Lab 1

Question 1

3 hallmarks of early devo

Answer 1

Fertilization, cleavage, gastulation

Question 2

fertilization

Answer 2

fusion of egg and sperm)

Question 3

cleavage

Answer 3

-rapid cell division of zygote, with NO gain
in mass.
-take on water to create space
-zygote undergoes karyokinesis (mitosis) then cytokinesis (distribution of cytoplasm)
-all cells are inside the zona pellucida or vitelline memb

Question 4

morula

Answer 4

solid ball of cells

Question 5

blastula

Answer 5

hollow ball of cells

-has space for cell movement

Question 6

gastrulation

Answer 6

involution of surface cells to form

three embryonic germ layers

Question 7

ectoderm

Answer 7

becomes integument, nervous system

Question 8

endoderm

Answer 8

becomes gut

Question 9

mesoderm

Answer 9

becomes blood, notochord, connective

tissue, muscle, bone cells

Question 10

protosomes

Answer 10

blastopore forms the mouth “first mouth”

Question 11

deuterostomes

Answer 11

blastopore forms the anus “second mouth”

-echinoderm, amphioxus, frog

Question 12

blastopore

Answer 12

start of gastrulation in which cells start moving

Question 13

isolecithal

Answer 13

sparse and equally distributed yolk

-starfish

Question 14

mesolecithal

Answer 14

intermediate amount of yolk

-frog

Question 15

centrolecithal

Answer 15

yolk in center

-insects

Question 16

telolecithal

Answer 16

only a small area that is yolk free

• huge area of yolk
• chicken

Question 17

animal hemisphere

Answer 17

area that is free of yolk

Question 18

vegetal hemisphere

Answer 18

lots of yolk

Question 19

meridonal cleavage

Answer 19

extends from animal to vegetal axis

Question 20

equatorial cleavage

Answer 20

is perpendiculat to animal-vegetal axis

-divides into animal and vegetal hemispheres

Question 21

holoblastic cleavage

Answer 21

• whole type
• cleavage is complete as the amount of yolk is small
• seen with alecithal, isoelecithal, mesolecithal

Question 22

meroblastic clevage

Answer 22

• type
• incomplete or partial due to the presence of large volumes of yolk
• seen in centrolecithal, telolecithal

Question 23

alecithal

Answer 23

negligible amount of yolk present

-mammal

Question 24

Radial holoblastic cleavage

Answer 24

Radial holoblastic cleavage: The blastomeres are arranged around
the axis from animal pole to vegetal pole. All of the three organisms
that we are investigating in the lab today belong to this category.

Question 25

Spiral holoblastic cleavage

Answer 25

Spiral holoblastic cleavage: Here the cleavage occurs oblique to the animal-vegetal axis. Examples: annelids, molluscs, flatworms

Question 26

Rotational holoblastic cleavage

Answer 26

Rotational holoblastic cleavage: Here the cleavage is slow. The first cleavage is meridional and two blastomeres are formed. Out of the two blastomeres one undergoes meridional cleavage and the second blastomere undergoes equatorial cleavage (perpendicular to the animal-vegetal axis). Example: mammals, nematodes.

Question 27

Bilateral holoblastic cleavage

Answer 27

Bilateral holoblastic cleavage: Here the cleavage splits the fertilized egg into right and left sides of the embryo. Example: tunicates.

Question 28

Discoidal meroblastic cleavage

Answer 28

Discoidal meroblastic cleavage: Cleavage is restricted to a small portion of the cytoplasm present on top of the large yolk. Example includes the embryo of aves, where the eggs are telolecithal

Question 29

Superficial meroblastic cleavage

Answer 29

Superficial meroblastic cleavage: Here the blastomeres occupy the periphery of the yolk. Example includes embryos of insects where the eggs are centrolecithal.

Question 30

Starfish Cleavage

Answer 30

eggs are isolecithal 1. meridional 2. meridional 3. equatorial 4 a) animal meridional b) vegetal unequal equatorial

Question 31

Amphioxus Cleavage

Answer 31

1. meridional 2. meridional 3. equatorial 4 meridional 5. equatprial

Question 32

Frog Cleavage

Answer 32

eggs are mesolecithal (most yolk in vegetal hem) 1. meridional 2. meridional (4 equal blastosomes) 3. equatorial (unequal blasyosomes w animal smaller blastocoel near animal pole)

Question 33

Blastocoel serves two functions in the formation of three germ layers characteristic of triploblastic animals

Answer 33

1) provides space for movement and rearrangement of cells during gastulation so cells are repoitioned in embryo 2) seperates amimal from vegetal hem cells so certain molecules or factors are not in contact with the incorrect germ layer, this facilitates the proper formation of germ layers

Question 34

5 cell movementa

Answer 34

``` invagination ingression involution epibody delamination ```

Question 35

Invagination

Answer 35

Here the sheet of cells (epithelium) bends inwards. Ex: Gastrulation in Amphioxus is primarily the invagination of the vegetal plate

Question 36

Ingression

Answer 36

The cells from the epithelium are set free and become freely migrating cells (mesenchyme). Ex: gastulation of sea urchins, ingression of primary mesenchyme cells In starfish the micromeres breakfree and migrate (type of cell movement during gastrulation called ingression) into the blastocoel at the vegetal end and differentiate into mesenchyme, which would develop into the skeleton of the larva.

Question 37

Involution

Answer 37

Movement of expanding outer layer of epithelial cells inwards so that it spreads over the internal surface Ex:gastulation of sea urchins involution of the vegetal plate itself.

Question 38

Epiboly

Answer 38

Movement of epithelial sheet over cells so as to enclose deeper layer of cells. ex: formation of the ectoderm in the frog

Question 39

Delamination:

Answer 39

Splitting of epithelial sheet into two sheets that are parallel to each other. Ex: in chicks, Cells from the epiblast delaminate into the subgerminal space forming the hypoblast

Question 40

Archentron formation and mak

Answer 40

- eupmade by invagination of vegetal plate - cells lining it are endodermal cells - mesenchymal cells are present at the base - secondary mesenchyme ingress from archentron - the opening is the blastopore that eventually closes by epiboly of ectoderm

Question 41

Frog Gastrulation

Answer 41

- initiates at marginal zone (intersection of pigmented micromeres and yolky macromeres) 1) cresencet dorsal blastopore lip formed - tissue=blast lip - space is blastopore 2) ectodermal cells proliferate, then move via epiboly to the blastopore a) first cells to involute through are endodermal and form archenteron b) mesodermal cells follow (inducers of mesoderm present thus forming the layers of mesoderm) c) chordomesodermal next through blastopore lip-->form notochord 3) cell movement continues and blastopore displaced to side of embryo 4) dorsal blastopore lip gets enlarged and has lateral and ventral lips 5) yolk cells fills blastopre-->this is yolk plus 6) blastopore lip will form anus - involution & amp; epiboly starts at dorsal lip (not vegetal plate)