1C - Development(2) Flashcards
Basic structure of chordate NS
hollow tube dorsal to notochord
True or False: The nerve cord is dorsal in chordates
True
In inveterbrates, where is the neural cord?
Ventral, and its solid
Differences in nerve cord; vertebrates and invertebrates
- Vertebrates: Dorsal, hollow nerve cord
- Invertebrates: Ventral, solid nerve cord
Myelin, who has it?
Vertebrates only
What happens when you rotate annelids (earthworms)? Earthworms are invertebrates
Nerve cord is ventral, but if you rotate 180 degrees, then the nerve cord is dorsal (just like chordates)
Geoffroy Saint-Hilaire proposed Inversion Theory. What is it?
- Common ancestry of invertebrates flipped itself around.
- Converted dorsal surface into ventral surface
- Swim on its back, nerve cord changed from being ventral in location to dorsal in location
What evidence proved the Inversion Theory?
Homebox genes
What are Homebox genes?
Series of genes expressed primarily in embryo
Features of homebox genes?
1) . Front to back order
2) . Expressed heavily in neural tissue precursors
3) . Expressed in adjacent tissue –> like vertebral column
What do hindbrain zones correspond to?
- Reflect basic segmentation pattern of vertebrae brain
- Anatomical markers
Where are homebox genes expressed?
Dorsal in embryo
Fruitfly vs Mouse homebox genes
-Mouse:
Homebox genes expressed dorsally
-Fruitfly:
Homebox genes expressed ventrally
What are the 3 layers of tissue present in all chordates?
1) . Ectoderm (outside)
2) . Mesoderm (inside)
3) .Endoderm (middle)
What does ectoderm give rise to?
outer most layer of skin, epidermis, glands
What does endoderm give rise to?
lining of gut, liver, pancreas
What does mesoderm give rise to?
bones, musculature
What layer of skin gives rise to CNS/PNS (Nervous system) ?
Ectoderm
What is the blastula?
-Hollow ball of cells
3 properties of blastula
- Has empty cavity inside it
- Cells form a single layer
- Cells undifferentiated
What is the process that converts blastula to gastrula? (converts a single layer blastula to a 3-cell layer)?
Gastrulation
What has not formed in early stage of blastula?
Primordium of gut
Does gastrulation occur the same way in all animals? why or why not?
No, because shape of gastrula is different
Blastula of amphioxus
- Hollow inside
- Cavity inside blastula is called blastocele
- Simple
- Single-cell layer
- Dorsally (no yolk)
- Ventrally (yes yolk)
Blastula of frog/amphibian
- Couple cells thick
- 2 layers are differentiated so basically 1 layer
- More yolk ventrally
Blastula of reptile/bird
- Large amount of yolk
- Does not divide
- Below blastocele in cellular disk
What is the cavity inside of the gastrula that is the precursor to the gut?
Gastrocele
In chordates, what does the blastopore become?
Anus, while mouth forms secondarily
In invertebrates, what does the blastopore become?
Mouth, while anus forms secondarily
Gastrulation in amphioxus
- short cube cells outside
- large columnar cells inside
- Outermost layer –> ectoderm
- Innermost layer –> endoderm and mesoderm
Does the blastopore open into the gastrocele?
Yes
Gastrulation in frog
-Yolk stops cells from moving, cannot change shape
Does in-rolling occur dorsally first, then involuation laterally?
Yes
-Dorsal lip of blastopore:
- dorsally located
- first point at which rolling occurs
- Cells from outside of embryo start at this point and move inward
- 1st tissue that involvues to give rise to notochord
What derives notochord?
Mesoderm
Fate map
- Tissue that rolls in at different times/places gives rise to different structures in embryo
- Fate Map maps different locations on outside where cells end up after gastrulation occurs (what adult structures will form)
T/F: There is 1 opening into gastrocele, which is the blastopore, and forms the anus first and mouth secondarily
True
Does endoderm line gastrocele?
Yes
T/F: Humans evolve from animals that have a lot of yolk
True
