Lecture 8

Question 1

Schizocoely

Answer 1

Band of mesoderm forms around the gut before a coelom forms
Coelom is formed by mesodermal cells dividing
can form all three body plans

Question 2

Enterocoely

Answer 2

Coelom Formation,
Mesoderm and coelom form at the same time
Gastrulation begins with one side of the blastula bending inward forming the archenteron (endoderm)
As archenteron elongates, the sides push outward and expand into a pouch- like coelomic compartment
Pouch-like compartment pinches off

Question 3

What are the three body plans

Answer 3

Acoelomate, pseudocoelomate, and eucoelomate

Question 4

Cytoplasmic Specification

Answer 4

The cytoplasmic determinants are not evenly distributed…
They partition unequally among blastomeres during cleavage
which Leads to cell differentiation

lesds to mosaic development

Question 5

Mosaic Development

Answer 5

Cytoplasmic Specification

in the early tunicate embryo. When the four blastomere pairs of the 8-cell embryo are dissociated, each forms structures that it would have formed if it had remained in the embryo.

Question 6

Regulative Development

Answer 6

Conditional specification (regulative development).

A) What a cell becomes depends upon its position in the embryo. Its fate is determined by interactions with neighboring cells.
B) If cells are removed from the embryo, the remaining cells can regulate and compensate for the missing part.

Question 7

Induction

Answer 7

capacity of some cells to evoke a developmental response from other cells

Question 8

What can the inducer and responder influence

Answer 8

each other
• i.e. the position of the cell in the embryo and signals from its neighbours determines its fate.Mechanisms of Development

Question 9

Mechanisms of Development

Answer 9

Cytoplasmic specification

Conditional specification

Question 10

What does Cytoplasmic specification lead to

Answer 10

mosaic development
• cytoplasmic determinants distribute unequally in blastomeres
• Individual blastomeres cannot produce whole embryo

Question 11

What does conditional specification lead to

Answer 11

regulative development
• Neighbouring cells induce cell fate
• Individual blastomeres can produce whole embryo

Question 12

Metazoa major clades

Answer 12

• Deuterostomia (Deuterostomes)

* Protostomia (Protostomes)

Question 13

How many metazoan phyla are there

Answer 13

34

Question 14

similar developmental patterns in metazoa

Answer 14

• Presence of blastula and gastrula stages

* Formation of germ layers

Question 15

Metazoa

Answer 15

kingdom of all unicellular animals

Question 16

PROTOSTOMIA

Answer 16

• Members generally possess trochophore larvae or a lophophore

Question 17

DEUTEROSTOMIA

Answer 17

E.g. Chordata, Echinodermata, Hemichordata

Question 18

four developmental characters in metazoans

Answer 18

1. Fate of blastopore
2. Cleavage patterns
3. Fate of cells
4. Mesoderm formation

Question 19

Protostome

Answer 19

• “First mouth”. i.e. the first embryonic opening

* Blastopore becomes the mouth

Question 20

Deuterostome

Answer 20

• “Second mouth” i.e. the second embryonic
opening (no name) becomes the mouth
• Blastopore becomes the anus

Question 21

Cleavage Patterns in Protostome

Answer 21

Spiral cleavage occurs in most lophotrochozoan protostomes
Blastomeres cleave at a45 degree angle to the animal-vegetal axis
Produces quartets of cells that lie in the furrows between cells of underlying layer
Upper layer of cells appear to be offset from the lower and shift in a spiral fashion
blastomeres pack tightly together compared to radial cleavage

Question 22

Cleavage patterns in Deuterostome

Answer 22

Radial cleavage occurs in most deuterostomes
Embryonic cells are arranged in radial symmetry around the animal-vegetal axis
First cleavage plane passes through the animal-vegetal axis giving rise to two identical blastomeres
Second cleavage occurs simultaneously in both blastomeres and oriented parallel to animal-vegetal axis but perpendicular to first cleavage
After third cleavage,upper tier of cells sits directly ontop of the tier of cells below

Question 23

Fate of cells in Protostome

Answer 23

• Mosaic development characterizes most lophotrochozoan protostomes
• Cytoplasmic determinants are partitioned unequally
• If separated, individual blastomeres still form structures that were dictated by the
cytoplasmic determinants
• Needs all the blastomeres to develop properly

Question 24

Fate of cells in deutersome

Answer 24

• Regulative Development characterizes most deuterostomes
• Fate of a cell depends on interactions with neighbouring cells
• Early blastomeres are capable of producing an entire embryo if separated from other cells
• Remaining blastomeres can compensate for the missing cell
• E.g.human identical twins.

Question 25

Mesoderm Formation in Protostome

Answer 25

• Coelom is formed by schizocoely

* Protostomes can be coelomate, acoelomate, or pseudocoelomate

Question 26

Mesoderm formation in deuterosome

Answer 26

• Coelom is formed by enterocoely

* All deuterostomes are coelomate