Transcript 投影片 1

Fig. 26-3
Species:
Panthera
pardus
Genus: Panthera
Family: Felidae
Order: Carnivora
Class: Mammalia
Phylum: Chordata
Kingdom: Animalia
Bacteria
Domain: Eukarya
Archaea
Fig. 26-4
Order
Family Genus
Species
Taxidea
Taxidea
taxus
Lutra
Mustelidae
Panthera
Felidae
Carnivora
Panthera
pardus
Lutra lutra
Canis
Canidae
Canis
latrans
Canis
lupus
• Linnaean classification and phylogeny
can differ from each other
• Systematists have proposed the
PhyloCode, which recognizes only
groups that include a common ancestor
and all its descendents
• A phylogenetic tree represents a
hypothesis about evolutionary
relationships
• Each branch point represents the
divergence of two species
• Sister taxa are groups that share an
immediate common ancestor
• A rooted tree includes a branch to
represent the last common ancestor of all
taxa in the tree
• A polytomy is a branch from which more
than two groups emerge
Fig. 26-5
Branch point
(node)
Taxon A
Taxon B
Taxon C
ANCESTRAL
LINEAGE
Taxon D
Taxon E
Taxon F
Common ancestor of
taxa A–F
Polytomy
Sister
taxa
Applying Phylogenies
• Phylogeny provides important information
about similar characteristics in closely
related species
• A phylogeny was used to identify the
species of whale from which “whale meat”
originated
Fig. 26-6
RESULTS
Minke
(Antarctica)
Minke
(Australia)
Unknown #1a,
2, 3, 4, 5, 6, 7, 8
Minke
(North Atlantic)
Unknown #9
Humpback
(North Atlantic)
Humpback
(North Pacific)
Unknown #1b
Gray
Blue
(North Atlantic)
Blue
(North Pacific)
Unknown #10,
11, 12
Unknown #13
Fin
(Mediterranean)
Fin (Iceland)
• Phylogenies of anthrax bacteria helped
researchers identify the source of a
particular strain of anthrax
Fig. 26-UN1
(a)
A
B
D
B
D
C
C
C
B
D
A
A
(b)
(c)
Sorting Homology from Analogy
• When constructing a phylogeny,
systematists need to distinguish whether
a similarity is the result of homology or
analogy
• Homology is similarity due to shared
ancestry
• Analogy is similarity due to convergent
evolution
Fig. 26-7
Evaluating Molecular Homologies
• Systematists use computer programs and
mathematical tools when analyzing
comparable DNA segments from different
organisms
Fig. 26-8
1
Deletion
2
Insertion
3
4
• It is also important to distinguish
homology from analogy in molecular
similarities
• Mathematical tools help to identify
molecular homoplasies, or coincidences
• Molecular systematics uses DNA and
other molecular data to determine
evolutionary relationships
Fig. 26-9
Amino acids specified by each codon sequence on mRNA
Ala: Alanine
Cys: Cysteine
Asp: Aspartic acid
Glu: Glutamic acid
Phe:
Phenylalanine
Gly: Glycine
His: Histidine
Ile: Isoleucine
Lys: Lysine
Leu: Leucine
Met: Methionine
Asn: Asparagine
Pro: Proline
Gln: Glutamine
Arg: Arginine
Ser: Serine
Thr: Threonine
Val: Valine
Trp: Tryptophane
Tyr: Tyrosisne
A = adenine G = guanine C = cytosine T = thymine U = uracil
Mus musculus lactate dehydrogenase C
(Ldhc), mRNA
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1 atcctggttt cttacctgtg ctgcggagtc agcagtaagg ctcaacatgt ccaccgtcaa
61 ggagcagctg attcagaacc tagttccgga agataaactt tcccggtgta agattactgt
121 ggtcggagtt ggaaatgtgg gcatggcgtg tgctattagt attttactga agggtttggc
181 tgatgaactt gcccttgttg acgctgatac gaacaaactg aggggagagg cactggatct
241 tctgcacggc agtcttttcc ttagcactcc aaaaatcgtc tttggaaaag attacaatgt
301 atctgccaac tccaaactgg ttattatcac agctggtgca agaatggtgt ctggagaaac
361 tcgccttgac ctgctccaac gtaatgtcgc tatcatgaaa gccattgttc cgggcattgt
421 ccaaaacagt ccggactgta aaataattat cgtcactaac ccagtggata ttttgacata
481 cgtggtttgg aagataagcg gcttccctgt aggccgtgtg atcggaagtg gctgtaacct
541 agactcagca cgttttcgtt acctgattgg ggagaagctg ggtgtcaacc ctacaagctg
601 ccacggctgg gttcttggag aacatgggga ctccagtgtg cccatatgga gtggtgtaaa
661 cgttgctggc gtaactctga agtcactgaa cccagcaata ggaactgact cagataagga
721 acactggaaa aatgttcaca agcaggtggt ggaaggcggc tatgaggtcc ttaacatgaa
