Jakob_PS6 Key - Problem
Set
6
­
Answers
 


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Unformatted text preview: Problem
Set
6
­
Answers
 
 Practice
Problems
 
 1.
Predict
if
each
mutation
below
will
most
likely
lead
to
a
loss
of
function,
dominant
 negative,
or
gain
of
function
allele.
 
 Frameshift
mutation
in
Ras
 Frameshift
mutations
generally
lead
to
early
truncation
of
the
protein
and
 complete
LOSS
OF
FUNCTION
 Nonsense
mutation
in
the
EGFR
that
eliminates
the
cytosolic
tail
of
the
receptor
 DOMINANT
NEGATIVE.
In
this
case
the
early
stop
codon
just
eliminates
the
 end
of
the
receptor.
The
truncated
receptor
is
still
expressed
and
dimerizes
with
 the
wild­type
receptors
but
cannot
phosphorylate
its
tyrosine
residues,
as
 described
in
lecture.
 Mutation
in
the
promoter
region
of
Ras
that
creates
a
novel
transcription
factor
 binding
site
 Most
likely
the
binding
of
this
novel
transcription
factor
will
promote
the
 expression
of
the
Ras
protein
leading
to
a
GAIN
OF
FUNCTION
 Mutation
in
the
splice
acceptor
site
between
the
middle
two
exons
of
Ras
 The
Ras
protein
will
either
fail
to
be
expressed
entirely
or
it
will
be
missing
an
 entire
exon.
Either
way,
this
mutation
is
likely
to
cause
a
LOSS
OF
FUNCTION.

 Point
mutation
in
Ras
that
destroys
the
binding
site
of
Ras‐GAP
 The
mutant
Ras
will
not
bind
Ras­GAP
and
as
a
result
the
hydrolysis
of
GTP
to
 GDP
will
be
much
slower
and
the
Ras
protein
will
be
active
longer
leading
to
a
 GAIN
OF
FUNCTION.
 
 2.
You
are
studying
recessive
mutations
in
two
unlinked
C.
elegans
genes.
One
mutation
 gives
rise
to
a
dumpy
phenotype
(Dpy)
and
the
other
causes
the
worms
to
be
 uncoordinated
(Unc).
For
all
the
questions
below
assume
that
worms
are
homozygous
for
 all
alleles.
 
 You
mate
an
Unc
hermaphrodite
with
a
wild‐type
male.
You
get
a
mix
of
wild‐type
and
Unc
 hermaphrodites,
but
all
the
males
are
Unc.
What
does
this
tell
you
about
the
location
of
the
 unc
gene?
 
 
 Unc
must
be
X­linked
 
 Next
you
mate
a
hermaphrodite
that
is
both
Unc
and
Dpy
with
a
wild‐type
male.
Predict
the
 phenotype(s)
of
the
resulting
offspring.
Which
hermaphrodites
are
self
progeny
and
which
 are
cross
progeny?
 
 
 Dpy
Unc
(self)
and
wild­type
(cross)
hermaphrodites.
All
Unc
males.

 
 MCB
104
–
Section
105/106
 Finally,
you
mate
a
Dpy
hermaphrodite
with
a
Dpy
and
Unc
male.
Predict
the
phenotype(s)
 of
the
resulting
offspring.
Can
you
distinguish
the
self
progeny
from
the
cross
progeny?
 
 
 All
worms
will
be
Dpy.
Cannot
distinguish
self
from
cross
progeny.

 
 3.
You
are
studying
the
assembly
of
the
car
protein
in
neurospora
(haploid),
which
is
 required
for
growth.
You
isolate
four
car
auxotrophs
(car1,
car2,
car3,
car4)
that
fail
to
 grow
on
minimal
media
but
grow
on
minimal
media
+
car.

 
 How
could
you
show
that
these
mutants
are
all
mutated
in
different
genes?
 
 Use
a
complementation
test.
All
combinations
of
double
mutants
should
grow
on
 minimal
media
if
mutations
are
all
in
different
genes.

 
 +
=
growth;
‐
=
no
growth
 
 Car1­
 Car2­
 Car3­
 Car4­
 Min
media
 ‐
 ‐
 ‐
 ‐
 






+
wheels
 ‐
 +
 +
 +
 






+
seats
 ‐
 +
 ‐
 +
 






+
engine
 ‐
 ‐
 ‐
 ‐
 






+
gas
 ‐
 +
 ‐
 ‐
 






+
car
 +
 +
 +
 +
 

 Using
the
table
above,
draw
the
biosynthetic
pathway
of
cars
in
neurospora.
Which
gene
is
 responsible
for
each
step
of
the
pathway?
 
