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13
GENETIC COUNSELING
CHAPTER REVIEW
Today, our knowledge of human genetics is sufficient to
allow genetic counselors to advise couples whether they
or an unborn child has a chromosomal mutation. Also, the
construction of pedigrees can be used to determine the
chances of certain genetic disorders being passed on.
Then, too, we can now test for certain genetic disorders
in an embryo or an egg before fertilization occurs in laboratory glassware.
In the future, genetic counseling will be able to do
much more. It is expected that most everyone will know
their genetic profile, and a counselor will be able to advise about the chances of anyone developing a disease and
what can be done in the way of behavior, medications, and
gene therapy to prevent or alleviate any symptoms.
CHAPTER KEY TERMS
After studying the key terms of this chapter, match the phrases below with the alphabetized list of terms.
bioinformatics
genome
deletion
genomics
DNA chip
inversion
DNA probe
karyotype
duplication
pedigree
gene therapy
proteome
genetic counseling
proteomics
genetic marker
translocation
a. duplicated chromosomes arranged by pairs _______________________
b. chromosome mutation in which the end of a chromosome breaks off _______________________
c. chromosome mutation in which a particular segment is present more than once_______________________
d. chromosome mutation in which a segment of a chromosome is turned around 180° _______________________
e. study of all proteins in an organism _______________________
f. study of all the genes in an organism _______________________
g. computer technology used to study the genome and the proteome _______________________
h. full set of genetic information in a cell _______________________
i. correction of a detrimental mutation by the insertion of normal DNA _______________________
j. movement of chromosomal segments between homologous chromosomes _______________________
k. very small glass square containing several rows of DNA probes _______________________
l. a difference in the sequence of bases at a particular location on a chromosome _______________________
m. advising prospective parents about genetic disorders in their family _______________________
n. piece of single-stranded DNA that will bind to a complementary piece of DNA _______________________
o. collection of proteins in a cell _______________________
p. chart showing which members of a family have a genetic disorder or are carriers of the
disorder _______________________
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S T U DY E X E R C I S E S
Study the text section by section. Answer the study questions so that you can fulfill the learning objectives for each
section.
13.1 COUNSELING
(PP. 196–199)
FOR
CHROMOSOMAL DISORDERS
• A karyotype is a visual display of an individual’s chromosomes arranged by pairs.
• Amniocentesis and chorionic villi sampling provide fetal cells for karyotyping.
• Chromosomal mutations can be due to a change in either number or structure.
1. A couple is concerned that their child might have Down syndrome (three copies of number 21 chromosome).
What procedure might a counselor advise? ___________________________________________________________
2. A karyotype tells a counselor which of these is present?
a. _____ abnormal chromosome number
b. _____ abnormal number of any of our 23 types of chromosomes
c. _____ chromosomal mutation
d. _____ genetic mutation on a particular chromosome
3. Two procedures can be used to acquire fetal cells. Place A for amniocentesis and C for chorionic villi
sampling on the appropriate lines:
a. _____ 14 to 17 weeks of pregnancy
b. _____ 5 weeks of pregnancy
c. _____ Cells are obtained by suction.
d. _____ Cells are obtained by needle.
e. _____ Cells are from a cavity around the embryo/fetus.
f. _____ Cells are from the extraembryonic membrane itself.
4. A couple wants to know what types of chromosomal mutations are possible. In the following diagram, identify
the types of chromosomal mutations using the same terminology a counselor would use:
a
b
c
d
a
b
c
b
c
c
d
d
e
a
b
d
e
e
e
f
f
f
f
g
g
g
g
a.
c.
a
b
c
l
m
n
a
b
c
l
m
n
a
b
c
a
b
c
d
o
d
o
d
d
e
p
e
p
e
e
f
q
q
f
f
d
g
r
r
g
g
e
f
b.
d.
e. Cri du chat syndrome is due to which of these mutations? ____________________
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13.2 COUNSELING
(PP. 200–207)
FOR
GENETIC DISORDERS:THE PRESENT
• Constructing a pedigree shows the pattern of gene inheritance and the chances a genetic disorder will be
passed on.
• Several genetic disorders are due to changes in single genes carried on either the autosomes or the X
chromosome.
• It is possible to test the individual, the fetus, the embryo, or the egg for a mutated gene.
5. From the information provided by the couple, a counselor decides to construct a pedigree. The following
pattern occurs quite often in the pedigree.
