NEWEST NYUCD GENERAL EMBRYOLOGY
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Question 1
The process by which a haploid spermatozoon and a haploid oocyte
fuse to form a diploid zygote is known as:
A) Gametogenesis
B) Fertilization
C) Cleavage
D) Implantation
Answer: B) Fertilization
Rationale: Fertilization is the fusion of male and female gametes (sperm
and oocyte) to form a diploid embryo. Gametogenesis is the process of
gamete formation. Cleavage refers to the rapid mitotic divisions of the
zygote. Implantation is the embedding of the blastocyst into the
endometrium.
Question 2
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Fertilization typically occurs in which region of the female reproductive
tract?
A) Fundus of the uterus
B) Isthmus of the uterine tube
C) Ampulla of the uterine tube
D) Infundibulum of the uterine tube
Answer: C) Ampulla of the uterine tube
Rationale: The ampulla is the widest and longest portion of the uterine
tube and is the site where fertilization most commonly occurs.
Spermatozoa reach the ampulla after capacitation, and the oocyte is
arrested at metaphase II waiting for fertilization. The isthmus is the
narrower portion nearer the uterus, and the infundibulum is the funnel-
shaped end near the ovary.
Question 3
The acrosome reaction is critical for fertilization. What is its primary
function?
A) To activate the oocyte and complete meiosis II
B) To release enzymes that digest the zona pellucida
C) To fuse the sperm membrane with the oolemma
D) To establish the block to polyspermy
Answer: B) To release enzymes that digest the zona pellucida
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Rationale: The acrosome reaction involves the release of proteolytic
enzymes (e.g., acrosin) from the sperm's acrosome. This allows the
sperm to penetrate the zona pellucida, the glycoprotein layer
surrounding the oocyte. The cortical reaction in the oocyte establishes
the block to polyspermy and sperm-egg fusion occurs after the sperm
has traversed the zona pellucida.
Question 4
Following fertilization, the zygote undergoes cleavage. Which
statement best describes cleavage?
A) A period of rapid cell division resulting in an increase in cytoplasmic
mass
B) A series of meiotic divisions that produce the blastocyst
C) A process of rapid mitotic divisions without an intervening growth
phase
D) The differentiation of the inner cell mass into the embryo
Answer: C) A process of rapid mitotic divisions without an intervening
growth phase
Rationale: Cleavage is a series of rapid mitotic divisions that occur after
fertilization. During this phase, the embryo does not grow; instead, the
large zygote is subdivided into smaller cells called blastomeres. This
maintains the overall size while increasing the number of cells, resulting
in a multicellular embryo. The cytoplasmic mass remains constant.
Question 5
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At approximately the 8-cell stage, the embryo undergoes a process
called compaction. What is the primary consequence of compaction?
A) The formation of the blastocoel
B) The separation of the embryo into inner and outer cell populations
C) The differentiation of the trophoblast
D) The initiation of the acrosome reaction
Answer: B) The separation of the embryo into inner and outer cell
populations
Rationale: Compaction involves blastomeres maximizing their contact
with each other, driven by increased E-cadherin expression and tight
junction formation. This creates an inner cell mass (ICM) and an outer
cell layer (trophectoderm), which is critical for establishing cell fate. The
blastocoel forms later. The trophoblast differentiates after blastocyst
formation.
Question 6
The blastocyst consists of two primary cell lineages. Which lineage gives
rise to the embryo proper?
A) Trophoblast
B) Trophectoderm
C) Inner Cell Mass (ICM)
D) Syncytiotrophoblast