Test Bank for LANGMAN’S Medical Embryology 20TH by
T. W. Sadler. National Board–Style MCQs with 100%
Correct Answers and Explanations Top Rated A+
,Table of Contents
Part 1: General Embryology
● Introduction: Clinical Relevance and Historical Perspective
● Chapter 1: Introduction to Molecular Regulation and Signaling
● Chapter 2: Gametogenesis: Conversion of Germ Cells into Male and Female
Gametes
● Chapter 3: First Week of Development: Ovulation to Implantation
● Chapter 4: Second Week of Development: Bilaminar Germ Disc
● Chapter 5: Third Week of Development: Trilaminar Germ Disc
● Chapter 6: Third to Eighth Weeks: The Embryonic Period
● Chapter 7: The Gut Tube and the Body Cavities
● Chapter 8: Third Month to Birth: The Fetus and Placenta
● Chapter 9: Birth Defects and Prenatal Diagnosis
Part 2: Systems-Based Embryology
● Chapter 10: The Axial Skeleton
● Chapter 11: Muscular System
● Chapter 12: Limbs: Growth, development, and musculature
● Chapter 13: Cardiovascular System
● Chapter 14: Respiratory System
● Chapter 15: Digestive System
● Chapter 16: Urogenital System
● Chapter 17: Head and Neck
● Chapter 18: Central Nervous System
● Chapter 19: Ear:
● Chapter 20: Eye
● Chapter 21: Integumentary System
,Topic 1: Introduction to Molecular Regulation and Signaling
1. A fetus is exposed to high doses of a retinoid (Vitamin A derivative). The child is born
with defects in the hindbrain and craniofacial structures. Retinoic acid acts as a
morphogen by binding to nuclear receptors that function as:
A. G-protein coupled receptors
B. Ion channels
C. Transcription factors
D. Proteases
E. Extracellular matrix proteins
Answer>>C
Explanation: Retinoic acid (RA) is a powerful morphogen that diffuses into cells and binds
to Retinoic Acid Receptors (RARs). These complexes then bind directly to DNA regulatory
elements (RAREs) to act as transcription factors, regulating the expression of HOX genes.
2. "Homeobox" genes (HOX) are highly conserved across species. In humans, a mutation
in a HOX gene that specifies the identity of the lumbar vertebrae might result in those
vertebrae taking on the characteristics of thoracic vertebrae (e.g., growing ribs). This
phenomenon is known as:
A. Metaplasia
B. Homeotic transformation
C. Apoptosis
D. Epigenesis
E. Hyperplasia
Answer>>B
Explanation: Homeotic transformation is the conversion of one body part into another
due to mutations in HOX genes. HOX genes provide "positional value" along the
craniocaudal axis; if the code is altered, a segment develops as if it were in a different
location.
3. A study of monozygotic twins reveals that one twin has a congenital heart defect while
the other does not, despite having identical DNA sequences. The difference is aflributed to
"epigenetic" changes. Which of the following is a primary mechanism of epigenetic
regulation mentioned in Chapter 1?
, A. DNA base substitution
B. Chromosomal translocation
C. DNA methylation
D. Frame-shift mutation
E. Gene deletion
Answer>>C
Explanation: Epigenetics refers to heritable changes in gene expression that do not
involve changes to the underlying DNA sequence. The two primary mechanisms are DNA
methylation (which usually silences genes) and histone modification
(acetylation/methylation of the tails of histone proteins).
4. BMP4 (Bone Morphogenetic Protein 4) is a member of the TGF-β superfamily. During
early gastrulation, BMP4 is secreted throughout the embryonic disc to "ventralize" the
mesoderm. Its action is countered by molecules like Noggin and Chordin. This interaction
is an example of:
A. A morphogen gradient and its antagonists
B. Autocrine feedback loop
C. Steroid hormone signaling
D. Juxtacrine inhibition
E. Primary active transport
Answer>>A
Explanation: BMP4 acts as a morphogen. Its activity is restricted by antagonists (Noggin,
Chordin, Follistatin) secreted by the node (organizer). The balance between the
morphogen and its inhibitors creates the dorsal-ventral axis of the embryo.
5. A child is born with Aniridia (absence of the iris). This is caused by a mutation in the
PAX6 gene. PAX genes are characterized by a specific DNA-binding domain called the
"paired box." What is the general function of PAX genes?
