Chapter 47: Animal Development

Question 1

What are the 4 steps of embryonic development?

Answer 1

1. Fertilization
2. Cleavage
3. Gastrulation
4. Organogenesis

Question 2

What is fertilization?

Answer 2

When the sperm enters the egg.

Question 3

How does the sperm enter the egg?

Answer 3

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.

Question 4

After an egg has been fertilized, what forms around the egg?

Answer 4

Fertilization envelope

Question 5

What spreads throughout the egg once it is fertilized?

Answer 5

A high concentration of calcium (Ca2+) is located at the sperm’s point of entry and it spreads throughout the egg

Question 6

What is cleavage?

Answer 6

Rapid cell division

- so rapid that some cells do not separate properly, called partitioning.

Question 7

When the cells divide in cleavage, what is its arrangement called?

Answer 7

Blastula

Question 8

What is a blastula?

Answer 8

When the cell is in cleavage, creating a hollow ball of cells.

Question 9

What is the purpose of the blastula?

Answer 9

This is the hollow hole in our bodies from mouth to anus.

Question 10

When does partitioning stop?

Answer 10

When the cells reach blastula.

Question 11

What is gastrulation?

Answer 11

When the cells reorganize into 3 germ layers

Question 12

What is the name of an egg that has reorganized its cells into 3 germ layers?

Answer 12

Gastrula

Question 13

What are the 3 germ layers of a gastrula?

Answer 13

Ectoderm
Mesoderm
Endoderm

EcMeEn (Ecmeen)

Question 14

How do the cells know whether to be in the ectoderm, mesoderm, or endoderm?

Answer 14

The cells go towards the blastopore and are randomly placed into the 3 layers

Question 15

What is organogenesis?

Answer 15

When the cells migrate and change shape to form organs

Question 16

In organogenesis, how does the outer layer of the ectoderm form?

Answer 16

• 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.

Question 17

Where does the Neural Tube form and what does the it become?

Answer 17

Underneath the Neural Folds

Head and spinal cord

Question 18

What are Neural Crest Cells?

Answer 18

Cells underneath the Neural Plate that receive signals to know what to become.

Question 19

What is cell fate?

Answer 19

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.

Question 20

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?

Answer 20

When the embryo is only one or two cells, any more than that and it’s fate will already be decided.

Question 21

What are P. granules?

Answer 21

Complexes of maternal RNA

The reproductive cells in C. elegans (worms).

Question 22

When an egg is newly fertilized, where are the P. granules distributed? What do the P. granules do after the embryo has divided more?

Answer 22

• 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.

Question 23

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

Answer 23

C

Question 24

What is pattern formation?

Answer 24

A developmental process that ensures organs develop in the correct orientation throughout the body.

Question 25

What is a limb bud?

Answer 25

A limb bud is the early stage of a limb on an embryo.

Question 26

What is the Apical Ectodermal Ridge (AER) and what does it do?

Answer 26

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).

Question 27

What are fibroblast growth factors?

Answer 27

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.

Question 28

What is the Zone of Polarizing Activity (ZPA) and what does it do?

Answer 28

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).

Question 29

What is sonic hedgehog (SHH)?

Answer 29

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).

Question 30

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?

Answer 30

The posterior side of your shoulder (the side that gets the acne).