Download End semester examination BSE652, Developmental Biology 23

End semester examination
9:00 AM
BSE652, Developmental Biology
23-4-2016, Saturday,
Question 1, 2 and 3 are compulsory. Attempt any two question from 4 to 7. Please be brief
and to the point when answering questions.
Question 1: (15 points)
A. From this figure explain how the bicoid
and nanos mRNAs are localized to the two
ends of the oocyte and what role does
gurken play in this process? (5 points)
B. Explain what would happen in a mutant
where the association between gurken and
the oocyte nucleus is lost. (2 points)
C. Torpedo is the receptor for Gurken and
is present on all follicle cells. How would you show that the torpedo gene is required
in the follicle cells whereas gurken is required in the oocyte? (8 points)
Question 2: (20 points)
Match the items listed on the left hand column (a-j) with the most appropriate item in the
middle column (1-10) and in the right hand column (i-x). Also provide a justification for each
match. Only one item the left will be the best match with one item in the middle and one item
on the right. All three correctly matched with the correct justification provided will be
awarded +2.
a.
Lineage tracing
b.
c.
Aggregation of cells from 2.
the same germ layer
Fetal alcohol syndrome
3.
d.
Morphogen
4.
e.
Stem cell niche
5.
f.
Epithelial mesenchymal 6.
transition
g.
h.
i.
j.
1.
Proximity to source of i
paracrine factors
Decreased cell adhesion
ii
No expression of Duffy in iii
red blood cells
Bone
morphogenetic iv
protein
Differential adhesion
v
Sonic
hedgehog
expression
is
downregulated
Dorsal blastopore lip
7. Quail-chick chimera
Interdigital mesenchyme 8. Distributed
in
a
monotonic gradient
Modularity of enhancers 9. Ventral cells of the
Drosophila embryo
Highest concentration of 10. Bone
morphogentic
the nuclear Dorsal
protein inhibitors
1
Specifying cell fate in a
concentration dependent
manner
Cadherin
Heterochromatin in nuclei
Breakdown of Basal lamina
vi
Resistance to malarial
parasite
Programmed cell death
vii
viii
Neural fate of ectoderm
Mesodermal fate
ix
Asymmetric cell division
x
Death of neural crest cells
Question 3: (15 points)
A. How can you demonstrate that the entire flank region of the developing chick
embryo is capable of forming limbs? How can you demonstrate that depending on
the axial position the ectopic limb formed will have characteristics of the fore- or the
hind-limb? (3+2 points)
en-1 plays major roles in
both determination of the position
of the AER as well as dorsalization
of the ectoderm. Please elaborate.
What experiment can you design
to examine whether these two
phenomena are dependent on
each other or not? (3 + 7 points)
B.
Choose any two questions to answer from questions 4, 5, 6 and 7.
Question 4: (15 points)
A. On the basis of the figure explain how snakes
have evolved to become limbless. Your answer must
state whether this is an example of heterotopy,
heterochrony, heterometry or heterotypy and also
explain why. (8 points)
B. What is the difference between pythons and
vipers in terms of their hindlimbs? What does this tell
you about the evolutionary relationship between
them? (2 points)
C. Among arthropods only insects have six legs. Provide and explanation for that and
explain how this is different from snakes losing their limbs. (5 points)
Question 5: (15 points)
This figure depicts the stem cell niche in the Drosophila testis. The Hub cells are somatic and
are attached to the germline
stem cells. The germ-line stem
cell divides to form another
germ-line stem cell and a
gonialblast which will further
divide to form sperm precursors
(spermatogonia
and
spermatocyte cysts).
2
A. Explain the mechanism by which the germ-line stem cell self-renews and at the same
time produces a gonialblast which will further produce differentiated cells. Your
answer must include the role of Unpaired, Cadherins and the centrosome in this
process (10 points)
B. Explain what will happen in the stem cell niche in a mutant fly that is mutant for
unpaired, a paracrine factor. You may assume that unpaired is not required for any
other function. Describe the mutant phenotype observed in this fly (5 points).
Question 6: (15 points)
Diethylstilbestrol or DES was prescribed to pregnant women as it was thought to ease
pregnancy and prevent miscarriages. However, it had no beneficial effects on pregnancy,
rather it lead to defects in the reproductive tracts of female foetuses whose mothers took
this drug.
A. Based on the statement made above would you classify DES as a teratogen? Justify
your answer. (5 points)
B. Exposure to DES leads to several defects in the reproductive tracts of female foetuses
which suggests that there is a defect in the fate specification of different sections of
the female reproductive tract such as the oviduct, the uterus and the cervix. Describe
an experimental strategy to identify the molecular basis of the effect of DES. You
should start by choosing the model organism/system in which you will carry out the
experiment and justify your choice. (10 points)
Question 7: (15 points)
As shown in the figure, in the frog blastula the
dorsal-most vegetal cells were found to have the
Nieuwkoop center which was capable of inducing
the tissue above it to become the dorsal mesoderm
which functions at the Spemann’s organizer.
A) Describe the experiments that led to the identification of the Nieuwkoop center
as the inducer of organizer? If you do not remember the experiments you can
devise your own and those would be acceptable provided they are logical. (7
points)
B) Describe a strategy that you would use to identify which molecules are emanating
from the Nieuwkoop center that are responsible for inducing the organizer. (8
points)
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