EXAM 1 Chapter 8, Principles of Development Flashcards
Epigenesis is
stages of development of an embryo (before, creation)
The stages of epigenesis are
gametes
fertilization
blastulation (cleavage)
gastrulation
organogenesis
growth
Gametes
these are both inherited from the male and the female
Fertilization
the two gametes come together to form the diploid zygote
Blastulation
zygote divides through mitosis and meiosis, the SIZE OF CELL DOESNT CHANGE
Gastrulation
the internal cavity start to form (which will eventually become organs)
Organogenesis
actual formation of individual organs
Growth
after all organs form, start to actually grow
Fertilization studied using…because…
sea urchin
used because it has external fertilization, male releases sperm in water, female releases egg, fertilization occurs outside the bodies so it is easily observed
Preformation
idea that within gametes, you have small version of adult
tiny baby in sperm, egg gave more genetic information, tiny baby grew then born
Eggs are…
- much larger than sperm
- takes more effort to make egg
- females only produce few hundred eggs, males produce thousands of sperm
Must prevent
polyspermy
Polyspermy
when multiple sperm fertilize one egg
The egg contributes…and the sperm contributes…
- egg = DNA and nutrients for development
- sperm = only contributes DNA
Need only one….to make…
haploid from female and male to make diploid
Fraternal twins
dizygotic, 2 eggs and 2 sperm, share 1/2 DNA
Identical Twins
monozygotic, 1 egg, 1 sperm, splits, share all DNA
Semi-identical twins
sesquizygotic, 1 egg, 2 sperm, splits, share 3/4 DNA
….prevent polyspermy
fast and slow block
the fast block…
triggers the slow block
(fertilization/blocks) step 1 (A)
- acrosomal process (point of sperm) contains egg recognition proteins
- these bind with sperm-binding receptors/species specific receptors on surface of egg
- this results in DEPOLARIZATION
Membrane electrical potential
- when the outside out the cell is positive (Na+) and the inside of the cell is negative
- difference of charges from outside to inside
- electrical potential energy
depolarization…
changes electrical membrane potential across the membrane
When depolarization occurs…
it spreads across the outside of the egg and turns off all of the sperm binding/species specific receptors
this makes it so no other sperm are received
This depolarization is…
the fast block, first step, starts 2 seconds after sperm binds, lasts ~60 seconds
(fertilization) step 1 (B)
- the depolarization also triggers release of Ca2+ from ER, which initiates step 3
(fertilization) step 2
- once sperm membrane fuses with the egg membrane, created fertilization cone
- this fertilization cone draw in the nucleus of the sperm
- draws nucleus under egg membrane and eventually into the egg
(fertilization) step 3
- Ca2+ causes cortical granules to discharge hypertonic fluid (high concentration of solute) into space between egg membrane and vitelline envelope
- water flows in, separates two membranes and space between membranes filled with water, other sperm lifted off
vitelline membrane is
outer most membrane
egg membrane is
inner most membrane
(fertilization) step 4
the vitelline envelope hardens and is then called the fertilization membrane (prevents additional fertilization from occurring)
Steps 3 and 4 are
the slow block to polyspermy, start about 60 seconds after step #1
(fertilization) step 5
12 min after step one, fusion of egg and sperm nuclei, this forms the diploid zygote
(fertilization) step 6
- 90 min after step 1, first cleavage
- mitosis and cytokinesis for daughter cells
- zygote divides into 100s of cells
The cells that the zygote divides into (the individual cells) are called
blastomeres
The cluster of cells (that is the same size as original zygote) is called
blastula
_________ on surface of cell….
contractile proteins
start to contract an pull together and this causes single cell to split into two
Mitosis is….Cytokinesis is…
Mitosis is duplication of DNA, one copy in each of the cells
Cytokinesis is equal splitting of cytoplasm
zygote through blastula stage is
cleavage and early development
yoke made up of…and is…
proteins and lipids
is food source
yolk effect is
because it is thicker than cytoplasm, there is an effect on the size of the cells that are formed, the more yolk that is present the bigger the cells that are formed are because it is harder for them to split/cleave into smaller cells
two main categories of yolk cleavage are
HOLOBLASTIC, MEROBLASTIC
Under holoblastic are…
isolecithal, mesolecithal
under meroblastic are…
telolecithal
holoblastic means
entire cell cleaves
meroblastic means
partial cleavage (too much yolk, only part of the cell cleaves)
isolecithal
sparse yolk, evenly distributed
all blastomeres have same amount of yolk, whole yolk divides into 2, then 4, then 8, etc.
