CMMB 403 Final Actual Questions and CORRECT Answers
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CMMB 403
CMMB 403 Final Actual Questions and
CORRECT Answers
72 hours (8 cells) (BEFORE BLASTOCYST STAGE) - CORRECT ANSWER- what is
the human MZT
Mid-blastula transition/maternal-zygotic transition - CORRECT ANSWER- when the
transcription of zygotic genes begins and maternal mRNAs are degraded, the ...
CMMB 403 Final Actual Questions and
CORRECT Answers
72 hours (8 cells) (BEFORE BLASTOCYST STAGE) - CORRECT ANSWER- ✔✔what is
the human MZT
Mid-blastula transition/maternal-zygotic transition - CORRECT ANSWER- ✔✔when the
transcription of zygotic genes begins and maternal mRNAs are degraded, the cell cycle
lengthens, gap stages are added (before is only M and S) and the synchronicity of cell
division is lost. - embryo runs on maternal resources (mRNAs and proteins in the egg @ time
of fertilization) until this. is when maternal effect genes are turned off.
gap genes - CORRECT ANSWER- ✔✔organize cells into groups of segments along anterior-
posterior axis - are activated OR repressed by MEG products expressed from the zygotic
genome (after MZT) and have broad expression domains - divide embryo into regions about
2 segments wide - when lose function causes large gaps in embryo where multiple segments
lost, missing several segments in a row - they have 1 or 2 broad stripes of expression and
define boundaries in the early embryo - are ZYGOTICALLY expressed - ex: Kruppel
maternal effect genes - CORRECT ANSWER- ✔✔A gene that, when mutant in the mother,
results in a mutant phenotype in the offspring, regardless of the genotype - mRNAs deposited
in oocyte set up early polarity translated at fertilization - dads genes do not matter for this -
create the anterior/posterior axis (cytoplasmic polarity) through bicoid and nanos that form
morphogen gradients possible due to syncytium and are incorporated into cells during
cellularization
pair-rule genes - CORRECT ANSWER- ✔✔organize cells into individual segments/ divide
the embryo into segment-sized units along the anterior/posterior axis - are activated OR
repressed by products of gap genes - helps to define the spatial domains of the homeotic
genes - expressed at ONSET of cellularization - have 7 stripes of expression - miss portions
of every other segments and may delete boundaries or reduce segment numbers - when
mutated have half as many segments and result in only 7 stripes instead of 14 and - ex: fushi
tarazu and even skipped
homeotic genes - CORRECT ANSWER- ✔✔Genes that determine basic features of where a
body part is - define the identities of each of the segments - their expression domain is
correlated with where they are on the chromosome - are all TFs that regulate segment specific
genes - have vertebrate homologs!
,segment polarity genes - CORRECT ANSWER- ✔✔activated by pair rule gene products
after cellularization, give each individual segment its polarity - have 14 stripes of expression -
when mutated polarity disrupted in each segment (segment number doesn't change will get
14) - encode for members of shh and wnt pathways
maternal effect - CORRECT ANSWER- ✔✔which gene is transcribed BEFORE and upon
fertilization
gap - CORRECT ANSWER- ✔✔which genes are transcribed after fertilization but before
cellularization and the MZT
pair rule - CORRECT ANSWER- ✔✔what genes are expressed at the onset of
cellularization/just before - with the MZT
segment polarity - CORRECT ANSWER- ✔✔what genes are expressed after cellularization
and the MZT
1 or 2 - CORRECT ANSWER- ✔✔how many stripes of expression do gap genes have
(broad)
7 - CORRECT ANSWER- ✔✔how many stripes of expression do pair rule genes have
14 - CORRECT ANSWER- ✔✔how many stripes of expression do segment-polarity genes
have
Parasegments - CORRECT ANSWER- ✔✔transient subdivisions that occur in the
Drosophila embryo prior to the formation of segments - are off register by one half from
