MCB 141

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MCB 141 Review Feb. 17, 2009
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Name and Student ID on every page of the exam.
TA (circle one) Jessica Lyons or Alberto
Stollfi Closed book and closed notebook. No
cell phones or other electronic devices. Exams
must be turned in at 1230 PM. Write your
answers with a pen. If you need extra space,
continue on the back of the page, but clearly
indicate this on the front page of the
question. Regrade policy Return your entire
exam to your TA within one week of getting your
exam back. Include a written explanation of why
you think you should get additional credit.
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Better image - Fig. 8.36 of the textbook
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coding region
brain enhancer
digit enhancer
spine enhancer
A particular gene may be expressed in the
brain, spinal cord, and digits of a mouse
embryo. Each of these domains of expression
is under the control of a different piece
of regulatory DNA (enhancer)
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Egg - larva 1 day Larva - pupa 4 days Pupa 5 days
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Imaginal Disks
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Fly Genetics 101 (same as all other
genetics) Most mutations are recessive - why?
White eye phenotype Genotype is w-/w- Red eye
phenotype Genotype is w/w or w/w-
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Wild-type
Ventralized (cactus mutant)
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Wild-type
Dorsalized (dorsal mutant)
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• In ventral follicle cells, Pipe
• modifies an unknown factor X
• Factor X Nudel act together
• to split (cleave) Gd, which
• activates Gd.
• Activated Gd cleaves and
• activates Easter.
• Activated Easter cleaves and
• activates Spätzle, which then
• Binds the Toll receptor.

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Gene nomenclature bicoid bcd Bicoid
protein bicoid mRNA bcd/bcd TollD/Toll
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Also found maternal effect mutants Three
classes terminal, anterior missing, posterior
missing Two key ones - bicoid (anterior
missing) and nanos (posterior) missing
Embryos from bcd-/bcd- mothers
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Gap mutants large contiguous deletions Krüppel g
iant knirps hunchback
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Pair-rule Two segment periodicity fushi
tarazu even-skipped paired odd-skipped runt hairy
odd-paired sloppy paired
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Segment polarity Deletions/duplications
in every segment gooseberry engrailed hedgehog w
ingless patched armadillo etc.....
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nanos
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Microtubules are polarized (/- ends) end is
posterior Proteins like swallow are motors that
carry cargo, like bcd mRNA) Some motors go in
direction, others go in - direction.
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nanos mRNA
bicoid mRNA
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Segment polarity Deletions/duplications
in every segment gooseberry engrailed hedgehog w
ingless patched armadillo etc.....
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Segment polarity Deletions/duplications
in every segment gooseberry engrailed hedgehog w
ingless patched armadillo etc.....
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Homeotic (Hox) Genes
Drosophila (fruit fly)
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Homeotic mutants in Drosophila
Wild-type Antennapedia
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Mn Mx La T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8
WT
Ubx
Mn Mx La T1 T2 T2 T2 A2 A3 A4 A5 A6 A7 A8
abd-A
Mn Mx La T1 T2 T3 A1 A1 A1 A1 A5 A6 A7 A8
Abd-B
Mn Mx La T1 T2 T3 A1 A2 A3 A4 A4 A4 A4 A4
In homeotic mutants, still the right number of
segments, but the identity of some are
transformed to the identity of others.
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Mn Mx La T1 T2 T3 A1 A2 A3 A4 A5 A6 A7 A8
WT
Ubx
Mn Mx La T1 T2 T2 T2 A2 A3 A4 A5 A6 A7 A8
abd-A
Mn Mx La T1 T2 T3 A1 A1 A1 A1 A5 A6 A7 A8
Abd-B
Mn Mx La T1 T2 T3 A1 A2 A3 A4 A4 A4 A4 A4
Ubx / abd-A
Mn Mx La T1 T2 T2 T2 T2 T2 T2 A5 A6 A7 A8
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Normal fly Ubx expressed T3 post.
Loss of Ubx expression from T3 late in
development
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Hunchback
Ubx
What happens to Ubx in a hunchback mutant?
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Hunchback
Ubx
Polycomb group genes provide cellular memory
and an epigenetic mechanism.
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Drosophila (fruit fly)
Homeotic (Hox) Genes
Present in all animals Organized into a
cluster Regionally expressed along the
anterior-posterior axis of the embryo Are
responsible for regionalization of the body
axis
Mouse
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Normal mouse 13T 6L 4S Hox10 expression
Lumbar to posterior Hox11 expression Sacral to
posterior
Hox 10 11 mutant 23 Thoracic vertebrae No
lumbar No sacral
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coding region
regulatory DNA
regulatory DNA
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inside
inside
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inside
inside
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inside
inside
Expression dictated by host, not by the source of
the enhancer
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inside
inside
Expression dictated by source of the enhancer,
not by the host