Animal Lesson 2 Flashcards
Multicellular embryonic stages
Unicellular zygote to multicellular embryo then get more cells.
Fertilization
Egg and sperm come together to make one cell with double the amount of genetic material.
Model organisms
Are easy to study but broadly representative of majority of animals out here.
Developmental genes and mechanisms are what?
very similar across animal species and to see this view animals with similar genes.
– E.g., Drosophila (fruit flies) and humans have similar genes that perform similar functions. Why they are a good model to study.
Studying development in model organisms
provides what?
Knowledge about development in general.
– E.g., Sea urchins, frogs
Sea Urchin and frog example of model organisms
They are external fertilization in aquatic areas. So it’s easy to observe and manipulate. Their eggs and embryos are kinda transparent, so it’s easy to see by using the microscope. Can see the divisions of the cell.
Haploid gametes
Sperm and egg
Life cycle
Multicellular adult where every cell id diploid. Then does through meiosis to become haploid gametes. Then two gametes come together to fertilization. Then diploid unicellular zygote. Then goes through mitosis to divide to become multicellular adult.
When does fertilization occur?
When the layers of the egg start to separate.
Fertilization in Sea Urchins
The egg is very very big compared to sperm. With so so much sperm.
Nucleus of the sperm
In sperm head. Where genetic material is.
Acrosome
Has digestive enzymes in it.
Jelly coat
most outside part that’s around the egg.
Where does the cytoplasm come from?
The mother
Sperm-binding receptor
Proteins where sperm head attacks and binds to.
Parts of the egg
Jelly coat, Sperm-binding receptor, Vitelline layer, egg plasma membrane, cortical granules, and cytoplasm.
Egg cytoplasm contains what?
many proteins and mRNA involved in early
development.
First step of sea urchin fertilization
Contact with the jelly coat triggers the acrosomal reaction. The hydrolytic enzymes are released from the sperm to digest the jelly coat to try to make their way through and try to bind to one of these receptors.
Second step of sea urchin fertilization
Surface proteins on acrosomal process bind to receptors on egg cell membrane. Specifically the ligands for sperm-binding receptors. The sperm-binding receptor try to extend and try to bind to the receptors that are embedded through the vitellin layer and the plasma membrane of the egg.
Third step of sea urchin fertilization
Plasma membranes fuse and binds together triggering fast block to polyspermy.
Fast block to polyspermy
Change in the egg’s membrane charge from negative to positive: depolarization. Prevents binding of other
sperm. Immediate but short-lived. The negative charge attracts sperm.
Forth step of sea urchin fertilization
Sperm nucleus enters and cortical reaction causes slow block to polyspermy.
Slow block to polyspermy
The vitalize layer and egg plasma membrane gets separated. Then cortical granule gets released from a plasma membrane, and fill the new space called the pervitelline space, which is a physical barrier to stop yjr other sperms to come in. After they separate the vitalize layer becomes the fertilization envelope.
Fifth step of sea urchin fertilization
Fusion of sperm and egg nuclei form the diploid nucleus of the zygote (diploid unicellular).
Cleavage
The process by which the unicellular zygote becomes multicellular (embryo).
Rapid cell division with little growth of individual cells
(G1 and G2 phases skipped). ie. mitosis. No growth, but they just keep on dividing. Size and volume of your multicellular zygote and embryo stay the same because the cells get more but smaller.
Cleavage results in what?
many smaller cells called blastomeres.
blastomeres
A cell with the same volume but cells are getting smaller.
In frogs the zygotes becomes what?
Blastula. Becomes from solid ball of cells to hollow ball of cells. Where it’s mostly surrounded by with hollowness inside of the ball.
Frog cleavage
From one cell to blastula
Blastula
a hollow ball of cells with a fluid filled cavity called the
blastocoel. The cells are not even all the way around. Has the two poles.
Animal poles
These cells are smaller. Where the sperm enters. The blastocele is closer to this side.
Vegetal pole
These cells are larger. Opposite end where the sperm entered.
How can cells that possess the same genome look and behave differently (despite having same genome)?
Differential gene expression
Differential gene expression
– Cells express different genes depending on their
location and the stage of development.
