TEST BANK FOR HUMAN GENETICS 14TH EDITION BY
RICKI LEWIS | 300 Q&A Complete Chapters Practice Exam
Questions & Detailed Answers
Section 1: Questions 1–100
1. The human genome consists of approximately how many protein-encoding genes?
A. 3,000
B. 10,000
C. 20,000
D. 100,000
Rationale: The human genome contains approximately 20,000 protein-encoding genes,
far fewer than the earlier estimate of 100,000, reflecting the complexity of gene
regulation and alternative splicing.
2. Which part of the human genome consists of highly repetitive sequences that do not
encode proteins?
A. Exons
B. Introns
C. Noncoding DNA
D. Promoters
Rationale: The vast majority of the human genome is noncoding DNA, including
repetitive sequences, regulatory elements, and introns. Only about 1.5% of the genome
encodes proteins.
3. A karyotype reveals 47 chromosomes with an extra copy of chromosome 21. This
finding is diagnostic of:
A. Turner syndrome
B. Klinefelter syndrome
C. Down syndrome
D. Edwards syndrome
Rationale: Trisomy 21 (47,XX,+21 or 47,XY,+21) is the chromosomal basis of Down
syndrome, caused by nondisjunction during meiosis.
4. During which phase of meiosis does crossing over occur?
A. Prophase I
B. Metaphase I
C. Anaphase I
D. Prophase II
Rationale: Crossing over occurs during prophase I of meiosis, when homologous
chromosomes pair and exchange genetic material at chiasmata.
5. A couple has a child with cystic fibrosis, an autosomal recessive disorder. Both
parents are unaffected. What is the probability that their next child will be affected?
, A. 0%
B. 25%
C. 25%
D. 50%
Rationale: Both parents must be carriers (heterozygotes). For two carriers, each child
has a 25% chance of being affected, 50% chance of being a carrier, and 25% chance of
being unaffected and non-carrier.
6. In a pedigree, an affected individual with an autosomal dominant disorder has one
affected parent. What is the probability that each offspring will inherit the disorder?
A. 25%
B. 50%
C. 75%
D. 100%
Rationale: An affected individual with an autosomal dominant disorder typically has
one mutant allele. Each offspring has a 50% chance of inheriting the mutant allele and
being affected.
7. A male with an X-linked recessive disorder has children with a female who is
homozygous normal. What is the expected outcome for their sons?
A. 50% affected
B. 100% affected
C. 0% affected
D. 25% affected
Rationale: Sons inherit their X chromosome from their mother. Since the mother is
homozygous normal, all sons will inherit a normal X chromosome and be unaffected.
Daughters will be carriers.
8. Which of the following is an example of a multifactorial trait?
A. Blood type
B. Cystic fibrosis
C. Height
D. Huntington's disease
Rationale: Height is a classic multifactorial (polygenic) trait influenced by multiple
genes and environmental factors, showing continuous variation in populations.
9. A woman is a carrier of the BRCA1 mutation. Which cancer is she at significantly
increased risk for developing?
A. Lung cancer
B. Breast and ovarian cancer
C. Colon cancer
D. Pancreatic cancer
Rationale: BRCA1 mutations confer a markedly increased lifetime risk of breast and
ovarian cancer, often prompting enhanced surveillance or prophylactic surgery.
10. Which enzyme is responsible for joining Okazaki fragments during DNA replication?
A. Helicase
B. DNA polymerase
, C. DNA ligase
D. Primase
Rationale: DNA ligase seals the nicks between Okazaki fragments on the lagging
strand, creating a continuous DNA molecule.
11. A mutation that changes a codon for an amino acid to a stop codon is called a:
A. Missense mutation
B. Nonsense mutation
C. Silent mutation
D. Frameshift mutation
Rationale: A nonsense mutation creates a premature stop codon, resulting in a
truncated and typically nonfunctional protein.
12. Which of the following is an example of a trinucleotide repeat expansion disorder?
A. Cystic fibrosis
B. Huntington's disease
C. Sickle cell anemia
D. Tay-Sachs disease
Rationale: Huntington's disease is caused by expansion of a CAG trinucleotide repeat in
the HTT gene, leading to progressive neurodegeneration.
13. A couple of Ashkenazi Jewish descent is considering carrier screening. Which
disorder is most appropriate to include in the screening panel?
A. Sickle cell anemia
B. Tay-Sachs disease
C. Thalassemia
D. Hemophilia
Rationale: Tay-Sachs disease has a significantly higher carrier frequency in the
Ashkenazi Jewish population, making carrier screening particularly appropriate.
14. A woman with a family history of breast cancer undergoes genetic testing and is
found to have a BRCA2 mutation. Which statement reflects appropriate genetic
counseling?
A. "You will definitely develop breast cancer."
B. "This mutation increases your risk, but does not guarantee you will develop
cancer."