781 gggctatacc tcttgggcta tcgggctgtc tgtgactgat ctggcgcgat ccatcttgaa
841 gaatcttaag agagtgcatc ctgttaccac gctggttaag ggcttccatg ggataaagga
901 agaggtcttc ctcagtatcc cttgtgtctt gggacaaagt ggtatcacag actttgtgaa
961 agtcaacatg accgctgagg aggagggtct cctcaagaag agtgcggaca cactctggaa
1021 tatgcagaag gatctgcagt tataaactcg ccaccttcga ccgtgtgaca gatgcctgat
1081 cacatcactg atcacggcag tcccactgaa agtgtttcca catcataaca aagttcaata
1141 aaattttgga aacctgttaa gatcaatctc aaggctagaa agattaatgc caaaggcatc
1201 tccctccccc tttttttgag acagggtctc actttatagc cttagctgac ctcaaacgga
1261 aatctgctag cctcccagtg tattaaaggc aaccaccacc aggcccagct
Cladistics
• Cladistics groups organisms by common
descent
• A clade is a group of species that
includes an ancestral species and all its
descendants
• Clades can be nested in larger clades,
but not all groupings of organisms qualify
as clades
• A valid clade is monophyletic, signifying
that it consists of the ancestor species
and all its descendants
Fig. 26-10
A
A
A
B
B
C
C
C
D
D
D
E
E
F
F
F
G
G
G
B
Group I
(a) Monophyletic group (clade)
Group II
(b) Paraphyletic group
E
Group III
(c) Polyphyletic group
• A shared ancestral character is a
character that originated in an ancestor of
the taxon
• A shared derived character is an
evolutionary novelty unique to a particular
clade
• A character can be both ancestral and
derived, depending on the context
Inferring Phylogenies Using Derived
Characters
• When inferring evolutionary relationships,
it is useful to know in which clade a
shared derived character first appeared
Fig. 26-11
TAXA
Tuna
Leopard
Lancelet
(outgroup)
Vertebral column
(backbone)
0
1
1
1
1
1
Hinged jaws
0
0
1
1
1
1
Lamprey
Tuna
Vertebral
column
Salamander
Hinged jaws
Four walking legs
0
0
0
1
1
1
Turtle
Four walking legs
Amniotic (shelled) egg
0
0
0
0
1
1
Hair
0
0
0
0
0
1
Amniotic egg
(a) Character table
Leopard
Hair
(b) Phylogenetic tree
• An outgroup is a species or group of
species that is closely related to the
ingroup, the various species being
studied
• Systematists compare each ingroup
species with the outgroup to differentiate
between shared derived and shared
ancestral characteristics
Phylogenetic Trees with Proportional
Branch Lengths
• In some trees, the length of a branch can
reflect the number of genetic changes
that have taken place in a particular DNA
sequence in that lineage
Fig. 26-12
Drosophila
Lancelet
Zebrafish
Frog
Chicken
Human
Mouse
• In other trees, branch length can
represent chronological time, and
branching points can be determined from
the fossil record
Fig. 26-13
Drosophila
Lancelet
Zebrafish
Frog
Chicken
Human
Mouse
PALEOZOIC
542
MESOZOIC
251
Millions of years ago
CENOZOIC
65.5
Present
• Maximum parsimony assumes that the
tree that requires the fewest evolutionary
events (appearances of shared derived
characters) is the most likely
• The principle of maximum likelihood
states that, given certain rules about how
DNA changes over time, a tree can be
found that reflects the most likely
sequence of evolutionary events
Fig. 26-14
Human
Mushroom
Tulip
0
30%
40%
0
40%
Human
Mushroom
0
Tulip
(a) Percentage differences between sequences
15%
5%
5%
15%
15%
10%
20%
25%
Tree 1: More likely
Tree 2: Less likely
(b) Comparison of possible trees
• Computer programs are used to search
for trees that are parsimonious and likely
Fig. 26-15-1
Species I
Species III
Species II
Three phylogenetic hypotheses:
I
I
III
II
III
II
III
II
I
Fig. 26-15-2
Site
1
2
3
4
Species I
C
T
A
T
Species II
C
T
T
C
Species III
A
G
A
C
Ancestral
sequence
A
G
T
T
1/C
I
1/C
II
I
III
III
II
1/C
II
III
1/C
I
1/C
Fig. 26-15-3
Site
1
2
3
4
Species I
C
T
A
T
Species II
C
T
T
C
Species III
A
G
A
C
Ancestral
sequence
A
G
T
T
1/C
I
1/C
II
I
III
III
II
1/C
II
III
I
1/C
3/A
2/T
I
2/T
3/A
3/A
4/C
II
II
2/T 4/C
III
2/T
4/C
III
3/A 4/C
I
III
II
4/C
1/C
I
2/T 3/A
Fig. 26-15-4
Site
