A. Fertilization- the union of the nucleus of an ovum, the unfertilized egg, and a sperm nucleus.
1. Cells, sperm, and egg are called
gametes.
a. sperm- male gametes
b. gametes- either an ovum
(egg cell) or a sperm cell. [in plants: ova & pollen]
B. Animal sperm
[and fern/moss sperm cells] has a flagellum they use to swim toward
egg.
1.
yolk- mass of nutrients stored in ovum
C. Each gamete has one-half of the
chromosome
set: haploid (1n).
D. Fertilization starts when sperm
cell
touches
surface of egg cell and fuses with it.
E. Sperm nucleus enters egg
cytoplasm, meets
egg nucleus and the two nuclei fuse. Fertilization is complete.
F. Joining of nuclei connects full
chromosome
set and pairs of DNA gene sequence in every cell. Newly formed zygote is said to be diploid (2n).
1.
zygote- fertilized egg
2.
embryo- an organism in its earliest stages of development
G. Fertilization turns on egg’s
metabolism and
activation usually occurs within seconds of
egg-sperm fusion.
1.
activation- the turning on of egg’s metabolism that
occurs in a
newly formed zygote after fertilization.
H. New proteins are made when cell
respiration
increases which use messenger RNA molecules
already in cytoplasm.
I. Activation has two major
effects
1.
rapid change in plasma membrane, which blocks fertilization by
second
sperm
2.
rearrangement of zygote cytoplasm by movements in the
cytoskeleton.
J. Events of activation start the
process of
changing zygote into a complex multicellular organism.
http://embryology.med.unsw.edu.au/Medicine/BGDlab8.htm
II. Growth, Differentiation, and Form
A. Animal development includes
growth, cell
specialization, and formations of tissues and
organs.
1.
differentiation- the process where embryonic cells divide
and
some become different from others.
B. Cell is completely
differentiated when it
contains all features of a specific cell type.
1.
ex. Muscle cell or a skin cell
C. Cells
organize to form the tissues and organs of complete animal as they differentiate.
1.
morphogenesis- embryonic development of structure of an
organism
D. Each type of cell that
differentiates during
development has a unique structure and function.
1.
skin cells are tough, thin, flat, and protect body
2.
skeletal muscle cells contain protein fibers which enable them
to
contract (flex the muscle)
3.
nerve cells have long, thin branches that are made to transmit
information (both electrically and chemically)
E. The human red blood cell doesn't
have a nucleus (it looses it soon after it is produced in the bone
marrow)
1. They are made to transport oxygen.
F. Each cell type (tissue) and
organ has a
specific
location and role (structure and function).
G. Proteins (coded for by the DNA)
are the keys to
differentiation in
animal cells
H. Specific groups of genes are
expressed in
each cell type which leads to production of specific
proteins (the other unneeded genes are turned off).
1.
outer skin layer cells make an extracellular matrix of keratin
(immune system functions)
2.
muscle cells contain banded fibers that have actin and myosin
proteins that form contractile units.
3.
nerve cells contain neurotransmitter molecules that carry nerve
impulses
from one cell to
another
J. Major protein in red blood cells
is
hemoglobin which transports oxygen to and from tissues
K. Differences between cells in
protein
synthesis lead to differences in cell form and function
(different genes are turned off or on in different tissues).
http://en.wikipedia.org/wiki/Cellular_differentiation#Overview
III. From
One Cell to Many: Making The Multicellular Organism
A. During cleavage, cells usually
divide and
double in number each cycle
1.
cleavage- period where zygote divides into two cells
after
fertilization
B. Embryo consists of a mass of
many cells
called blastula at end of cleavage
1.
blastula- an animal embryo after cleavage stage (a small
ball of cells)
C. Shape of blastula depends on
structure of
original egg and how its yolk is arranged
D. Differentiation and
morphogenesis becomes
obvious when some cells move from surface to
interior
of blastula
E. Embryo becomes three-layered
gastrula
1.
gastrula- two or three-layered, cup shaped embryonic stage
F. Three layers are called primary
germ layers
1.
primary germ layers- form all of body’s tissues
a. ectoderm- outer layer;
will form skin,
nervous system and related structures
b. endoderm- inner layer;
usually a tube
that will become lining of the digestive system.
c. mesoderm-
in-between-layer; will make
skeleton, muscles, heart, blood, and other
internal organs
G. Gastrulation:
changing
blastula into a gastrula, involves major changes
H. Morphogenesis
includes:
1.
coordinated movements of individual cells and tissues
2.
changing cell shapes
3.
folding or splitting of cell layers
4.
tissue masses formation by local cell division
5.
shaping of organs by genetically timed death of some cells
I. Cell movement during
morphogenesis involves
controlled breaking and remaking of
chemical bonds.
