Developmetal Genetics Flashcards
What is Developmental Genetics ?
Developmental Genetics: describes how genes regulate process of transformation and change in development
-Development controls how cells divide and coordinate their activities with each other
Discuss what occurs in Human development
Human development:
-we go from a single cell to 37 trillion cells
(single fertilized egg to a developed human )
What are the experimental models of development?
To study development we study animals
Experimental models of development:
1. Sea urchins
2. African clawed frogs (big eggs that people experiment with)
3. Chickens (big eggs that people work with)
What is observed in genetic models of development? What are the 4 main genetic models used ?
Genetic models of development: Look at mutations that change the developmental process itself
Genetic models
1. Fruit flies (Thomas Hungt Morgan studied flies; leading model of development)
2. Nematodes (worms) another common model
3. Zebrafish (their fish eggs are followed external; study genetics by crossing fish)
4. Mice (have similar biological effects in humans; models for how mammals (like us) work)
What happens to cells in development ?
In development, cells divide rapidly and form patterns accurately
What is the outline of Development? What are the major phases?
Outline of Development
1. Fertilization
2. Cleavage (cells quickly divide)
-Cell proliferation
-Establishing the body plan
3. Gastrulation (gut moves into the center of animal)
-cell migrations
-Establishing tissues layers
4. Organogenesis (body begins to form recognizable muscles, vertebrate, limbs and other structures)
-The neural tube
-Somites
-Appendages
What occurs in Fertilization ?
Fertilization: start of a new life
-Sperm will fertilize a large egg
(egg provides most of the material for new life)
Describe the Acrosomal Reaction that occurs in Sperm during
Sperm: The Acrosomal reaction initiates fertilization
1. Egg is surrounded by Zona pellucida.
2. As sperm reaches zone pellucida, it moves through follicle cells that protect the egg, and then initiate the Acrosomal reaction
3. The Sperm has vacuole (with enzymes), when it contacts zone pellucida, the vacuole will dump its enzymes on egg that digests zone pellucida, so sperm can fuse with egg.
Process (bind sperm to zona pellucida, acrosome reaction (vesicle dumps acrosome contents, enzyme) , sperm penetrate through pellucid, fuse with plasma membranes, and sperm nucleus enter egg cytoplasm)
The egg has to respond very quickly to prevent another sperm from coming into egg
What occurs in egg during fertilization ? What kind of reaction occurs.
Egg: the Cortical Reaction BLOCKS Polyspermy (multiple sperm from entering egg)
A system where the egg has been set up for years, developing vesicles of its own to allow it to act quickly and prevent polyspermy.
process:
1. The egg has cortical granules with hydrolytic enzymes
2. As soon as sperm make contact and sperm enter cytoplasm they signal for egg with granules to fuse with membrane and dump their contents to the outside
3. their contents cause zona pellucida to change in structure (make HARD boundary) to prevent other sperm from getting through.
For development to work, things are set up in advance
so they can proceed quickly.
two steps: Cortical reaction (exocytosis; dump contents of granule on outside)
2. Block to polyspermy (make impermeable barrier to prevent another sperm from contacting egg)
What must occur in sperm and egg to form nucleus ?
The sperm and egg pronucleus (haploid) merge to produce the nucleus
process:
1. Egg pronucleus and sperm pronucleus that has centrosome.
2. They move towards each other .The centrosome duplicate, and nuclei emerge (nuclear envelopes of both egg and sperm)
they then break apart, chromosomes duplicate and a lot of mitosis occurs (lot of mitosis in cleavage phase of developing embryo)
(chromosomes from egg and sperm align on single metaphase spindle and division produces two diploid cells)
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what is role of the Xenopus fertilization?
Xenopus fertilization starts organizing the body plan
When sperm fertilizes egg in African frogs, it causes surface of egg to rotate inside; makes ventral surface (where a lot of yolk is) , and at opposite ends it makes dorsal surface (mirror image )
(hence, some information about body plan is already being worked out as a result of fertilization and early cleavage events)
What occurs during Cleavage? What are the four steps of the cell cycle?
