GAMETOGENESIS
August Weismann (1834-1914) – germ plasm vs. somatoplasm
death
reproductive life cycle
senescence
ADULT
juvenile
gametogenesis
egg
hatching or birth
sperm
ADULT
gametogenesis
fetal growth
fertilization
organogenesis
cleavage
gastrulation
FIG. 1-2
GAMETOGENESIS
What is gametogenesis (oogenesis and spermatogenesis)?
Four phases:
1.
origin and migration to the gonads
2.
germ cell multiplication
3.
meiosis
4.
final maturation prior to fertilization
Origin
amphibian
endodermal
mammal
bird
FIG. 3-1
GAMETOGENESIS
Germ cell migration routes
mammals
birds/reptiles
33 hrs.
24 hrs.
18 hrs.
4 hrs.
72 hrs.
48 hrs.
FIG. 3-3
GAMETOGENESIS
number of germ cells (millions)
Germ cell proliferation pattern
males = spermatogonia
females = oogonia
age
FIG. 3-6
GAMETOGENESIS
Germ cell meiosis
2n2c
Meiosis I
1n2c
2n4c
1n2c
1n2c
1n1c
Meiosis II
FIG. 3-7
GAMETOGENESIS
Spermatogenesis and oogenesis compared
spermatogonium
primary spermatocyte
secondary spermatocytes
spermatids
spermatazoa
2N2C
2N4C
2N2C
2N4C
oogonium
primary oocyte
(arrested meiosis I)
1N2C
1N1C
1N2C
secondary oocyte
(arrested meiosis II)
+ polar body I)
fertilization –
meiosis II completed
1N1C
+ sperm
fertilized ovum
+ polar body II
FIG. 3-8 and 3-9
SPERMATOGENESIS
Three principal phases:
1. mitosis
2.
meiosis
3.
spermiogenesis
Cell types:
1. spermatogonia
2.
primary spermatocytes
3.
secondary spermatocytes
4.
spermatids
5.
spermatozoa
FIG. 3-10
SPERMATOGENESIS
Spermiogenesis
FIG. 3-11 and 3-12
SPERMATOGENESIS
Gene expression during spermatogenesis
Sperm maturation
external fertilizers
mammals
time in the ductus epididymis
activation
capacitation
OOGENESIS
Ovarian cycle in mammals
Primordial follicle
Primary unilaminar follicle
(zona pellucida)
Primary multilaminar follicle
Secondary follicle
(antrum formation)
Tertiary (Graafian) follicle
Ovulation
Corpus luteum
Corpus albicans
Atresia
FIG. 3-21
OOGENESIS
Follicles in detail
primary follicles
antrum
follicular cells
coronary radiata
zona pellucida
secondary follicles
secondary oocyte
(arrested in meiosis II)
cumulus oophorus
tertiary follicles
FIG. 3-21
OOGENESIS
Hormonal control of mammalian (human) oogenesis
ACCESSORY COVERINGS OF EGGS
Why have coverings?
Comparison of various eggs
AMPHIBIAN
vitelline envelope
SEA URCHIN
jelly
coat
BIRD
zona pellucida
MAMMAL
corona radiata
FIG. 3-25
ACCESSORY COVERINGS OF EGGS
Vitelline envelope
glycoprotein make-up, including species-specific sperm receptors
Jelly coat
mostly polysaccharides, with some glycoproteins and peptides
Corona radiata
follicular cells surrounding zona pellucida
protective role (?)
required for transport of ovum down oviduct in some mammals
secrete estrogen, then form corpus luteum after ovulation to
secrete estrogen and progesterone
Zona pellucida
glycoprotein make-up, including species-specific sperm receptors