J. In vertebrates the general
shape, or body
plan, of organism appears during gastrulation
1.
body plan- general form of an organism’s boy structure
K. First mesoderm becomes the
notochord
1.
notochord- stiff rod that develops into part of the
backbone/spinal chord.
L. Notochord runs down middle of
embryo beneath
dorsal ectoderm
M. This development establishes the
anterior-posterior axis running
from head to tail
N. At this time, dorsal-ventral
direction, from
back to belly, and right and left become obvious
O. Later, a large head, segmented
backbone, and
limbs complete vertebrate body plan
P. Above notochord, dorsal ectoderm
folds up to
become neural tube
1.
neural tube- foundation of nervous system that will form
brain,
spinal chord, and nerves.
Q. Unlike mammals and birds who
develop directly
into young that are like the adult, others like
frogs,
sea stars, and insects first form a larva and them the larva forms into
an adult. [example: egg, tadpole, frog]
1.
larva- feeding individual that looks nothing like the
adult
R. Larva goes through metamorphosis
http://www.encyclopedia.com/html/e/embryo.asp
A. Basic developmental pattern
varies among
animals
B. In some animals like snails and
worms, first
two cells are unequal
1.
small cell becomes ectoderm, large cell leads to mesoderm and
endoderm
C. If two cells are separated
experimentally,
each develops only into its limited types of tissues
D. During cleavage, each cell
receives molecules
that control its fate
1.
In all these embryos, opening of gastrula becomes the mouth
E. When sea star or vertebrate
zygote cleaves,
first two cells are identical
1.
cell separation experiments show both cells can make all three
kinds of
tissue and develop into a complete embryo
2.
accidental separation of these two cells makes identical twins
(clones)
a. in these animals, first opening
of gut forms
the anus, while mouth forms later at other end
of gut.
F. Developmental patterns are a
clue to
relationships among living groups of animals [field of embryology]
1.
differences suggest a more distant relationship or adaptation to
different environments
G. Charles Darwin was among the
first biologists
to compare developmental patterns to help
determine
relationships among animal species
H. Related species posses many of
the same genes
1.
similar genes in many animals are responsible for segmentation
a. segmentation- division of
body into a
number of similar sections
I. Segments of vertebrates are
clearest in the
skeleton (back bone is segmented)
J. Body-pattern genes were first
discovered in
fruit flies that carried errors in these genes
1.
errors in these homeotic genes can transform one organ into
another
a. homeotic genes- genes
that determine
which body parts are made at which locations on
developing organisms
K. To study these genes, biologists
compared DNA
between abnormal flies and normal flies
1.
found 11 homeotic genes close together on one chromosome
a. homeobox– DNA sequence
that is
virtually identical in certain homeotic genes
3.
each gene encodes a protein that includes the 60 amino-acid
homeodomain
a. this part of protein bonds to
DNA, regulating
transcription of important genes
L. Homeotic genes are located close
together, in
same order as the body segments, whose development
they control
M. Nearly identical gene sequences
were found in
mice
1.
Mouse genes were names Hox genes for homeoboxes they contain
a. Hox genes- group of
homeotic genes
found in all animals
N. Changes in homeotic genes often
lead to
embryonic death or severe abnormalities
1. mutation in homeotic gene could produce a sudden evolutionary change
http://www.zoo.utoronto.ca/dgodt/ZOO328/Zoo328%20Thea%20notes%2013+14.html
V. Human
Development
A. Human egg (ova) is about 0.1 mm
in
diameter and
contains no yolk
B. Fertilized zygote cleaves as it
moves down
the oviduct from ovary into uterus
C. About 5 days after
fertilization, embryo,
called a blastocyst, is a hollow blastula similar
to that of
other animals
1.
blastocyst- mammalian embryonic stage that corresponds to
blastula of other animals
2.
blastocyst sinks into wall of mother's uterus to develop and
grow [called implantation]
D. Thick mass of cells inside of
blastocyst
forms disk that becomes embryo
1.
gastrulation occurs here and rest of blastocyst develops into
membranes
which surround,
nourish, and
protects embryo
E. Amnion immediately surrounds
embryo
1.
amnion- sac or membrane filled with amniotic fluid which
encloses
the
embryo
F. Chorion encloses all other
membranes, and
forms blastocyst’s thin outer wall
1.
chorion- embryonic membrane that surrounds all other
embryonic
membranes
G. Chorion extends finger like
projections
called villi into lining of uterus as gastrulation begins
1.
villi-finger like projections
H. Chorionic villi and uterine
lining form
placenta
1.
placenta- structure in uterus for exchange of materials
between a
fetus and the mother's blood supply, partly
formed by each.
