OUTLINE 6

VI. Morphogenesis

A. General features of gastrulation

B. Cell movement

1. extension and contraction

2. adhesion

C. Gastrulation in the sea urchin

D. Gastrulation in the frog

E. Three layers of cells

1. ectoderm

2. mesoderm

3. endoderm

F. Neurulation

animal pole

vegetal pole

After this point, Protostomes and Deuterostomes depart

Acoelomates

ProtostomesDeuterostomes

Arthropods Mollusks Annelids Echinoderms Chordates

TIME

Mouth develops:

First Second

Cleavage planes:

Spiral Radial

Early development:

Not totipotent Totipotent

MORULA

EGG

SEA URCHIN

BLASTULA

Fig 47.16

Fig 47.9

Animal pole

Vegetal pole

Blastocoel

Start of invagination(blastopore)

Fig 47.9

Archenteron

Fig 47.9

Mouth

Anus

Archenteron

Digestive tract

Fig 47.9

ectodermmesoderm

Archenteron

endoderm

Fig 47.7

Fig 47.7

Fig 47.8

FROGBLASTULA

Fig 47.10

Frog blastula

blastocoel

Dorsal lip.The invagination for gastrulation starts here

Fig 47.10

Fig 47.10

Fig 47.10

ScanningElectionMicrographs

Fig. 47.11

Neurulation in the frog

OUTLINE 7VII. Mechanisms of Animal Development

A. Cytoplasmic determinants1. axes of symmetry in amphibians2. bicoid gene in Drosophila

B. Cell communication1. Holtfreter’s work2. mechanisms of cell recognition3. induction

C. Morphogens and pattern formation (chick limb bud)D. Hormones (in amphibian development)

1. pattern of metamorphosis2. role of thyroxin3. evidence

ectoderm endodermmesoderm

3. resegregation

1. dissociation

2. reaggregation

Holtfretter 1955

Fig. 47.22Spemann and Mangold: an organizer

Fig. 47.24 Pattern formation: the chick limb bud

Fig. 47.24Pattern formation: the chick limb bud

Tadpole

AquaticGillsHerbivorousSwimming

Frog

TerrestrialLungsCarnivorousJumping

metamorphosis

How do hormones turn on and off the genes that control development?

Thyroxin level (increasing w ith time)G

rou

p o

f g

enes

exp

ress

ed

Fig. 21.23

Development in the fly

Fig. 21.24

Determination of anterior - posterior axis in the fly

Natural variation in hormone levels can cause developmental plasticity

Size of tadpole

Time

Pond dries, metamorphosis

or death

larger

smaller

Bigger is better!

20 mm 20 mm

Stage 36

O

C

Stage 27

C

O

Stage 42

O

C

Omnivore Carnivore

Omnivore Carnivore

Comparison of beaks of spadefoot tadpoles

Size of tadpole

Time

Pond dries, metamorphosis

larger

smaller

Natural and experimental variation in hormone levels can change the timing of development and

metamorphosis: this provides an avenue for evolutionary innovation

Evolution of Vertebrate body plan

Amphioxus

Larva

Adult HeterochronyNeotenyPaedomorphosis

Chemical pollutants can influence hormones and alter development

Lake Apopka

Concentration of toxins in

water

Lake Apopka

higher

lower

Lake Woodruff

Lake Apopka

larger

smaller

Lake Woodruff

Alligatorpenissize

Alligatorpenissize

Concentration of toxins in water

higherlower

larger

smaller

Effects of Atrazine on frog development