1
2
3
4
Species I
C
T
A
T
Species II
C
T
T
C
Species III
A
G
A
C
Ancestral
sequence
A
G
T
T
1/C
I
1/C
II
I
III
III
II
1/C
II
III
I
1/C
3/A
2/T
I
2/T
3/A
3/A 4/C
3/A
4/C
III
II
2/T
4/C
II
III
6 events
I
III
II
4/C
1/C
I
2/T 3/A
2/T 4/C
I
I
III
II
III
II
III
II
I
7 events
7 events
Phylogenetic Trees as Hypotheses
• The best hypotheses for phylogenetic
trees fit the most data: morphological,
molecular, and fossil
• Phylogenetic bracketing allows us to
predict features of an ancestor from
features of its descendents
Fig. 26-16
Lizards
and snakes
Crocodilians
Common
ancestor of
crocodilians,
dinosaurs,
and birds
Ornithischian
dinosaurs
Saurischian
dinosaurs
Birds
• This has been applied to infer features of
dinosaurs from their descendents: birds
and crocodiles
Animation: The Geologic Record
Fig. 26-17
Front limb
Hind limb
Eggs
(a) Fossil remains of Oviraptor
and eggs
(b) Artist’s reconstruction of the dinosaur’s posture
Gene Duplications and Gene Families
• Gene duplication increases the number of
genes in the genome, providing more
opportunities for evolutionary changes
• Like homologous genes, duplicated
genes can be traced to a common
ancestor
• Orthologous genes are found in a single
copy in the genome and are homologous
between species
• They can diverge only after speciation
occurs
• Paralogous genes result from gene
duplication, so are found in more than
one copy in the genome
• They can diverge within the clade that
carries them and often evolve new
functions
Fig. 26-18
Ancestral gene
Ancestral species
Speciation with
divergence of gene
Species A
Orthologous genes
Species B
(a) Orthologous genes
Species A
Gene duplication and divergence
Paralogous genes
Species A after many generations
(b) Paralogous genes
Molecular Clocks
• A molecular clock uses constant rates of
evolution in some genes to estimate the
absolute time of evolutionary change
• In orthologous genes, nucleotide
substitutions are proportional to the time
since they last shared a common
ancestor
• In paralogous genes, nucleotide
substitutions are proportional to the time
since the genes became duplicated
• Molecular clocks are calibrated against
branches whose dates are known from
the fossil record
Fig. 26-19
90
60
30
0
0
30
60
90
Divergence time (millions of years)
120
From Two Kingdoms to Three Domains
• Early taxonomists classified all species as
either plants or animals
• Later, five kingdoms were recognized: Monera
(prokaryotes), Protista, Plantae, Fungi, and
Animalia
• More recently, the three-domain system has
been adopted: Bacteria, Archaea, and Eukarya
• The three-domain system is supported by data
from many sequenced genomes
Animation: Classification Schemes
Fig. 26-21
EUKARYA
Dinoflagellates
Forams
Ciliates Diatoms
Red algae
Land plants
Green algae
Cellular slime molds
Amoebas
Euglena
Trypanosomes
Leishmania
Animals
Fungi
Sulfolobus
Green nonsulfur bacteria
Thermophiles
Halophiles
(Mitochondrion)
COMMON
ANCESTOR
OF ALL
LIFE
Methanobacterium
ARCHAEA
Spirochetes
Chlamydia
Green
sulfur bacteria
BACTERIA
Cyanobacteria
(Plastids, including
chloroplasts)
Fig. 26-UN2
Node
Taxon A
Taxon B
Sister taxa
Taxon C
Taxon D
Taxon E
Most recent
common
ancestor
Polytomy
Taxon F
Fig. 26-UN3
Monophyletic group
A
A
A
B
B
B
C
C
C
D
D
D
E
E
E
F
F
F
G
G
G
Paraphyletic group
Polyphyletic group
Fig. 26-UN4
Salamander
Lizard
Goat
Human
Fig. 26-UN5
Nutritional Mode
• Animals are heterotrophs that ingest their
food
Cell Structure and Specialization
• Animals are multicellular eukaryotes
• Their cells lack cell walls
• Their bodies are held together by
structural proteins such as collagen
• Nervous tissue and muscle tissue are
unique to animals
Reproduction and Development
• Most animals reproduce sexually, with the diploid
stage usually dominating the life cycle
• After a sperm fertilizes an egg, the zygote
undergoes rapid cell division called cleavage
