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

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Chiasmata:Visual evidence of crossing-over,

genetic recombination

Lampbrush Chromosome:“Open” DNA structure overtly

transcribing mRNA in adiapause oocyte