1. 32-3: Fertilization + Development
Occurs in series of specific, sequential stages

2. Fertilization + Early Development
Fusion of two gametes – sperm + egg
Combines 2 haploid cells = 1 diploid cell
Called a zygote
Once a zygote is formed, DNA is replicated and cell division starts

3. Fertilization + Early Development
Rapid cell division is known as cleavage
Cell increases the number of cells (2, 4, 8, etc.)
Becomes a giant hollow ball of cells (blastula) with an empty central cavity (blastocoel)

4. Gastrulation
The blastula starts to collapse inward – called a blastopore
Gastrulation
Process of changing blastula to gastrula
Creating a multilayered embryo
Marked by the changes in cell shapes

5. Let’s look at Gastrulation

6. Gastrulation (cont.)
As the infolding continues, a deep cup-shaped cavity is formed
This is called the archenteron
This cavity will give rise to the gut

7. Gastrulation (cont.) 3 germ layers emerge
Ectoderm – outer layer of gastrula
Endoderm – inner layer
Mesoderm – middle layer; between ectoderm + endoderm (in triploblast)

8. Organogenesis
Each of the germ layers formed during gastrulation develops into certain organs
ENDODERM
Lining of urinary system, reproductive system, + most of the digestive tract, pancreas, liver, lungs, + gills
ECTODERM
Outer layer of skin, hair, nails, + nervous system
MESODERM
Skeleton, muscles, inner layer of skin, circulatory system, + lining of body cavities

9. What do the 3 germ layers form?

10. Patterns of Development
Coelom
A body cavity completely lined by mesoderm
Can be used to help classify organisms

11. 3 types of Body Cavities Acoelomates Body cavity is absent
Mesoderm connects endodermic gut to outer covering

12. 3 types of Body Cavities Pseudocoelomates Means “false” body cavity
Mesoderm lines fluid-filled coelom + gut is suspended in the fluid of the coelom

13. 3 types of Body Cavities Coelomates Means a “true” body cavity
Mesoderm lines body cavity and surrounds + supports endodermic gut
Forms attachments for organs

14. 2 patterns of development
Protostome
Deuterostome
Blastopore becomes the mouth (“1st mouth”)
Blastopore becomes the anus (“2nd mouth”)
Spiral cleavage
Radial cleavage
Determinate cleavage
Indeterminate cleavage
Schizocoely – coelom up
Enterocoely – coelom down
Annelids, Arthropods, Mollusks
Echinoderms, Chordates