• Cleavage leads to formation of a blastula
• The blastula undergoes gastrulation, forming a
gastrula with different layers of embryonic tissues
Video: Sea Urchin Embryonic Development
Fig. 32-2-3
Blastocoel
Cleavage
Endoderm
Cleavage Blastula
Ectoderm
Zygote
Eight-cell stage
Gastrulation
Blastocoel
Cross section
of blastula
Gastrula
Blastopore
Archenteron
•
One important class of transcription factors is encoded by the so-called homeotic, or Hox, genes.
Found in all animals, Hox genes act to "regionalize" the body along the embryo's anterior-toposterior (head-to-tail) axis. In a fruit fly, for example, Hox genes lay out the various main body
segments—the head, thorax, and abdomen. Here we see a representation of a fruit fly embryo
viewed from the side, with its anterior end to the left and with various Hox genes shown in different
colors. Each Hox gene, such as the blue Ultrabithorax or Ubx gene, is expressed in different areas,
or domains, along the anterior-to-posterior axis. The arced, colored bars give an idea of the full
range, or domain, of each gene's expression.
Synopsis of Drosophila development from egg to adult fly
•
•
The upper diagrams show the fates
of the different regions of the
egg/early embryo and indicate (in
white) the parts that fail to develop if
the anterior, posterior, or terminal
system is defective. The middle row
shows schematically the
appearance of a normal larva and of
mutant larvae that are defective in a
gene of the anterior system (for
example, bicoid), of the posterior
system (for example, nanos), or of
the terminal system (for example,
torso). The bottom row of drawings
shows the appearances of larvae in
which none or only one of the three
gene systems is functional. The
lettering beneath each larva
specifies which systems are intact
(A P T for a normal larva, -P T for a
larva where the anterior system is
defective but the posterior and
terminal systems are intact, and so
on).
Inactivation of a particular gene
system causes loss of the
corresponding set of body
structures; the body parts that form
correspond to the gene systems that
remain functional. Note that larvae
with a defect in the anterior system
can still form terminal structures at
their anterior end, but these are of
the type normally found at the rear
end of the body rather than the front
of the head. (Slightly modified from
D. St. Johnston and C. NüssleinVolhard, Cell 68:201–219, 1992.)
•
•
Edward B.Lewis at the California Institute of
Technology in Pasadena was interested in
questions concerning certain developmental
changes in the Drosophila fly and how the
genes causing them cooperate during body
segmentation. The answers he got, laid the
foundation of one of the most surprising
discoveries in developmental biology - the
same type of genes which controls the early
embryonic development of Drosophila also
controls the early embryogenesis of a lot of
higher organisms, including man. This means
that the genetic control mechanisms have
been preserved roughly unchanged through
650 million years of evolution!
A starting point for Lewis in his research on
the genetic basis for so-called homeotic
transformations during early embryonic
development was his work with the now
famous Drosophila-mutant with four wings
instead of two. Homeotic genes control
specialization of the segments. In the mutantcase inactivity of the first gene in a complex of
homeotic genes (the bithorax complex) caused
other homeotic genes to duplicate the segment
with two wings. Lewis' pioneering work on the
bithorax genes led to his discovery of the colinearity principle. According to this principle
there is a co-linearity in time and space
between the order of the genes in the bithorax
complex and their effect regions in the
segments. This discovery has had a very large
influence on later developmental research.
