NYUCD General Embryology UPDATED ACTUAL Exam
Questions and CORRECT Answers - 148 Questions
This rigorous exam covers advanced concepts in gametogenesis and fertilization, including molecular
mechanisms, genetic regulation, and clinical implications. Designed to test deep conceptual understanding and
application to novel scenarios. It contains 148 multiple-choice questions, each with four distractors and a fully
worked rationale that explains why the keyed answer is correct. Content is organized into 10 focused sections:
Gametogenesis and Fertilization, Cleavage, Blastocyst Formation, and Implantation, Formation of Germ Layers
and Early Embryonic Folding, Neurulation and Development of the Nervous System, Pharyngeal Arches, Pouches,
and Clefts, Development of the Cardiovascular System, Development of the Gastrointestinal and Respiratory
Systems, Development of the Urogenital System, Development of the Musculoskeletal and Limb Systems, Placenta,
Fetal Membranes, and Twinning. Targeted learning outcomes include: Analyze the molecular and cellular events
of gametogenesis; Evaluate the mechanisms of fertilization and early embryonic development; Integrate genetic
and epigenetic regulation in germ cell formation. Every item has been reviewed for clinical accuracy, current
guidelines, and clarity so that students can study with confidence and self-correct as they work through the bank.
Use it as a high-yield review immediately before the exam, or as a structured practice tool during the unit - the
rationales double as concise teaching notes. The recommended writing time is 3 hours, with a passing score of
85%. Aligned with Meets US dental/medical school accreditation standards for basic science competency.
Section 1: Gametogenesis and Fertilization (Questions 1-15)
1 A male patient presents with azoospermia due to a mutation in the gene
encoding the catalytic subunit of protein kinase A (PKA). Which step of
spermatogenesis is most likely directly impaired?
A) Mitotic proliferation of spermatogonia
B) Meiotic recombination in primary spermatocytes
C) Acrosome formation during spermiogenesis
D) Flagellar assembly in spermatids
Answer: C
Rationale: PKA signaling is crucial for acrosome biogenesis during
spermiogenesis. Mitotic proliferation and meiotic recombination rely on
different kinases (e.g., CDKs). Flagellar assembly involves intraflagellar
transport proteins, not PKA directly.
2 In a mouse model, deletion of the gene encoding ZP3 results in female
infertility. Which step of fertilization is primarily disrupted?
A) Sperm capacitation in the female tract
B) Acrosome reaction upon zona binding
C) Sperm-zona pellucida binding
D) Fusion of sperm and oolemma
,Answer: C
Rationale: ZP3 is the primary sperm receptor in the zona pellucida; its absence
prevents initial binding. Capacitation occurs before zona contact, acrosome
reaction requires binding, and fusion involves ZP2 and other proteins.
3 A researcher observes that oocytes from a knockout mouse fail to arrest at
metaphase II after ovulation. Which protein is most likely absent?
A) Cyclin B1
B) C-mos
C) Emi2
D) APC/C
Answer: C
Rationale: Emi2 (Endogenous meiotic inhibitor 2) prevents
anaphase-promoting complex/cyclosome (APC/C) activity, maintaining
metaphase II arrest. C-mos activates MAPK pathway to stabilize Emi2; its
absence causes parthenogenetic activation. Cyclin B1 is degraded at anaphase;
APC/C promotes anaphase.
4 A couple undergoing IVF has embryos that consistently arrest at the 2-cell
stage. Analysis reveals abnormal epigenetic reprogramming. Which process
is most likely defective?
A) Genomic imprinting erasure in primordial germ cells
B) Demethylation of paternal pronucleus post-fertilization
C) X-chromosome inactivation in female embryos
D) Histone modification during oocyte maturation
Answer: B
Rationale: Zygotic genome activation occurs at the 2-cell stage and requires
proper demethylation of the paternal genome. Failure leads to transcriptional
defects. Imprinting erasure occurs earlier in PGCs; X-inactivation happens
later. Histone modifications are important but not directly linked to 2-cell
block.
5 Which of the following best explains why polyspermy is prevented in
mammals?
A) Rapid depolarization of the oocyte membrane
B) Exocytosis of cortical granules that modify the zona pellucida
,C) Release of proteases that digest sperm receptors on the oolemma
D) Formation of a fertilization envelope by the zygote
Answer: B
Rationale: In mammals, the slow block to polyspermy involves cortical granule
exocytosis releasing enzymes that cleave ZP2 and ZP3, hardening the zona.
Fast block via membrane depolarization is seen in sea urchins. Proteases act on
zona, not oolemma. Fertilization envelope is an invertebrate feature.
6 A mutation in the gene encoding SPACA1 (sperm acrosome associated 1)
leads to infertility in mice. Sperm from these mice show normal motility and
acrosome reaction but fail to fertilize. Which step is most likely impaired?
