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Embryology of the OvaryBiology of Reproduction
ZOO 4926Spring 2008
Outline1. Origin and migration of primordial germ cells2. Formation of basic gonad architecture3. Proliferation of oogonia and formation of
syncytium4. Oogenesis and Folliculogenesis
Red= origin of primordial germ cells inmultiple species
Origin and migration ofprimordial germ cells
(similar in almost all animals)
3-week human
4-week human
Female Male
Formation of basicgonad architecture
1. Germ cells2. Somatic gonad derived cells3. Mesonephros derived cells
8 weekhuman
7 weekhuman
Medulla: inner part Cortex: outermost layer
16-20 weekhuman
20-24 weekhuman
4 month human
Proliferation ofoogonia and formation
of syncytium
Syncytium: a large cell-likestructure filled with cytoplasm
containing many nuclei.
Cytokinesis: the processwhereby the cytoplasm of a single
cell is divided to spawn twodaughter cells
Meiotic prophase I
http://embryology.med.unsw.edu.au/Notes/images/week1/ovary/oocytenumber.jpg
Programmed germ celldeath is normal and
frequent
Folliculogenesis: maturation of a ovarian follicle
Oogenesis: creation and differentiation of an ovum
Embryonicdevelopment
Embryonicdevelopment
Meiotic prophase I
MeioticProphase I
Leptotene: Chromosomes condense andhomologs begin to align,
Zygotene: Full homologous chromosomesalignment, “synapsis” forming “tetrads” (4N)
Pachytene: Crossing over occurs, though notvisible
Diplotene: Homologous chromosomes pullapart, but stay connected a chiasmata
•Diapause arrest of meiosis until puberty•However, mRNA is synthesized and stored
Interphase: DNA replication 2N->4NFormation of sister chromatids
www.answers.com/topic/meiosis
Cyst Breakdown, Follicle Formation &
Recombination
Cys
t Bre
akdo
wn,
Fo
llicle
For
mat
ion
& R
ecom
bina
tion
Chiasmata:Visual evidence of crossing-over,
genetic recombination
Lampbrush Chromosome:“Open” DNA structure overtly
transcribing mRNA in adiapause oocyte
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