1
2
3
a. Using A = dominant, a = recessive, give the genotype of all persons involved. __________________________
_______________________________________________________________________________________________
b. Shaded individuals are affected. What is the pattern of inheritance for the condition? ____________________
6. For another couple, this pattern occurs quite often in the pedigree:
1
2
3
a. Using A = dominant, a = recessive, give the genotype of all persons involved. __________________________
_______________________________________________________________________________________________
b. Shaded individuals are affected. What is the pattern of inheritance for the condition? ____________________
7. Use D if the condition is autosomal dominant and R if the condition is autosomal recessive.
a. _____ Affected children can have unaffected parents.
b. _____ Heterozygotes have a normal phenotype.
c. _____ Affected children must have at least one affected parent.
d. _____ Heterozygotes are affected.
8. Decide whether the condition is autosomal dominant or recessive. __________________________ Indicate
the genotype of each person in the middle row, using the letters A and a:
9. Decide whether the condition is autosomal dominant or recessive. __________________________ Indicate
the genotype of each person in the middle row, using the letters A and a:
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10. Complete the following statements to indicate that a condition is X-linked:
a. More males than females are (unaffected/affected). _________________________________________________
b. An affected son is more likely to have parents who are (normal/abnormal) ____________________ phenotype.
c. For a female to have the characteristic, her father must (have it/not have it) ________________________. Her
mother must (have it/not have it) _________________________________________________________ or be a carrier.
11. The following pedigree is for color blindness. Supply the genotype for the grandfather, the daughter, and the
grandson:
XB XB
XB Y
b.
a.
daughter
grandfather
XB Y
Xb Xb
Xb Y
XB Y
XB XB
XB Xb
c.
grandson
12. Match the following disorders to each of the statements:
1. Marfan syndrome
4. cystic fibrosis
2. Huntington disease
5. phenylketonuria
3. Tay-Sachs disease
6. sickle cell disease
a.
a defect in an elastic connective tissue protein, called fibrillin
b.
accumulation of phenylalanine in urine and blood
c.
brain cell degeneration causing muscle spasms
d.
Red blood cells are sickle-shaped and clog arteries.
e.
Mucus builds up in respiratory system.
f.
buildup of lipid in storage bodies
13. Huntington disease (H) is dominant. A heterozygote reproduces with a person who does not have Huntington
disease.
a. Write out the cross. _____________________________________________________________________________
b. What are the chances of an offspring developing Huntington disease? _________________________________
14. Mary is 50 years old and has Huntington disease. Her father was killed accidentally at a young age; her mother is 80
years old and is normal. What is the most likely genotype of all persons involved?
a. Mary’s mother ________
b. Mary’s father ________
c. Mary ________
15. Cystic fibrosis (c) is recessive. Both parents appear to be normal but have a child with cystic fibrosis. What
are the genotypes of all persons involved?
a. parents ________________________________________ b. child ________________________________________
16. Duchenne muscular dystrophy (X d ) is X-linked recessive. A woman who is a carrier is married to a normal
man.
a. Write out the cross. _____________________________________________________________________________
b. What are the chances of a son with Duchenne muscular dystrophy? ___________________________________
c. What are the chances of a daughter who is a carrier? ________________________________________________
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17. A counselor decides to test a couple for a genetic disorder. Sometimes it is possible to test for the level of a
a.
____________ in the body and sometimes it is possible to test the b. ____________ itself.
18. The counselor also decides to test the following stages. Match them to each of the statements:
1. fetal cells
2. embryo
3. egg
a.
can be acquired from mother’s blood
b.
must be done before IVF
c.
test the polar body
d.
remove one cell and test it
13.3 COUNSELING
(PP. 208–209)
FOR
GENETIC DISORDERS:THE FUTURE
• The Human Genome Project has revealed the sequence of all the base pairs in the human genome.
• DNA chips (DNA microarrays) contain the entire human genome and can be used to create a genetic profile of
an individual.
• Genetic profiles will lead to better preventive care, drug therapies, and gene therapy.
19. Place a check beside the statements that are true. Knowing the sequence of bases in our DNA holds great
promise for which of these?
a. helping locate genes on the chromosomes
b. helping determine why some people get sick
c. helping develop drugs that are specific for the various causes of the same type of disorder
20. In the future, you will have your genetic profile done and go right to a genetic counselor. What will the
genetic counselor discuss with you? _________________________________________________________________
_________________________________________________________________________________________________
13.4 GENE THERAPY (PP. 210–211)
• Ex vivo techniques involve genetic engineering of a patient’s cells outside the body.
• In vivo techniques involve attempting to alter cells without removing them.
21. Describe the steps in ex vivo gene therapy:
2.
2
3
recombinant
RNA
retrovirus
3
normal
gene
3.
recombinant DNA
reverse transcription
defective
gene
recombinant RNA
normal
gene
1.