Cleavage- initial burst of cell division (happens rapidly)
The typical cell cycle has four steps: M (mitotic) , G1 (pause), S (synthesis) and G2 (pause).
-Cell cycle
M, G1, S, G2 (pause phase)
(normally When cells divide: new cell is formed and has 2 copies of every chromosomes, absorbs nutrients; duplicate DNA and go through mitosis to make two daughter cells)
slow state: where there are pauses before and after DNA synthesis
How many steps are the cell cycle for frog cleavage ?
The cell cycle of frog cleavage have only 2 steps: M and S. mitotic phase and synthesis phase back and forth rapidly
This process works in frogs because the proteins that control division/cycles are regulated. The Kinases add phosphate groups to proteins to turn on and phosphatase groups remove phosphate to turn off.
What occurs in Drosophila Cleavage ?
Drosophila Cleavage:
-cells are expressing a GFP: tubulin fusion protein that labels the asters
(easily observed due to green flurousecent protein)
-Division occurs rapidly and synchronously
-Courtesty of Rosalind V Silverma- Gavrila
(tubulin helps separates chromosome during mitosis)
How does cleavage occur in Mice?
Cleavage in Mice:
-Cleavage produces cells that organize to an inner mass and an outer group that will go on to form the placenta.
reproduction in mice and humans do not involve laying eggs, and eggs form placenta to continue take up new material from mom
placental mammals rely on mother for protection
-slower development compared to other animals.
(form hollowed out ball; outer side of ball form placenta; cells on inside of ball form new mouse or human)
process:
fertilized mouse egg– 2 cells (1 1/2 days) –> morula (8 cells; 2 1/2 days) , compaction—-> 16 cells (3 days) —> section of blastocyst (4 days)
What occurs in Gastrulation?
Gastrulation: process of forming the basic body plan (form gut in the middle of body; how we bring in, process and excrete food for energy)
How does gastrulation occur in sea urchins? What are the major layers of cells in human body and which body parts are they found
Gastrulation in sea urchins (also same process for humans, mice and other animals )
1. after cleavage, sea urchin forms hollow ball of cells.
2. At one end, some of cells start to migrate into interior)
3. The pinch becomes bigger and bigger forming a tube; when tube hits other wall, it forms hole, and push hole through to form full gut (from mouth to anus)
cells give rise to three layers: endoderm, ectoderm, mesoderm (middle part of body)
In humans;
skin, nervous system- ectoderm
gut- endoderm
muscles, liver- mesoderm
What are the tissue layers in frog embryo ?
Tissue layers in frog embryo:
Gut in middle (lined by endoderm)
ectoderm pinches down to from neural crest
**neural crest (in ectoderm) where spinal cord forms
mesoderm- where notochord and somites are
(neural tube also part of ectoderm)
Describe what occurs in human gastrulation
Human gastrulation :
a group of cells on one end of inside hollow ball: which form placenta
Humans have flatter disk to where invagination and migration to interior of cell occurs.
it form same basic structures as sea urchin and frog (ectoderm, endoderm and mesoderm)
What is the role of gastrulation? What are the major products formed?
Gastrulation forms layer of inner, middle and outer tissues that give basic animal its structure
ectoderm- outer layer of skin, lining of the nose and mouth and nervous system,
endoderm- Digestive tract, respiratory tract, liver, gut, pancreas
mesoderm- muscles, skeletal
(gastrulation: second phase of development, where migration of blastocyst cells inward lead to multiple distinct layers of cell)
What occurs in Organogenesis ?
During Organogenesis, cells organize into organs and systems.
-once broad tissues have formed, cells need to adopt more specific identities.
-Groups of cells interact to form organs.
-organs contain many cells of the same type (ex: the heart is made of many muscle cells )
-Organs also contain cells of different types (ex: bone contains bone cells and blood cells)
-Organs interact to make complicated systems
What can cause severe problems in development?
*Early defects during development can cause more severe problems *
(if have mistake during early phase of development, may take out half body ; if defect near end of die, might affect less tissues and organs; not as severe)