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AP Bio- Regulation 2: Development

2 of 7 of my Regulation Domain. Image Credits: Biology (Campbell) 9th edition, copyright Pearson 2011, & The Internet Provided under the terms of a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. By David Knuffke.
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David Knuffke

on 9 December 2014

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Transcript of AP Bio- Regulation 2: Development

Development
Animals
Plants
Overview
Animal Development occurs in stages
Development continues after birth, until maturity
Fertilization
Cleavage
Gastrulation
External Development of frog eggs
Internal Development of a Dog Embryo
Yolk
Umbilicus/Placenta
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:
Amnion
: Protect fetus
Chorion
: Gas Exchange
Allantois
: Waste Storage
Yolk
: Food Source
Fertilization events in sea urchins
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
"
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
"
Fertilization events in mammals
Notice any differences?
The fertilized cell is a "
zygote
"
The zygote divides...
And divides...
And divides again, and again
Eventually, it's a "
morula
"
Then, it's a "
blastula
"
"Inner cell mass"
"n + n = 2n"
"splitting"
"organization"
Early gastrulation
Mid gastrulation
Complete Gastrula
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.
Gastrulation in Sea Urchins
Gastrulation in Frogs
Fates of the three primary germ layers (learn this!)
Just Think Layers
Protostomes vs. Deuterostomes
A major division line among animals.
Deuterostomes
: Chordates, Echinoderms
Protostomes
: Everyone else
Differences:
Direction of
cleavage
Fate of
blastopore
during gastrulation
"getting fancy"
Neurulation &
Organogenesis

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
Neurulation in a frog embryo
Organogenesis in a chicken embryo
Morphogenesis:
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.
Convergent Extension:
Human
Development

"how you came to be"
Early events in human development
Implantation is crucial
Development progresses
The fetus remains small for most of the pregnancy,
only really increasing in mass during the last trimester.
Sesame seed size
plum size
soda can size
Parturition
The Placenta
A temporary organ.
fluid is exchanged between mother and fetus.
blood cells are not exchanged
Hormonal control of labor
Positive or Negative feedback?
Polarity &
Cell Fate

"what goes where and how it's done"
One of the major developmental questions:
How do cells know where they are in the embryo, and what they should become?

Roughly: Cues from two main sources-
uneven distribution of protein molecules
signals from nearby cells ("
induction
")
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
Fate mapping
: done by staining cells in early stage embryos
Fate map of the
C. elegans
embryo (intestine map shown)
"things get freaky, easy"
Other
experiments

Funky Frog Fetuses:
By manipulating frog embryos at early stages of development, polarity is disturbed (with disturbing ease)
Removal of a specific region (the "
gray crescent
"), leads to an embryo lacking any dorsal structures
Transplantation of a specific region (the "
dorsal lip
") onto another embryo leads to a duplication of the embryo in opposite polarity.
Limb Development:
Chicken limb development is dependent upon specific "
organizer regions
"
transplantation of the organizer region (ZPA) leads to limb duplication.
What's true for one chordate...
Urchin Larvae
Overview
Plant development continues throughout the plant life cycle

Meristem
: Permanently undifferentiated, embryonic tissue.

There is meristematic tissue throughout the plant
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
.
Primary vs. Secondary Growth
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
Primary growth of the root meristem

Apical meristem is in the Zone of Cell Division.
Formation of a lateral root
Time
Lateral Roots originate from the
pericycle
, the outermost layer of the vascular cylinder
Tissue Structure of young roots
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.
Tissue Structure of young stems
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
Plant Tissues
Secondary growth of the vascular cambium leads to development of additional layers of xylem & phloem

initially, xylem is produced more rapidly than phloem
Once primary growth of stems is complete, only secondary growth occurs.

Vascular cambium
-
produces secondary xylem and phloem
Wood Production
"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
Why does a tree put on more secondary growth every year?
Wood is easily the most commercially important non-food plant product
Alive
or
Dead?

Dendrochronology
The study of tree rings.

Learn all sorts of things.

Pine tree data: wider rings = hotter years

Conclusions?
Tissue Structure of leaves
This is not anything new for us. But here it is (C3 leaf shown).
The sequence of the
Arabidopsis
genome
Arabidopsis
is the major model organism for plant development.
6 week generation time
5000 seeds per plant

first plant genome sequenced.
look at the numbers
Parenchymal cells: undifferentiated plant cells
We have a better understanding of plant development now than we ever did.
Here are some of the broad strokes
Genetics of Plant Development
Symmetry & Cell Division
Old thought:
Plane of division affected organ form.

New thought:
Plane isn't so important
even though these mutants are wacky, the leaves they make look fine
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?
However...
Pattern Formation
Overexpression of the
KNOTTED-1
gene in tomato mutants leads to "super compound" leaves compared to the wild type
Animal cells differentiate due to lineage based mechanisms (who they are).

Plant cells differentiate due to position based mechanisms (where they are).
Pretty flowers?
Flowering is under genetic control.

Mutations in flower pattern formation genes lead to abnormalities
Any Questions?
Any Questions?
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?
Big Questions
Make sure you can
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.
And Away We Go
At this point, each cell can still become a whole organism ("
totipotency
")
(All "
Blue
" light micrographs depict sea urchin embryos)
Frog embryo shown
Cork Cambium
-
Produces productive bark (
periderm
)
Cleavage in a frog embryo
Gastrulation in a sea urchin
Gastrulation & Neurulation in a frog
Full transcript