4
1
bone
marrow
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22. Change these false statements to true statements:
a. Ex vivo methods of gene therapy require that the therapeutic gene be placed in the body either directly or
by using a viral vector. Rewrite: __________________________________________________________________
_______________________________________________________________________________________________
b. A common ex vivo method is to microinject normal genes into bone marrow stem cells removed from the
patient. Then the stem cells are returned to the patient. Rewrite: ______________________________________
_______________________________________________________________________________________________
c. Gene therapy is currently restricted to curing genetic diseases and is not used to treat illnesses, such as
cystic fibrosis or cardiovascular diseases. Rewrite: __________________________________________________
_______________________________________________________________________________________________
K E Y WO R D C RO S S WO R D
Review key terms by completing this crossword puzzle, using the following alphabetized list of terms:
1
2
4
3
5
6
8
9
10
11
7
chorionic villi sampling
color blindness
cystic fibrosis
deletion
DNA probe
hemophilia
Huntington
inversion
Marfan syndrome
pedigree
proteome
sickle cell
Tay-Sachs
12
Across
1 genetic diseases marked by progressive deterioration of the nervous system
3 congenital disorder of connective tissues (two words)
5 prenatal test in which cells are removed for testing
(three words)
8 collection of proteins
9 lethal genetic disease; faulty lysosomal digestive enzyme
10 piece of single-stranded DNA (two words)
11 change in chromosome structure; end of chromosome
breaks off
12 autosomal recessive disorder; dysfunction of the
exocrine glands (two words)
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Down
1 blood-clotting disorder
2 deficiency in one or more of the three kinds of cones
in the eye (two words)
4 hereditary disease; red blood cells are narrow and
curved (two words)
6 change in chromosome structure; segment of chromosome is turned around 180°
7 chart showing the relationships of relatives and
which ones have a particular trait
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CHAPTER TEST
OBJECTIVE QUESTIONS
Do not refer to the text when taking this test.
1. Which phrase best describes the human karyotype?
a. 46 pairs of autosomes
b. one pair of sex chromosomes and 23 pairs of
autosomes
c. X and Y chromosomes and 22 pairs of autosomes
d. one pair of sex chromosomes and 22 pairs of
autosomes
2. The gene arrangement on a chromosome changes
from ABCDEFG to ABCDEDEFG. This is an example of
a. deletion.
b. duplication.
c. inversion.
d. linkage.
3. Which chromosomal mutation does require the
presence of another chromosome?
a. translocation
b. duplication
c. inversion
d. All of these are correct.
4. Which type of chromosomal mutation occurs
when two simultaneous breaks in a chromosome
lead to the loss of a segment?
a. inversion
b. translocation
c. deletion
d. duplication
Questions 5 and 6 pertain to this pedigree chart.
grandfather
normal
color blind
daughter
normal
carrier
normal
grandson
normal
normal
color blind
carrier
5. The allele for this disorder is
a. dominant.
b. recessive.
c. X-linked and recessive.
d. None of these is correct.
6. The genotype of the starred individual is
a. Aa.
b. aa.
c. X A X a .
d. X A Y a .
7. A woman who is a carrier for color blindness
reproduces with a man who has normal color
vision. What is the chance they will have a colorblind daughter?
a. 50%
b. 25%
c. 100%
d. no chance
8. A color-blind woman reproduces with a man who
has normal color vision. Their sons will
a. be like the father because the trait is X-linked.
b. be like the mother because the trait is X-linked.
c. all have normal color vision.
9. A girl is color blind.
a. She received an allele for color blindness from
her mother.
b. She received an allele for color blindness
from her father.
c. All her sons will be color blind.
d. Her father is color blind.
e. All of these are correct.
10. Which chromosome has genes to determine male
genital development?
a. chromosome 5
b. chromosome 10
c. chromosome 21
d. X chromosome
e. Y chromosome
11. The _____ genotype indicates carrier female for
color blindness.
a. X B X B
b. X B X b
c. X b X b
d. X B Y
e. X b Y
12. Genomics
a. is the study of cellular protein structure.
b. sequences mutant genes.
c. is the study of the human genome.
d. is a mechanism used in DNA fingerprinting.
13. Which of the following statements is NOT correct?
a. Females have an XX genotype.
b. Males have an XY genotype.
c. An egg always bears an X chromosome.
d. Each sperm cell has an X and Y chromosome.
e. The sex of the newborn child is determined by
the father.
