Fertilization

Gametes = mature sex cells

Male = sperm Female = egg or ovum Both Haploid

Sperm passage through outer layers of egg = activates embryonic development.

The egg = single cell with nucleus, cytoplasm, and cell membrane (plasma membrane).

Egg in ovary accumulates vitellogenin from the liver. Once in egg it is called yolk platelets - nourish embryo

Union of sperm and egg = zygote Diploid

Sea Urchin Fertilization:

1. sperm penetrates jelly coat and contacts vitelline envelope (above plasma membrane)

2. acrosomal process of sperm releases egg recognition protein.

3. fertilization cone appears. Changes occur that prevent polyspermy.

electrical potential change in egg membrane

4. cortical reaction - 1000's of enzyme rich cortical granules are released.

5. vitelline envelope hardens = fertilization membrane

6. sperm loses tail, nuclear envelope breaks apart and enlarged spermn or pronucleus migrates towards female pronucleus

7. fusion and diploid zygote.

8. cleavage

Pattern of cleavage affected by two things:

1. quantity of yolk and its distribution in the egg

2. genes controlling the symmetry of cleavage

Radial cleavage - cleavage planes produce cells on top of one another

Spiral cleavage - cleavage planes produce cells oblique to the animal-vegetal axis. Cells in furrows of others cells.

Radial cleavage - regulative

Spiral cleavage - mosaic

Blastulation:

blastula - cluster of cells

cavity forms in middle = blastocoel

Gastrulation:

gastrula - establishment of the body plan

a. eggs with little yolk - cell indent by invagination

cavity formed is the archenteron or primitive gut.

Movement of cells form three germ layers

outer layer = ectoderm (skin)

inner layer = endoderm (gut)

middle layer = mesoderm (coelom)

b. eggs with more yolk - movement of cells different

animal pole - many more blastomeres than vegetal pole

Vertebrate Development

Anamniotic eggs - fishes and amphibians

Amniotic eggs - reptiles, birds, and mammals

1. first extraembryonic membrane to form - yolk sac

provided both anamniotes and amniotes with food

Amniotic egg - contained three additional extraembryonic membranes:

2. amnion - fluid-filled sac that encloses the embryo; protection and aqueous environment

3. allantois - outgrowth of hindgut; respiratory surface and repository for metabolic waste as embryo grows

4. chorion - outermost membrane and encloses rest of system. Fuses with allantois as major respiratory surface = chorioallantoic membrane