GENETICS EXAM QUESTIONS AND
CORRECT SOLUTIONS
Which would NOT be an effective way to diagnose
sickle cell anemia?
A Enzymatic assay for hemoglobin activity.
B PCR exon 1 of the b-globin gene, followed by ASO
hybridization with oligonucleotides specific for normal
and betaS alleles.
C Restriction digest of genomic DNA with MstII,
followed by Southern blot, using a b-globin gene
product.
D PCR exon 1 of the b-globin gene, followed by
restriction digest with MstII.
E Hemoglobin electrophoresis.
A
All of the following provide supporting evidence for
the clonal origin of a tumor EXCEPT:
A All cells from the tumor carry exactly 46
chromosomes.
B All cells from the tumor carry the same abnormal
chromosome.
C In a person heterozygous for a particular DNA
polymorphism, all tumor cells show reduction to
homozygosity for the same marker allele.
D All cells from the tumor carry an identical
rearrangement of the immunoglobin gene cluster.
E The tumor is from a female heterozygous for a G6PD
,polymorphism. All of the cells from the tumor express
the same G6PD allele.
A
Which of the following conditions should not occur in
a single individual:
A Both b-thalassemia and hemoglobin SC disease.
B A total of 5 copies of the a-globin gene sequence
(aaa/aa).
C Both a-thalassemia and hemoglobin SS disease.
D Both a-thalassemia and hemoglobin SC disease.
E Both a-thalassemia and b-thalassemia.
A
If 1 out of every 250,000 people have Disease X, a
nonlethal autosomal recessive disorder, what is the
approximate carrier frequency of this disease?
(Assume Hardy-Weinberg equilibrium.)
A 1/1000
B 1/500
C 1/250
D 1/50
E 1/25
C
Why is b-thalassemia major usually evident only after
birth?
A The fetal Hb persists after birth when it should have
been shut off.
B The product of the b-globin pseudogene is highly
expressed only after birth.
C The switch from g-gene to b-gene expression
occurs around the time of birth.
D The Hb subunits encoded by the a cluster (which
,has two copies of the a-globin gene) are sufficient
until after birth.
E The mother's normal red blood cells provide oxygen
to the fetus in utero.
C
Which of the following observations is the strongest
evidence for an important genetic component in the
causation of type-1 diabetes mellitus (IDDM)?
A Pancreatic b-cell autoantibodies are frequently
present.
B Approximately 10% of affected indivifuals have an
affected sibling.
C Onset of disease is usually in childhood.
D The concordance rate in monozygotic twins is
approximately 30%.
E The concordance rate in monozygotic twins is five
times that in dizygotic twins.
E
Consider an autosomal recessive disease with an
incidence of 1/10,000 in the general population
(assume 100,000 people in Ann Arbor). Your best
friend comes to you very upset--he has just taken a
screening test for this disease and gotten a positive
result. He is convinced he is a carrier, despite having
no family history of the disease. You try to reassure
him, but he says, "Don't bother. The Clinic said this
test has 98% sensitivity and 90% specificity. With that
level of sensitivity, it must be correct!" What is the
chance your friend is NOT a carrier?
A 2%
B 10%
, C 17%
D 49%
E 83%
E
Severe b-thalassemia may not become clinically
apparent until a child is several months old because:
A The oxygen needs of a newborn are minimal.
B The a-globin genes don't turn on until several
months after birth.
C Overexpression of z-globin (zeta) compensates for
the missing b-chain.
D The g (gamma) to b-globin switch is not complete
until several months after birth.
E Elevated hemoglobin A2 compensates for the
missing b-globin genes.
D
All of the following karyotypes are found in
spontaneous abortuses. Which of the following is
least likely to be found in a live-born infant?
A 46, XY
B 45, X
C 47, XX, +21
D 47, XX, +16
E 69, XXX
D
You would appropriately suspect a possible collagen
disorder in a patient who has any of the following
symptoms except:
A joint hypermobility or laxity
B rupture of the bowel
C blue sclerae
CORRECT SOLUTIONS
Which would NOT be an effective way to diagnose
sickle cell anemia?
