorders. From the project came the new science of bioinformatics, the creation and
use of databases and other computing tools to manage data. Bioinformatics launched
genomics, the study of whole genomes.
▶ The human genome project pinpointed genes and associated particular sequences in those
genes with numerous diseases and disorders. It also found that the DNA of all humans
matches base-for-base at most sites, but can vary at 3 million sites.
▶ The 1000 Genomes Project, launched in 2008, will catalogue the variation among 1000
people.
Lesson 14.3 • Workbook A • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
222
Name
Class
Date
Manipulating DNA
For Questions 1–4, write True if the statement is true. If the statement is false, change the
underlined word to make the statement true.
True
1. Bacteria produce restriction enzymes that cut the DNA molecule into
smaller pieces.
nucleotides
True
2. Restriction fragments are always cut at a particular sequence of proteins.
3. The technique that separates differently sized DNA fragments is gel
electrophoresis.
polymerase
4. The enzyme that copies DNA is DNA restrictase.
5. Complete the graphic organizer to summarize the steps used to determine the sequences
of bases in DNA.
Purpose
Tool or Technique Used
Outcome
Cutting DNA
Restriction enzymes
Large molecule of DNA is cut into
smaller fragments.
Separating DNA
Gel electrophoresis
Smaller DNA fragments move
faster on the gel, so fragments are
separated according to size.
Reading DNA
Dye-labeled nucleotides
and gel electrophoresis
Labeled nucleotides stop the
synthesis of a new strand at
different lengths. Gel
electrophoresis then separates
them so they can be read.
For Questions 6–10, complete each statement by writing in the correct word or words.
6. By using tools that cut, separate, and then replicate DNA, scientists can now read the
base
sequence in DNA from any cell.
7. Restriction enzymes cut pieces of DNA sometimes called restriction
8. Each restriction enzyme cuts DNA at a different sequence of
9. The smaller the DNA, the
electrophoresis.
faster
fragments
nucleotides
.
and farther it moves during gel
10. After chemically dyed bases have been incorporated into a DNA strand, the order of
colored
bands
on the gel reveals the exact sequence of bases in DNA.
Lesson 14.3 • Workbook A • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
223
.
Name
Class
Date
The Human Genome Project
For Questions 11–16, write the letter of the correct answer on the line at the left.
A
11. What technology made the Human Genome Project possible?
A. DNA sequencing
B. RNA replication
C. protein synthesis
D. enzyme activation
C
12. What were the “markers” that the researchers of the Human Genome Project
used?
A. restriction enzymes
B. gel electrophoresis
C. base sequences
D. restriction fragments
B
13. What does “shotgun sequencing” do?
A. separate fragments using gel electrophoresis
B. find overlapping areas of DNA fragments
C. cut DNA into millions of “puzzle pieces”
D. bind colored dyes to base sequences
D
14. What are SNPs?
A. points where a restriction enzyme cuts a DNA molecule
B. missing sequence of base pairs in a restriction fragment
C. proteins formed by a mutated gene
D. differences in a base between two individuals
C
15. Bioinformatics would not have been possible without
A. microscopes.
B. genes.
C. computers.
D. genomics.
A
16. In humans, single-base differences
A. occur at about 3 million sites.
B. occur rarely in the sex chromosomes.
C. seldom occur in normal DNA.
D. cannot be identified from DNA analysis.
17. What were the goals of the Human Genome Project?
The main goals were to sequence the base pairs of DNA and identify all human genes.
Other goals included sequencing genomes of model organisms, developing technology
for research, exploring gene functions, studying variation in humans, and training
future scientists.
Lesson 14.3 • Workbook A • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
224
Name
18.
Class
Date
The field of bioinformatics combines both life sciences and modern
technology. Fill in the Venn diagram to show how.
Information
nce
Life Scie
Statistics
Sc i e
nce
Data Analyses
Observations
Visualizations
Experiments
Predictions
Computer
Modeling
Databases
Hypotheses
19. The Icelandic people have always placed high importance on knowing about their
ancestors. In fact, 80% of all the Icelandic people who have ever lived can be added to
a family tree. Medical records are just as detailed. The population is quite isolated, so
the gene pool is considered to be homogeneous. Why would these conditions make the
genome of the Icelandic population ideal for studying rare inherited disorders associated
with gene sequencing errors?
The homogeneous population makes the task of finding DNA sequences easier.
Unusual base pairs, such as those associated with disorders, would stand out. Since
people are aware of their family’s medical histories, scientists would be able to test
descendants with no signs of the disorder to see just how it is inherited between
generations.
Lesson 14.3 • Workbook A • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
225
Name
Class
Date
Chapter Vocabulary Review
For Questions 1–11, match the term with its definition.
Definition
C
E
G
I
F
J
H
K
B
D
A
1. The X chromosome or the Y chromosome
2. A gene on the X chromosome or the Y
chromosome
3. The failure of homologous chromosomes to
separate during meiosis
4. A technology used to separate fragments of DNA
5. A chart that shows family relationships and
inheritance of traits
6. A field of study that includes the operation of
databases
7. An enzyme that cuts a DNA molecule into small
pieces
Term
A. genome
B. karyotype
C. sex chromosome
D. autosome
E. sex-linked gene
F. pedigree
G. nondisjunction
H. restriction enzyme
I. gel electrophoresis
J. bioinformatics
K. genomics
8. The study of whole genomes, including genes and
their functions
9. A picture that shows chromosomes arranged in
pairs
10. Any chromosome that is not a sex chromosome
11. The full set of genetic information in an
organism’s DNA
For Questions 12–19, complete each statement by writing in the correct word or words.