A. They are structural proteins of the lens
B. They are enzymes that degrade the extracellular matrix
C. They are transcription factors that regulate organogenesis
T. W. Sadler. National Board–Style MCQs with 100%
Correct Answers and Explanations Top Rated A+
,Table of Contents
Part 1: General Embryology
● Introduction: Clinical Relevance and Historical Perspective
● Chapter 1: Introduction to Molecular Regulation and Signaling
● Chapter 2: Gametogenesis: Conversion of Germ Cells into Male and Female
Gametes
● Chapter 3: First Week of Development: Ovulation to Implantation
● Chapter 4: Second Week of Development: Bilaminar Germ Disc
● Chapter 5: Third Week of Development: Trilaminar Germ Disc
● Chapter 6: Third to Eighth Weeks: The Embryonic Period
● Chapter 7: The Gut Tube and the Body Cavities
● Chapter 8: Third Month to Birth: The Fetus and Placenta
● Chapter 9: Birth Defects and Prenatal Diagnosis
Part 2: Systems-Based Embryology
● Chapter 10: The Axial Skeleton
● Chapter 11: Muscular System
● Chapter 12: Limbs: Growth, development, and musculature
● Chapter 13: Cardiovascular System
● Chapter 14: Respiratory System
● Chapter 15: Digestive System
● Chapter 16: Urogenital System
● Chapter 17: Head and Neck
● Chapter 18: Central Nervous System
● Chapter 19: Ear:
● Chapter 20: Eye
● Chapter 21: Integumentary System
,Topic 1: Introduction to Molecular Regulation and Signaling
1. A fetus is exposed to high doses of a retinoid (Vitamin A derivative). The child is born
with defects in the hindbrain and craniofacial structures. Retinoic acid acts as a
morphogen by binding to nuclear receptors that function as:
A. G-protein coupled receptors
B. Ion channels
C. Transcription factors
D. Proteases
E. Extracellular matrix proteins
Answer>>C
Explanation: Retinoic acid (RA) is a powerful morphogen that diffuses into cells and binds
to Retinoic Acid Receptors (RARs). These complexes then bind directly to DNA regulatory
elements (RAREs) to act as transcription factors, regulating the expression of HOX genes.
2. "Homeobox" genes (HOX) are highly conserved across species. In humans, a mutation
in a HOX gene that specifies the identity of the lumbar vertebrae might result in those
vertebrae taking on the characteristics of thoracic vertebrae (e.g., growing ribs). This
phenomenon is known as:
A. Metaplasia
B. Homeotic transformation
C. Apoptosis
D. Epigenesis
E. Hyperplasia
Answer>>B
Explanation: Homeotic transformation is the conversion of one body part into another
due to mutations in HOX genes. HOX genes provide "positional value" along the
craniocaudal axis; if the code is altered, a segment develops as if it were in a different
location.
3. A study of monozygotic twins reveals that one twin has a congenital heart defect while
the other does not, despite having identical DNA sequences. The difference is aflributed to
"epigenetic" changes. Which of the following is a primary mechanism of epigenetic
regulation mentioned in Chapter 1?
, A. DNA base substitution
B. Chromosomal translocation
C. DNA methylation
D. Frame-shift mutation
E. Gene deletion
Answer>>C
Explanation: Epigenetics refers to heritable changes in gene expression that do not
involve changes to the underlying DNA sequence. The two primary mechanisms are DNA
methylation (which usually silences genes) and histone modification
(acetylation/methylation of the tails of histone proteins).
4. BMP4 (Bone Morphogenetic Protein 4) is a member of the TGF-β superfamily. During
early gastrulation, BMP4 is secreted throughout the embryonic disc to "ventralize" the
mesoderm. Its action is countered by molecules like Noggin and Chordin. This interaction
is an example of:
A. A morphogen gradient and its antagonists
B. Autocrine feedback loop
C. Steroid hormone signaling
D. Juxtacrine inhibition
E. Primary active transport
Answer>>A
Explanation: BMP4 acts as a morphogen. Its activity is restricted by antagonists (Noggin,
Chordin, Follistatin) secreted by the node (organizer). The balance between the
morphogen and its inhibitors creates the dorsal-ventral axis of the embryo.
5. A child is born with Aniridia (absence of the iris). This is caused by a mutation in the
PAX6 gene. PAX genes are characterized by a specific DNA-binding domain called the
"paired box." What is the general function of PAX genes?
A. They are structural proteins of the lens
B. They are enzymes that degrade the extracellular matrix
C. They are transcription factors that regulate organogenesis
