Fig. 26-3

1
Fig. 26-3
Species Panthera pardus
Genus Panthera
Family Felidae
Order Carnivora
Class Mammalia
Phylum Chordata
Kingdom Animalia
Archaea
Domain Eukarya
Bacteria
2
Fig. 26-4
Species
Order
Family
Genus
Pantherapardus
Panthera
Felidae
Taxidea taxus
Taxidea
Carnivora
Mustelidae
Lutra lutra
Lutra
Canis latrans
Canidae
Canis
Canis lupus
3

• 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

4

• 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

5

• 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

6
Fig. 26-5
Branch point (node)
Taxon A
Taxon B
Sister taxa
Taxon C
ANCESTRAL LINEAGE
Taxon D
Taxon E
Taxon F
Common ancestor of taxa AF
Polytomy
7
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

8
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)
9

• Phylogenies of anthrax bacteria helped
  researchers identify the source of a particular
  strain of anthrax

10
Fig. 26-UN1
A
B
D
B
C
D
B
C
C
A
D
A
(a)
(c)
(b)
11
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

12
Fig. 26-7
13
Evaluating Molecular Homologies

• Systematists use computer programs and
  mathematical tools when analyzing comparable DNA
  segments from different organisms

14
Fig. 26-8
1
Deletion
2
Insertion
3
4
15

• 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

16
Fig. 26-9
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
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
23
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

24
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

25

• A valid clade is monophyletic, signifying that it
  consists of the ancestor species and all its
  descendants

26
Fig. 26-10
A
A
A
Group I
B
B
B
C
C
C
D
D
D
Group III
Group II
E
E
E
F
F
F
G
G
G
(b) Paraphyletic group
(a) Monophyletic group (clade)
(c) Polyphyletic group
27

• 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

28
Inferring Phylogenies Using Derived Characters

• When inferring evolutionary relationships, it is
  useful to know in which clade a shared derived
  character first appeared

29
Fig. 26-11
TAXA
Lancelet (outgroup)
Lancelet (outgroup)
Salamander
Lamprey
Lamprey
Leopard
Turtle
Tuna
Tuna
Vertebral column (backbone)
0
1
1
1
1
1
Vertebral column
Hinged jaws
0
0
1
1
1
1
Salamander
Hinged jaws
CHARACTERS
1
0
0
0
1
1
Four walking legs
Turtle
Four walking legs
0
0
0
0
1
1
Amniotic (shelled) egg
Amniotic egg
Leopard
Hair
0
0
0
0
0
1
Hair
(a) Character table
(b) Phylogenetic tree
30

• 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

31
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

32
Fig. 26-12
Drosophila
Lancelet
Zebrafish
Frog
Chicken
Human
Mouse
33

• In other trees, branch length can represent
  chronological time, and branching points can be
  determined from the fossil record

34
Fig. 26-13
Drosophila
Lancelet
Zebrafish
Frog
Chicken
Human
Mouse
CENOZOIC
MESOZOIC
PALEOZOIC
Present
65.5
251
542
Millions of years ago
35

• 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

36
Fig. 26-14
Human
Mushroom
Tulip
40
30
0
Human
40
0
Mushroom
0
Tulip
(a) Percentage differences between sequences
5
15
5
15
15
10
25
20
Tree 1 More likely
Tree 2 Less likely
(b) Comparison of possible trees
37

• Computer programs are used to search for trees
  that are parsimonious and likely

