Vertebrate Development Flashcards
Fertilization, Cleavage, Gastrulation, then what?
Phylotypic Stage (Distinct head)
Phylotypic Stage
- Forms the distinct head
- Neural Tube is formed (place where future brain & nervous system will be
- Notochord- place where future spine will be, flanked by somites (which are blocks of cells for future muscle & skeleton)
Anamniotes
No amnion, fish and amphibians
Amniotes
Amnion- extra embryonic membrane (mammals & birds)
Frog (Xenopus)
- Have easy access to zygotes where can inject hormones to make them mate
- They have 100 eggs in one large blastula (which is easy to manipulate)
- They are hardy eggs where no infections after surgery
Which is better for genetic studies X. tropicalis (diploid) or X. laevis?
X. tropicalis which is diploid
Frog life cycle: The egg
- Polar where it has two region a dark region that is the animal region & a light region that is vegetal region (yolk/proteins)
- Stopped at meiosis - 1
- Fertilization- one sperm enters the animal region where it starts meiosis 2 & pronuclei fuse
What happens during the 1st cleavage of a frog egg?
1st cleavage occurs 90 mins after fertilization through animal- vegetal axis where it cuts both animal & vegetal region
2nd Cleavage of frog egg
Occurs after 30 mins where it cuts through animal- vegetal axis perpendicular to the 1st cleavage where it cuts both animal & vegetal region (all cells are equivalent)
3rd cleavage
Occurs at the equatorial axis where it separates the animal & vegetal region- 4 small animal cells & 4 large vegetal cells (both blastomeres)
Cleavage of the frog eggs
Its synchronous initially but at 4th division, not synchronous where thick vegetal yolk impedes which results in the vegetal region having fewer but larger cells
Blastula
Occurs after the 12th cleavage where it has 1,000 cells& in the animal region the blastocoel is the fluid cavity (the 3-germ layer are allocated but not moved)
Gastrulation
- Has a little mitosis where it moves & rearrangement of germ layers
- blastopore –infoldings on future dorsal side
- dorsal lip–organizer of AP axis structures
Gastrulation also involves what during the frog egg cycle?
- involution- endoderm, mesoderm occurs where they move inside through blastopore
- epiboly- ectoderm spreads & covers embryo
Neurulation (neurula)
Occurs after fertilization where the neutral tube precursor to CNS