A Enzymatic assay for hemoglobin activity.
B PCR exon 1 of the b-globin gene, followed by ASO
hybridization with oligonucleotides specific for normal
and betaS alleles.
C Restriction digest of genomic DNA with MstII,
followed by Southern blot, using a b-globin gene
product.
D PCR exon 1 of the b-globin gene, followed by
restriction digest with MstII.
E Hemoglobin electrophoresis.
A
All of the following provide supporting evidence for
the clonal origin of a tumor EXCEPT:
A All cells from the tumor carry exactly 46
chromosomes.
B All cells from the tumor carry the same abnormal
chromosome.
C In a person heterozygous for a particular DNA
polymorphism, all tumor cells show reduction to
homozygosity for the same marker allele.
D All cells from the tumor carry an identical
rearrangement of the immunoglobin gene cluster.
E The tumor is from a female heterozygous for a G6PD
,polymorphism. All of the cells from the tumor express
the same G6PD allele.
A
Which of the following conditions should not occur in
a single individual:
A Both b-thalassemia and hemoglobin SC disease.
B A total of 5 copies of the a-globin gene sequence
(aaa/aa).
C Both a-thalassemia and hemoglobin SS disease.
D Both a-thalassemia and hemoglobin SC disease.
E Both a-thalassemia and b-thalassemia.
A
If 1 out of every 250,000 people have Disease X, a
nonlethal autosomal recessive disorder, what is the
approximate carrier frequency of this disease?
(Assume Hardy-Weinberg equilibrium.)
A 1/1000
B 1/500
C 1/250
D 1/50
E 1/25
C
Why is b-thalassemia major usually evident only after
birth?
A The fetal Hb persists after birth when it should have
been shut off.
B The product of the b-globin pseudogene is highly
expressed only after birth.
C The switch from g-gene to b-gene expression
occurs around the time of birth.
D The Hb subunits encoded by the a cluster (which
,has two copies of the a-globin gene) are sufficient
until after birth.
E The mother's normal red blood cells provide oxygen
to the fetus in utero.
C
Which of the following observations is the strongest
evidence for an important genetic component in the
causation of type-1 diabetes mellitus (IDDM)?
A Pancreatic b-cell autoantibodies are frequently
present.
B Approximately 10% of affected indivifuals have an
affected sibling.
C Onset of disease is usually in childhood.
D The concordance rate in monozygotic twins is
approximately 30%.
E The concordance rate in monozygotic twins is five
times that in dizygotic twins.
E
Consider an autosomal recessive disease with an
incidence of 1/10,000 in the general population
(assume 100,000 people in Ann Arbor). Your best
friend comes to you very upset--he has just taken a
screening test for this disease and gotten a positive
result. He is convinced he is a carrier, despite having
no family history of the disease. You try to reassure
him, but he says, "Don't bother. The Clinic said this
test has 98% sensitivity and 90% specificity. With that
level of sensitivity, it must be correct!" What is the
chance your friend is NOT a carrier?
A 2%
B 10%
, C 17%
D 49%
E 83%
E
Severe b-thalassemia may not become clinically
apparent until a child is several months old because:
A The oxygen needs of a newborn are minimal.
B The a-globin genes don't turn on until several
months after birth.
C Overexpression of z-globin (zeta) compensates for
the missing b-chain.
D The g (gamma) to b-globin switch is not complete
until several months after birth.
E Elevated hemoglobin A2 compensates for the
missing b-globin genes.
D
All of the following karyotypes are found in
spontaneous abortuses. Which of the following is
least likely to be found in a live-born infant?
A 46, XY
B 45, X
C 47, XX, +21
D 47, XX, +16
E 69, XXX
D
You would appropriately suspect a possible collagen
disorder in a patient who has any of the following
symptoms except:
A joint hypermobility or laxity
B rupture of the bowel
C blue sclerae