38
Fig. 26-15-1
Species III
Species I
Species II
Three phylogenetic hypotheses
I
I
III
II
II
III
I
III
II
39
Fig. 26-15-2
Site
4
3
2
1
1/C
Species I
T
C
T
A
I
I
III
1/C
Species II
C
C
T
T
III
II
II
1/C
Species III
C
A
A
G
II
III
I
1/C
1/C
T
T
A
G
Ancestral sequence
40
Fig. 26-15-3
Site
4
3
2
1
1/C
Species I
T
C
T
A
I
I
III
1/C
Species II
C
C
T
T
III
II
II
1/C
Species III
C
A
A
G
II
III
I
1/C
1/C
T
T
A
G
Ancestral sequence
3/A
3/A
2/T
I
I
III
3/A
2/T
4/C
III
II
II
2/T
4/C
4/C
II
I
III
3/A
3/A
2/T
2/T
4/C
4/C
41
Fig. 26-15-4
Site
4
3
2
1
1/C
Species I
T
C
T
A
I
I
III
1/C
Species II
C
C
T
T
III
II
II
1/C
Species III
C
A
A
G
II
III
I
1/C
1/C
T
T
A
G
Ancestral sequence
3/A
3/A
2/T
I
I
III
3/A
2/T
4/C
III
II
II
2/T
4/C
4/C
II
I
III
3/A
3/A
2/T
2/T
4/C
4/C
I
III
I
II
III
II
I
II
III
7 events
7 events
6 events
42
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

43
Fig. 26-16
Lizards and snakes
Crocodilians
Ornithischian dinosaurs
Common ancestor of crocodilians, dinosaurs, and
birds
Saurischian dinosaurs
Birds
44

• This has been applied to infer features of
  dinosaurs from their descendents birds and
  crocodiles

Animation The Geologic Record
45
Fig. 26-17
Front limb
Hind limb
Eggs
(a) Fossil remains of Oviraptor and eggs
(b) Artists reconstruction of the dinosaurs
posture
46
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

47

• Orthologous genes are found in a single copy in
  the genome and are homologous between species
• They can diverge only after speciation occurs

48

• 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

49
Fig. 26-18
Ancestral gene
Ancestral species
Speciation with divergence of gene
Orthologous genes
Species A
Species B
(a) Orthologous genes
Species A
Gene duplication and divergence
Paralogous genes
Species A after many generations
(b) Paralogous genes
50
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

51

• Molecular clocks are calibrated against branches
  whose dates are known from the fossil record

52
Fig. 26-19
90
60
Number of mutations
30
0
120
90
60
30
0
Divergence time (millions of years)
53
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
54
Fig. 26-21
EUKARYA
Dinoflagellates
Land plants
Forams
Green algae
Ciliates
Diatoms
Red algae
Amoebas
Cellular slime molds
Euglena
Trypanosomes
Animals
Leishmania
Fungi
Sulfolobus
Green nonsulfur bacteria
Thermophiles
(Mitochondrion)
Spirochetes
Chlamydia
Halophiles
COMMON ANCESTOR OF ALL LIFE
Green sulfur bacteria
BACTERIA
Methanobacterium
Cyanobacteria
(Plastids, including chloroplasts)
ARCHAEA
55
Fig. 26-UN2
Node
Taxon A
Taxon B
Sister taxa
Taxon C
Taxon D
Taxon E
Most recent common ancestor
Taxon F
Polytomy
56
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
Polyphyletic group
Paraphyletic group
57
Fig. 26-UN4
Salamander
Lizard
Goat
Human
58
Fig. 26-UN5
59
Nutritional Mode

• Animals are heterotrophs that ingest their food

60
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

61
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
62
Fig. 32-2-3
Blastocoel
Endoderm
Cleavage
Cleavage
Blastula
Ectoderm
Archenteron
Zygote
Eight-cell stage
Gastrulation
Gastrula
Blastocoel
Blastopore
Cross section of blastula
63

• 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-to-posterior (head-to-tail) axis. In a
  fruit fly, for example, Hox genes lay out the
  various main body segmentsthe 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.

64
Synopsis of Drosophila development from egg to
adult fly
65

• 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. Nüsslein-Volhard, Cell 68201219, 1992.)

66
(No Transcript)
67
(No Transcript)
68

• 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 mutant-case 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 co-linearity 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.

69

• 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 T1T3, thoracic segments
  A1A9, 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 headtail 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/CEH-20
  (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 PBCLAB-heterodimer
  -binding sites are shown. Consensus logos were
  generated using all verified Hox-binding sites
  with WEBLOGO113.