J. Mother’s blood flows through
cavities in
placenta
1.
chorionic villi extend into these cavities
2.
nutrients and wastes pass (diffuse) through villi and blood vessels, but
the two
blood supplies remain completely separate
K. Human takes about 40 weeks to
develop in
uterus
1.
after beginning of eighth week, embryo is called a fetus
a. fetus- an older human
embryo, first bone cells laid down
L. After 3 months, most organs
begin to form and
skeleton is visible in ultrasound images
1.
rapid growth and maturation of organ systems occurs in last 3
months
http://nmhm.washingtondc.museum/collections/hdac/anatomy.htm
A. Some birth defects may be caused
by defective
genes or environmental factors (genetic or environmental diseases)
B. Polydactyly, condition of having
extra
fingers or toes is caused by an altered gene (genetic disease)
C. Biologists do not yet know how
gene alters
human limb development but did an experiment on
chickens and got an idea
1.
as first bud of chick’s limb begins to grow, particular gene is
active
in only posterior part of
bud
a. it produces protein that seems
to control
pattern of digits in limb by regulating transcription
of genes
2.
experimenters exposed cells in anterior part of limb bud to
protein
a.
as embryo developed, treated limb developed extra digits in a
mirror-image pattern
D. Neural-tube defects happen when
part of
neural tube does not close completely. Ex: spine bifida.
1.
in spine bifida, posterior end of neural tube does not close and
body
wall remains open. Surgeons can sometimes
partially fix it but,
problems persist through out life. The lower on the spine this
happens, the less the disability.
2.
when anterior part does not close, large part of brain does not
develop
a. this is
called anencephaly,
exposed brain
degenerates and top of skull fails to form.
These
individuals usually don't survive
after birth
.
E.
Both genes and environmental factors affect neural-tube development
F. Experiments suggest half of
neural-tube
defects could be prevented if pregnant women took folic acid and
vitamin
B12
http://www.ask.com/web?q=pics+of+birth+defects&qsrc=0&o=0
http://www.kidshealth.org/parent/system/ill/birth_defects.html
VII. Mechanisms of Cell Differentiation
A. Just describing development of
an embryo
cannot tell us what cellular and molecular processes
control this
series of events
1.
scientists came up with experiments to test their hypothesis on
this
subject
a. early experiments with embryo’s
involved
surgery
i.
scientists removed certain cells or moved tissues to new
locations
b. later method involved replacing
nucleus of
unfertilized egg with nucleus of differentiated
cell
B. Molecular methods help determine
which genes
are active in particular cell
1.
scientists can make large quantities of particular gene’s DNA
and use
chemicals to separate the DNA’s two strands
2.
they match dye molecules to DNA to make visible
a. tagged molecules are used as
probes to detect
RNA with matching nucleotide sequence
i.
this method is called DNA-RNA hybridization
a. DNA-RNA hybridization-
paring of DNA
molecules with RNA molecules by hydrogen bonds
between complementary base pairs
b. cells that have transcribed the
gene contain
mRNA that matches probe’s sequence
http://en.wikipedia.org/wiki/Cellular_differentiation#Overview
A. What happens to genes not used
when cell
differentiates?
1.
selective gene-loss hypothesis says differentiating cells lose
some
genes
2.
genetic-equivalence hypothesis states all cells contain same
genes, but
some become inactive during differentiation
B.
In 1952, Robert Briggs and Thomas King injected nuclei of
differentiated
cells from leopard
frogs into unfertilized frog eggs. (they cloned a frog!)
1.
replaced egg’s nucleus with one of differentiated cell
a. egg’s never meet sperm;
injection activated
egg
b. nucleus from blastula supported
development
of egg all the way to becoming a tadpole
c. when researches used skin cell,
development
stopped after gastrulation
i.
more
differentiated cell still had all genes needed for development, but nucleus could not support production of all kinds of
cells
1.
nuclei from adult skin cells did not support development past
the
tadpole stage, no genes were lost as cell
differentiated
http://en.wikipedia.org/wiki/Cellular_differentiation#Overview
IX. Determination and Differentiation
A. Determination- process by
which cell
commits to particular course of development
B.