•
a | The panel on the left shows a stage 13 Drosophila melanogaster embryo that has been coloured in the schematic to
indicate the approximate domains of transcription expression for all Hox genes except proboscipedia (pb)85. The
segments are labelled (Md, mandibular; Mx, maxillary; Lb, labial; T1–T3, thoracic segments; A1–A9, abdominal
segments). The panel on the right shows a mouse (Mus musculus) embryo, at embryonic day 12.5, with approximate
Hox expression domains depicted on the head–tail axis of the embryo. The positions of hindbrain RHOMBOMERES R1,
R4 and R7 are labelled. In both diagrams the colours that denote the expression patterns of the Hox transcripts are
colour-coded to the genes in the Hox cluster diagrams shown in b. Anterior is to the left, dorsal is at the top. b | A
schematic of the Hox gene clusters (not to scale) in the genomes of Caenorhabditis elegans, D. melanogaster and M.
musculus. Genes are coloured to differentiate between Hox family members, and genes that are orthologous between
clusters and species are labelled in the same colour. In some cases, orthologous relationships are not clear (for example,
lin-39 in C. elegans). Genes are shown in the order in which they are found on the chromosomes but, for clarity, some
non-Hox genes that are located within the clusters of nematode and fly genomes have been excluded. The positions of
three non-Hox homeodomain genes, zen, bcd and ftz, are shown in the fly Hox cluster (grey boxes). Gene abbreviations:
ceh-13, C. elegans homeobox 13; lin-39, abnormal cell lineage; mab-5, male abnormal 5; egl-5, egg-laying
defective 5; php-3, posterior Hox gene paralogue 3; nob-1, knob-like posterior; lab, labial; pb, proboscipedia; zen,
zerknullt; bcd, bicoid; Dfd, Deformed; Scr, Sex combs reduced; ftz, fushi tarazu; Antp, Antennapedia; Ubx,
Ultrabithorax; abd-A, abdominal-A; Abd-B, Abdominal-B. c | A compilation of in vivo DNA binding sequences
arranged by the structural type of homeodomain that is encoded by the Hox genes. The three classes are Labial, Central,
and Abdominal-B. The listed DNA binding sequences that are bound by Hox monomers and Pre-B-cell homeobox/CEH20 (PBC)–Hox heterodimers are those that are required for the function of one or more Hox-response elements in
developing mouse36, 92, 101, 102, 103, 104, 105, 106, fly28, 36, 44, 45, 46, 51, 52, 53, 54, 95, 100, 107, 108, 109, 110,
111 or nematode29, 112. As no known HOX1-monomer-binding (mouse) or LAB-monomer-binding (fly) sites have been
found to be functional in vivo, only PBC–LAB-heterodimer-binding sites are shown. Consensus logos were generated
using all verified Hox-binding sites with WEBLOGO113.
Concept 32.2: The history of animals spans
more than half a billion years
• The animal kingdom includes a great diversity
of living species and an even greater diversity
of extinct ones
• The common ancestor of living animals may
have lived between 675 and 875 million years
ago
• This ancestor may have resembled modern
choanoflagellates, protists that are the closest
living relatives of animals
Fig. 32-3
Individual
choanoflagellate
Choanoflagellates
OTHER
EUKARYOTES
Sponges
Animals
Collar cell
(choanocyte)
Other animals
Concept 32.3: Animals can be characterized
by “body plans”
• Zoologists sometimes categorize animals according
to a body plan, a set of morphological and
developmental traits
• A grade is a group whose members share key
biological features
• A grade is not necessarily a clade, or monophyletic
group
Fig. 32-6
100 µm
RESULTS
Site of
gastrulation
Site of
gastrulation
Symmetry
• Animals can be categorized according to
the symmetry of their bodies, or lack of it
• Some animals have radial symmetry
Fig. 32-7
(a) Radial symmetry
(b) Bilateral symmetry
精子和卵子各帶一半染色體進行受精作用
II. Animal Development
A. Fertilization
B. Cleavage
C. Gastrulation
D. Neurulation
E. Extraembryonic Membranes
F. Human Development
Cleavage
Figure 2-11: Events during the first week of human development. 1,
Oocyte immediately after ovulation. 2, Fertilization, approximately 12 to
24 hours after ovulation. 3, Stage of the male and female pronuclei. 4,
Spindle of the .rst mitotic division. 5, Twocell stage (approximately 30
hours of age). 6, Morula containing 12 to 16 blastomeres (approximately 3
days of age). 7, Advanced morula stage reaching the uterine lumen
(approximately 4 days of age). 8, Early blastocyst stage (approximately
4.5 days of age). The zona pellucida has disappeared. 9, Early phase of
implantation (blastocyst approximately 6 days of age). The ovary shows
stages of transformation between a primary follicle and a preovulatory
follicle as well as a corpus luteum. The uterine endometrium is shown in
the progestational stage.
