Fertilization- the fusion of secondary oocyte and spermatozoon - forms a zygote

Amphimixis (both mixed together)

Fusion of the male and female pronuclei

Hyaluronidase

enzyme contained in the acrosome of each sperm that breaks down the bonds between adjacent follicle cells

Oocyte activation

involves a series of changes in the metabolic activity of the oocyte the trigger for activation is contact and fusion of the plasma membranes of the sperm and oocyte the process is accompanied by depolarization of the oocyte due toan increased permiability to sodium ions. The entry of sodium ions in turn cause a release of calcium ions from the smooth endoplasmic reticulum

The sudden rise in Ca ion levels has the following important effects

* Exocytosis of vesicles adjacent to the oocyte membrane - process called the cortical reaction- releases enzymes called zonal inhibiting proteins or ZIPs, that both inactivate the sperm receptors and harden the zona pellucida - preventing polyspermy or fertization by more than one sperm which would create a zygote that is incapable of normal development * Completion of Meiosis II and formation of the second polar body - the sperm enters the oocyte and loses its plasma membrane. Meiosis II, which began in the tertiary follicle, can now be completed because fertilization occured. The fertilized oocyte is now called an ovum * Activation of enzymes that cause a rapid increase in the cell's metabolic rate - the mRNA in the cytoplasm which where previously inactivated by special proteins are now activated so protein synthesis accelerates quickly - most of the synthesized proteins are required for development to proceed

How many chromosomes are contained within a human zygote?

46 chromosomes

Name two sperm enzymes important to secondary oocyte penetration

Hyaluronidase Acrosin

4. Amphimixis occurs and cleavage begins

Metaphase of first cleavage division

5. Cleavage begins

the first cleavage division nears completion about 30 hrs after fertilization it yields two daughter cells, each one half the size of the original zygote these cells are called blastomeres

1. Fertilization and Oocyte activation

the first step is the binding of the spermatozoon to sperm receptors in the zona pellucida - thick envelope surrounding the oocyte - this binding triggers the rupture of the acrosome the hyaluronidase and acrosin then digest a path through the zona pellucida toward the surface of the oocyte Acrosomal enzymes from multiple sperm create gaps in the corona radiata a single sperm then breaks contact with the oocyte membrane and membrane fusion occurs, triggering oocyte activation and the completion of meiosis

Fertilization

the fusion of two haploid gametes, each containing 23 chromosomes, producing a zygote that contains 46 chromosomes, the normal diploid number in a human somatic cell

3. Spindle formation and cleavage preparation

the male pronucleus develops and spindle fibers appear in preparation for the first cleavage division

2. Pronucleus formation begins

the sperm is absorbed into the cytoplasm and the femalr pronucleus develops