Experiments with two-cell embryo’s of snail and frog demonstrate
two
extremes of determination
1.
each frog cell produced complete tadpole, but snails did not
produce
normal larvae
a. in a snail, both cell continued
to cleave,
but smaller
cell produced only ectoderm, larger cell made
mesoderm and endoderm
2.
snail embryo’s cells were already irreversibly determined, frog
embryo’s
two cells were
not determined yet
C.
Some proteins and other molecules are distributed unevenly in
egg cell
which determines fates of snail embryonic cell
http://en.wikipedia.org/wiki/Cellular_differentiation#Overview
A.
What makes snail’s first two cells different?
1.
scientists used microneedles to remove lobe from zygote
a. first cleavage produced two
cells of unequal
size that developed into abnormal larva with no heart or intestine
i.
evidence supported idea that large cell becomes mesoderm and
endoderm from something received in lobe
B. Factors in snail lobes are still
unknown, but
embryo’s of tunicates (sea squirts) include RNA and proteins
a. cleavage distributes molecules
to different
cells
C. Yellow cells grown in isolation
produce
molecules found in muscle
1.
RNA-DNA hybridization has shown RNA molecules attached to
cytoskeleton, moving
with pigment.
a. some RNA’s encode regulatory
proteins that
turn on genes that lead to muscle differentiation
D. Cells form anterior, middle, or
posterior
tissues
1.
one kind of abnormal fly produces headless larvae, have two
posterior
ends and don't survive.
E. They develop normally when
anterior end of
zygote is injected with anterior cytoplasm
taken from normal embryo.
F. Experimental results supported hypothesis that RNA and proteins in egg cytoplasm help control differentiation by regulating gene expression.
http://www.fasebj.org/cgi/content/full/15/13/2390XI. Cell-Cell Interactions
A. Hans Spemann and Hilde Mangold demonstrated that differentiation is more flexible in vertebrate embryo’s than in sea squirts, in 1920's using salamander embryo’s
1.
hypothesized that signal from notochord shifts neighboring
dorsal
ectoderm cells from skin to neural-tube
differentiation
2.
transferred pieces of ectoderm between two gastrulas
a. cells that normally form skin
moved to dorsal
region, produced neural tube instead
b. dorsal cells that should form
neural tube
were placed in ventral area, produced skin
B. Experiment showed cells respond
to other
cells nearby as they become determined.
C. Signals to become neural tissue
have
received, and tissue does not turn back to become skin, called embryonic
induction
1.
embryonic induction- influence of one embryonic tissue on
another, causing second
tissue to specialize
D. Spemann and Mangold’s next
experiment showed
notochord is source of inducing individual
1.
took piece of tissue that would later become notochord from
blastula or
early gastrula
2.
when transplanted to another embryo, tissue formed extra
notochord
a. extra notochord induced
neighboring ectoderm
to forms second neural tube
i.
second notochord started series of events, led to a nearly
complete
second larva attached to
individual
E. When piece of notochord is
cultured with
ventral ectoderm, ectoderm cells soon induce to
become
neural cells
F. To determine whether induction
requires cells
to be touching, scientists cultured tissues on
opposite sides of plaster filter
1.
pores of filter were so small, no cell contact could occur, but
molecules could pass through.
2.
induction occurred therefore contact is not required
a. notochord communicates with
ectoderm by
releasing substance that can pass through
filter
G. Biologists started searching for
inducing
substance because of these experiments
H. More than 20 years later,
molecular
techniques finally revealed induction involves number
of genes and
proteins
1.
two inducing proteins that notochord produces are called chordin
and
noggin
a. DNA-RNA hybridization shows
chordin and
noggin genes are active in cells that will
form notochord
2.
scientists injected chordin protein into ventral side of frog
embryo
a. chordin induced ventral cells to
form second
anterior-posterior axis
i.
showed chordin is important in notochord formation and
establishing anterior-posterior axis of frog
embryo
3.
noggin protein causes ventral ectoderm in laboratory tissue
cultures to
become nervous tissue instead of skin
I. Chordin and noggin proteins do
not regulate
gene transcription directly
1.
each interferes with action of another protein that controls
production
of family of other proteins
a. these latter proteins regulate
transcription
of many specific genes involved in development
of nerve cells
J. Scientists have found more than
10
developmental control proteins in notochord cell alone.
http://www.ucalgary.ca/~browder/meso_induction_I.html
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By: Michelle, WHS student, 3-22-06. Back to Weekly Lesson Plans