A) Sperm binding to the zona pellucida
B) Sperm-egg fusion
C) Sperm penetration through the zona
D) Sperm migration through the female tract
Answer: B
Rationale: SPACA1 is an acrosomal membrane protein involved in
sperm-oolemma fusion. Binding and penetration are unaffected because
acrosome reaction and motility are normal. Migration depends on flagellar
function.
7 During oogenesis, why do oocytes remain arrested in prophase I from fetal
life until ovulation?
A) High levels of MPF (maturation promoting factor) maintain arrest
B) cAMP-dependent PKA activity inhibits activation of MPF
C) Luteinizing hormone (LH) suppresses meiotic resumption
D) Cyclin B synthesis is completely repressed
Answer: B
Rationale: High cAMP levels in oocytes activate PKA, which phosphorylates
and inhibits CDC25, preventing MPF activation. MPF levels are low during
arrest. LH triggers resumption by reducing cAMP. Cyclin B is synthesized but
degraded; its levels are regulated.
8 A researcher treats mouse sperm with a calcium ionophore to induce
acrosome reaction in vitro. However, these sperm fail to fertilize zona-intact
eggs. What is the most likely reason?
, A) Ionophore treatment damages the sperm DNA
B) Premature acrosome reaction prevents zona binding
C) Ionophore inhibits sperm motility
D) The acrosome reaction is incomplete without zona proteins
Answer: B
Rationale: Acrosome reaction must occur after binding to the zona; premature
reaction leads to loss of acrosomal enzymes and surface proteins needed for
binding. DNA damage is not a direct effect. Motility may be unaffected. The
reaction can be complete even without zona proteins.
9 Which of the following is a direct consequence of the formation of the
second polar body during oogenesis?
A) Reduction in cytoplasmic volume of the oocyte
B) Elimination of one set of homologous chromosomes
C) Establishment of the embryonic body axes
D) Activation of the embryonic genome
Answer: B
Rationale: Second polar body formation completes meiosis II, extruding half
the chromatids (one set of sister chromatids). Cytoplasmic volume reduction is
minimal. Body axes are established later. Genome activation occurs after
fertilization, not at polar body extrusion.
10 A genetic abnormality results in sperm that lack the equatorial segment.
Which step of fertilization would be most directly affected?
A) Capacitation
B) Acrosome reaction
C) Zona penetration
D) Sperm-egg fusion
Answer: D
Rationale: The equatorial segment is the region of the sperm head that fuses
with the oolemma. Capacitation and acrosome reaction involve the anterior
acrosome. Zona penetration requires acrosomal enzymes from the anterior
head.
Questions and CORRECT Answers - 148 Questions
This rigorous exam covers advanced concepts in gametogenesis and fertilization, including molecular
mechanisms, genetic regulation, and clinical implications. Designed to test deep conceptual understanding and
application to novel scenarios. It contains 148 multiple-choice questions, each with four distractors and a fully
worked rationale that explains why the keyed answer is correct. Content is organized into 10 focused sections:
Gametogenesis and Fertilization, Cleavage, Blastocyst Formation, and Implantation, Formation of Germ Layers
and Early Embryonic Folding, Neurulation and Development of the Nervous System, Pharyngeal Arches, Pouches,
and Clefts, Development of the Cardiovascular System, Development of the Gastrointestinal and Respiratory
Systems, Development of the Urogenital System, Development of the Musculoskeletal and Limb Systems, Placenta,
Fetal Membranes, and Twinning. Targeted learning outcomes include: Analyze the molecular and cellular events
of gametogenesis; Evaluate the mechanisms of fertilization and early embryonic development; Integrate genetic
and epigenetic regulation in germ cell formation. Every item has been reviewed for clinical accuracy, current
guidelines, and clarity so that students can study with confidence and self-correct as they work through the bank.
Use it as a high-yield review immediately before the exam, or as a structured practice tool during the unit - the
rationales double as concise teaching notes. The recommended writing time is 3 hours, with a passing score of
85%. Aligned with Meets US dental/medical school accreditation standards for basic science competency.
Section 1: Gametogenesis and Fertilization (Questions 1-15)
1 A male patient presents with azoospermia due to a mutation in the gene
encoding the catalytic subunit of protein kinase A (PKA). Which step of
spermatogenesis is most likely directly impaired?
A) Mitotic proliferation of spermatogonia
B) Meiotic recombination in primary spermatocytes
C) Acrosome formation during spermiogenesis
D) Flagellar assembly in spermatids
Answer: C
Rationale: PKA signaling is crucial for acrosome biogenesis during
spermiogenesis. Mitotic proliferation and meiotic recombination rely on
different kinases (e.g., CDKs). Flagellar assembly involves intraflagellar
transport proteins, not PKA directly.
2 In a mouse model, deletion of the gene encoding ZP3 results in female
infertility. Which step of fertilization is primarily disrupted?