example of isolecithal cleavage occurs in
sea stars, seas urchins
mesolecithal
moderate amount of yolk at one end of egg
the top half cleaves faster than bottom half
- animal pole cleaves fast, not much yolk present
- all yolk goes to bottom in vegetal pole, this cleaves at a slower rate
- smaller cells in animal pole, large cells in vegetal pole
- BUT whole yolk still dividing, so still holoblastic
example of mesolecithal is
a frog
telolecithal
a lot of yolk at one end of egg
so much yolk present that it does not divide, stays as solid yolk form
telolecithal is meroblastic because
there is only cleavage of part of the cell, only animal pole, vegetal pole does NOT divide
Example of telolecithal is
a chick
The chick develops
in just the part where the cells are cleaving
Holoblastic cleavages are
RADIAL
Meroblastic cleavages are
DISCOIDAL because develops like a disc
During frog development which is….the…
mesolecithal, the animal pole shifts a bit to form a little window, called grey crescent
during frog development polarization occurs which is…
determination of dorsal and ventral even at single stage development
cortex is
outer most layer
medulla is
inner most layer
sperm entry point is
only in animal pole
the yolk…
is very dense because it has all the nutrients so it gravitates to bottom of egg
after sperm binds during development…
the animal cortex rotates around the surface of the egg, as well as the vegetal pole
when the animal cortex shifts the inner contents…
of the egg do NOT shift, they remain level
this results in
the vegetal cortex is now over some of the less dense inner cytoplasm part of the inside of the egg
creates lighter little window
the grey crescent is
this part where the vegetal pole is over less dense lighter cytoplasm
the gray crescent region becomes
dorsal side of animal
…..is found is this grey crescent region and is important because…
beta catenin
very important to the development of nervous system in an organism
inner cytoplasm creates cavity called
blastocoel
beta catenin is
cell to cell signaling molecule
necessary for cells to communicate with one another and initiate response to one another
this is why it is present in nerve tissue
originally, before fertilization (locations of b-catenin, GSK-3, and GSK-3 Inhibitor)
beta catenin distributed equally throughout cell
cell contains GSK-3 enzyme that breaks down beta catenin (INACTIVE until fertilization)
GSK-3 inhibitor is ONLY IN VEGETAL POLE
as soon as fertilization happens (sperm nucleus transported)…
- GSK-3 inhibitor transported from vegetal pole to grey crescent region
- GSK 3 is now active and can break down beta catenin
so in grey crescent region
although GSK3 is activated because cell fertilized and break down beta catenin everywhere else, it does NOT break down beta catenin is gray crescent region because of the GSK-3 inhibitor
the end result is
gray crescent region contains beta catenin, inhibitor, and GSK 3
ONLY GSK3 found everywhere else
Other patterns of cleavage (in addition to holoblastic and meroblastic) include
radial cleavage
(regulative development)
spiral cleavage
(mosaic development)
radial cleavage
new cells form directly on top of each other, form layers
another term that is generally related to radial cleavage is
regulative development
regulative development is
if blastomeres separate early, each can become own whole organism, arent dependent on others
identical genetic copy of each other
spiral cleavage
new cells form in furrows in between the individual blastomeres (pack tight)
almost twisted as they form
spiral cleavage related to
mosaic development
mosaic development
if blastomeres separate early, each does not become whole organism, fate dependent on others
(SECOND STEP AFTER FERT) blastulation is
separation of single cell into multiple cells , takes mitosis and cytokinesis
formation of blastula, cluster of blastomeres
develops fluid filled cavity called blastocoel
SAME SIZE as original zygote
no cell differentiation yet (cells may still need each other to develop properly)(mosaic development)
cleavage and blastocyst formation in humans is as follows…
1.) zona pellucida - protein coat that prevent implantation; morula “hatches” from this, then implants
2.) Morula (mulberry fruit) - solid ball of cells
3.) Blastocyst in mammals same as blastula in others
4.) inner cell mass becomes baby; trophoblast forms placenta
gastrulation (STEP AFTER BLASTULATION 3RD STEP)
formation of inner cavity and results in formation of germ layers
germ layers are
endoderm - inner most layer
ectoderm - outer most layer
mesoderm - middle layer
gastrulation will looks different in different organisms because of
yolk effect on cell size
sea star gastrulation
sea star is isolecithal
invagination (cells migrating) forms archenteron
bottle cells on outer layer pinch inward and pull outermost layers inward
new cavity formed by pinching is the archenteron
ectoderm becomes
epidermis and nervous system
endoderm becomes
lining of digestive and respiratory systems
mesoderm becomes
muscular, skeletal, cardiovascular, urogenital systems
frog gastrulation different because
mesolecithal, big cells with yolk in vegetal pole
blastocoel not as big
step 1 frog gastrulation
- on dorsal lip of blastopore bottle cells pinch inward and pull the animal cells inward creating new tissue and layers
when it gets pulled inward
- bottle cells pull inward
- animal pole spread outward coming around the other side, this displaces blastocoel and creates new cavity called archenteron
derm layers at this point
ectoderm - animal pol cells
endoderm - lines archenteron
mesoderm - in between ecto and endoderm