C. "You should not have children."
D. "Your daughters are not at risk."
Rationale: BRCA mutations are risk factors, not deterministic. Genetic counseling
should communicate increased risk while acknowledging incomplete penetrance.
15. A karyotype shows a Robertsonian translocation involving chromosomes 14 and 21.
What is the clinical significance?
A. The individual has Down syndrome.
B. The individual may be a carrier of a translocation that can cause Down
syndrome in offspring.
C. The individual has Turner syndrome.
D. The individual has no risk of genetic disorders.
, Rationale: A Robertsonian translocation between 14 and 21 can lead to unbalanced
gametes and offspring with translocation Down syndrome. Carriers are typically
phenotypically normal.
16. Which of the following best describes a balanced translocation?
A. Loss of genetic material
B. Exchange of material between nonhomologous chromosomes without net
loss or gain
C. Duplication of a chromosome segment
D. Deletion of a chromosome
Rationale: A balanced translocation involves exchange of segments between
nonhomologous chromosomes with no net gain or loss of genetic material.
17. Mitochondrial DNA is inherited:
A. From both parents equally
B. Only from the mother
C. Only from the father
D. Randomly from either parent
Rationale: Mitochondrial DNA is maternally inherited because sperm mitochondria are
typically destroyed after fertilization.
18. A patient with Leber hereditary optic neuropathy (LHON) asks about the inheritance
pattern. The nurse should explain:
A. "It is inherited in an autosomal dominant pattern."
B. "It is caused by mitochondrial DNA mutations and is inherited from the
mother."
C. "It is an X-linked recessive disorder."
D. "It is not inherited; it occurs spontaneously."
Rationale: LHON is a mitochondrial disorder caused by mutations in mitochondrial
DNA, inherited maternally.
19. In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele is
0.2. What is the frequency of carriers (heterozygotes)?
A. 0.04
B. 0.32
C. 0.64
D. 0.16
Rationale: q = 0.2, p = 0.8. Carrier frequency = 2pq = 2(0.8)(0.2) = 0.32.
20. Which evolutionary force introduces new alleles into a population?
A. Genetic drift
B. Mutation
C. Gene flow
D. Natural selection
Rationale: Mutation is the ultimate source of new genetic variation in a population.
Drift, gene flow, and selection alter existing allele frequencies.
21. A small population is founded by a few individuals who happen to carry an unusually
high frequency of a rare allele. This is an example of:
RICKI LEWIS | 300 Q&A Complete Chapters Practice Exam
Questions & Detailed Answers
Section 1: Questions 1–100
1. The human genome consists of approximately how many protein-encoding genes?
A. 3,000
B. 10,000
C. 20,000
D. 100,000
Rationale: The human genome contains approximately 20,000 protein-encoding genes,
far fewer than the earlier estimate of 100,000, reflecting the complexity of gene
regulation and alternative splicing.
2. Which part of the human genome consists of highly repetitive sequences that do not
encode proteins?
A. Exons
B. Introns
C. Noncoding DNA
D. Promoters
Rationale: The vast majority of the human genome is noncoding DNA, including
repetitive sequences, regulatory elements, and introns. Only about 1.5% of the genome
encodes proteins.
3. A karyotype reveals 47 chromosomes with an extra copy of chromosome 21. This
finding is diagnostic of:
A. Turner syndrome
B. Klinefelter syndrome
C. Down syndrome
D. Edwards syndrome
Rationale: Trisomy 21 (47,XX,+21 or 47,XY,+21) is the chromosomal basis of Down
syndrome, caused by nondisjunction during meiosis.
4. During which phase of meiosis does crossing over occur?
A. Prophase I
B. Metaphase I
C. Anaphase I
D. Prophase II
Rationale: Crossing over occurs during prophase I of meiosis, when homologous
chromosomes pair and exchange genetic material at chiasmata.
5. A couple has a child with cystic fibrosis, an autosomal recessive disorder. Both
parents are unaffected. What is the probability that their next child will be affected?
, A. 0%
B. 25%
C. 25%
D. 50%
Rationale: Both parents must be carriers (heterozygotes). For two carriers, each child
has a 25% chance of being affected, 50% chance of being a carrier, and 25% chance of
being unaffected and non-carrier.
6. In a pedigree, an affected individual with an autosomal dominant disorder has one
affected parent. What is the probability that each offspring will inherit the disorder?
A. 25%
B. 50%
C. 75%
D. 100%
Rationale: An affected individual with an autosomal dominant disorder typically has
one mutant allele. Each offspring has a 50% chance of inheriting the mutant allele and
being affected.
7. A male with an X-linked recessive disorder has children with a female who is
homozygous normal. What is the expected outcome for their sons?
