Chapter 47: Animal Development Flashcards
What are the 4 steps of embryonic development?
- Fertilization
- Cleavage
- Gastrulation
- Organogenesis
What is fertilization?
When the sperm enters the egg.
How does the sperm enter the egg?
Step 1:
- Vesicles inside the acrosome digest the jelly coat surrounding the egg.
Step 2:
- Actin polymerizes, creating a branch that extends from within the sperm to the sperm-binding receptors.
Step 3:
- The sperm binds to the receptors.
Step 4:
- There’s an electrochemical gradient that causes cortical granules (organelles) to fuse through the membrane, allowing the sperm to enter.
After an egg has been fertilized, what forms around the egg?
Fertilization envelope
What spreads throughout the egg once it is fertilized?
A high concentration of calcium (Ca2+) is located at the sperm’s point of entry and it spreads throughout the egg
What is cleavage?
Rapid cell division
- so rapid that some cells do not separate properly, called partitioning.
When the cells divide in cleavage, what is its arrangement called?
Blastula
What is a blastula?
When the cell is in cleavage, creating a hollow ball of cells.
What is the purpose of the blastula?
This is the hollow hole in our bodies from mouth to anus.
When does partitioning stop?
When the cells reach blastula.
What is gastrulation?
When the cells reorganize into 3 germ layers
What is the name of an egg that has reorganized its cells into 3 germ layers?
Gastrula
What are the 3 germ layers of a gastrula?
Ectoderm
Mesoderm
Endoderm
EcMeEn (Ecmeen)
How do the cells know whether to be in the ectoderm, mesoderm, or endoderm?
The cells go towards the blastopore and are randomly placed into the 3 layers
What is organogenesis?
When the cells migrate and change shape to form organs
In organogenesis, how does the outer layer of the ectoderm form?
- Within the embryo, the ectoderm makes a dip called the Neural Plate.
- The Neural Folds on either side of the plate join together.
- The outer layer of the ectoderm is formed.
Where does the Neural Tube form and what does the it become?
Underneath the Neural Folds
Head and spinal cord
What are Neural Crest Cells?
Cells underneath the Neural Plate that receive signals to know what to become.
What is cell fate?
Once a cell has been assigned to a role, it is very committed and cannot change its role.
At 64 cells, the cells are very committed.
If you were to change the cell in order to alter the fate of a cell, when would be the best time to do it?
When the embryo is only one or two cells, any more than that and it’s fate will already be decided.
What are P. granules?
Complexes of maternal RNA
The reproductive cells in C. elegans (worms).
When an egg is newly fertilized, where are the P. granules distributed? What do the P. granules do after the embryo has divided more?
- When the egg has just been fertilized, the P. granules are spread evenly throughout the egg.
- After multiple divisions, the P. Granules migrate over to the right side of the embryo.
If the P granule-expressing cell was removed from a four-cell C. elegans embryo and transferred to a different four-cell embryo which maintained its own P granule-expressing cell, what would you expect to observe in the adult organism that received the extra P granule?
A. No germ fells formed
B. Germ cells formed but mispositioned along the body axis
C. Two sites of germ cells formed
D. A worm that is twice the average size
C
What is pattern formation?
A developmental process that ensures organs develop in the correct orientation throughout the body.
What is a limb bud?
A limb bud is the early stage of a limb on an embryo.
What is the Apical Ectodermal Ridge (AER) and what does it do?
The AER is a population of cells on the top of the limb bud.
It secretes fibroblast growth factors like a gradient (highly concentrated at the AER, less concentrated towards the body of the embryo).
What are fibroblast growth factors?
Signaling molecules that tell the cells in the limb bud whether to be distal or proximal.
E.g., a hand would’ve had a high concentration of FGF, whereas a shoulder has a low concentration.
What is the Zone of Polarizing Activity (ZPA) and what does it do?
The ZPA is a zone nearer the posterior side of the limb bud.
It secretes Sonic Hedgehog (SHH) in a gradient (highly concentrated near the posterior, less so at the anterior).
What is sonic hedgehog (SHH)?
A protein that tells the cells of the limb bud whether to be anterior or posterior.
E.g., if there’s a low concentration of SHH among certain cells those cells will become the anterior side of your arm (palm facing up).
In the development of an arm, if there’s a low concentration of fibroblast growth factors but a high concentration of sonic hedgehog, what part of the arm is this most likely to be?
The posterior side of your shoulder (the side that gets the acne).
