Development Two (Test Two)

Question 1

Development is largely under the control of what?

Answer 1

gene expression

Question 2

Generally, how do cells differentiate themselves?

Answer 2

Cells differentiate themselves by expressing different sets of genes, which are determined by cytoplasmic specification, and induction.

What genes are expressed will guide the cells’ behavior and allow them to communicate with neighboring cells, which will coordinate development.

Question 3

Explain the role of Cytoplasmic Specification in the process of cell differentiation.

Answer 3

The role of cytoplasmic specification is that since fertilized eggs contains a cytoplasm that is unequally distributed, the “information” (cytoplasmic components) that a newly divided cell inherits vary, and this vital information will influence the commitment of a cell to a particular cell type, and specify which type of cell it can become.

Question 4

What is embryonic induction, how does it work, and why is it important?

Answer 4

Induction is the (positional) extracellular information that is received from the cells surroundings.

One cell releases a signal that binds to a receptor on another cell, which will change its fate.

It is important because the fate of a cell depends on its interactions with neighboring cells

Question 5

Thinking long-term, how does an inductor cell affect the rest of development for a particular cell?

Answer 5

1. Once an inductor cell sets in motion a specific developmental pattern in other cells, other inductions follow
2. Each step in the developmental system is a necessary preliminary event for the next step.

Question 6

Give a real example of induction / cytoplasmic specification in a liver cell / neuron.

Answer 6

The cytoplasmic components inherited and induction affect which genes will be expressed in a cell.

For a liver cell, it’s cytoplasmic specification, and the interactions with neighboring cells affected its gene expression so that the gene for alcohol dehydrogenase is turned on and the neurotransmitter gene is turned off.

Question 7

What is a clear indicator of common ancestry in vertebrates?

Answer 7

The commonality in the embryonic stages.

Question 8

What are the five ancestral traits of chordates, known as the chordate hallmarks?

Answer 8

1. Dorsal neural tube (spinal cord)
2. Notochord (discs) lost in humans
3. Pharyngeal gill pouches and aortic arches (becomes mouth)
4. Ventral heart
5. Postanal tail

Question 9

What are amniotes?

Answer 9

Amniotes are a group of animals that have embryos that develop within the amnion sac.

Question 10

Explain what an amnion sac is, and what it does for the embryo.

Answer 10

It is a fluid-filled sac that encloses the embryo.

1. It provides an aqueous environment in which the embryo floats
2. It serves as protection from shock and adhesions

Question 11

Why is protecting against adhesions so especially important?

Answer 11

Because, things will stick to a developing embryo and the embryo will absorb them, which is disastrous.

Question 12

Describe the structure of an amniotic egg.

(draw the picture and then check)

Answer 12

From outside in, goes:

1. The shell
2. The shell membrane
3. The chorion
4. The yolk sac (below the amnion)
5. Allantois (next to the amnion)
6. The amnion (with embryo inside)

Question 13

Explain the chorion membrane.

Answer 13

The chorion lies under the egg shell and encloses the embryo and all the other membranes.

Question 14

Explain the yolk sac.

Answer 14

The yolk sac is a membrane that pre-dates amniotes by millions of years and is found in all fish embryos.

It stores the yolk that sustains the embryo

Question 15

Explain the allantois.

Answer 15

The allantois is a membrane that stores metabolic waste during development.

It also serves as the respiratory surface for exchange of oxygen and carbon dioxide.

Question 16

What happens when the embryo grown in regards to gas exchange?

Answer 16

The need for oxygen increases and the allantois and the chorion fuse to form a respiratory surface called the chorioallantoic membrane.

Question 17

Why is the amniotic egg so significant to development and evolution?

Answer 17

1. It provides a complete life support system for the embryo
2. The evolution of the shelled amniotic egg made internal fertilization a requirement.
3. Requiring internal fertilization had many repercussions in evolution

Question 18

What proportion of mammals have a placenta?

Answer 18

94% of the class mammalia

Question 19

How did evolution of the placenta for embryonic development change things?

Answer 19

1. It required reconstruction of the extra-embryonic membranes
2. It modified the oviduct, which formed the expanded region called the uterus.

Question 20

Describe the early stages of human development in the notes (days 1-10)

Answer 20

1. The blastocyst moves down the oviduct to the uterus
2. By the 6th days the blastocyst consists of around 100 cells
3. When it comes into contact with the uterine endometrium, trophoblast (pre-placental) cells increase rapidly
4. The blastocyst then produces enzymes that break down the epithelium of the endometrium, which allows the blastocyst to implant.

Question 21

Describe the early stages of human development in our notes (days 11-12)

Answer 21

1. Implantation is complete and the blastocyst is buried in the uterus, surrounded by maternal blood
2. The trophoblast thickens and extends thousands of tiny chorionic villi

Question 22

What happened to the amnion in placental mammals?

Answer 22

The amnion remained unchanged and still surrounds the embryo, with its aqueous nature.

Question 23

What happened to the yolk sac in placental mammals?

Answer 23

The yolk sac then contained no yolk, but instead fluid-filled

Also became the source of stem cells that give rise to blood cells, lymphoid cells, and gametes.

Question 24

What happened to the allantois in placental mammals?

Answer 24

The allantois was no longer needed to store wastes and became a contributor to the formation of the umbilical cord.

Question 25

What happened to the chorion in placental mammals?

Answer 25

1. The chorion then formed most of the placenta along with the adjacent uterine endometrium.
2. The chorion also now secretes material that block normal maternal immune response

Question 26

Describe the structure of the entire summation of the embryonic membranes in placental mammals.

Answer 26

Draw picture and check with notes.

Question 27

What are the derivatives of the ectoderm in the notes? (3)

Answer 27

1. The brain
2. The spinal cord
3. Outer epithelial structures

Question 28

Describe the formation of the the neural plate and onward.

Answer 28

1. The ectoderm first thickens to form a neural plate
2. Next, the edges of the neural plate fold to create an elongated hollow neural tube
3. Finally the anterior end enlarges and forms the brain and the cranial nerves, while the posterior end forms the spinal cord and spinal motor nerves

Question 29

What are the derivatives of the endoderm in the notes? (4)

Answer 29

The gastrocoel forms as the primitive gut, and this endodermal cavity eventually produces:

1. Digestive tract lining
2. Lining of the pharynx
3. Most of the liver and pancreas
4. Thyroid, parathyroid and thymus

Question 30

What are the derivatives of the mesoderm? (4)

Answer 30

1. Axial skeleton
2. Dermis of dorsal skin
3. Muscle of the back, body wall and limbs
4. First functional organ - heart

Question 31

Describe the process of mesoderm turning into its derivatives.

Answer 31

The mesoderm divides into a linear series of somites by splitting, fusion, and migration.

These somites then differentiate into the derivatives that are mentioned previously