 
 
 







Car2
 
 

Car4
 
 
 Car3
 
 









Car1
 
 engine
­­­­­­­­­­­­­­­­>
gas
­­­­­­­­­­­­­­­­­­>seats
­­­­­­­­­­­­­­­­­>
wheels
­­­­­­­­­­­­­­­>
car
 
 Next
you
generate
the
heterokaryons
listed
below
(fusion
of
2
or
3
haploid
neurospora
to
 generate
one
organism
with
a
shared
cytoplasm).
Predict
if
each
heterokaryon
will
or
will
 not
grow
on
minimal
media.
For
each
mutant
that
you
predict
would
fail
to
grow,
name
one
 supplement
(other
than
car)
that
could
restore
growth.
 
 Heterokaryon
 Growth?
 Supplement
 Car1‐
&
Car3‐
 Yes
 
 Car1‐,Car2‐
&
Car2‐
 No
 Gas,
seats,
or
wheels
 Car2‐,
Car3‐
&
Car4‐,
Car3‐
 No
 wheels
 Car1‐,
Car2‐
&
Car3‐,
Car4‐
&
Car3‐
 Yes
 
 
 
 4.
You
are
studying
a
plant
that
has
red
flowers
when
all
genes
are
wild‐type.
You
isolate
 three
mutants
that
give
rise
to
white,
green,
and
blue
flowers
respectively.
You
perform
the
 following
crosses:
 
 Cross
 white
x
green
 green
x
blue
 F1
Phenotypes
 F2
Phenotypes
 all
red
 9
red
:
3
green
:
4
white
 all
red
 9
red
:
3
blue
:
4
green
 
 What
ratio
of
phenotypes
would
you
predict
from
a
white
x
blue
cross?
What
is
the
order
of
 these
genes
in
the
synthetic
pathway
for
red?
 
 The
first
two
crosses
tell
us
that
all
three
mutations
are
recessive
and
that
white
is
 epistatic
to
green
and
green
is
epistatic
to
blue.
Therefore
white
and
blue
must
also
be
 in
the
same
pathway
and
white
must
be
epistatic
to
blue.

 
 
 F2:
9
red
:
3
blue
:
4
white
 
 white
­­­­­­­­­­­­>
green
­­­­­­­­­­>
blue
 
 5.
Name
the
component
of
the
RTK
signaling
pathway
encoded
by
each
of
the
following
C.
 elegans
genes.
 
 lin‐1
__transcription
factor
downstream
of
Ras__
 
 let‐23
____EGFR____
 
 
 let‐60
______Ras________
 
 lin‐3
________EGF___________
 
 Which
gene(s)
is
required
in
the
anchor
cell
for
vulval
development?
Which
gene(s)
is
 required
in
the
Pn.p
cells
for
vulval
development?
 
 
 lin­3
is
required
in
the
anchor
cell,
the
other
three
are
all
required
in
the
Pn.p
cells.

 
 What
type
of
mutation
in
let‐60
leads
to
a
multi‐vulva
phenotype?
What
type
of
mutation
in
 let‐23
leads
to
a
vulvaless
(bag
of
worms)
phenotype?

 
 Gain
of
function
mutations
in
let­60(Ras)
cause
the
signaling
pathway
to
be
turned
on
 in
the
absence
of
the
EGF
ligand
and
results
in
multiple
cells
adopting
the
vulval
fate.
 Loss
of
function
mutations
in
let­23
disrupt
the
signaling
pathway
so
that
none
of
the
 Pn.p
cells
adopt
the
vulval
fate
and
the
worm
is
vulvaless.
 
 What
would
be
the
phenotype
of
a
lin‐1
loss
of
function,
lin‐3
gain
of
function
double
 mutant?
 
 I
made
a
mistake
on
this
problem.
Lin­1
loss
of
function
and
lin­3
gain
of
function
both
 give
a
multivulva
phenotype,
so
the
double
mutant
would
of
course
also
be
multivulva
 but
it
wouldn’t
be
informative
in
any
way.


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This note was uploaded on 04/05/2010 for the course MCB 104 taught by Professor Urnov during the Spring '09 term at University of California, Berkeley.

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