– Expressing different genes leads to the production
of different proteins. Which in turn determine the structure and behaviour of the cell at any given time.
Is every gene is being expressed in the genome?
No
What activates a particular gene?
Usually has something to do with some sort of protein or enzyme or chemical.
The two mechanisms that trigger gene expression
- Cytoplasmic determinants: The signal comes from within the cell.
- Inductive signals: The signal comes from outside the cell (chemical/hormone).
Cytoplasmic determinants
– Molecules within the cytoplasm that regulate
gene expression.
– Can be differentially distributed to daughter cells
resulting in differences in gene expression.
Sperm came and changed the makeup of the animal poles vs. the vegatable pole region. Certain stuff will be on one side then when they divide it will only be in one cell.
Inductive signals
The signal molecules that a cell is exposed to depend on its location within the embryo, and the stage of development. ie. Stem call placed in muscle cell will turn into muscle cell. Stem cells make more of other cells through inductive signalling.
Preventing polyspermy ensures the zygote has the correct balance of maternal and paternal of what?
chromosomes
True or False. A frog blastula is essentially the same size as the zygote from which it developed.
True
True or False. Every (somatic) cell in a multicellular organism contains an identical genome.
True. However, false because red blood cells don’t have a nucleus/genome.
Somatic cells
All cells in your body but egg/sperm.
If a cell that normally develops into a muscle cell develops into a skin cell when moved to a different part of the embryo, which mechanism is
responsible for determining this cell’s fate?
Induction.
Morphogenesis
The rearrangement of cells or sheets of cells in the embryo. How fully functioning organism with different shapes and structures and things like that.
Gastrulation
Formation of the gut. Stage when the three germ layers are established (entirety of the future body plan), and the basic body plan is set up.
Organogenesis
is the formation of the organs through rearranging cells and tissues.
− E.g., neurulation = formation of the nervous
system. Happens at the embryonic stage.
The three layers?
Ectoderm, mesoderm, endoderm.
Ectoderm
Outside lining
Mesoderm
Bones, blood, muscles. Any connective tissues.
Endoderm
Inside lining. ie. gut.
Folding of the cells
Create head and neurolation.
First step of frog gastrulation?
Cells in the vegetal hemisphere push inward. Animal pole is the future ectoderm. Vegative pole is the the future endoderm. Has the blastopore.
Blastopore
Where cells form and move inwards and becomes the anus. Opposite to where sperm came in.
Protostomes
Where the first opening becomes mouth. ie. earthworm.
Deuterstomes
Where the first opening becomes anus. ie. us and frogs.
Second step of frog gastrulation?
Outer cells (future endoderm and mesoderm) roll
inward.
Third step of frog gastrulation?
Blastocoel collapses and new cavity - archenteron is
formed.
Archenteron
Future gut, open space, made from cells from vegetive pole.
Fourth step of frog gastrulation?
Cells at the animal pole (future ectoderm) spread
over the outer surface, and covers the negative pole.
How is the mesoderm formed?
Different depending on the animal
Overal frog gastrulation
Cells form inward to make the gut.
True of false: Endodermal cells express different genes than those expressed by the ectodermal cells.
True. Differential gene expression. From different poles, that take different sizes.
How is morphogenesis is achieved through what?
changes in cell position, shape, and survival (aka in different ways).
Convergent extension
Example of cells changing their position to change its shape. Produces a longer, narrower structure, by pushing inward then apart. From 2 by 3 to 6 by 1.
How Ectodermal cells change shape during neural
tube formation?
Start with square shaped sizes. Then arrange and elongate. So it elongates the cell to become long and skinny because of microtubules (called neural plate). Then the actin filaments gets shorter cause shape to look like a triangle. See the pinching of it. Forms this curvature into the layer of the ectoderm cells as a result. Then the curvature increases and more pinching in. The tube breaks off and breaks off and becomes its own thing.
What does programmed cell death do
Also shapes embryos. Fluorescing cells are undergoing apoptosis (death of cells). E.g., Removal of webbing between digits.
What causes changes in cell position, shape, and survival?
The position of the cell within the embryo.
The cytoplasmic determinants within a cell.
Changes in gene expression within a cell.
The proteins that are produced within a cell.
