Chapter 6 Flashcards
why are drosophila good model organisms?
- rapid life cycle (one week)
- produce 30 eggs/day
- easy to breed -> hardy, tolerant, breeding techniques well knwon
- polytene chromosomes -> able to see mutations
- exchange network of any mutant
- genetics & sequencing are well known, able to follow phenotypes for generations
why NOT drosophila as model organsims?
- complex development (syncitium, skin is opaque, more cells & variability)
- cell lineage isn’t fixed
- cell # isn’t fixed
- metamorphosis is complex
describe the process of forward genetics
- blindly break DNA
- observe defects & find broken gene
- clone gene & name it
- characterize gene sequence, expression patterns, and functions
when is a drosphila egg activated? what does this cause in the cytoplasm?
egg isn’t activated until ovulation
- once cytoplasm moves, tln of stored mRNAs come from somatic cells
describe sperm entry in drosophila
enters on ANTERIOR side
- enters through microphyle in the chorion
how do drosophila prevent polyspermy?
sperm tal is very thick & clogs tunnel
- no fast or slow blocks
what type of cleavage do drosophila do?
superficial cleavage (syncicium, centrolethical)
how long is early cleavage in drosophila?
8 min. about 10x
what happens at the MBT in drosophila?
divisions take a lot longer now
describe late cleavage in drosophila
nuclei migrate toward outside
- cleavage occurs b/w nuclei, leaving middle only yolk (blastoderm)
where do pole cells develop in the embryo and what do they become?
posterior side
- become germ line cells
what is the cephalic furrow?
b/w the head and abdomen of a fly
what is the ventral furrow?
the area that cells fold inward in a fly
what are imaginal discs?
cells held in reserve (not in larve) that eventually produce things needed for the adult form (wings, eyes, etc.)
what are the three axes?
anteroposterior
dorsoventral
proximodistal
what are maternal effect genes?
mom’s gonad cells determine what the baby will look like (no genes inside egg or sperm)
- only mom’s germarium makes embryo’s genetic makeup
- made by the follicle cells through ring canals
describe the experiment with torpedo determining the function of maternal efffect genes
switched the pole cells of the embryo of a wild-type mom & torpedo deficient mom
- mutant egg, normal mom = normal d/v axis
- normal egg, mutant egg = no d/v axis
what side is the egg in the germarium?
posterior side
- follicle cells send material to posterior side through ring canals
what does the torpedo gene (receptor) do? what does it bind and where?
specify DORSAL fates (back)
- binds gurken made by oocyte nucleus
- torpedo receptor is only on dorsal side of oocyte in the posterior follicle cells
what does the dorsal gene do?
specify VENTRAL fates (belly)
what does bicoid protein do?
specify ANTERIOR fates (head)
- turns on hunchback (gap gene)
what does nanos protein do?
specify POSTERIOR fates (tail)
- turns on giant, knirpes (gap gene)
what does torso gene do?
specify TERMINAL fates (tips: antenna, rear)
- signal only found on ends, not floating around
- makes acron & telson
what are the five regions of a fly?
acron
head
thorax
abdomen
telson
are hunchback & caudal localized?
no
- unlike maternal effect genes which are localized
during early cleavage, describe how hunchback and caudal are higher at a certain end (anterior, posterior) if they aren’t localized
bicoid blocks caudal, nanos blocks hunchback
- hunchback higher at anterior end
- caudal higher at posterior end
what does the short gastrulation gene do?
specifies midline fates (P/D axis)
- helps create a grid of cell fates
describe how genes create a grid to specify location of salivary glands
scr makes salivary glands (inhibited by dpp & dorsal)
- the area where dpp & dorsal aren’t expressed, scr makes a salivary gland
what axis do hox genes specify?
midline fates (P/D axis)
how many segments are there in a drosophila?
14
what are compartments and how many are there in drosophila?
the posterior and anterior regions of each segment (28)
what are parasegments and how many are there in drosophila?
overlaps each segment through the compartments (14)
- allows for communication b/w each segment
- EX: nerves go to each parasegment to allow for fluid motion of muscles in crayfish tail
describe the classes of genes involved in segmentation, in order
- cytoplasmic polarity
- hunchback gradient
- gap genes
- pair-ruled genes
- segment polarity genes
- homeotic genes (activated by both segment and pair-ruled genes)
what are the four gap genes? how many stripes does it make and how does a mutation effect the fly?
giant, hunchback, kripple, knirpes
- makes a giant stripe (1-2)
- mutations lead to lack in large body regions
describe how the gap genes create lanes of expression
they all inhibit eachother (turn off in middle, leave them alone on outsides)
- level of hierarchy & can be conc. dependent
- all of them compete for binding sites by limiting each other’s expression
describe mutually exclusive gap genes
Kni and Hb equally inhibit eachother
Kr and Gt equally inhibit eachother
describe concentration dependent gap genes
Large amount of Hb inhibits Kr
Small amount of Hb activates Kr
what activates the gap genes? what does this gene also inhibit at the same time as activating the gap genes?
bicoid actiavtes the gap genes and inhibits caudal
what are the two pair-ruled genes? how many stripes does it make and how does a mutation effect the fly?
fushi tarazu (even)
eve (odd)
- every other parasegment (7)
- mutations lead to lack in portions of every other segment
what are the two segment polarity genes? how many stripes does it make and how does a mutation effect the fly?
engrailed, hedgehog
- only posterior or anterior part of each segment (14)
- mutations lead to a lack in portions of every segment
describe the pathway of how fushi tarazu activates engrailed
- fushi tarazu activates engrailed
- causes the engrailed cells to have affinities toward eachother & stick to form a stripe
- engrailed releases short-range inducer hh that contains ciD
- only the first row near hh, anterior side, allows for binding of hh to patched
- this causes dpp, long range inducer, to be activated & form a gradient & reach cells at different concentrations
what do homeotic genes do in relation to segmentation?
get activated one-by-one, arranged in a tandem on chromosome that encodes TFs
- binds to specific enhancers to turn on genes that cause organs to develop in the right place
what are the two complexes that make up the homeotic complex (hom-c)?
antennapedia complex
bithorax complex
