Transcript Rider BRIDGE 2001-2002

Rider BRIDGE 2001-2002
BIO115: Introductory Biology
J. Drawbridge
What the students see
What I see (Fridays)
Pilot Experiment SP/02
Developmental Biology
• Craig Nelson - 5 point, take-home
– students complete in blue ink
– in class revision in groups (red ink)
– class discussion of answers
Example
• On 5 point sheet
– Explain how Hox genes specify the location of
limb buds along the anterior-posterior axis.
– If Hox genes specify limb bud location, why can
you get extra limbs if you implant FGF beads into
the flank?
• On Exam
– Would a limb form if you implanted an FGF bead
in the flank of a snake embryo? Why, why not?
Would it be a forelimb or hindlimb? Why?
Raccoon
Snake
Sample Answers:
If Hox genes specify where limb buds form, why can you
get extra limbs if you implant FGF bead into the flank.
 " FGF is a paracrine factor secreted by the lateral plate mesoderm
and induces the AER. Hox genes code for FGF proteins, so the FGF
would induce the AER as if the Hox gene was there and had turned
on FGF. Hox gene  FGF  AER Limb. FGF is downstream of
Hox genes "
"because the FGF paracrine factor is capable of limb forming
interactions between the ectoderm and mesoderm. If the beads are
placed ectopically beneath the flank ectoderm, extra limbs emerge.
FGF bead bypasses HOX genes"
Sample Answers:
Explain how Hox genes specify the location of limb
buds along the anterior-posterior axis.
 " Hox genes along the anterior posterior axis specifies the limb
buds. Hox genes on the 3' end are for the anterior.....Also, there is
a gradient of retinoic acid that may activate certain Hox genes and
specify them to be included in the limb field. position of the limbs
defined by location of Hox genes"
"arms between Hox 5 & 6; legs between Hox 9 & 10. position of
limbs determined where Hox genes are located"
Sample Answers (exam):
Would a limb form if you implanted an FGF bead in the flank
of a snake embryo? Why, why not? Would it be a forelimb or
hindlimb? why?
 " Yes, a limb bud would form...downstream of Hox genes is FGF. This doesn't
happen in a normal snake because it doesn't express the proper Hox genes in the
proper location. It would form a forelimb because snakes have mostly thoracic
vertebrae and the forelimb is made at the junction of the cervical and thoracic
vertebrae. Hindlimbs are made at the lumbar-sacral junction which snakes don't
have, so they wouldn't make hindlimbs "
"...FGF bead would form a limb. Since a snake is nearly all thoracic vertebrae,
and FGF bead would create small forelimbs by expressing the Tbx5 transcription
factor"
Summary
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5 point sheets must count
misconceptions MUST be addressed
thought questions
follow up questions on exam
• BIO300 Exam average FA/99 - 60.5
• BIO300 Exam average SP/02 - 73.4