Amnion becomes filled with amniotic fluid
Yolk sac becomes part of the gut, earliest blood cells
Allantois constructs umbilical cord linking embryo to placenta and part of urinary bladder
Chorion helps form placenta and is the outermost membrane which encloses the embryonic
body
Gastrulation
Ectoderm:
Epidermis
Epithelia of oral and nasal cavities
Nervous system
Lens and cornea
Inner ear
Mesoderm:
Dermis
Muscle
Skeleton (bone and cartilage and muscle)
Circularatory system
Organs of urogenital system
Kidneys
Outer (body cavity) layers of digestive and respiratory tracts
Endoderm
Epithelium of digestive and respiratory tracts
Liver
Pancreas
Specialisation of endoderm
•
•
•
•
•
•
•
Forms all body parts except:
• Nervous
• Skin
• Epidermal derivatives
• Epithelial and glandula derivates of mucosa
1st evidence of mesodermal differentiation is appearance of notochord
Aggregates form either side of notochord e.g. somites
Around those are the intermediate mesoderm and lateral mesoderm
Each somite has 3 functional parts:
• Sclerotome - forms vertebrae and ribs
• Dermatome - forms dermis of skin in dorsal part of body
• Myotome - forms skeletal muscles of neck, body trunk, limbs
Intermediate mesoderm - forms gonads, kidneys and adrenal cortex
Lateral mesoderm:
• Somatic - forms dermis of skin in ventral body region and limb buds
• Splanchic - forms cardiovascular system, organs and most connective tissue
Specialisation of the Mesoderm
•
•
The ectoderm germ layer forms a variety of structures in the body. By far the most complicated and interesting
structure formed from the ectoderm is the nervous system. From the established ectoderm layer of the gastrula,
neural tissue is derived by a series of tissue inductions, movements, and differentiations. There are a huge
number of proteins, genes, and other factors which take part in this complex process. New differentiation factors
are discovered each day. This site will only cover a few primary factors.
The general differentiation of the neural tissue starts with the notochord. The notochord (derived from the
mesoderm) is the primary inducer of the neural plate. Two signaling molecules, noggin and chordin, which are
released by the notochord, induce the overlying ectoderm to thinken into the neural plate. The two molecules both
function by blocking the action of bone morphogenic protein-4 (BMP-4). BMP-4 is also critical in mesodermic and
hematopoietic development. It inhibits ectoderm from differentiating to neural plate tissue. This in vivo action has
been reproduced in in vitro experiments. Under these conditions, the neural plate develops forebrain
characteristics. Neural ectoderm induced in the presence of Fibroblast Growth Factor-8 (FGF-8) will develop more
caudal features of the spinal chord. FGF's also play a role in liver development.
Along the length of the neural tube,
neuroepithelial cells proliferate.
Within this neuroepithelium exist
multipotential stem cells of the
nervous system. During the
development of the embryo, these
ES cells differentiate into a variety
of cell lineages which eventually
give rise to the multiple types of
mature cells of the adult nervous
system (see photo below). Many of
these stem cells are only found in
certain areas of the developing
nervous system. As they begin to
differentiate, certain cells must
migrate from these primordial
locations to the proper location of
the adult cell. Of particular interest
is the O-2A progenitor cell lineage
because it gives rise to
oligodendrocytes and type-2
astrocytes.
