Echinoderm Fertilization (LP.2) Flashcards
What are the 3 key events?
- Fertilization (creation of diploid zygote)
- Cell Division
- Cell movements (move inside embryo)
When does development begin for many animals & some plants?
-BEFORE FERTILIZATION= Oogenesis (egg production)
What 2 things does fertilization accomplish?
- Activates oocyte (egg) to complete its development
- Helps haploids from both parents to become diploid to then create a zygote
What is the first thing that happens in Sea Urchin fertilization?
-The Fertilization membrane lifts off the surface of the egg once the first sperm makes contact w/ it
What is the role of the Fertilization Membrane?
-To prevent Polyspermy (more than one sperm entering egg)= ensures the zygote will be diploid
What was the purpose of this lab?
-To see the stages of development of a sea star
How was gamete shredding induced?
-Via injecting the urchins with .53 M KCL
At what objective did we observe the eggs under?
10x
What occurs once the Fertilization Membrane begins to blister?
- It marks the beginning of it encompassing the whole egg
- The male pronucleus migrates towards the female pronucleus while the tail of the sperm (flagella) is left outside
What is the cleavage of sea urchin like?
-They’re Holoblastic= they cut through the entire embryo vertically (animal pole to vegetal pole) & results in 2 blastomeres
What kind of environment do Echinoderms develop from?
-From eggs with little or no yolk
What is a key characteristic of the eggs?
-They have polarity
What is the nucleus like in an Echinoderm egg?
-It is offset towards Animal pole (Top of the egg)
Where is the Vegetal Pole located on an egg?
-At the bottom
What is the 2nd cleavage like?
-It is also verticle but at a right angle to the first cleavage= results in 4 blastomeres
What is the 3rd cleavage like?
-Horizontal which cuts the 4 blastomeres into 8 blastomeres, then these blastomeres further divide to create the Morula
What is the difference between Cell Division and Cleavage?
-There is no cell growth when in cleavage= cell size decreases as the cleavage continues
What is a Blastocoel?
-The balls of cells that are in the cleavage process forming a cavity in the middle
What happens during Gastrulation?
- The cells at the vegetal plate= Primary Mesenchyme cells detach & migrate within the embryo
- Then the vegetal plate buckles inward to form the endoderm= makes archenteron (primitive gut)
What are Primary Mesenchyme cells?
-They are Mesoderm cells used in gastrulation to form the skeleton of the larvae that develops
Where is the Ectoderm located within all this process?
-It is left outside to develop into the outer regions of the larvae
What happens when the Archenteron is makin’ its way up inside the embryo?
-It makes contact w/ the sidewall of the gastrula & then breaks through that point to form the Oral Opening
What is the Blastopore?
-The original opening of the gastrula which then becomes the anus of the larvae
What family do Echinoderms belong to?
-Deutrosomes
What is the overall process then?
Zygote–>Cleavage+ more Cleavage–>Morula (16) –>Cleavage–>Blastula–>Early Gastrula–>Late Gastrula
What is a Morula?
-Compact mass of embryonic cells
What is a Blastula & what is the name of the cells surrounding it?
- Hollow ball of cells (has the cavity in the middle)
- The wall of cells around the cavity= Blastoderms
What is the cavity in the middle of a Blastula called?
-Blastocoel= has fluid
What is the difference between an Oocyte and an Egg?
-An oocyte hasn’t finished meiosis