A) Sperm capacitation in the female tract
B) Acrosome reaction upon zona binding
C) Sperm-zona pellucida binding
D) Fusion of sperm and oolemma
,Answer: C
Rationale: ZP3 is the primary sperm receptor in the zona pellucida; its absence
prevents initial binding. Capacitation occurs before zona contact, acrosome
reaction requires binding, and fusion involves ZP2 and other proteins.
3 A researcher observes that oocytes from a knockout mouse fail to arrest at
metaphase II after ovulation. Which protein is most likely absent?
A) Cyclin B1
B) C-mos
C) Emi2
D) APC/C
Answer: C
Rationale: Emi2 (Endogenous meiotic inhibitor 2) prevents
anaphase-promoting complex/cyclosome (APC/C) activity, maintaining
metaphase II arrest. C-mos activates MAPK pathway to stabilize Emi2; its
absence causes parthenogenetic activation. Cyclin B1 is degraded at anaphase;
APC/C promotes anaphase.
4 A couple undergoing IVF has embryos that consistently arrest at the 2-cell
stage. Analysis reveals abnormal epigenetic reprogramming. Which process
is most likely defective?
A) Genomic imprinting erasure in primordial germ cells
B) Demethylation of paternal pronucleus post-fertilization
C) X-chromosome inactivation in female embryos
D) Histone modification during oocyte maturation
Answer: B
Rationale: Zygotic genome activation occurs at the 2-cell stage and requires
proper demethylation of the paternal genome. Failure leads to transcriptional
defects. Imprinting erasure occurs earlier in PGCs; X-inactivation happens
later. Histone modifications are important but not directly linked to 2-cell
block.
5 Which of the following best explains why polyspermy is prevented in
mammals?
A) Rapid depolarization of the oocyte membrane
B) Exocytosis of cortical granules that modify the zona pellucida
,C) Release of proteases that digest sperm receptors on the oolemma
D) Formation of a fertilization envelope by the zygote
Answer: B
Rationale: In mammals, the slow block to polyspermy involves cortical granule
exocytosis releasing enzymes that cleave ZP2 and ZP3, hardening the zona.
Fast block via membrane depolarization is seen in sea urchins. Proteases act on
zona, not oolemma. Fertilization envelope is an invertebrate feature.
6 A mutation in the gene encoding SPACA1 (sperm acrosome associated 1)
leads to infertility in mice. Sperm from these mice show normal motility and
acrosome reaction but fail to fertilize. Which step is most likely impaired?
A) Sperm binding to the zona pellucida
B) Sperm-egg fusion
C) Sperm penetration through the zona
D) Sperm migration through the female tract
Answer: B
Rationale: SPACA1 is an acrosomal membrane protein involved in
sperm-oolemma fusion. Binding and penetration are unaffected because
acrosome reaction and motility are normal. Migration depends on flagellar
function.
7 During oogenesis, why do oocytes remain arrested in prophase I from fetal
life until ovulation?
A) High levels of MPF (maturation promoting factor) maintain arrest
B) cAMP-dependent PKA activity inhibits activation of MPF
C) Luteinizing hormone (LH) suppresses meiotic resumption
D) Cyclin B synthesis is completely repressed
Answer: B
Rationale: High cAMP levels in oocytes activate PKA, which phosphorylates
and inhibits CDC25, preventing MPF activation. MPF levels are low during
arrest. LH triggers resumption by reducing cAMP. Cyclin B is synthesized but
degraded; its levels are regulated.
8 A researcher treats mouse sperm with a calcium ionophore to induce
acrosome reaction in vitro. However, these sperm fail to fertilize zona-intact
eggs. What is the most likely reason?
, A) Ionophore treatment damages the sperm DNA
B) Premature acrosome reaction prevents zona binding
C) Ionophore inhibits sperm motility
D) The acrosome reaction is incomplete without zona proteins
Answer: B
Rationale: Acrosome reaction must occur after binding to the zona; premature
reaction leads to loss of acrosomal enzymes and surface proteins needed for
binding. DNA damage is not a direct effect. Motility may be unaffected. The
reaction can be complete even without zona proteins.
9 Which of the following is a direct consequence of the formation of the
second polar body during oogenesis?
A) Reduction in cytoplasmic volume of the oocyte
B) Elimination of one set of homologous chromosomes
C) Establishment of the embryonic body axes
D) Activation of the embryonic genome
Answer: B
Rationale: Second polar body formation completes meiosis II, extruding half
the chromatids (one set of sister chromatids). Cytoplasmic volume reduction is
minimal. Body axes are established later. Genome activation occurs after
fertilization, not at polar body extrusion.
10 A genetic abnormality results in sperm that lack the equatorial segment.
Which step of fertilization would be most directly affected?
A) Capacitation
B) Acrosome reaction
C) Zona penetration
D) Sperm-egg fusion
Answer: D
Rationale: The equatorial segment is the region of the sperm head that fuses
with the oolemma. Capacitation and acrosome reaction involve the anterior
acrosome. Zona penetration requires acrosomal enzymes from the anterior
head.
