Exam 2: Fertilization, Amphibian, Fish, Avian, pregnancy, Mammalian development

What are the major questions of fertilization?

How sperm and egg meet, recognize species, prevent polyspermy, and fuse nuclei

What are the main components of sperm?

Head (nucleus), flagellum (movement), acrosome (enzymes)

What is the function of the acrosome?

Releases enzymes to penetrate the egg

What is capacitation?

Process that enables sperm to fertilize the egg

What does the egg contain?

Nutrients, maternal mRNA, transcription factors, and protective molecules

How do sperm find the egg in external fertilization?

Chemotaxis via sperm-activating peptides (SAPs)

What is bindin?

Species-specific protein that allows sperm-egg binding

What is the fast block to polyspermy?

Membrane depolarization preventing sperm binding

What is the slow block to polyspermy?

Cortical granule reaction forming fertilization envelope

What triggers egg activation?

Calcium wave

What does egg activation cause?

DNA replication and cell division restart

Where does fertilization occur in mammals?

Ampulla of oviduct

What is the zona pellucida?

Glycoprotein layer surrounding egg for sperm binding

What prevents polyspermy in mammals?

Cortical granules cleaving ZP proteins

What is a hydatidiform mole?

Fertilization of an egg lacking DNA → abnormal growth

What is parthenogenesis?

Development from an unfertilized egg

What are the animal and vegetal poles?

Animal = less yolk, active division; Vegetal = more yolk, slower division

What is the gray crescent?

Region that determines dorsal axis

Why is vegetal cleavage slower?

High yolk content

What happens at the mid-blastula transition?

Zygotic gene expression begins and cells become motile

What is gastrulation?

Formation of three germ layers

What initiates gastrulation?

Dorsal lip of blastopore

What is the archenteron?

Primitive gut formed during gastrulation

What is the Spemann-Mangold organizer?

Region that induces formation of the body axis

What does the organizer do?

Forms dorsal structures and neural tissue

What molecule accumulates dorsally?

Beta-catenin

What signals help form the organizer?

VegT, Vg1, and nodal-related proteins

What is the default fate of ectoderm?

Neural tissue

What promotes epidermis instead?

BMP signaling

What inhibits BMP to form neural tissue?

Noggin and Chordin

What patterns head vs tail?

Wnt and retinoic acid gradients

What determines left-right asymmetry?

Nodal and Pitx2 signaling

What is the yolk syncytial layer (YSL)?

Nutrient layer involved in signaling

What are deep cells?

Cells that form the embryo

What is epiboly?

Expansion of cells over yolk

What is the embryonic shield?

Organizer equivalent in fish

What forms the dorsal axis?

Beta-catenin accumulation

What does Bozozok do?

Activates organizer genes and blocks inhibitors

What specifies dorsal vs ventral?

BMP (ventral) vs inhibitors like Chordin (dorsal)

What patterns anterior-posterior axis?

Wnt, FGF, and retinoic acid

What structure controls left-right asymmetry?

Kupffer's vesicle (cilia-driven flow)

What signals define left vs right?

Left = Nodal, Right = FGF

Meroblastic cleavage

Partial cleavage due to large yolk

Blastodisc

Region of cytoplasm where cleavage occurs

Calcium waves in fertilization

Trigger egg activation at each sperm entry point

Egg activation

Ca²⁺ spike resumes meiosis II and activates development

Principal sperm nucleus

The sperm nucleus that fuses with the egg nucleus

Infundibulum

Site of fertilization

Magnum

Adds albumen (egg white)

Isthmus

Forms shell membranes

Subgerminal cavity

Separates embryo from yolk

Area pellucida

Forms embryo proper

Area opaca

Forms extraembryonic tissues

Marginal zone

Helps determine cell fate

Hypoblast

Contributes to extraembryonic tissues and signaling

Epiblast

Forms the entire embryo

Primitive streak

Site where cells migrate inward

Primitive groove

Opening where cells move during gastrulation

Hensen's node

Organizer; controls body axis formation

Mesoderm formation

Cells migrate through primitive streak

Endoderm formation

First cells through primitive streak

Ectoderm formation

Remaining outer layer

Anterior mesoderm

Forms head and notochord

Middle mesoderm

Forms heart and kidneys

Posterior mesoderm

Forms extraembryonic tissues

EMT (epithelial → mesenchymal transition)

Cells become migratory during gastrulation

Epiboly

Ectoderm spreads around yolk

Yolk sac

Nutrient supply

Amnion

Surrounds embryo with fluid

Chorion

Outer protective layer

Allantois

Gas exchange and waste removal

Posterior marginal zone (PMZ)

Equivalent to Nieuwkoop center

Dorsal-ventral axis

Controlled by BMP inhibitors (Chordin, Noggin)

Anterior-posterior axis

Controlled by retinoic acid

Left-right axis

Controlled by Nodal and Pitx2

Role of pH

Creates electrical gradient for axis formation

Role of gravity

Positions embryo and defines posterior side

Infertility rates

~9% men, ~11% women

infertility Common causes

Hormonal issues, sperm problems, menstrual issues

Uterus

Site of embryo development

Endometrium

Inner lining; supports embryo

Myometrium

Smooth muscle for contractions

Cervix

Opening for sperm entry and birth

Cycle length

~28 days

menstration Controlled by

FSH, LH, estrogen, progesterone

Menstrual phase (days 1-5)

Shedding of endometrium

Proliferative phase (days 6-14)

Endometrium rebuilds

Ovulation

Egg released due to LH/FSH surge

Luteal phase

Corpus luteum secretes hormones

FSH

Stimulates follicle growth

LH

Triggers ovulation

Estrogen

Builds endometrium

Progesterone

Maintains pregnancy

hCG

Maintains corpus luteum early in pregnancy

Placenta takeover

Produces estrogen and progesterone after ~10 weeks

Gestational age

Measured from last menstrual period

Fetal age

Begins at fertilization

Full term

~40 weeks gestation

Decidua basalis

Interacts with placenta

Decidua capsularis

Covers embryo