12. A circle represents a female in a(n)
pedigree
.
13. The protein that cuts DNA into pieces is a restriction
enzyme
.
14. An inherited disorder that appears more often in males than females is probably caused
by a sex-linked gene .
15. The 23 pairs of human chromosomes are arranged from largest to smallest in a
karyotype
.
16. Humans have 22 pairs of
autosomes
.
17. The cause of Down syndrome is nondisjunction during meiosis.
18. Humans have 3 billion base pairs in their
genome
.
19. The new field of bioinformatics resulted from the Human Genome Project.
Chapter 14 • Workbook A • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
226
Name
Class
Date
In the Chapter Mystery, you learned how
genetic testing can help identify risk for
an inheritable disease, such as sickle-cell
anemia. Geneticists have made great strides
in recent years to develop many more
DNA-based genetic tests.
THE CROOKED CELL
Learning
NOTE: This topic may be difficult for students who are
dealing with or have family members dealing with hereditary diseases. You may want to
evaluate whether this exercise is appropriate for your students before assigning it.
Genetic Testing: A Personal Choice
Today, more than 1000 genetic tests are available to determine whether patients carry genes
associated with diseases from breast cancer to the degenerative neurological disorder known
as Huntington’s disease. But the genetic tests pose a difficult dilemma for many people at risk
for genetic disease.
The choice is especially difficult for those conditions, such as Huntington’s disease, for
which there are no treatments or cures. Recent polls have found that a significant majority of
people say they would want to undergo genetic testing for a treatable disease. But respondents
remain almost evenly split on whether they would undertake testing for an untreatable
condition. Many people are concerned that testing positive for an untreatable genetic disease
could lead to employment discrimination, denial of medical insurance, or other types of
discrimination. The National Institutes of Health has issued the following information to help
people make their decisions.
How Do I Decide
Whether to Be Tested?
But in some cases, there is no treatment
or cure available. There are no preventive
steps or cures for Huntington’s disease, for
example. Some people simply do not want
to know that they will develop a serious
illness for which there is no treatment or
cure. Others, however, feel that knowing the
test results might help them make decisions
such as career choices, family planning, or
insurance coverage.
To help make such decisions, people
can seek advice from a genetic counselor.
Genetic counselors help individuals
and families think about the scientific,
emotional, and ethical factors that affect
their decision whether or not to test. But the
difficult decision is still up to the individual
or family.
People have many different reasons for
being tested or not being tested. For many, it
is important to know whether a disease can
be prevented if a gene alteration causing a
disease is found. For example, those who have
inherited forms of breast or colon cancer have
options such as screening or early treatment.
Pharmacogenetic testing can find the best
medicine or dose of a medicine for a certain
person. (Pharmacogenetic testing involves the
analysis of a person’s genetic makeup in order
to prescribe the most effective medications
for that person.)
Continued on next page ▶
Chapter 14 • Workbook A • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
227
Name
Class
Themes
Date
Science and Health Literacy
1. What is a genetic test?
A genetic test examines a patient’s DNA to determine whether that patient carries
a gene associated with a given disease.
2. How many genetic tests are currently available?
more than 1000
3. According to the National Institutes of Health, why would someone want to undergo a
genetic test?
to find out whether a disease can be prevented, to begin early treatment, to find
the best medicine or dose of a medicine, to make more appropriate decisions
4. What major factor, according to polls, affects the way people feel about a particular
genetic test?
People would want to undergo genetic testing for a treatable disease, but are almost
evenly split on whether they would undertake genetic testing for an untreatable condition.
5. Do you think anti-discrimination laws should be put in place to protect people who test
positive for an untreatable condition like Huntington’s disease? Why or why not?
Students may express different viewpoints, which should be supported by logical
rationales.
An Individual’s Case
The skills used in this activity include information and media literacy; communication
skills; and problem identification, formulation, and solution.
Use Internet or library resources to research the case of neuropsychologist Nancy Wexler.
Twenty years ago, Wexler identified the gene that causes Huntington’s disease. She was
spurred on in her research because Huntington’s disease runs in her family. Wexler spent
much of her career working to develop a genetic test for Huntington’s disease. But when the
test finally became available, she decided that she would rather not know whether she carried
the gene because no treatment exists for the disease.
Organize into groups to present your findings in a panel discussion about genetic testing.
Here are some questions you might consider:
▶ What are the arguments that someone should consider about the decision to undergo
genetic testing?
▶ Should a genetic test even be offered for an untreatable condition like Huntington’s? If so, why?
Evaluate the students’ performance in the panel discussion based on the reasons
why people want to be tested, as well as scientific, emotional, and ethical factors
that affect the testing decision.
Chapter 14 • Workbook A • Copyright © by Pearson Education, Inc., or its affiliates. All Rights Reserved.
228