Animal Development I: Fertilization and Cleavage PDF

FOR GROUP 1 =========== UNIT 5 ====== Learning Outcomes ----------------- 1. list the sequence of early animal development, 2. explain the features of fertilization and cleavage, 3. differentiate between intrinsic and extrinsic factors determining cell specialization, and 4. draw and l...

FOR GROUP 1 =========== UNIT 5 ====== Learning Outcomes ----------------- 1. list the sequence of early animal development, 2. explain the features of fertilization and cleavage, 3. differentiate between intrinsic and extrinsic factors determining cell specialization, and 4. draw and label the different stages of fertilization of a sea urchin. Content ------- Fertilization -------------  1. Sperm is attracted to and contacts the zona pellucida. 2. The acrosome reaction is initiated where digestive enzymes are released and destroy the zona pellucida creating a pathway for the sperm to reach the egg (Figure 5.2). 3. The sperm reaches the egg and fuses. This process is species-specific and is mediated by sperm bindin proteins. 4. The fusion of the gametes initiates electrical depolarization that lasts for 10-20 seconds preventing any other sperm from fusing with the egg plasma membrane. Such a process is called **"fast block".** 5. Calcium is released across the plasma membrane. 6. The calcium wave initiates the cortical reaction. 7. The cortical reaction lifts the vitalline layer and creates the fertilization envelope, which serves as a barrier that prevents additional sperm from reaching the egg, and this process is the \"**slow block**\". 8. Egg activation is culminated, causing the egg to recognized that fertilization has already occurred. After which, development is initiated. Cleavage and Blastula Stage --------------------------- Determining the Body Axes -------------------------