Gametogenesis & The Cycle
A 19-year-old woman is learning about oogenesis. She is told that all of her primary oocytes were formed during fetal life and remained arrested until puberty. In which stage are primary oocytes arrested?
A. Prophase I
B. Metaphase I
C. Anaphase I
D. Prophase II
E. Metaphase II
Answer: A — Prophase I
Explanation: Primary oocytes enter meiosis I during fetal life and remain dormant in prophase I from approximately month 5 of fetal life until puberty. The secondary oocyte, in contrast, arrests in metaphase II.
During an IVF procedure, a sperm penetrates the zona pellucida of a secondary oocyte. A reaction subsequently makes the oocyte impermeable to additional sperm. Which mechanism is responsible?
A. Capacitation
B. Acrosomal reaction
C. Cortical reaction
D. Cleavage
E. Compaction
Answer: C — Cortical reaction
Explanation: Penetration of the zona pellucida triggers the cortical reaction, which makes the secondary oocyte impermeable to additional sperm and thereby prevents polyspermy. This mechanism is specifically tested in Sankova’s question bank.
A woman undergoing IVF has an embryo transferred into her uterus on day 5 after fertilization. The embryo has developed a fluid-filled cavity and is preparing for implantation. Which developmental stage is present?
A. Zygote
B. Blastomere
C. Morula
D. Blastocyst
E. Gastrula
Answer: D — Blastocyst
Explanation: By this stage, the conceptus has progressed from the morula into a blastocyst. The blastocyst is the developmental stage that implants into the uterine wall.
During week 3, an embryo undergoes a developmental process that transforms its bilaminar disc into a trilaminar disc containing ectoderm, mesoderm, and endoderm. Which process is occurring?
A. Cleavage
B. Implantation
C. Gastrulation
D. Folding
E. Capacitation
Answer: C — Gastrulation
Explanation: Gastrulation converts the bilaminar embryonic disc into the trilaminar germ disc, establishing ectoderm, mesoderm, and endoderm.
A pregnant woman is exposed to a potentially damaging agent while her embryo is undergoing organogenesis. During which developmental period is the embryo maximally susceptible to teratogens?
A. Weeks 1–2
B. Weeks 3–8
C. Weeks 9–16
D. Weeks 17–24
E. Weeks 25–38
Answer: B — Weeks 3–8
Explanation: The embryonic period, weeks 3–8, is the period of maximum susceptibility because organ morphogenesis is occurring. Weeks 1–2 are the resistant/all-or-none period, while weeks 9–38 have lowered susceptibility and exposure generally produces functional derangement.
A 24-year-old woman with a regular 28-day menstrual cycle undergoes testing around day 14. Her physician confirms that ovulation has just occurred. Which cell was released from the mature ovarian follicle?
A. Oogonium
B. Primary oocyte
C. Secondary oocyte
D. Mature ovum
E. Primordial germ cell
Answer: C — Secondary oocyte
Explanation: Before ovulation, the primary oocyte completes meiosis I and becomes a secondary oocyte (23, 2N). The secondary oocyte enters meiosis II, arrests in metaphase II, and is the cell released at ovulation.
A 28-year-old woman becomes pregnant following successful IVF. Her physician explains that fusion of the male and female pronuclei produced a zygote. Which chromosome number should this cell contain?
A. 23
B. 44
C. 46
D. 69
E. 92
Answer: C — 46 chromosomes
Explanation: Fertilization restores the diploid chromosome number. Fusion of the male and female pronuclei produces a 46-chromosome zygote.
A blastocyst reaches the uterus but remains completely surrounded by the zona pellucida. Which change is necessary before normal implantation can occur?
A. Formation of the primitive streak
B. Degeneration of the zona pellucida
C. Closure of the posterior neuropore
D. Formation of somites
E. Completion of gastrulation
Answer: B — Degeneration of the zona pellucida
Explanation: The zona pellucida normally degenerates/disappears around days 4–5 after conception. Its disappearance is necessary for the blastocyst to implant. Sankova’s question bank similarly tests shedding of the zona pellucida before implantation.
During week 3, epiblast cells migrate inward through a newly formed structure. Some cells displace the hypoblast to form embryonic endoderm, while others form embryonic mesoderm. Which structure are these cells migrating through?
A. Neural tube
B. Primitive streak
C. Notochord
D. Somite
E. Yolk stalk
Answer: B — Primitive streak
Explanation: During gastrulation, epiblast cells migrate through the primitive streak. Some form embryonic mesoderm, others replace the hypoblast to form embryonic endoderm, and the epiblast cells remaining at the surface become ectoderm.
A conceptus is exposed to a teratogen 1 week after fertilization. The physician explains that exposure at this stage generally results in either death of the conceptus or survival without an abnormality. Which phenomenon describes this response?
