Development: Amphibians and Birds (LP.2)

Question 1

What environment do Ambhibians develop from?

Answer 1

-From eggs w/ a moderate amount of yolk

Question 2

What environment do birds develop from?

Answer 2

-Develop from eggs w/ large amounts of yolk

Question 3

What does the amount of yolk in an egg influence?

Answer 3

-It influences the way development occurs w/ respect to cleavage patterns & morphogenesis

Question 4

What are the key characteristics of amphibian eggs?

Answer 4

• They have more yolk in them than echinoderms

- The yolk is more dense & concentrated in animal pole= animal-vegetal polarity

Question 5

What occurs after the fertilization of an Amphibian egg?

Answer 5

-There is a shift in animal-hemisphere pigment which forms the grey crescent= the dorsal region of the embryo

Question 6

How does cleavage begin in Amphibian eggs?

Answer 6

• It is vertical= begins are animal pole & works its way down to the vegetal pole
• But the Cleavage Furrow is slow as it gets to the vegetal pole bc there’s more yolk there

Question 7

What is the 2nd cleavage like in Amphibian eggs?

Answer 7

-It’s Vertical & starts before the first one even completes

Question 8

What is the 3rd cleavage like in Amphibian eggs?

Answer 8

-It is Horizontal BUT it doesn’t cut the blastomeres into equal animal/ vegetal sets bc the plane is offset towards animal pole= upper tier of blastomeres is smaller than the lower one

Question 9

Why do the animal hemisphere blastomeres get cleaved quicker in Amphibian eggs?

Answer 9

-Bc theres less yolk than in the vegetal pole

Question 10

What is the Blastoceol like in Amphibian eggs?

Answer 10

-It is formed normally but it is restricted to the animal-hemisphere

Question 11

Why isn’t the Blastoceol formed in the Vegetal Hemisphere of Amphibian Eggs?

Answer 11

-Bc its solid w/ large yolk-packed cells

Question 12

What are the beginning stages of Gastrulation like in Amphibian eggs?

Answer 12

• The cells in the ventral margin of where the grey crescent was migrate to the interior of the embyro which produces a blastopore & archenteron on the side of the blastula
• (DOES NOT BEGIN IN VEGETAL POLE)

Question 13

What occurs as Gastrulation proceeds in Amphibian eggs?

Answer 13

• The blastocoel reduces in volume by the Invaginating Mesoderm & Endoderm cells
• Then the 3 germ layers are formed

Question 14

What are the 3 germ layers in Amphibian Gastrulation?

Answer 14

• The Endoderm (inside)= Lungs, &digestive organs like the Gut, pancreas, liver
• The Mesoderm (middle)=bone, muscle, blood, kidneys, gonads
• Ectoderm (outside)= outer layer of the skin, nervous system

Question 15

What is the Archenteron Roof?

Answer 15

• In amphibians

- The upper layer of cells of the archenteron

Question 16

How does the Central Nervous system of Amphibians develop?

Answer 16

• Begins when the thickening of the Archenteron Roof

- The neural plate folds into neural tube that becomes brain & spinal cord

Question 17

What are the steps in Amphibian development?

Answer 17

1) Egg/zygote
2) 2 cell
3) early cleavage
4) blastula
5) early gastrula
6) Gastrula
7) Neural Plate
8) Neural Groove
9) Neural tube

Question 18

What does the Blastula stage of Amphibian development consist of?

Answer 18

-The Blastula formation at the animal pole

Question 19

What does the Early Gastural stage of the Amphibian Development consist of?

Answer 19

• Blastocoel at animal pole
• Arhenteron starting to form
• The blastopore (dorsal lip) starting to form from that archenteron forming

Question 20

What does the Gastrula stage of Amphibian development consist of?

Answer 20

• The blastopore still in the animal-hempishere
• The dorsal lip forming around the
• Yolk plug in the middle

Question 21

What does the Neural Plate stage of Amphibian development consist of?

Answer 21

• Notochord starting to form on top of the archenteron
• The archenteron takes on an upsidedown “U” shape
• The mesoderm starts to form

Question 22

What does the Neural Groove stage of Amphibian development consist of?

Answer 22

• The notochord is fully formed on top of archenteron
• Archenteron has same upsidedown “U” shape but its thicker
• Neural fold starts to form at the animal-hempishere
• Somites take place in the “empty” space

Question 23

What does the Neural Tube stage of Amphibian development consist of?

Answer 23

• The neural tube is now pinching off
• The notochord is till on top of “archenteron”
• The archenteron has now formed into a gut
• Somite is everything else inside

Question 24

What are Bird eggs like?

Answer 24

• They have hella yolk
• BUT the blastodisc at animal pole has a little less yolk to allow for cleavage
• Has very distinct animal-vegetal polarity

Question 25

How are the first cleavages like in Bird eggs?

Answer 25

-They are vertical but extend only a short distance downward

Question 26

How is the 3rd cleavage of Bird eggs like?

Answer 26

-It is horizontal= gives rise to several layers of blastomeres that make up the disc cells at the top of the yolk

Question 27

How does Gastrulation start in Bird eggs?

Answer 27

-It starts by the separation of cells from the lower surface of the blastoderm which forms the hypoblast below the Epiblast

Question 28

What is the Hypoblast?

Answer 28

• Only in Bird eggs

- Flimsy layer of endoderm

Question 29

What is an Epiblast?

Answer 29

• Only in birds

- It is a layer of cells above the hypoblast

Question 30

What’s in the Middle of the Epiblast and Hypoblast?

Answer 30

-The blastocoel

Question 31

What happens as Gastrulation in Bird eggs continues?

Answer 31

• The hypoblast expands to form complete layer
• Cells of the Epiblast migrate toward posterior & central region to form a thickened region of the epiblast= Primitive Streak

Question 32

What do some cells in the Primitive Streak do?

Answer 32

-Migrate to a space between the Epiblast and Hypolast = forms middle layer of cells (notochord in midline & lateral mesoderm flanking it)

Question 33

When does the Primitive Streak regress & what is the consequence of this?

Answer 33

• When the middle layer of cells begin to move inward

- It leaves the notochord & lateral mesoderm in its wake

Question 34

When does the Neural Plate of Bird eggs form?

Answer 34

-When the ectoderm above the notochord thickens

Question 35

Where does the Neural Tube form in Bird eggs?

Answer 35

-It forms the brain on the broad anterior end & the spinal cord at the narrower posterior end

Question 36

What are the 6 general stages of development like in Birds?

Answer 36

1) develops optic vesicles
2) then the cerebral vesicles
3) these cerebral vesicles turn into cerebral hemispheres
4) Lateral to neural tube=blocks of mesoderm=Somites
5) Structures like vertebrate, dermis, muscles, develop from the somites
6) Heart develops from tube that forms lateral mesoderm

Question 37

What developed in the 16-18 hours of incubation in Birds?

Answer 37

-The primitive streak

Question 38

What develops in the 33 hour of incubation in birds?

Answer 38

-The brain, optic vesicles, spinal cord, somites, heart

Question 39

What develops in the 48 hour of incubation in birds?

Answer 39

-Brain, optic cups, spinal cord, lenses, somites, heart, limb buds, pharyngeal slits, somites

Question 40

What develops in the 72 hour of incubation in birds?

Answer 40

-Everything in 48 hour plus cerebral vesicles