70
(No Transcript)
71
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

72
Fig. 32-3
Individual choanoflagellate
Choanoflagellates
OTHER EUKARYOTES
Sponges
Animals
Collar cell (choanocyte)
Other animals
73
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

74
Fig. 32-6
RESULTS
100 µm
Site of gastrulation
Site of gastrulation
75
Symmetry

• Animals can be categorized according to the
  symmetry of their bodies, or lack of it
• Some animals have radial symmetry

76
Fig. 32-7
(a) Radial symmetry
(b) Bilateral symmetry
77
(No Transcript)
78
(No Transcript)
79
??????????????????
80
II. Animal Development A. Fertilization B.
Cleavage C. Gastrulation D. Neurulation E.
Extraembryonic Membranes F. Human Development
81
(No Transcript)
82
(No Transcript)
83
Cleavage
84
(No Transcript)
85

• 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.

86
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
87
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
88
Specialisation of endoderm                      
                                                  
                                                  
                                     
                                                  
                       
89

• 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

90
Specialisation of the Mesoderm
91

• 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.

92
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.
93
(No Transcript)
94
(No Transcript)
95
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
96

• 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)

97
(No Transcript)
98
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
99
(No Transcript)
100
(No Transcript)
101
(No Transcript)
102
(No Transcript)
103
(No Transcript)
104
(No Transcript)
105
(No Transcript)
106
(No Transcript)
107
Critical Periods of Human Development
Light blue bars indicate periods when organs are
most sensitive to damage from alcohol, viral
infection, etc.
108

• 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

109
Tissues

• Animal body plans also vary according to the
  organization of the animals 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

110

• Ectoderm is the germ layer covering the embryos
  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

111
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

112
Fig. 32-8
Coelom
Body covering (from ectoderm)
Tissue layer lining coelom and suspending internal
organs (from mesoderm)
Digestive tract (from endoderm)
(a) Coelomate
Body covering (from ectoderm)
Pseudocoelom
Muscle layer (from mesoderm)
Digestive tract (from endoderm)
(b) Pseudocoelomate
Body covering (from ectoderm)
Tissue- filled region (from mesoderm)
Wall of digestive cavity (from endoderm)
(c) Acoelomate
113
Protostome and Deuterostome Development

• Based on early development, many animals can be
  categorized as having protostome development or
  deuterostome development

114
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

115
Fig. 32-9
Protostome development (examples
molluscs, annelids)
Deuterostome development (examples
echinoderm, chordates)
(a) Cleavage
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(b) Coelom formation
Key
Coelom
Ectoderm
Mesoderm
Archenteron
Endoderm
Coelom
Mesoderm
Blastopore
Mesoderm
Blastopore
Solid masses of mesoderm split and form coelom.
Folds of archenteron form coelom.
(c) Fate of the blastopore
Anus
Mouth
Digestive tube
Mouth
Anus
Mouth develops from blastopore.
Anus develops from blastopore.
116

• One hypothesis of animal phylogeny is based
  mainly on morphological and developmental
  comparisons

117
Fig. 32-10
Porifera
Cnidaria
ANCESTRAL COLONIAL FLAGELLATE
Metazoa
Ctenophora
Eumetazoa
Ectoprocta
Brachiopoda
Deuterostomia
Echinodermata
Chordata
Bilateria
Platyhelminthes
Rotifera
Protostomia
Mollusca
Annelida
Arthropoda
Nematoda
118

• One hypothesis of animal phylogeny is based
  mainly on molecular data

119
Fig. 32-11
Silicea
Porifera
Calcarea
ANCESTRAL COLONIAL FLAGELLATE
Metazoa
Ctenophora
Cnidaria
Eumetazoa
Acoela
Echinodermata
Deuterostomia
Chordata
Bilateria
Platyhelminthes
Rotifera
Ectoprocta
Lophotrochozoa
Brachiopoda
Mollusca
Annelida
Nematoda
Ecdysozoa
Arthropoda
120
Fig. 32-13
Lophophore
Apical tuft of cilia
Mouth
100 µm
Anus
(a) An ectoproct
(b) Structure of a trochophore larva
121
Fig. 32-UN1
Common ancestor of all animals
Sponges (basal animals)
Metazoa
Ctenophora
Eumetazoa
Cnidaria
True tissues
Acoela (basal bilaterians)
Deuterostomia
Bilateria (most animals)
Bilateral summetry
Lophotrochozoa
Three germ layers
Ecdysozoa