1. Chapter 53 Sila and Kharee
Animal Develepment
Chapter 53
Sila and Kharee

2. Fertilization
Fertilization, the union of male and female gametes, is the first step in reproduction.
Sperm must penetrate to the plasma membrane
Saclike organelle named the acrosome is positioned between the plasma membrane and nucleus of sperm, digestive enzymes within create a hole in eggs membrane
The egg is protected by coats
zona pellucide (mammals)
Jelly layer (urchin, frogs)
Chorion (insects)

3. Membrane Fusion Activates the Egg
The egg remain dormant until the sperm activates it
Polyspermy: response to sperm fusion of additional sperm
Sperm penetration of egg can also cause:
Many eggs did not complete meiosis, therefore not a haploid yet, sperm penetration activates
Triggers movement of egg cytoplasm
Sharp increase of protein synthesis and metabolic activity in general

4. The Fusion of Nuclei Final Stage of Fertilization
The haploid male nuclei and the haploid female form the diploid zygote
Two nuclei migrate toward each other along a aster

6. Clevage and Blastula Stage
Cleavage: The rapid division of the zygote into a larger and larger number of smaller cells.
Blastomere: Each individual cell
Animal Pole and Vegetal Pole

7. Blastula The blastula is a hollow mass of cells
Outermost blastomeres join together through protein belt which create a seal that isolates the interior cell mass
Cleavage patterns are diverse in every animal cell

8. Cleavage Patterns
Eggs with moderate or little yolk go through Hoboblastic Cleavage (Complete)
Echinoderms
Annelids, Mollusks, and Flatworms
Eggs with Dense Yolk go through Meroblastic Cleavage (incomplete)
Fish, Reptiles, Birds
Insects

9. Cleavage in Mammals Contain little yolk
Holoblastic, forms a structure called a blastocyst
A single layer of cells surrounds a blastocoel
Inner cell mass (ICM) located at one pole of of blastocoel
Trophoblast, the outer cells, part of them enter the maternal uterus lining and forms placenta

11. Gastrulation
Gastrulation: Cells of blastula rearrange themselves to form the body plan
Forms the three germ bilayers
Converts the blastula into a bilaterally symmetrical embryo with a gut, visible anterior and posterior, and dorsal ventral axis.

13. How the Cells Move Lamellipdoa: crawl over neighbor cells
Filopodia: feel out the surfaces of other cells and pull the cell forward
Tightly attached cells move in sheets

14. Gastrulation in Chordates
The movement of surface cells into the interior, by folding as a sheet ("invagination“)
The cells of vegetal plate move inward to the blastocoel cavity
The cells produce a tube (primitive gut) called archenteron and the opening (anus)

16. Gastrulation in Amphibians
By rolling as a sheet ("involution")
Cells from animal pole move to vegetal pole
When on the dorsal lip, cells involute into interior
Movement of the cells forms a new internal cavity
Organogenesis then begins (explained later)

17. Amphibian Gastrulation

18. Gastrulation in Reptiles /Birds/ and Mammals
The Gastrulation of all are similar by internalization/separation of cells from an epithelium ("ingression "),
The embryo develops from flattened collection of cells forming two layers (endoderm and ectoderm) lower cells migrate out to line cavity to form yolk (ectoderm) mesoderm cells migrate to the interior

20. Three Germ Layers
Endoderm: formed by cells that move into embryo to form the tube of a primitive gut
Epidermis of skin, nervous system, sense organs
Ectoderm: formed by the cells that remain on the exterior
Skeleton, muscles, blood vessels, heart, blood, gonads, kidneys, dermis of skin
Mesoderm: formed by the cells that move into the space between endoderm and ectoderm
Lining of digestive and respiratory tracts, liver, pancreas, thymus, thyroid