A. Cortical reaction
B. Compaction
C. All-or-none phenomenon
D. Gastrulation
E. Neurulation
Answer: C — All-or-none phenomenon
Explanation: During weeks 1–2, the conceptus is in the resistant period. Sankova describes this as the all-or-none phenomenon: the conceptus either dies from the teratogenic exposure or survives unaffected.
A 30-year-old woman undergoing fertility evaluation has an ovarian ultrasound shortly before ovulation. A follicle measuring approximately 20 mm with a fully developed antrum is identified. Which stage of follicular development is present?
A. Primordial follicle
B. Primary follicle
C. Secondary follicle
D. Graafian follicle
E. Corpus luteum
Answer: D — Graafian follicle
Explanation: The mature vesicular/Graafian follicle has a fully developed antrum and is at least approximately 10 mm. Sankova’s question bank specifically uses a 20-mm follicle to test recognition of a Graafian follicle.
During an assisted reproductive procedure, a sperm successfully fertilizes a secondary oocyte that had been arrested in metaphase II. Which event occurs as a direct consequence of fertilization?
A. Primary oocyte completes meiosis I
B. Secondary oocyte completes meiosis II
C. Secondary oocyte enters meiosis I
D. Zona pellucida begins to form
E. Oogonia begin mitosis
Answer: B — Secondary oocyte completes meiosis II
Explanation: Fertilization stimulates the secondary oocyte to complete meiosis II, producing the mature ovum and second polar body. Sankova’s review specifically lists completion of meiosis II as a result of fertilization.
A 29-year-old woman has regular ovulation but difficulty becoming pregnant. Her physician explains that fertilization may occur normally, but inadequate hormone production after ovulation could prevent the endometrium from becoming suitable for implantation. Which hormone is most important in this situation?
A. FSH
B. LH
C. Progesterone
D. GnRH
E. hCG
Answer: C — Progesterone
Explanation: Progesterone from the corpus luteum prepares the endometrium for implantation. Sankova uses essentially this same fertility scenario in her question bank to test the requirement for adequate corpus-luteum progesterone.
A newborn has a severe neural tube defect involving the lumbosacral region. The mother reports taking a potentially damaging medication during pregnancy. Exposure during which developmental week would most directly coincide with failure of neural tube closure?
A. Week 1
B. Week 2
C. Week 4
D. Week 16
E. Week 32
Answer: C — Week 4
Explanation: Neural tube closure occurs during weeks 3–4, with the neuropores closing during week 4. Sankova uses essentially this same clinical structure in her question bank, asking students to connect a neural tube defect with exposure during week 4.
Routine antenatal ultrasonography reveals a mass in the sacrococcygeal region of a fetus. The mass contains incompletely differentiated bone, nerve, and hair. Persistence of which embryonic structure most likely caused this lesion?
A. Notochord
B. Neural tube
C. Primitive streak
D. Yolk stalk
E. Amnion
Answer: C — Primitive streak
Explanation: A sacrococcygeal teratoma arises from remnants of the primitive streak, which normally degenerates and disappears by the end of week 4. Because the primitive streak participates in formation of the germ layers, these tumors may contain incompletely differentiated tissues such as bone, nerve, and hair.
A 29-year-old woman is evaluated for infertility. She ovulates normally, but laboratory studies show inadequate progesterone production during the second half of her menstrual cycle. Dysfunction of which structure most likely explains this finding?
A. Primary follicle
B. Secondary follicle
C. Corpus luteum
D. Corpus albicans
E. Corona radiata
Answer: C — Corpus luteum
Explanation: After ovulation, LH transforms the collapsed follicular wall into the corpus luteum. The corpus luteum produces mainly progesterone, which prepares the endometrium for implantation.
A 30-year-old woman undergoes successful IVF. The embryologist observes repeated cleavage divisions of the zygote. Although the number of cells rapidly increases, the overall size of the developing conceptus does not increase. Which statement best explains this observation?
A. Blastomeres enlarge after each division
B. Total cytoplasmic volume remains essentially constant
C. DNA replication does not occur
D. The zona pellucida immediately disappears
E. The zygote accumulates additional cytoplasm
Answer: B — Total cytoplasmic volume remains essentially constant
Explanation: During cleavage, the zygote undergoes repeated mitotic divisions while its cytoplasm is divided among progressively smaller blastomeres. Sankova’s own IVF-style question specifically tests that the overall size/cytoplasmic volume remains essentially constant during cleavage.
A woman with a positive pregnancy test presents with lower abdominal pain and vaginal bleeding. Imaging reveals that the blastocyst implanted outside the uterine cavity. Which location is the most common site of an ectopic pregnancy according to the review?
A. Ovary
B. Abdominal cavity
C. Ampulla of the uterine tube
D. Cervix
E. Posterior uterine wall
Answer: C — Ampulla of the uterine tube
Explanation: Sankova’s review identifies the ampulla of the uterine tube as the most common site of ectopic pregnancy. Tubal ectopic pregnancy can result when transport of the blastocyst toward the uterus is delayed.