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14. Which of the following genotypes is not paired
with the correct number of Barr bodies?
a. XY — none
b. XO — one
c. XX — one
d. XXY — one
e. XXX — two
15. Which of the following is NOT a characteristic
of an X-linked recessive disorder?
a. More males than females are affected.
b. An affected son can have parents who have
the normal phenotype.
c. For a female to have the characteristic, her
father must also have it.
d. The characteristic often skips a generation
from the grandmother to the granddaughter.
e. If a woman has the characteristic, all of her sons
will have it.
16. Which of the following is NOT considered an
X-linked recessive disorder?
a. Tay-Sachs disease
b. color blindness
c. hemophilia
d. muscular dystrophy (some forms)
17. If a cell is altered while outside the human body
for gene therapy, it is considered _____ therapy.
a. ex vivo
b. in vivo
c. in vitro
d. extraneous
e. intravenous
18. The X-linked disease prevalent among royal families of Europe at the turn of the century was
a. muscular dystrophy.
b. color blindness.
c. hemophilia.
d. Williams syndrome.
e. cri du chat syndrome.
CRITICAL THINKING QUESTIONS
The introduction to this chapter discussed pre-implantation genetic diagnosis (PGD).
19. Why might a counselor advise you that this procedure is available? __________________________________________
_____________________________________________________________________________________________________________
20. What are some ethical concerns about PGD? ________________________________________________________________
21. Also available today, physicians can test the egg instead of the embryo. Ethically speaking, why is this
procedure preferable? ______________________________________________________________________________________
22. Assume the disorder is recessive and the egg carries the dominant, normal allele. If a sperm happens to have
the recessive allele, what genotype will the offspring have? _________________________________________________
23. A counselor would suggest PGD and not suggest testing the egg if the disorder is dominant. Why? ____________
_____________________________________________________________________________________________________________
Test Results: ______ number correct ÷ 23 = ______ × 100 = ______ %
EXPLORING
THE
INTERNET
ARIS, the Essentials of Biology website: http://www.mhhe.com/maderessentials
ARIS, the website for Essentials of Biology, offers access to a wide variety of tools to help students learn biological
concepts and to reinforce their knowledge. Online study aids such as practice quizzes, interactive activities, animations, labeling exercises, flashcards, and much more are organized according to the major sections of each chapter.
There is even an online tutorial service!
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ANSWER KEY
CHAPTER KEY TERMS
a. karyotype b. deletion c. duplication d. inversion
e. proteomics f. genomics g. bioinformatics h. genome
i. gene therapy j. translocation k. DNA chip l. genetic
marker m. genetic counseling n. DNA probe o. proteome p. pedigree
KEYWORD CROSSWORD
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1. karyotyping 2. a, b, c 3. a. A b. C c. C d. A e. A
f. C 4. a . inversion b. translocation c. deletion d. duplication e. deletion 5. a. (1) Aa (2) Aa (3) aa b. autosomal dominant 6. a. (1) Aa (2) Aa (3) aa b. autosomal
recessive 7. a. R b. R c. D d. D 8. dominant; Aa,
Aa; aa; aa; A? A? 9. recessive; aa, Aa; aa, A?; A?, A?
10. a. affected b. normal c. have it, have it 11. a. X b Y
b. X B X b c. X b Y
12. a. 1 b. 5 c. 2 d. 6 e. 4 f. 3 13.
a. Hh x hh b. 50% 14. a. hh b. Hh c. Hh 15. a. Cc
b. cc 16. a. X D X d x X D Y b. 50% c. 50% 17. a. protein b. DNA 18. a. 1 b. 3 c. 3 d. 2 19. a, b, c
20. Your risk of developing a particular genetic disorder,
what precautions to take, and what new medications or
what gene therapy can help. 21. (1) Remove bone marrow stem cells. (2) Use retroviruses to infect bone marrow stem cells with normal gene. (3) recombinant DNA
carries normal gene into host genome. (4) Return genetically engineered cells to patient. 22. a. In vivo b. . . .
use a viral vector to carry normal genes . . . c. . . . is not
restricted to curing genetic disease and is used to treat illnesses . . .
E
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STUDY EXERCISES
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CHAPTER TEST
1. d 2. b 3. c 4. c 5. c 6. c 7. d 8. b 9. e
10. e 11. b 12. c 13. d 14. b 15. d 16. a
17. a 18. c 19. A genetic disorder runs in the family
and you want to be sure your child will not have it.
20. Unused embryos are discarded; some people use it only
for gender selection. 21. The egg alone can not develop.
22. heterozygote 23. Under these circumstances, the
sperm might have the dominant allele for the condition
and you can’t test the sperm. Therefore, it would do no
good to test the egg for the recessive allele.
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