DEVELOPMENT & LIFE HISTORIES Flashcards
Is the Animal Pole the top or bottom pole of an egg? What does it become?
Top. Becomes other regions of the embryo besides the digestive system
Is the Vegetal Pole the top or bottom pole of an egg? What does it tend to become?
Bottom. Tends to become the digestive system
Isolethical
Yolk distributed uniformly through egg
Centrolecithal
Yolk distributed in center around nucleus
Telolecithal
Yolk concentrated at vegetal pole
What is the name for a fertilized egg?
Zygote
What are the resulting cells when a zygote splits?
Blastomeres
define Holoblastic Cleavage
What egg types does this occur in
cleavage planes pass all the way thru the cell
Occurs in isolecithal and weakly telolecithal cells
define Merbolastic cleavage
What egg types does it occur in
cleavage planes do not pass through dense yolk so the blastomeres are not separated from each other
Occurs in telolecithal eggs
Define determinate development
(in spiral cleavage)
fates of early blastomeres is fixed.
embryo will die if cells are removed
Define indeterminate development
(usually radial cells)
cell fate is determined later in development. Can remove a blastomere and cells develop normally
what type of egg forms a Coeloblastula
formed from isolecithal eggs that undergo radial cleavage
what type of egg forms a Stereoblastula
Egg formed from spiral cleavage
what type of egg forms a Discoblastula
Egg formed from meroblastic cleavage
what type of egg forms a Periblastula
formed from centrolecithal eggs
What does endoderm form
the gut
What does ectoderm form
skin and nervous system
What does mesoderm form
muscles, circ system, and internal support system
What is gastrulation by invagination?
What type of blastula often does this?
cells near the vegetal pole grow inward leading to an archenteron and a blastopore. Inner cells are endoderm and outer cells are ectoderm.
Coeloblastulae often gastrulate by invagination
What is gastrulation by ingression?
What type of blastula does this?
cells near the vegetal pole grow to fill the blastocoel. leads to a solid gastrula called a stereogastrula
Some coeloblastulae undergo ingression.
What is gastrulation by epiboly?
What type of blastula does this?
cells from the animal pole grow over the rest of the blastula. The archenteron occurs secondarily
Stereoblastulae that result from holoblastic cleavage
What is gastrulation by involution?
What type of blastula does this?
Cells around the disc proliferate and grow under the disc. Yolk is still present
Discoblastulae often gastrulate this way
What is true mesoderm?
Derived from endoderm
What is Schizocoely?
In organisms with spiral cleavage, the 4d micromere proliferates between the archenteron and the ectoderm to form a solid mass of mesoderm
