Mini Exam 4 Flashcards
what type of cleavage do c. elegans do?
rotational holoblastic
what side of the egg do the sperm enter in c. elegans?
posterior side
what happens to the egg once the sperm enters on the posterior side?
- Sperm organizes microtubules (asters) on posterior side
- actin filaments cause cytoplasmic flow
- fluid moves toward anterior side
- captures Par-2 into the cortical cytoplasm
what is autonomous specification?
the P1 lineages are random
- cytoplasmic factors determine their fate, not their neighbors (Par-2, Mex-5, PIE-1, etc.)
what is the difference between P1 and AB cells in c. elegans?
P1 = germ line cells
AB = cells that do mitosis
- the two cells after the first cleavage
what is Par-2? where is it located?
posterior cell (P1) = germ line cell
- partitioned to the cortical cytoplasm
- helps create two separate cells
where is Mex-5 located?
anterior cell (AB) = mitotic cells
where is PIE-1 located? what does it do?
posterior cell (P1) = germ line cell
- inhibit RNA poly to allow for the germ line cells to not turn into somatic cells
what is activating and inhibiting in the AB cell? (anterior, somatic cells)
Mex-5 inhibits PIE-1
what is activating and inhibiting in the P1 cell?
Par-2 inhibits Mex-5
- allows PIE-1 to be activated and inhibit RNA poly
what do P-granules do?
Glow fluorescent & Indicate which cells are going to be the germ line cells
- keep the cell as a primordial germ cell
- Blocks gene transcription, translation, and gene expression
- Keep things inert
what blocks P-granule formation?
Mex-5
why are c. elegans used as a model for development?
small number of chromosomes
- Easy to identify genes needed for development
Follows a set lineage pattern (fixed)
- Can follow cell and know what it’s going to become
- Very few cell types and cells overall
- Set number of cells
1mm long
- can study millions of them at a time
Transparent cuticle
- able to watch easily
- (cleavage, forming organs, etc.)
easy to keep alive
only takes 16 hours to develop
- able to watch internal fertilization
how many cells are in a newly hatched c. elegans larve?
558
how many somatic cells are in a c. elegans adult?
959
how many genes are in c. elegans?
20,000
- same as humans
how can c. elegans and humans have the same number of genes?
- No space between genes
- Not alternatively spliced (no differential splicing)
- RNA gene expression!!!
- One protein -> one function
- No isoforms
- Has lots of duplicate genes
what is the organ called that stores the sperm in c. elegans?
Spermatheca
why are drosophila used as model organisms for development?
- one week life cycle
- easy to breed (hardy, tolerant, techniques known)
- produce 30 eggs a day
- able to follow for generations (can see phenotypes)
- mutant bank started by thomas hunt morgan
why aren’t drosophila good model organisms?
Complex development
- more cells
- start off in a syncitium (lots of nuclei in one cell)
- Too small to see cells
- Skin is opaque (can’t see inside)
- No cleavage studies
Cell lineage is not fixed
Cell number is not fixed
Life cycle is complex
Complex metamorphosis
describe the process of forward genetics
- random mutagenesis (Break DNA blindly)
- observe defects and find broken genes
- clone mutant genes
- name the gene for what the mutant looks like (ex: wingless)
- characterize gene sequence
- characterize expression patterns
- characterize functions
when does a drosophila egg activated?
once it is ovulated
- the sperm enters an egg that is already activated
what side of the drosophila egg does the sperm enter?
anterior side
what is the structure called that the sperm enters? how does this prevent multiple fertilization (no fast or slow block)?
micropyle
- tunnel in the chorion (outer shell)
- sperm tail is much longer than other species (very thick)
- once a sperm enters it, the tail clogs the tunnel so not other sperm can get it
describe cleavage in drosophila
Superficial Cleavage (syncicium)
- Several nuclei in the cell
- Only takes 8 minutes (no cytokinesis!)
- After 10 divisions, the nuclei migrate away from middle towards the outside
-cleavage only on the outside between the nuclei once they have migrated
- Middle is all yolk
what happens after the mid-blastula transition in drosophila?
divisions take much longer
what side are the pole cells on of the egg?
posterior side
- eventually migrate inward toward the middle
what is the cephalic furrow?
formed during drosophila gastrulation
- between head and abdomen
what is the ventral furrow?
formed during drosophila gastrulation
- where cells start to fold in on themselves
what are the three segments in drosophila during Segmentation?
Head Segment -> Ma, Mx, Lb
Thorax Segment -> T1-3
Abdomen Segment -> A1-8
what are imaginal discs?
Cells held in reserve (not in larvae), that produce things needed for the adult form (wings, eyes, etc.)
- Don’t move between segments though!
what are Maternal effect genes?
Mom’s gonad cells (diploid, mitotic) determine what the baby will look like
- No genes inside the egg, or sperm decide what the baby looks like
- Only what is going on in the mom’s germanium is what matters for the genetic makeup of the baby
how do ring canals form an axis?
Ring canal send materials from the nurse cells (mitosis) to the oocyte cell (meiosis)
- Only send materials from anterior side of the cell
- Oocyte is near the posterior follicle cells
what does the torpedo gene do?
Specify dorsal fates (back)
- receptor only on the dorsal side of egg
what is gurken?
made by the nucleus to bind to torpedo (receptor)
- when bound, creates the dorsal side
what does the dorsal gene do?
Specifies ventral fates (stomach)
- without it, creates two backs
what does the bicoid protein do?
Specifies Anterior Fates
- placing bicoid in a place where it is not found, creates another head
- turns on other proteins like hunchback
what does the nanos protein do?
Specifies Posterior Fates
- turns on other proteins like giant, knirps
what are the 5 regions of a fly? what creates them?
bicoid and nanos
- Acron Region -> cap of the head, antennas
- Head Region
- Thorax Region -> wings, legs afer metamorphosis
- Abdomen Region
- Telson Region -> rear
