Name ____________________________________________ PCB5065 Exam 4 page 1 of 5

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Name ____________________________________________
PCB5065 Exam 4 page 1 of 5
Question 1 ___________________________
Question 2 ___________________________
Question 3 ___________________________
Question 4 ___________________________
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Name ____________________________________________
PCB5065 Exam 4 page 2 of 5
1. (15 pt.) The table below lists several
organelle genetic systems discussed in class and
a number of attributes associated with organelle
genetics. Complete the table by indicating which
attributes pertain to each system. Use the
symbol to indicate that the attribute is commonly
observed or even occasionally observed under
special circumstances as described in class. Use
the ? symbol to indicate that the attribute has
not been associated with an organelle genetic
system to date. A few of the combinations below
are currently controversial or uncertain and
those will get credit for either answer. (1/2
point each)
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Name ____________________________________________
PCB5065 Exam 4 page 3 of 5
2. (35 pt.) The crosses below reveal an unusual
pattern of inheritance in the arabidopsis plant.
The recessive nuclear mutation sin1 conditions
abnormal ovule morphology and flowering times.
Homozygous mutant sin1 / sin1 plants are,
however, male and female fertile, and so can be
used in crosses with the following results
2a) Which pair of reciprocal crosses above
result in different outcomes with respect to
progeny survival? The only reciprocal pair
listed above is / X sin1/sin1 and sin1/sin1 x
/ (4 pt) 2b) Considering all of the data
presented above, could the differences in
reciprocal crosses result from a mitochondrial
mutation? Explain why or why not. Yes (2 pt.)
Arabidopsis mitochondria are maternally inherited
(3 pt.) if the sin1/sin1 female was
heteroplasmic (3 pt.) for such a mutation she
could pass it to some of her offspring note the
mit mutation might be independent of the sin
mutation, or perhaps be caused by the sin1/sin1
nuclear genotype mutation (1) 2c) Considering
all of the data presented above, could the
differences in reciprocal crosses result from a
gametophytic or segregation distortion effect at
the sin1 locus? Explain why or why not. No (2
pt.) Note that all genotypes are recovered at
Mendelian frequency, hence there is no bias or
distortion in the transmission. (6 pt.) 2d)
Considering all of the data presented above,
could the differences in reciprocal crosses
result from a maternal effect mutation at the
sin1 locus? Explain why or why not. Yes (2 pt.)
We only see embryo lethality in the progeny of
sin1 / sin1 females (3 pt.) hence the genoype of
the mother determines the phenotype of the
progeny. (3 pt.) I also accepted No (2 pt.) if
you said that, in a classic maternal effect, all
the progeny of the sin 1/ sin 1 female should
have the same phenotype. Here they do not, for
unknown reasons. (6 pt) 2e) Considering all of
the data presented above, could the differences
in reciprocal crosses result from imprinting at
the sin1 locus? Explain why or why not. No (2
pt.) If the lethality were due to expression of
only the maternal allele, some progeny of the /
sin1 females should also inherit the mutant
allele through the female and should therefore be
lethal (6 pt.)
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Name ____________________________________________
PCB5065 Exam 4 page 5 of 5
4. (30 pt.) The diagrams below show leaf
primorida that develop from a zone of
meristematic (m) cells.
Leaf primordium
Apical ? Basal Axis
adaxial
m
m
m
m
abaxial
a
b
c
e
4a) On the leaf primoridium a diagramed above,
label the adaxial side and the abaxial side. 4
pt. See blue text above ad towards axis, ab
away from axis 4b) In arabidopsis, the
PHABULOSA gene product functions in establishing
abaxial-adaxial polarity. On the leaf primoridium
b diagrammed above, shade the area where
PHABULOSA gene expression is expected to occur.
See blue shading above (4 pt) PHB determines,
and is located in the adaxial domain 4c) In
arabidopsis, the KANADI gene product also
functions in establishing abaxial-adaxial
polarity. On the leaf primoridium c diagrammed
above , shade the area where KENADI gene
expression is expected to occur. See blue
shading above (4 pt) KANADI determines, and is
located in the abaxial domain 4d) Describe
genetic evidence (ie evidence involving mutants)
that RNA silencing plays a role in establishing
the adaxial abaxial polarity in leaf
development. 6 pt One example is the Argonaute
mutation in a conserved RISC component argonaute
mutations in arabidopsis fail to establish
correct polarity another example is the site
directed mutations in the miRNA binding regions
of PHV or PHB, which render these messages
resistant to RNA silencing, resulting in an
expanded domain of expression and adaxialization.
4e) The micro RNA (miRNA) 165 also functions in
establishing adaxial-abaxial polarity in leaf
development by controlling the domain of
PHABULOSA gene expression through
post-transcriptional gene silencing. On the leaf
primordia e diagrammed above, shade the area
where miRNA 165 is expected to accumulate. See
blue shading above (4 pt) The miRNA restricts
the domain of PHB expression it cleaves and
destroys the PHB message in the abaxial domain,
thereby restricting PHB to the adaxial domain (4
pt.) 4f) What feature of miRNAs make them ideally
suited to function in the establishment of
polarity gradients during plant development? The
can move cell to cell ( 4 pt.) 4g) In addition
to their functions in establishing polarity,
miRNAs appear to be regulate many other important
aspects of development. Based on our discussion
paper, what key aspect of plant development is
regulated by miRNA-jaw? miRNA jaw regulated the
transition between cell division and
differentiation (4 pt.)