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Details may vary, but Gastrulation is crucial.
The three primary germ layers will be established.
All tissues and organs will come from these germ layers.
The primitive gut tube ("archenteron") will form.
How does a multicellular organism develop from a zygote?
How is the development of an animal different from the development of a plant? How are they similar?
How is the position ("polarity") of the parts of an organism determined?
How does differentiation of cell type occur in animals and plants?
How are genetics and development connected? What about the environment?
The zygote divides...
And divides...
And divides again, and again
Notice any differences?
Sperm releases enzymes from acrosome at tip to penetrate jelly coat of ovum
Fusion of sperm and ovum triggers the formation of an mostly impenetrable "fertilization envelope" by an immediate cortical reaction.
This is the "Fast Block"
At this point, each cell can still become a whole organism ("totipotency")
Animal Development occurs in stages
Development continues after birth, until maturity
Yolk
The fertilized cell is a "zygote"
The fusion of gametes triggers a massive wave of Calcium ion release across the ovum membrane.
This prevents any other sperm from entering the ovum ("polyspermy").
The process takes 30 seconds
This is the "Slow Block"
The evolution of the amniotic egg was a major adaptation that allowed reptiles (and subsequently birds & mammals) to spend their entire life cycle on land. Four membranes:
(All "Blue" light micrographs depict sea urchin embryos)
Eventually, it's a "morula"
Then, it's a "blastula"
Umbilicus/Placenta
Fates of the three primary germ layers (learn this!)
A major division line among animals.
Deuterostomes: Chordates, Echinoderms
Protostomes: Everyone else
Differences:
Neurulation: The development of the primitive notochord (in chordates, obviously)
Organogenesis: The development of "somites", patches of cells which will give rise to organs
Neurulation begins with the infolding of the neural plate.
After the neural tube is formed, somite formation is initiated
Changes in cell shape during development are referred to as "morphogenesis".
This is a very important aspect of developmental biology (structure and function relationships).
Cells can do all sorts of neat things due to changing shape.
Funky Frog Fetuses:
By manipulating frog embryos at early stages of development, polarity is disturbed (with disturbing ease)
Transplantation of a specific region (the "dorsal lip") onto another embryo leads to a duplication of the embryo in opposite polarity.
The fetus remains small for most of the pregnancy,
only really increasing in mass during the last trimester.
One of the major developmental questions:
Roughly: Cues from two main sources-
Removal of a specific region (the "gray crescent"), leads to an embryo lacking any dorsal structures
Fate mapping: done by staining cells in early stage embryos
Limb Development:
Chicken limb development is dependent upon specific "organizer regions"
unequal distribution of proteins in an early stage C. elegans embryo
Polarity of frog embryo's is determined by cues present prior to fertilization, and by direction of fertilization
A temporary organ.
fluid is exchanged between mother and fetus.
blood cells are not exchanged
Any Questions?
Positive or Negative feedback?
Since plants are continually growing, distinction is made between "primary" and "secondary" growth
Primary Growth: Growth in a "Vertical" direction, accomplished by the apical meristem of roots and shoots.
Secondary growth: Growth in a "horizontal" direction, accomplished by the lateral mersitem that comprises the vascular and cork cambium.
A major difference between monocots and dicots is seen in the organization of root tissue.
Monocots (pictured right) have a layer of parenchymal cells surrounding the vascular cylinder in the middle of the root.
Dicots (pictured left) generally lack this feature.
Plant development continues throughout the plant life cycle
Meristem: Permanently undifferentiated, embryonic tissue.
There is meristematic tissue throughout the plant
Primary growth of the shoot meristem
leaf primordia-
young leaf organ
axillary bud meristem-
will give rise to lateral stems, if
far enough away from apical bud
Time
Lateral Roots originate from the pericycle, the outermost layer of the vascular cylinder
Primary growth of the root meristem
Apical meristem is in the Zone of Cell Division.
We have a better understanding of plant development now than we ever did.
Here are some of the broad strokes
Secondary growth of the vascular cambium leads to development of additional layers of xylem & phloem
initially, xylem is produced more rapidly than phloem
Another major difference between monocots and dicots is seen in the organization of the stem.
Dicot stems (pictured left) have a ring of vascular bundles.
Monocot stems (pictured right) have a scattered bundle pattern
Old thought:
Plane of division affected organ form.
New thought:
Plane isn't so important
Once primary growth of stems is complete, only secondary growth occurs.
Vascular cambium-
produces secondary xylem and phloem
even though these mutants are wacky, the leaves they make look fine
Cork Cambium-
Produces productive bark (periderm)
Flowering is under genetic control.
Mutations in flower pattern formation genes lead to abnormalities
"Wood" is built up secondary growth
As a woody plant ("tree") grows, vascular tissue closer to the interior of the tree becomes non functional. This becomes "heartwood".
Vascular tissue nearer to the outside of the tree remains functional ("sapwood").
lignin- a polymer present in the secondary cell walls of woody plants
However...
This is not anything new for us. But here it is (C3 leaf shown).
Why does a tree put on more secondary growth every year?
Wood is easily the most commercially important non-food plant product
Symmetry is very important in determining cell fate
Symmetry is also important in determining polarity of a developing plant
Normal early divisions are asymmetrical. What happens when they are symmetrical?
Overexpression of the KNOTTED-1 gene in tomato mutants leads to "super compound" leaves compared to the wild type
Arabidopsis is the major model organism for plant development.
first plant genome sequenced.
look at the numbers
Alive
or
Dead?
Animal cells differentiate due to lineage based mechanisms (who they are).
Plant cells differentiate due to position based mechanisms (where they are).
The study of tree rings.
Learn all sorts of things.
Pine tree data: wider rings = hotter years
Conclusions?
Explain the major phases of animal development.
Demonstrate how differentiation, induction, and morphogenesis all function in development.
Compare development in plants and animals.
Explain the causes and effects of developmental disruptions.
Provide some evidence of genetic control of development in animals and plants.