GAMETOGENESIS

August Weismann (1834-1914) – germ plasm vs. somatoplasm

death

ADULT

senescence

ADULT

gametogenesis gametogenesis

egg sperm

fertilization

cleavage gastrulation

organogenesis

fetal growth

hatching or birth

juvenile

repr

oduc

tive

life

cycl

e

FIG. 1-2

GAMETOGENESIS

What is gametogenesis (oogenesis and spermatogenesis)?Four phases:

1. origin and migration to the gonads2. germ cell multiplication3. meiosis 4. final maturation prior to fertilization

FIG. 3-1

Originendodermal

amphibian

mammalbird

GAMETOGENESIS

Germ cell migration routesmammals

FIG. 3-3

birds/reptiles

4 hrs.

33 hrs.

24 hrs.

18 hrs.

72 hrs.

48 hrs.

GAMETOGENESIS

Germ cell proliferation patternmales = spermatogonia

FIG. 3-6

females = oogonia

age

num

ber o

f ger

m c

ells

(mill

ions

)

GAMETOGENESIS

Germ cell meiosis

FIG. 3-7

Meiosis I

Meiosis II

1n1c1n2c1n2c

2n4c

2n2c

1n2c

GAMETOGENESIS

Spermatogenesis and oogenesis compared

FIG. 3-8 and 3-9

spermatogonium

primary spermatocyte

secondary spermatocytes

spermatids

spermatazoa

oogonium

primary oocyte(arrested meiosis I)

fertilized ovum+ polar body II

secondary oocyte(arrested meiosis II)+ polar body I)

2N2C 2N2C

2N4C

1N2C

1N1C

2N4C

1N2C

fertilization – meiosis II completed

1N1C+ sperm

SPERMATOGENESIS

Three principal phases: 1. mitosis 2. meiosis 3. spermiogenesis

FIG. 3-10

Cell types: 1. spermatogonia 2. primary spermatocytes 3. secondary spermatocytes 4. spermatids 5. spermatozoa

Spermiogenesis

FIG. 3-11 and 3-12

SPERMATOGENESIS

Gene expression during spermatogenesis

SPERMATOGENESIS

Sperm maturationexternal fertilizersmammals

time in the ductus epididymisactivationcapacitation

OOGENESIS

Ovarian cycle in mammals

FIG. 3-21

Primordial folliclePrimary unilaminar follicle (zona pellucida)Primary multilaminar follicleSecondary follicle (antrum formation)Tertiary (Graafian) follicleOvulationCorpus luteumCorpus albicansAtresia

FIG. 3-21

OOGENESIS

Follicles in detail

primary follicles

tertiary follicles

secondary follicles

antrum

coronary radiata

cumulus oophorus

zona pellucida

secondary oocyte(arrested in meiosis II)

follicular cells

Hormonal control of mammalian (human) oogenesis

OOGENESIS

ACCESSORY COVERINGS OF EGGS

Why have coverings?

FIG. 3-25

Comparison of various eggs

MAMMAL

BIRD

vitelline envelope

jelly coat

zona pellucida

corona radiata

AMPHIBIAN

SEA URCHIN

Corona radiatafollicular cells surrounding zona pellucidaprotective role (?)required for transport of ovum down oviduct in some mammalssecrete estrogen, then form corpus luteum after ovulation to

secrete estrogen and progesterone

ACCESSORY COVERINGS OF EGGS

Vitelline envelopeglycoprotein make-up, including species-specific sperm receptors

Jelly coatmostly polysaccharides, with some glycoproteins and peptides

Zona pellucidaglycoprotein make-up, including species-specific sperm receptors