Test Bank For Langman’s Medical
Embryology (Twelfth Edition) by T. W.
Sadler.
National Board–Style MCQs with 100% Correct
Answers and Explanations
,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 researcher identifies a mutation in a regulatory sequence located 50
kilobases upstream of a gene essential for limb development. Although the
gene's coding sequence (exons) is normal, the gene is not expressed in the
developing limb bud. This regulatory sequence, which can act at a distance to
increase the rate of transcription, is most likely a(n):
A. Promoter
B. Enhancer
C. Silencer
D. Splice site
E. Transcription factor
Correct Answer: B
Explanation: Enhancers are regulatory elements of DNA that can be located far upstream,
downstream, or even within an intron of a gene. They bind transcription factors to increase the rate
of transcription by looping the DNA to interact with the promoter. Unlike promoters, which are
immediately adjacent to the gene, enhancers are tissue-specific and act at a distance.
2. A newborn is diagnosed with a specific form of Wilms tumor. Genetic analysis reveals that the
WT1 gene is present, but the variety of protein isoforms produced is significantly reduced
compared to healthy controls. This defect most likely involves which of the following processes? A.
DNA methylation
B. Histone acetylation
C. Alternative splicing
D. Protein phosphorylation
E. Gene duplication
Correct Answer: C
Explanation: Alternative splicing allows a single gene to produce multiple different proteins
(isoforms) by selecting different combinations of exons. The WT1 gene is a classic example where
different splice variants have distinct roles in renal and gonadal development. Defects in this process
result in a loss of functional diversity in proteins.
, 3. During the process of induction, a signal from the notochord induces the overlying ectoderm to
become the neural plate. If the responding ectodermal cells lack the specific cell-surface receptors to
recognize the signaling molecule, they are said to lack:
A. Induction
B. Determination
C. Competence
D. Differentiation
E. Specification
Correct Answer: C
Explanation: Competence is the ability of a "responder" cell to react to an inductive signal from an
"inducer." It requires the responder to have the appropriate molecular machinery, such as receptors
and signal transduction components, to interpret the signal.
4. A child is born with holoprosencephaly, a severe midline defect of the brain and face. The
underlying molecular cause is a "haploinsufficiency" of a signaling molecule that normally establishes
the midline. Which pathway is most likely affected?
A. Wnt pathway
B. Fibroblast Growth Factor (FGF) pathway
C. Notch pathway
D. Sonic Hedgehog (Shh) pathway
E. Transforming Growth Factor-beta (TGF-β) pathway
Correct Answer: D
Explanation: Sonic Hedgehog (Shh) is the "master gene" for midline patterning in the CNS. Loss of
one Shh allele (haploinsufficiency) or interference with its signaling (e.g., by cholesterol inhibitors)
prevents the brain from dividing into two hemispheres, leading to holoprosencephaly.
5. A patient presents with a rare skeletal dysplasia characterized by the premature fusion of cranial
sutures (craniosynostosis). The condition is traced to a "gain-of-function" mutation in a receptor that
normally regulates mesenchymal cell proliferation and differentiation through tyrosine kinase
activity. This receptor belongs to which family?
A. Hedgehog receptors (Patched)
B. Fibroblast Growth Factor Receptors (FGFRs)
Embryology (Twelfth Edition) by T. W.
Sadler.
National Board–Style MCQs with 100% Correct
Answers and Explanations
,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 researcher identifies a mutation in a regulatory sequence located 50
kilobases upstream of a gene essential for limb development. Although the
gene's coding sequence (exons) is normal, the gene is not expressed in the
developing limb bud. This regulatory sequence, which can act at a distance to
increase the rate of transcription, is most likely a(n):
A. Promoter
B. Enhancer
C. Silencer
D. Splice site
E. Transcription factor
Correct Answer: B
Explanation: Enhancers are regulatory elements of DNA that can be located far upstream,
downstream, or even within an intron of a gene. They bind transcription factors to increase the rate
of transcription by looping the DNA to interact with the promoter. Unlike promoters, which are
immediately adjacent to the gene, enhancers are tissue-specific and act at a distance.
2. A newborn is diagnosed with a specific form of Wilms tumor. Genetic analysis reveals that the
WT1 gene is present, but the variety of protein isoforms produced is significantly reduced
compared to healthy controls. This defect most likely involves which of the following processes? A.
DNA methylation
B. Histone acetylation
C. Alternative splicing
D. Protein phosphorylation
E. Gene duplication
Correct Answer: C
Explanation: Alternative splicing allows a single gene to produce multiple different proteins
(isoforms) by selecting different combinations of exons. The WT1 gene is a classic example where
different splice variants have distinct roles in renal and gonadal development. Defects in this process
result in a loss of functional diversity in proteins.
, 3. During the process of induction, a signal from the notochord induces the overlying ectoderm to
become the neural plate. If the responding ectodermal cells lack the specific cell-surface receptors to
recognize the signaling molecule, they are said to lack:
A. Induction
B. Determination
C. Competence
D. Differentiation
E. Specification
Correct Answer: C
Explanation: Competence is the ability of a "responder" cell to react to an inductive signal from an
"inducer." It requires the responder to have the appropriate molecular machinery, such as receptors
and signal transduction components, to interpret the signal.
4. A child is born with holoprosencephaly, a severe midline defect of the brain and face. The
underlying molecular cause is a "haploinsufficiency" of a signaling molecule that normally establishes
the midline. Which pathway is most likely affected?
A. Wnt pathway
B. Fibroblast Growth Factor (FGF) pathway
C. Notch pathway
D. Sonic Hedgehog (Shh) pathway
E. Transforming Growth Factor-beta (TGF-β) pathway
Correct Answer: D
Explanation: Sonic Hedgehog (Shh) is the "master gene" for midline patterning in the CNS. Loss of
one Shh allele (haploinsufficiency) or interference with its signaling (e.g., by cholesterol inhibitors)
prevents the brain from dividing into two hemispheres, leading to holoprosencephaly.
5. A patient presents with a rare skeletal dysplasia characterized by the premature fusion of cranial
sutures (craniosynostosis). The condition is traced to a "gain-of-function" mutation in a receptor that
normally regulates mesenchymal cell proliferation and differentiation through tyrosine kinase
activity. This receptor belongs to which family?
A. Hedgehog receptors (Patched)
B. Fibroblast Growth Factor Receptors (FGFRs)