those of the segments, is made up of the cells in the posterior compartment of one segment
and the anterior compartment of the next segment. the expression patterns of early
segmentation genes are at THESE boundaries - is the "fundamental unit of embryonic
expression"
kruppel - CORRECT ANSWER- ✔✔gap gene expressed in parasegments 4-6, is repressed by
hunchback, if mutated will be missing several segments in a row (4-6ish)
,fushi tarazu (ftz) - CORRECT ANSWER- ✔✔pair rule gene in drosophila that is expressed in
even # parasegments, if mutated results in no boundaries btw parasegments and reduced (by
half) segment number from 14 to 7
even-skipped (eve) - CORRECT ANSWER- ✔✔pair rule gene in drosophila that is expressed
in ODD # parasegments, if mutated results in no parasegment boundaries and reduced
segment number from 14 to 7
engrailed (en) - CORRECT ANSWER- ✔✔segment polarity gene expressed in cells w high [
] of either even skipped or fushi tarazu proteins, is a hedgehog pathway regulator that marks
the anterior compartment of each parasegment (which is also the posterior part of each
segment) - this reinforces parasegment boundaries - is a TRANSCRIPTION FACTOR so
NOT secreted outside cells - allows polarized ventral denticle patterns
wingless (wg) - CORRECT ANSWER- ✔✔segment polarity gene expressed transcribed
when neither even skipped (eve) or fushi tarazu (ftz) gene are active, is a wnt pathway
regulator that marks the posterior compartment of each parasegment (which is also the
anterior of each segment) - this reinforces parasegment boundaries - is a SECRETED protein
- allows polarized ventral denticle patterns
high
hh
anterior
posterior - CORRECT ANSWER- ✔✔engrailed (en) segment polarity gene is expressed with
a (high/low) level of ftz or eve and is a regulator of the ____ pathway, marking the ____
compartment of parasegments aka the ___ compartment of segments
low
wnt
posterior
anterior - CORRECT ANSWER- ✔✔wingless (wg) segment polarity gene is expressed with
a (high/low) level of ftz or eve and is a regulator of the ____ pathway, marking the ____
compartment of parasegments aka the ___ compartment of segments
, paracrine - CORRECT ANSWER- ✔✔en and wg create parasegment boundaries through
____ signalling
frizzled - CORRECT ANSWER- ✔✔wingless (wg) can activate an adjacent cell at the
parasegment boundary to produce engrailed (en) (which then turns on hh transcription)
through binding the receptor ____
patched - CORRECT ANSWER- ✔✔hedgehog (hh) can induce the secretion of wingless
(wg) in an adjacent cell at the parasegment boundary by binding to the receptor _____
hedgehog (hh) - CORRECT ANSWER- ✔✔is a secreted protein, is activated by the TF
engrailed in the posterior part of segments (anterior of parasegments) - allows polarized
ventral denticle patterns
b - CORRECT ANSWER- ✔✔what would be the effect on the development if a drosophila
embryo has a homozygous null mutation of the bicoid gene?
a) the embryo would be headless (no anterior structure)
b) it is impossible to say, we need moms genotype
c) the embryo would develop normally
d) the embryo would develop w/o posterior structures
e) the embryo would develop w 2 heads
c - CORRECT ANSWER- ✔✔the bicoid gene (maternal effect gene!!) of drosophila is
haploSUFFICIENT. if oocyte from hetero bicoid mutant mom is fertilized by a sperm w a
bicoid mutation to produce a homozygous bicoid null-mutant embryo, how would you expect
embryonic development to be affected?
a) develop w/o anterior structures
b) develop w/o posterior structures
c) no disruption of normal development
d) develop w 2 heads
a - CORRECT ANSWER- ✔✔mom of xenopus embryo has hetero mutation of gene =
haploINSUFFICIENT which codes for protein needed in early cleavage (before cycle 10 and
MZT). but embryo is homo WT. would early cleavage be abnormal in the embryo? why?
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