Ectoderm
Mesoderm
Endoderm
skin
notochord
lining of gut
brain
muscles
lining of lungs
spinal cord
blood
lining of bladder
all other neurons
bone
liver
sense receptors
sex organs
pancreas
•
The two lateral ends
of the neural plate
then fold up to meet
at the midline of the
gastrula to form the
neural tube. (See
photo above) A
variety of genes give
the tube a
cranial/caudal
polarity (see left
photo) and guide the
formation of the
various structures of
the nervous system.
Another set of genes
and signaling factors
(most notably Slug
and Sonic Hedgehog
(Shh) ) establish the
dorsal/lateral polarity
also essential for
proper formation of
the nervous system.
(See photo below)
Module 1932: The Cell
Differentiation and Development 1
Neurulation
A: Embryonic disc accomplished gastrulation - ectoderm thickens
B: Neural plate forms neural folds and neural groove
C: Neural folds close
D: Neural tube detached from surface ectoderm
Critical Periods of Human Development
Light blue bars indicate periods when organs are most sensitive to damage
from alcohol, viral infection, etc.
• Two-sided symmetry is called bilateral
symmetry
• Bilaterally symmetrical animals have:
–
–
–
–
A dorsal (top) side and a ventral (bottom) side
A right and left side
Anterior (head) and posterior (tail) ends
Cephalization, the development of a head
Tissues
• Animal body plans also vary according to
the organization of the animal’s tissues
• Tissues are collections of specialized
cells isolated from other tissues by
membranous layers
• During development, three germ layers
give rise to the tissues and organs of the
animal embryo
• Ectoderm is the germ layer covering the
embryo’s surface
• Endoderm is the innermost germ layer and
lines the developing digestive tube, called
the archenteron
• Diploblastic animals have ectoderm and
endoderm
• Triploblastic animals also have an
intervening mesoderm layer; these include
all bilaterians
Body Cavities
• Most triploblastic animals possess a
body cavity
• A true body cavity is called a coelom and
is derived from mesoderm
• Coelomates are animals that possess a
true coelom
Fig. 32-8
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
(a) Coelomate
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
(b) Pseudocoelomate
Body covering
(from ectoderm)
Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
(c) Acoelomate
Protostome and Deuterostome
Development
• Based on early development, many
animals can be categorized as having
protostome development or
deuterostome development
Cleavage
• In protostome development, cleavage is spiral
and determinate
• In deuterostome development, cleavage is radial
and indeterminate
• With indeterminate cleavage, each cell in the early
stages of cleavage retains the capacity to develop
into a complete embryo
• Indeterminate cleavage makes possible identical
twins, and embryonic stem cells
Fig. 32-9
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderm,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
(a) Cleavage
Radial and indeterminate
(b) Coelom formation
Key
Coelom
Ectoderm
Mesoderm
Endoderm
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
Mesoderm
Folds of archenteron
form coelom.
Anus
Mouth
(c) Fate of the blastopore
Digestive tube
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
• One hypothesis of animal phylogeny is
based mainly on morphological and
developmental comparisons
Fig. 32-10
“Porifera”
Eumetazoa
Metazoa
ANCESTRAL
COLONIAL
FLAGELLATE
Cnidaria
Ctenophora
Deuterostomia
Ectoprocta
Brachiopoda
Echinodermata
Bilateria
Chordata
Platyhelminthes
Protostomia
Rotifera
Mollusca
Annelida
Arthropoda
Nematoda
• One hypothesis of animal phylogeny is
based mainly on molecular data
Metazoa
Silicea
Calcarea
Ctenophora
Eumetazoa
ANCESTRAL
COLONIAL
FLAGELLATE
“Porifera”
Fig. 32-11
Cnidaria
Acoela
Bilateria
Deuterostomia
Echinodermata
Chordata
Platyhelminthes
Lophotrochozoa
Rotifera
Ectoprocta
Brachiopoda
Mollusca
Annelida
Ecdysozoa
Nematoda
Arthropoda
Fig. 32-13
Lophophore
Apical tuft
of cilia
100 µm
Mouth
(a) An ectoproct
Anus
(b) Structure of a trochophore
larva
Fig. 32-UN1
Common ancestor
of all animals
Metazoa
Sponges
(basal animals)
Eumetazoa
Ctenophora
Cnidaria
Acoela (basal
bilaterians)
Deuterostomia
Bilateral
summetry
Three germ
layers
Lophotrochozoa
Ecdysozoa
Bilateria (most animals)
True
tissues