Download Mid-semester examination Developmental Biology (BSE652

Mid-semester examination
Date – 15th February, 2016
Developmental Biology (BSE652/BSE652a)
Full marks – 80, All questions should be answered.
Question 1: The fin of the zebrafish is homologous to the limb of the mouse.
A) Describe a method for identifying all the genes that are required for development of the
zebrafish fin. (5 marks)
B) Using the method described above you have identified 60 genes required for fin development in
zebrafish. Now describe in a step by step manner how you would find some genes required for
limb development in the mouse. (10 marks)
Question 2: Match the phrases listed on the left hand column (a-j) with the most appropriate phrase on
the right hand column (i-x). Also provide a justification for each match. Each pair correctly matched with
the correct justification provided will be awarded +2. If you match the phrases (correctly or incorrectly)
and do not provide a justification 0.5 marks will be deducted. (20 marks)
a. Signaling through Notch-Delta
b. Mutation in a gene that causes cell death
leads to a bigger sized brain
c. Transplantation of dorsal blastopore lip of
one embryo to the presumptive epidermis
region of another embryo
d. Homologous recombination
i
ii
iii
Absence of inductive signals
Separation of presumptive neural tube from
presumptive epidermis
Fate mapping in the zebrafish embryo
iv
During development the number of neurons
generated are in excess of the number needed
e. Removal of optic vesicle leads to failure of v
Production of a clone of cells that are mutant for
lens formation
a particular gene and also are marked by GFP
f. Cadherin mediated differential cell vi Amplification of stochastic variations in levels of
adhesion
ligand expression in adjacent cells.
g. Gene conferring identity to body segment vii Prevented by balancer chormosomes
h. Infecting with low number of retroviruses viii Drosophila with four wings instead of two
expressing alkaline phosphatase
i. Lipophilic dye conjugated with large ix Retinal progenitor cells in the rat are able to
dextran molecule.
generate multiple cell types
j. Mitotic recombination
x
Duplication of the embryonic axis
1
Question 3: The notochord is a temporary structure of mesodermal origin lying below i.e. ventral to the
neural tube as shown in the image to the left. The
notochord is responsible for imparting the floor plate
fate to the ventral cells of the neural tube.
A) Describe how you will demonstrate that the floor
plate fate is imparted to cells of the neural tube by the
notochord. Start by choosing the model organism in
which you will demonstrate this and then describe the
experiment(s) you will perform to show this. (7 marks)
B) Describe how you would go about finding the
molecule(s) that are responsible for this inductive
ability of the notochord. (8 marks)
Question 4: In the image below panel A shows the canonical Wnt signaling pathway with all the members
acting downstream of Wnt. Panel B is a schematic showing that Wnt secreted from the organ X is acting
on organ Y during its development.
A) Describe an experiment that you would do to show that Wnt from organ X is essential for cell
proliferation OR differentiation in organ Y. (5 marks)
B) How would you demonstrate
that Wnt plays no role in the
development of organ X. (5 marks)
C) If you have demonstrated that
Wnt is essential for proliferation of
cells in organ Y, predict the phenotype
in each case for loss of function
mutations in all the members of the
Wnt signaling signaling pathway
shown in panel A. (10 marks)
D) Describe how you will identify
the genes transcribed downstream of
Wnt signaling which are required for
cell proliferation in organ Y. (10
marks)
2