Chapter 6

Question 1

why are drosophila good model organisms?

Answer 1

• 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

Question 2

why NOT drosophila as model organsims?

Answer 2

• complex development (syncitium, skin is opaque, more cells & variability)
• cell lineage isn’t fixed
• cell # isn’t fixed
• metamorphosis is complex

Question 3

describe the process of forward genetics

Answer 3

1. blindly break DNA
2. observe defects & find broken gene
3. clone gene & name it
4. characterize gene sequence, expression patterns, and functions

Question 4

when is a drosphila egg activated? what does this cause in the cytoplasm?

Answer 4

egg isn’t activated until ovulation
- once cytoplasm moves, tln of stored mRNAs come from somatic cells

Question 5

describe sperm entry in drosophila

Answer 5

enters on ANTERIOR side
- enters through microphyle in the chorion

Question 6

how do drosophila prevent polyspermy?

Answer 6

sperm tal is very thick & clogs tunnel
- no fast or slow blocks

Question 7

what type of cleavage do drosophila do?

Answer 7

superficial cleavage (syncicium, centrolethical)

Question 8

how long is early cleavage in drosophila?

Answer 8

8 min. about 10x

Question 9

what happens at the MBT in drosophila?

Answer 9

divisions take a lot longer now

Question 10

describe late cleavage in drosophila

Answer 10

nuclei migrate toward outside
- cleavage occurs b/w nuclei, leaving middle only yolk (blastoderm)

Question 11

where do pole cells develop in the embryo and what do they become?

Answer 11

posterior side
- become germ line cells

Question 12

what is the cephalic furrow?

Answer 12

b/w the head and abdomen of a fly

Question 13

what is the ventral furrow?

Answer 13

the area that cells fold inward in a fly

Question 14

what are imaginal discs?

Answer 14

cells held in reserve (not in larve) that eventually produce things needed for the adult form (wings, eyes, etc.)

Question 15

what are the three axes?

Answer 15

anteroposterior
dorsoventral
proximodistal

Question 16

what are maternal effect genes?

Answer 16

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

Question 17

describe the experiment with torpedo determining the function of maternal efffect genes

Answer 17

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

Question 18

what side is the egg in the germarium?

Answer 18

posterior side
- follicle cells send material to posterior side through ring canals

Question 19

what does the torpedo gene (receptor) do? what does it bind and where?

Answer 19

specify DORSAL fates (back)
- binds gurken made by oocyte nucleus
- torpedo receptor is only on dorsal side of oocyte in the posterior follicle cells

Question 20

what does the dorsal gene do?

Answer 20

specify VENTRAL fates (belly)

Question 21

what does bicoid protein do?

Answer 21

specify ANTERIOR fates (head)
- turns on hunchback (gap gene)

Question 22

what does nanos protein do?

Answer 22

specify POSTERIOR fates (tail)
- turns on giant, knirpes (gap gene)

Question 23

what does torso gene do?

Answer 23

specify TERMINAL fates (tips: antenna, rear)
- signal only found on ends, not floating around
- makes acron & telson

Question 24

what are the five regions of a fly?

Answer 24

acron
head
thorax
abdomen
telson

Question 25

are hunchback & caudal localized?

Answer 25

no - unlike maternal effect genes which are localized

Question 26

during early cleavage, describe how hunchback and caudal are higher at a certain end (anterior, posterior) if they aren't localized

Answer 26

bicoid blocks caudal, nanos blocks hunchback - hunchback higher at anterior end - caudal higher at posterior end

Question 27

what does the short gastrulation gene do?

Answer 27

specifies midline fates (P/D axis) - helps create a grid of cell fates

Question 28

describe how genes create a grid to specify location of salivary glands

Answer 28

scr makes salivary glands (inhibited by dpp & dorsal) - the area where dpp & dorsal aren't expressed, scr makes a salivary gland

Question 29

what axis do hox genes specify?

Answer 29

midline fates (P/D axis)

Question 30

how many segments are there in a drosophila?

Answer 30

14

Question 31

what are compartments and how many are there in drosophila?

Answer 31

the posterior and anterior regions of each segment (28)

Question 32

what are parasegments and how many are there in drosophila?

Answer 32

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

Question 33

describe the classes of genes involved in segmentation, in order

Answer 33

1. cytoplasmic polarity 2. hunchback gradient 3. gap genes 4. pair-ruled genes 5. segment polarity genes 6. homeotic genes (activated by both segment and pair-ruled genes)

Question 34

what are the four gap genes? how many stripes does it make and how does a mutation effect the fly?

Answer 34

giant, hunchback, kripple, knirpes - makes a giant stripe (1-2) - mutations lead to lack in large body regions

Question 35

describe how the gap genes create lanes of expression

Answer 35

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

Question 36

describe mutually exclusive gap genes

Answer 36

Kni and Hb equally inhibit eachother Kr and Gt equally inhibit eachother

Question 37

describe concentration dependent gap genes

Answer 37

Large amount of Hb inhibits Kr Small amount of Hb activates Kr

Question 38

what activates the gap genes? what does this gene also inhibit at the same time as activating the gap genes?

Answer 38

bicoid actiavtes the gap genes and inhibits caudal

Question 39

what are the two pair-ruled genes? how many stripes does it make and how does a mutation effect the fly?

Answer 39

fushi tarazu (even) eve (odd) - every other parasegment (7) - mutations lead to lack in portions of every other segment

Question 40

what are the two segment polarity genes? how many stripes does it make and how does a mutation effect the fly?

Answer 40

engrailed, hedgehog - only posterior or anterior part of each segment (14) - mutations lead to a lack in portions of every segment

Question 41

describe the pathway of how fushi tarazu activates engrailed

Answer 41

1. fushi tarazu activates engrailed 2. causes the engrailed cells to have affinities toward eachother & stick to form a stripe 3. engrailed releases short-range inducer hh that contains ciD 4. only the first row near hh, anterior side, allows for binding of hh to patched 5. this causes dpp, long range inducer, to be activated & form a gradient & reach cells at different concentrations

Question 42

what do homeotic genes do in relation to segmentation?

Answer 42

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

Question 43

what are the two complexes that make up the homeotic complex (hom-c)?

Answer 43

antennapedia complex bithorax complex