Rider BRIDGE 2001-2002

BIO115: Introductory Biology

J. Drawbridge

What the students see

What I see (Fridays)

Pilot Experiment SP/02Developmental 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 If Hox genes specify where limb buds form, why can you get extra limbs if you implant FGF bead into the flank.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 Explain how Hox genes specify the location of limb buds along the anterior-posterior axisbuds 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 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 of a snake embryo? Why, why not? Would it be a forelimb or hindlimb? why?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

• 5 point sheets must count• misconceptions MUST be addressedmisconceptions MUST be addressed• thought questions• follow up questions on exam

• BIO300 Exam average FA/99 - 60.5• BIO300 Exam average SP/02 - 73.4