NYUCD GENERAL EMBRYOLOGY VERIFIED EXAM SOLUTIONS -
COMPREHENSIVE QUESTIONS AND ANSWERS - CURRENT
VERSION 2026/2027
Q: What is embryology? ANSWER The study of the formation and
development of an organism from fertilization to birth.
Q: What is the pre-embryonic period? ANSWER The first two weeks of
development, from fertilization to the bilaminar disc.
Q: What is the embryonic period? ANSWER Weeks 3 to 8, when all
major organ systems are established.
Q: What is the fetal period? ANSWER Week 9 until birth, characterized
by growth and maturation of existing structures.
Q: What is meiosis? ANSWER A specialized cell division that reduces
the chromosome number from diploid (46) to haploid (23).
Q: Where does spermatogenesis occur? ANSWER In the seminiferous
tubules of the testes.
Q: What is the product of meiosis I in spermatogenesis? ANSWER Two
secondary spermatocytes.
Q: What is the product of meiosis II in spermatogenesis? ANSWER Four
spermatids, which mature into spermatozoa.
Q: Where does oogenesis occur? ANSWER In the ovarian follicles.
Q: When does meiosis I begin in oogenesis? ANSWER During fetal life,
but it arrests in prophase I until puberty.
Q: When is meiosis I completed? ANSWER Just prior to ovulation,
resulting in a secondary oocyte and a first polar body.
Q: When does meiosis II occur in oogenesis? ANSWER It is triggered by
sperm penetration and is completed only after fertilization.
Q: What is the acrosome reaction? ANSWER The release of digestive
enzymes from the sperm head to penetrate the zona pellucida.
,Q: What is the cortical reaction? ANSWER The release of cortical
granules from the oocyte to prevent polyspermy.
Q: What blocks polyspermy fast? ANSWER Depolarization of the oocyte
membrane.
Q: What blocks polyspermy slowly and permanently? ANSWER The
cortical reaction (zona reaction).
Q: What is the diplosome? ANSWER The two centrioles in the sperm
that help form the mitotic spindle in the zygote.
Q: What does the sperm contribute to the zygote genetically? ANSWER
23 chromosomes (including either an X or Y).
Q: What does the oocyte contribute to the zygote? ANSWER 23
chromosomes, mitochondria, ribosomes, and most cytoplasm.
Q: Define totipotency. ANSWER The ability of a cell to differentiate into
any cell type, including extraembryonic membranes (e.g., zygote).
Q: Define pluripotency. ANSWER The ability of a cell to differentiate into
any of the three germ layers, but not extraembryonic membranes (e.g.,
inner cell mass).
Q: What is the normal karyotype of a human male? ANSWER 46, XY.
Q: What is the normal karyotype of a human female? ANSWER 46, XX.
Q: What is the role of SRY? ANSWER Sex-determining region on the Y
chromosome; triggers testis development.
Q: What is parthenogenesis? ANSWER Development of an embryo from
an oocyte without fertilization (does not occur naturally in humans).
Q: What is a zygote? ANSWER The single cell formed by the fusion of
sperm and oocyte.
Q: How long does it take for the zygote to reach the uterus? ANSWER
Approximately 3 to 4 days.
Q: What is cleavage? ANSWER A series of rapid mitotic divisions of the
zygote without growth in size.
Q: What are blastomeres? ANSWER The daughter cells produced by
cleavage of the zygote.
, Q: What is a morula? ANSWER A solid ball of 12-32 blastomeres,
resembling a mulberry.
Part 2: Implantation & Early Placenta (31-60)
Q: When does the morula enter the uterine cavity? ANSWER Around
day 4.
Q: What fluid transforms the morula into a blastocyst? ANSWER Fluid
secreted by the blastomeres (uterine fluid also contributes).
Q: What are the two parts of the blastocyst? ANSWER The embryoblast
(inner cell mass) and the trophoblast (outer cell mass).
Q: What does the embryoblast form? ANSWER The embryo proper.
Q: What does the trophoblast form? ANSWER The fetal portion of the
placenta.
Q: What is the blastocoel? ANSWER The fluid-filled cavity inside the
blastocyst.
Q: When does implantation normally begin? ANSWER Day 6.
Q: Where does implantation normally occur? ANSWER The posterior
superior wall of the uterus.
Q: What part of the blastocyst attaches to the endometrium? ANSWER
The embryonic pole (where the inner cell mass is located).
Q: What hormone prepares the endometrium for implantation?
ANSWER Progesterone.
Q: What is the decidua? ANSWER The functional layer of the
endometrium during pregnancy.
Q: What is the decidua basalis? ANSWER The part of the decidua
directly beneath the embryo (forms maternal part of placenta).
Q: What is the decidua capsularis? ANSWER The part of the decidua
that covers the blastocyst.
Q: What is the decidua parietalis? ANSWER The remaining decidua
lining the rest of the uterine cavity.
Q: What are the two layers of the trophoblast? ANSWER
Cytotrophoblast (inner) and syncytiotrophoblast (outer).