A pregnant woman has an elevated maternal serum AFP. Further evaluation reveals failure of the cranial end of the neural tube to close during week 4. Which abnormality is most likely?
A. Sacrococcygeal teratoma
B. Spina bifida with rachischisis
C. Anencephaly
D. Ectopic pregnancy
E. Placenta previa
Answer: C — Anencephaly
Explanation: Anencephaly results from failure of the anterior neuropore to close during week 4. The review describes failure of brain development and the bony cranial vault and notes that NTDs may be associated with elevated AFP.
A developmental abnormality selectively affects the portion of paraxial mesoderm that normally contributes to formation of the vertebrae and ribs. Which component is affected?
A. Dermatome
B. Myotome
C. Sclerotome
D. Intermediate mesoderm
E. Lateral plate mesoderm
Answer: C — Sclerotome
Explanation: Paraxial mesoderm forms somites. The sclerotome forms the axial skeleton, including vertebrae and ribs. The myotome forms skeletal muscles of the trunk and limbs, while the dermatome contributes to the dermis.
A woman with a normal 28-day cycle does not become pregnant following ovulation. Approximately 10–12 days later, the temporary ovarian endocrine structure responsible for progesterone secretion degenerates. Which sequence correctly describes what happens next?
A. Corpus luteum → Graafian follicle → menstruation
B. Corpus luteum → corpus albicans → decline in progesterone
C. Corpus albicans → corpus luteum → increased progesterone
D. Graafian follicle → corpus luteum of pregnancy → menstruation
E. Corpus luteum → secondary follicle → increased estrogen
Answer: B — Corpus luteum → corpus albicans → decline in progesterone
Explanation: Without fertilization, the corpus luteum degenerates after approximately 10–12 days and ultimately becomes the corpus albicans. Loss of corpus luteum function decreases progesterone support of the endometrium.
An embryologist follows a fertilized oocyte as it develops while traveling toward the uterus. Which sequence correctly describes its progression toward the stage capable of implantation?
A. Zygote → morula → blastomeres → blastocyst
B. Blastomeres → zygote → blastocyst → morula
C. Zygote → blastomeres → morula → blastocyst
D. Morula → zygote → blastomeres → blastocyst
E. Zygote → blastocyst → morula → blastomeres
Answer: C — Zygote → blastomeres → morula → blastocyst
Explanation: Cleavage begins with the zygote, producing progressively smaller blastomeres. At approximately 16 cells the conceptus is a morula; accumulation of fluid and formation of a cavity then produces the blastocyst. This sequence appears directly in Sankova’s question bank.
An embryologist examines a normally developing conceptus during the second week. The embryoblast has differentiated into two layers, and the trophoblast has also differentiated into two layers. Which combination is correct?
A. Ectoderm + mesoderm; cytotrophoblast + epiblast
B. Epiblast + hypoblast; cytotrophoblast + syncytiotrophoblast
C. Epiblast + mesoderm; hypoblast + syncytiotrophoblast
D. Endoderm + ectoderm; cytotrophoblast + hypoblast
E. Epiblast + endoderm; mesoderm + cytotrophoblast
Answer: B — Epiblast + hypoblast; cytotrophoblast + syncytiotrophoblast
Explanation: Week 2 is the “week of twos.” The embryoblast becomes the epiblast and hypoblast, while the trophoblast differentiates into cytotrophoblast and syncytiotrophoblast. Two major cavities—the amniotic cavity and yolk sac—are also present.
A newborn has an open neural tube defect in the lumbosacral region and paralysis below the lesion. Which developmental event most likely failed?
A. Anterior neuropore closure on days 24–25
B. Posterior neuropore closure on days 27–28
C. Primitive streak disappearance at the end of week 4
D. Formation of the bilaminar disc during week 2
E. Zona pellucida degeneration on days 4–5
Answer: B — Posterior neuropore closure on days 27–28
Explanation: Failure of the posterior neuropore to close produces spina bifida with rachischisis. Sankova’s review gives posterior neuropore closure at approximately days 27–28, around the 25-somite stage. The lesion is usually lumbosacral and may produce paralysis below the defect.
A researcher examines an embryo during week 4. Rapid growth of the neural tube, somites, and amnion is accompanied by repositioning of the yolk sac, heart, and developing body cavities. The initially flat trilaminar disc becomes a cylindrical three-dimensional body. Which developmental mechanism is responsible?
A. Gastrulation
B. Embryonic folding
C. Neurulation
D. Primitive streak regression
E. Implantation
Answer: B — Embryonic folding
Explanation: During week 4, craniocaudal and lateral embryonic folding transform the flat 2D trilaminar disc into a 3D cylindrical embryo and help establish the gut, body wall, and body cavities. This is extremely close to how Sankova herself frames the concept in her question bank: rapid growth and repositioning during week 4 → identify embryonic folding.