A. 50% affected
B. 100% affected
C. 0% affected
D. 25% affected
Rationale: Sons inherit their X chromosome from their mother. Since the mother is
homozygous normal, all sons will inherit a normal X chromosome and be unaffected.
Daughters will be carriers.
8. Which of the following is an example of a multifactorial trait?
A. Blood type
B. Cystic fibrosis
C. Height
D. Huntington's disease
Rationale: Height is a classic multifactorial (polygenic) trait influenced by multiple
genes and environmental factors, showing continuous variation in populations.
9. A woman is a carrier of the BRCA1 mutation. Which cancer is she at significantly
increased risk for developing?
A. Lung cancer
B. Breast and ovarian cancer
C. Colon cancer
D. Pancreatic cancer
Rationale: BRCA1 mutations confer a markedly increased lifetime risk of breast and
ovarian cancer, often prompting enhanced surveillance or prophylactic surgery.
10. Which enzyme is responsible for joining Okazaki fragments during DNA replication?
A. Helicase
B. DNA polymerase
, C. DNA ligase
D. Primase
Rationale: DNA ligase seals the nicks between Okazaki fragments on the lagging
strand, creating a continuous DNA molecule.
11. A mutation that changes a codon for an amino acid to a stop codon is called a:
A. Missense mutation
B. Nonsense mutation
C. Silent mutation
D. Frameshift mutation
Rationale: A nonsense mutation creates a premature stop codon, resulting in a
truncated and typically nonfunctional protein.
12. Which of the following is an example of a trinucleotide repeat expansion disorder?
A. Cystic fibrosis
B. Huntington's disease
C. Sickle cell anemia
D. Tay-Sachs disease
Rationale: Huntington's disease is caused by expansion of a CAG trinucleotide repeat in
the HTT gene, leading to progressive neurodegeneration.
13. A couple of Ashkenazi Jewish descent is considering carrier screening. Which
disorder is most appropriate to include in the screening panel?
A. Sickle cell anemia
B. Tay-Sachs disease
C. Thalassemia
D. Hemophilia
Rationale: Tay-Sachs disease has a significantly higher carrier frequency in the
Ashkenazi Jewish population, making carrier screening particularly appropriate.
14. A woman with a family history of breast cancer undergoes genetic testing and is
found to have a BRCA2 mutation. Which statement reflects appropriate genetic
counseling?
A. "You will definitely develop breast cancer."
B. "This mutation increases your risk, but does not guarantee you will develop
cancer."
C. "You should not have children."
D. "Your daughters are not at risk."
Rationale: BRCA mutations are risk factors, not deterministic. Genetic counseling
should communicate increased risk while acknowledging incomplete penetrance.
15. A karyotype shows a Robertsonian translocation involving chromosomes 14 and 21.
What is the clinical significance?
A. The individual has Down syndrome.
B. The individual may be a carrier of a translocation that can cause Down
syndrome in offspring.
C. The individual has Turner syndrome.
D. The individual has no risk of genetic disorders.
, Rationale: A Robertsonian translocation between 14 and 21 can lead to unbalanced
gametes and offspring with translocation Down syndrome. Carriers are typically
phenotypically normal.
16. Which of the following best describes a balanced translocation?
A. Loss of genetic material
B. Exchange of material between nonhomologous chromosomes without net
loss or gain
C. Duplication of a chromosome segment
D. Deletion of a chromosome
Rationale: A balanced translocation involves exchange of segments between
nonhomologous chromosomes with no net gain or loss of genetic material.
17. Mitochondrial DNA is inherited:
A. From both parents equally
B. Only from the mother
C. Only from the father
D. Randomly from either parent
Rationale: Mitochondrial DNA is maternally inherited because sperm mitochondria are
typically destroyed after fertilization.
18. A patient with Leber hereditary optic neuropathy (LHON) asks about the inheritance
pattern. The nurse should explain:
A. "It is inherited in an autosomal dominant pattern."
B. "It is caused by mitochondrial DNA mutations and is inherited from the
mother."
C. "It is an X-linked recessive disorder."
D. "It is not inherited; it occurs spontaneously."
Rationale: LHON is a mitochondrial disorder caused by mutations in mitochondrial
DNA, inherited maternally.
19. In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele is
0.2. What is the frequency of carriers (heterozygotes)?
A. 0.04
B. 0.32
C. 0.64
D. 0.16
Rationale: q = 0.2, p = 0.8. Carrier frequency = 2pq = 2(0.8)(0.2) = 0.32.
20. Which evolutionary force introduces new alleles into a population?
A. Genetic drift
B. Mutation
C. Gene flow
D. Natural selection
Rationale: Mutation is the ultimate source of new genetic variation in a population.
Drift, gene flow, and selection alter existing allele frequencies.
21. A small population is founded by a few individuals who happen to carry an unusually
high frequency of a rare allele. This is an example of:
