Development Flashcards
Two major categories of animals
deuterostomes and protostomes
deuterostomes
First opening is the anus; mouth forms second
ex: echinoderms (sea urchins), vertebrates (fish, amphibians, reptiles, birds, mammals)
protostomes
First opening is the mouth; anus forms second
ex: worms, mollusks, arthropods
deuterostomes vs. protostomes
- Cleavage - protostomes undergo spiral cleavage; deuterostomes undergo radial cleavage
- Determinant vs indeterminate development - protostomes have determinate development; deuterostomes have indeterminate development
- Fate of blastopore - protostomes - blastopore becomes mouth; deuterostomes - blastopore becomes anus
- Formation of coelom - protostomes have no folding occur in the mesoderm layer to form the coelom; deuterostomes have extra folding that occurs to form coelom
determinate vs. indeterminate development
indeterminate development means the cells at the 8-16 cell stage are not fixed in their development; you can remove one and the other cells can make up for it.
determinate development - causes damage if you remove a cell
leydig cells
make testosterone
sperm structure
- head - acrosomal vesicle, nucleus
- mid piece - mitochondria
- tail - flagellum
oogenesis
- primary oocyte begins meiosis but is arrested in prophase 1
- when girls hit puberty, primary oocyte begins meiosis again
- secondary oocyte arrests in metaphase II
- meiosis II completes only if the sperm fertilizes the egg
zygote
is the result of nuclear fusion - egg and sperm fuse nuclei
zona pellucida
an egg membrane layer underneath the corona radiata . Found in mammals. When the sperm fuses with the egg membrane it causes a hardening of the zone pellucida, which prevents multispermy in mammals
corona radiata
outer layer of cells protecting the egg in a mammal.
Sea urchin fertilization
sperm acrosomal enzymes digest the jelly coat of the egg. Actin monomers in the sperm start polymerizing to form microfilaments that push further into the egg. This nose pushes out and binding in the sperm can bind to their receptors on the egg. The membranes can then fuse and sperm can dump DNA into the egg.
When sperm gets into the egg, it signals Vitellin membrane to jump up - the cortical reaction is how sea urchins prevent multispermy
vitellin membrane
the membrane in sea urchins that jumps up when sperm fuses with egg membrane. Vitellin membrane jumping up is what prevents multispermy in sea urchins.
cleavage
the second stage of development that produces a blastula. This process is characterized by rapid cell division without any growth.
sea urchin cleavage
radial and holoblastic
holoblastic cleavage
cells divide all the way through
blastula
cells are not differentiated into tissues yet. 1000-3000 cell stage. The embryo arrives in the uterus in blastula form.
blastocoel
hollow space within the blastula
mammalian cleavage
mammals undergo holoblastic and radial cleavage. Blastocoel forms underneath the inner cell mass.
inner cell mass
found in the blastula stage of mammals and this group of cells goes on to form the embryo
trophoblast cells
the outer cells of the blastula that go on to form extra-embryonic structures (as opposed to inner cell mass, which forms embryo)
gray crescent
found in amphibian stage of fertilization. We don’t know what it is or how it works exactly, but if you fuck up the gray crescent material, you fuck up development.
cleavage in amphibians
asymmetric holoblastic radial cleavage. The result of this type of cleavage is that you end up with many more and smaller cells at the top of the embryo (animal pole) than the bottom (vegetal pole).
blastocoel is offset in frogs due to yolk presence