rapid specification in snails and nematodes Flashcards
what happens during fertilization
sperm and egg create a zygote with a new genetic blueprint
what happens during cleavage
rapid cell division
increases cell number but not the size
what happens during axis formation
establishment of body plan
timing and mechanism may vary among species, some during oocyte formation, cleavage, or gastrulation
types of axes (3)
dorsal-ventral
anterior-posterior
left-right symmetry
three layered structure (germ layers) formed in gastrulation
endoderm (inner layer)
mesoderm (middle layer)
ectoderm (outer layer
what is the dorsal-ventral axis and factors establishing it
back-belly
gravity and sperm entry point
what is the anterior-posterior axis and what type of molecules form them
head-tail
signaling molecules from the dorsal region of the blastopore
what is the left-right symmetry and what are the molecules and genes involved in its formation
asymmetry
molecules and genes involved in bilateral symmetry
what happens during the primary organ formation
differentiation of the germ layers into tissues and organs
what happens during organogenesis
further development of organs from the tissues
what is a zygote
fertilized egg
what happens during gastrulation
dramatic cell arrangement
establishes body axes
formation of 3 germ layers
what is a blastopore
mouth-like opening in the archenteron
what determines the coiling direction of snails
axis formation or during cleavage and gastrulation, specifically during the formation of left-right symmetry
azz
species used for studying development due to ease of lab maintenance
model organisms
when and how does cell fate determination happen
during cleavage and gastrulation, embryonic cells acquire their specific functions
what are eukaryotic organisms and to what do they divide into
has a nucleus and distinct chromosomes (genetic material) that undergo cell division (mitosis)
- multicellular eukaryotic organism
- metazoan
what are multicellular eukaryotic organisms
cells from mitosis stay together, forming a complete organism (plant, fungus, or animal)
what are metazoans
(animals) defined by undergoing gastrulation - which further leads to the formation of body axes
how many animal development pathways are there
35 metazoan phyla: 35 animal development pathways (not linear)
how does mitosis happen
cell divison that creates new cells with identical genetic material
(basal animal key points) what are dipoblasts
animals with two germ layers (endoderm and ectoderm) with little to no mesoderm
- ex. cnidarians (jellyfish) / ctenophores (comb jellies)
(basal animal key points) what does ectoderm develop into
outer layer - skin, nervous system
(basal animal key points) what does mesoderm develop into
middle layer - muscles, bones, connective tissues
(basal animal key points) what does endoderm develop into
inner layer - lining of digestive tract
(basal animal key points) info
Recent studies suggest Ctenophores, not sponges, are the most ancient animal group.
(Cnidarians having the oldest lineage is still debated)
(basal animal key points) info (challenges for traditional distinctions)
(1) Sponges have genes for a nervous system, but lack one, suggesting it was lost in their evolution.
(2) Some Cnidarians might have a form of mesoderm and exhibit bilateral symmetry in certain life stages, challenging the traditional distinction between diploblasts and triploblasts.
(basal animal key points) what gives rise to organs and tissues
germ layers
(basal animal key points) characteristics of animals that gives them a left and right side that are mirror images of each other
bilateral symmetry
(basal animal key points) traits evolving independently in different lineages
evolutionary divergence
(animal body plans distinction) traditional: what are the characteristics of dipoblasts - cnidarians and ctenophores (3)
(1) Radial symmetry (body parts arranged around a central axis)
(2) Two germ layers (ectoderm & endoderm)
(3) No mesoderm
(animal body plans distinction) traditional: what are the characteristics of tripoblasts - all other animals (3)
(1) Bilateral symmetry (left-right mirror image)
(2) Three germ layers (ectoderm, mesoderm, endoderm)
(3) Mesoderm forms muscles, bones, etc.
(tripoblastic animals) advantages of having a mesoderm (2)
mobility: supported by muscles
body size: mesoderm gives rise to a circulatory system which supports larger bodies
(tripoblastic animals) what are the two main branches of tripoblastic animals
protostomes
deuerostomes
tripoblastic animals that forms the mouth first during gastrulation
protostomes
ex. mollusks (snails), arthropods (spiders)
how does the coelom of protostomes form
schizocoely - develops from a solid mass of mesoderm cells hollowing out
what are the two main branches of protostomes
(ecdysozoans) - to shed / arthropods, nematodes (molt their external skeletons)
(lophotrochozoans) characterized by spiral cleavage, trochophore larva (free-swimming larval stage with cilia), and lophophore (feeding structure in some adults / ex. clams)
what does planktonic mean
living in open water and drifting with the currents
tripoblastic animals that forms the anus first during gastrulation
deuterostomes
ex. chordates (humans, fish, frogs), echinoderms (starfish, sea urchins)
how does the coelom of deuterostomes form
enterocoely - pouches from the gut extend to form the body cavity
what features do chordates and vertebrates share (2)
notochord
pharyngeal arches
what are notochords
a rod-shaped a that precedes the development of the backbone
what are pharyngeal arches
structures in developing embryos that eventually form parts of the head and neck
what are maternally active genes
genes in the egg that are inherited from the mother and influence development before the zygote’s genes are activated.
what are blastomeres
cells formed by cleavage
the classification of deuterostomes and protostomes is based on ____________
embryonic development
(snails as devbio model) why are snails longstanding model organisms?
abundance
easy lab maintenance
variation
rapid development and cfd
(snails as devbio model) mosaic development of snails (2)
(1) early blastomere removal leads to missing adult structures
(2) cells responsible for specific organs are highly localized
differentiate autonomous and regulative development
autonomous: cfd is predetermined and removing a cell early results in a missing structure
regulative: cells can compensate for the loss of neighboring cells, adjusting their fates
characteristics of snail embryo cleavage
(1) spiral cleavage (planes are not straight, but at oblique angles
(2) blastomeres are packed tightly together like bubbles
(3) fewer cell divisions before gastrulation
(snails as devbio model) cfd of blastomeres
predetermined (mosaic development)
(snails as devbio model) characteristics during blastula stage
early embryo with a hollow center (blastocoel)
blastocoeal are absent or very small - called stereoblastulae
cleavage
gastrula
