5a: Drosophila

Question 1

Drosophila helped us with

Answer 1

rediscovery of Mendel’s laws
proof of chromosome theory of inheritance (genes are in fact on chromosomes)
proof that X-rays are mutagenic
Hox genes

bc they are small, short gen time, smll num of chromosomes, ample visible markers, mutations easily recovered

Question 2

Micropyle

Answer 2

single site of sperm entry so prevention of polyspermy may be sinply a physocal blockage of only one sperm being able to enter at a tim e

Question 3

Facts about sperm in dropsophila

Answer 3

femal can retain it so one mating is good for lifetime of fertilization

sperm have long tail

no cortical granules on egg but thre is changes in corical cytoplasm when egg is activated

Question 4

most of the space of the abdomin of drosophila is

Answer 4

male: occupied by testes

female: occupied by ovaries

Question 5

Cleavage

Answer 5

Superficial cleave: large central yolk mass, rapid syncticial nuclear division created the syncytium
cycle 9: pole cells are enclosed by membranes at extreme posterior of egg
-nuclei migrate to cortec nad undergo three addition cortical divisions (synticial blastoderm)
-cellulariation (splitting into individual cells) occurs during interphase of cycle 14 to create cellular blastoderm
-gonomeric division for first (share spindle amle and female chroms stay on either side
-pole cells are germ line and become cellularized before other cells

Question 6

syncytial divisions

Answer 6

1st zygotic transcription: cycle 11
cycle 14: cellularization occurs, produces 6000 individual blastoderm cells ad envelops entire yolk in a membrane

Question 7

zygotic gene transcripton

Answer 7

before this, the embryo relies on mothers mrna to do transcriptoon, after it relies on its own

Question 8

first cellular blastodrerm division

Answer 8

after cycle 14, division 14 is what has patches of cells undergoing mitosis
-syncticial blastoderm transformed into cellular blastoderm
-parasynchronous as patches of cells enter mitosis together

Question 9

MBT vs MZT and what is it controlled by

Answer 9

Mid Blastula Transition:
slowing of nuclear division, onset cellularization, increase in rna transcripton

Maternla to zygotic transition:
maternal mrnas are degraded and control of development passed over to zygotic genome

happen at the same time in drosophola so they have same control

1. ratio of chromatin to cytoplasm
   -dilutes repressors when overall dna amount increases
   2.Smaug protein and targeted degration od mom mrna
   -smaug is rna binding pritein that represses translation
   -targets mom mrna for degredation
   -slows down nuclear divisin
2. zelda protein (transcription factor) and activation of zygotic genes
   -binds to enhancer on promoters of zygotic genes that are first transcribed
   -genes with highest affinity for zelda are first activated
   -sex determin and dorsal ventral polarity normally very expressed in early zygote expression so a mutant of zelda would lead to less expression

Question 10

Drosophila gastrulaton

Answer 10

Mesoderm: forms from ventral furrow (pinches and becomes tube)
endoderm invag: anterior to post midgut invagination
Cephalic furrow forms

Germ band: ectoderm and mesoderm cells that converge and extend into posterior ventral midline
during germ band extension, organogenesis begins, segmentation becomes apparent and precursors of the adult fly are specified (small groups of cells that will form the imaginal discs).

germ band retraction: tail brough back to posterior

The following all happen at the same time

ventral furrow formation

anterior midgut invagination

posterior midgut invagination

germ band extension