after ectoderm wraps all around…
have little area where yolk is still present called yolk plug
after gastrulation
more division of cells occurs and a bit of a fold occurs in animal cortex develops into neural fold which becomes neural plate and brain stem
notocord comes from
mesoderm
nervous system comes from
ectoderm
dorsal and ventral lip of blastopore create cavity that becomes
anus
another part of gastrulation is
formation of coelom (body cavity with organs) (from archenteron)
the gut and hollow part of body forms
two ways that the coelom can form
schizocoelous and enterocoelous
both ways have the
same result
schizocoelous
-cells at lip of the blastopore split and break off of the lip area and mirgrate toward middle of body forming the pockets
- once cavity is formed, the outer most layers fuse together creating new complete structure
- cells that split off fuse together and form organs of the gut
peritoneum
MESODERMALLY DERIVED tissue that covers the lining of your body
enterocoelous
- piece of archenteron pinches off (near the top part of arch)
- instead of little pieces breaking off, you have pockets that form and pinch together and separate from that main cavity
- the pouches fuse and separate into actual development body cavity of organism
bilateral
one place of symmetry, if want equal halves need to take one split down the middle
only 1 longitudinal plane creates equivalent right and left halves
coelom
fluid filled (in some animals) space around gut (cavity)
three different categories regarding coelom
acoelomate
pseudocoelomate
eucoelomate
acoelomate
no body cavity
- space filled with another tissue type called parenchyma (mesoderm)
- fills and surround internal organs of body
pseudocoelomate
- cavity partially lined with mesoderm
- false cavity, but difference between eucolemate is the innermost organs are not completely covered with mesoderm
eucoelomate
true coelom fully lined with peritoneum (mesoderm)
organogenesis (4TH AND FINAL STAGE)
creation of organs
most of organ development
is going to be derived from mesoderm tissue
example of this is….which is…
neurulation
formation of nervous system from ectoderm
development of neural tube
- ectoderm thicken to form neural plate
- edges rise and join to form tube - enlarges anteriorly (brain), and posteriorly (spinal cord)
- crest cells (peripheral nervous system) will migrate outwward, they are guidence molecules from neuron are target which guide neuron growth
again this neural tube is where
there is high concentration of beta catenin which helps with cell to cell signaling and will help develop nervous system
around nerve tube is development of another structure which is the……which…
notochord
- critical for development of nervous system
- gives support and structure during development of nervous system
- mesodermally derived
- hard rod like structure
chordates
have notochord sometime in development
there is a quote from textbook
essentially stating that development of nervous system is so complex that it almost appears there were predestinated destinations and they carry out a purpose
major division in animal kingdom includes
protostome, deuterostome
protostome
- blastopore develops into mouth first
- ex. annelids (earthworm)
- spiral cleavage
- schizocoelus
- mosaic development
deuterostome
- blastopore becomes mouth second (anus 1st)
- ex chordates, echinoderms (sea starts, sea urchins)
- radial cleavage
- entercoelous
- regulative development
*** MOST MAMMALS ARE DEUTEROSTOMES BUT SHOW SCHIZOCOELUS FORMATION
how did scientists figure out how information got split within the different cells, or how…
do you get all the different kinds of cells from one cell (liver cells, nerve cells, blood cells, etc)
original thought was
as cells divide, genome divided up till piece left is what cell type is
DNA splits up until only one type of DNA is left in that one cell (for example only liver DNA so becomes liver cell)
Experiments done by _______ disproved this original thought
Spermann
His experiment was…
he took a very thin hair and tied it around a salamander zygote at the single cell stage and watched it develop with the hair tied around the egg
experiment 1…conclusion of this…
hair splits gray crescent region
- nucleus only on one side, as nucleus divided, at about 16 cell stage, one of the nucleus cells jumped to other side and started developing as well
- two embryos formed
conclusion: all early cells contain same nuclear information (cell totipotent)
experiment 2…and conclusion…
- split with the nucleus on one side and the gray crescent on the other
- as nucleus divides, and at 16 cell stage one of blastomeres goes to other side
- ONLY cell on same side of gray crescent develops into a viable embryo
- other part just becomes cells with no organization
- conclusion: cytoplasm in gray crescent area has essential info for development which is beta catenin
experiment 3 performed..
with another researcher so it was Spemann-Mangold
induction
capacity of some cells to evoke a specific developmental response in other cells
certain cells cause other cells to develop
experiment 3
- took some cell from area away from the dorsal lip of blastopore, and then took cells from around the lip of a DIFFERENT blastopore and inserted them back into the original blastopore
- primary neural fold begins to develop by dorsal lip, and then a secondary neural development also occurs where ells were transferred
- two conjoined salamanders form
- proves that there are certain properties of the cells around the dorsal lip region that induces other cell to develop properly (beta catenin)
