Development Two (Test Two) Flashcards
Development is largely under the control of what?
gene expression
Generally, how do cells differentiate themselves?
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.
Explain the role of Cytoplasmic Specification in the process of cell differentiation.
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.
What is embryonic induction, how does it work, and why is it important?
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
Thinking long-term, how does an inductor cell affect the rest of development for a particular cell?
- Once an inductor cell sets in motion a specific developmental pattern in other cells, other inductions follow
- Each step in the developmental system is a necessary preliminary event for the next step.
Give a real example of induction / cytoplasmic specification in a liver cell / neuron.
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.
What is a clear indicator of common ancestry in vertebrates?
The commonality in the embryonic stages.
What are the five ancestral traits of chordates, known as the chordate hallmarks?
- Dorsal neural tube (spinal cord)
- Notochord (discs) lost in humans
- Pharyngeal gill pouches and aortic arches (becomes mouth)
- Ventral heart
- Postanal tail
What are amniotes?
Amniotes are a group of animals that have embryos that develop within the amnion sac.
Explain what an amnion sac is, and what it does for the embryo.
It is a fluid-filled sac that encloses the embryo.
- It provides an aqueous environment in which the embryo floats
- It serves as protection from shock and adhesions
Why is protecting against adhesions so especially important?
Because, things will stick to a developing embryo and the embryo will absorb them, which is disastrous.
Describe the structure of an amniotic egg.
(draw the picture and then check)
From outside in, goes:
- The shell
- The shell membrane
- The chorion
- The yolk sac (below the amnion)
- Allantois (next to the amnion)
- The amnion (with embryo inside)
Explain the chorion membrane.
The chorion lies under the egg shell and encloses the embryo and all the other membranes.
Explain the yolk sac.
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
Explain the allantois.
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.
What happens when the embryo grown in regards to gas exchange?
The need for oxygen increases and the allantois and the chorion fuse to form a respiratory surface called the chorioallantoic membrane.
Why is the amniotic egg so significant to development and evolution?
- It provides a complete life support system for the embryo
- The evolution of the shelled amniotic egg made internal fertilization a requirement.
- Requiring internal fertilization had many repercussions in evolution
What proportion of mammals have a placenta?
94% of the class mammalia
How did evolution of the placenta for embryonic development change things?
- It required reconstruction of the extra-embryonic membranes
- It modified the oviduct, which formed the expanded region called the uterus.
Describe the early stages of human development in the notes (days 1-10)
- The blastocyst moves down the oviduct to the uterus
- By the 6th days the blastocyst consists of around 100 cells
- When it comes into contact with the uterine endometrium, trophoblast (pre-placental) cells increase rapidly
- The blastocyst then produces enzymes that break down the epithelium of the endometrium, which allows the blastocyst to implant.
Describe the early stages of human development in our notes (days 11-12)
- Implantation is complete and the blastocyst is buried in the uterus, surrounded by maternal blood
- The trophoblast thickens and extends thousands of tiny chorionic villi
What happened to the amnion in placental mammals?
The amnion remained unchanged and still surrounds the embryo, with its aqueous nature.
What happened to the yolk sac in placental mammals?
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.
What happened to the allantois in placental mammals?
The allantois was no longer needed to store wastes and became a contributor to the formation of the umbilical cord.