COMPREHENSIVE QUESTIONS AND ANSWERS - CURRENT
VERSION 2026/2027
Q: What is embryology? ANSWER The study of the formation and
development of an organism from fertilization to birth.
Q: What is the pre-embryonic period? ANSWER The first two weeks of
development, from fertilization to the bilaminar disc.
Q: What is the embryonic period? ANSWER Weeks 3 to 8, when all
major organ systems are established.
Q: What is the fetal period? ANSWER Week 9 until birth, characterized
by growth and maturation of existing structures.
Q: What is meiosis? ANSWER A specialized cell division that reduces
the chromosome number from diploid (46) to haploid (23).
Q: Where does spermatogenesis occur? ANSWER In the seminiferous
tubules of the testes.
Q: What is the product of meiosis I in spermatogenesis? ANSWER Two
secondary spermatocytes.
Q: What is the product of meiosis II in spermatogenesis? ANSWER Four
spermatids, which mature into spermatozoa.
Q: Where does oogenesis occur? ANSWER In the ovarian follicles.
Q: When does meiosis I begin in oogenesis? ANSWER During fetal life,
but it arrests in prophase I until puberty.
Q: When is meiosis I completed? ANSWER Just prior to ovulation,
resulting in a secondary oocyte and a first polar body.
Q: When does meiosis II occur in oogenesis? ANSWER It is triggered by
sperm penetration and is completed only after fertilization.
Q: What is the acrosome reaction? ANSWER The release of digestive
enzymes from the sperm head to penetrate the zona pellucida.
,Q: What is the cortical reaction? ANSWER The release of cortical
granules from the oocyte to prevent polyspermy.
Q: What blocks polyspermy fast? ANSWER Depolarization of the oocyte
membrane.
Q: What blocks polyspermy slowly and permanently? ANSWER The
cortical reaction (zona reaction).
Q: What is the diplosome? ANSWER The two centrioles in the sperm
that help form the mitotic spindle in the zygote.
Q: What does the sperm contribute to the zygote genetically? ANSWER
23 chromosomes (including either an X or Y).
Q: What does the oocyte contribute to the zygote? ANSWER 23
chromosomes, mitochondria, ribosomes, and most cytoplasm.
Q: Define totipotency. ANSWER The ability of a cell to differentiate into
any cell type, including extraembryonic membranes (e.g., zygote).
Q: Define pluripotency. ANSWER The ability of a cell to differentiate into
any of the three germ layers, but not extraembryonic membranes (e.g.,
inner cell mass).
Q: What is the normal karyotype of a human male? ANSWER 46, XY.
Q: What is the normal karyotype of a human female? ANSWER 46, XX.
Q: What is the role of SRY? ANSWER Sex-determining region on the Y
chromosome; triggers testis development.
Q: What is parthenogenesis? ANSWER Development of an embryo from
an oocyte without fertilization (does not occur naturally in humans).
Q: What is a zygote? ANSWER The single cell formed by the fusion of
sperm and oocyte.
Q: How long does it take for the zygote to reach the uterus? ANSWER
Approximately 3 to 4 days.
Q: What is cleavage? ANSWER A series of rapid mitotic divisions of the
zygote without growth in size.
Q: What are blastomeres? ANSWER The daughter cells produced by
cleavage of the zygote.
, Q: What is a morula? ANSWER A solid ball of 12-32 blastomeres,
resembling a mulberry.
Part 2: Implantation & Early Placenta (31-60)
Q: When does the morula enter the uterine cavity? ANSWER Around
day 4.
Q: What fluid transforms the morula into a blastocyst? ANSWER Fluid
secreted by the blastomeres (uterine fluid also contributes).
Q: What are the two parts of the blastocyst? ANSWER The embryoblast
(inner cell mass) and the trophoblast (outer cell mass).
Q: What does the embryoblast form? ANSWER The embryo proper.
Q: What does the trophoblast form? ANSWER The fetal portion of the
placenta.
Q: What is the blastocoel? ANSWER The fluid-filled cavity inside the
blastocyst.
Q: When does implantation normally begin? ANSWER Day 6.
Q: Where does implantation normally occur? ANSWER The posterior
superior wall of the uterus.
Q: What part of the blastocyst attaches to the endometrium? ANSWER
The embryonic pole (where the inner cell mass is located).
Q: What hormone prepares the endometrium for implantation?
ANSWER Progesterone.
Q: What is the decidua? ANSWER The functional layer of the
endometrium during pregnancy.
Q: What is the decidua basalis? ANSWER The part of the decidua
directly beneath the embryo (forms maternal part of placenta).
Q: What is the decidua capsularis? ANSWER The part of the decidua
that covers the blastocyst.
Q: What is the decidua parietalis? ANSWER The remaining decidua
lining the rest of the uterine cavity.
Q: What are the two layers of the trophoblast? ANSWER
Cytotrophoblast (inner) and syncytiotrophoblast (outer).
