Germ Cells and FertilizationLecture 30 BSCI 420, 421 Nov 11, 2002
“The final aim of all love intrigues, be they comic or tragic,is the composition of the next generation”
- A. Schopenhauer
1. Sexual reproduction2. Meiosis3. Oogenesis4. Spermatogenesis5. Fertilization
1. Sexual reproduction
Has an advantage over asexual reproduction:
Increases diversity by producing offspring that are a mixture of the traits of the parents.
Is diversity an advantage?
If so,Why is diversity an advantage?
1. Meiosis
A pair of nuclear divisions that produce four different haploid cells, usually but not always gametes.
Gametes are haploid cells capable of fusing to produceA diploid cell called a Zygote.
Gametes can be of identical size and shape (isogamy).Or they can be different in size and or shape (anisogamy).
4. Spermatogenesis
Spermatozoon is a small, highly streamlined cell,specialized to deliver a nucleus to an egg far away, and to activate development of the egg.
5. Fertilization
Involves:a. Activation of the sperm and the acrosomal reaction
b. Activation of the egg
1. The fast block to polyspermy
2. The slow block to polyspermy
3. Initiation of protein, RNA, & DNA synthesis
4. Fusion of the egg and sperm and male and femalepronuclei
Activation of the sperm:
Contact wZonaPellucida
AggregatesReceptors
Opens Na+Channels
Release ofV change opens Exocytosis lytic enzymesVS Ca2+ Ca2+ of AcrosomalChannels influx vesicle Exposure
of fertilins
b. Egg Activation: 1. Fast block to polyspermy
Sperm binding to Egg cell membraneBy fertilin and its receptor on egg
Receptor linked Na+ channels open
Na+ influx
Membrane potential change 0
Fast block to polyspermy-70 1 2
(Discovered by mV time, minE.E. Just contactAfro-Amer Dev.Biologist)
Starfish egg injected with the dye aequorin that fluorescesWhen the Ca2+ conc increases.
At time 0, the egg was fertilized, and a wave of Ca2+ sweepsOver the egg in about 1 min. initiating cortical granule Exocytosis and the slow block to polyspermy.
2. Slow block to polyspermy
Binding of fertilin to receptor on egg
Tyrosine kinase activation (both IP3 gated& Ca-Induced)
Phospholipase C-activation IP3 Ca2+ release
DAG production PKC activation Cortical granuleexocytosis
Stimulation of Slow block to3. protein syn polyspermy
RNA synDNA synthesis