Transcript Chapter 3: Handy Genes - JBHA-Sci-US-tri1

Chapter 3: Handy Genes
Your Inner Fish by Neil Shubin
GENES AND
DNA
• Every cell contains
the same DNA
• Cells differ based on
activated genes
during development
Photo from:
http://publications.nigms.nih.gov/thenewgeneti
cs/images/ch1_dnagenes.jpg
IDENTIFYING ZPA
• 1950’s and 1960’s,
biologists Edgar Zwilling
and John Saunders
• Zone of polarizing activity
(ZPA)
– Essential to limb growth
– Mirror-image
– Concentration
Photos from: http://www.utm.utoronto.ca/~w3bio380/picts/lectures/lecture19/LIMBDEV6.jpg and
http://www.nature.com/nrg/journal/v10/n12/images/nrg2681-f2.jpg
IDENTIFYING HEDGEHOG
GENE
1993, Cliff Tabin
•
• Fly’s Hedgehog
gene
• Looked for
Hedgehog
sequence in other
animals
• Sonic Hedgehog
• Only active in ZPA
• Sonic Hedgehog
exists in every
animal
Photos from: http://www.nature.com/nature/journal/v445/n7125/images/nature05436-f2.0.jpg and
http://scienceblogs.com/pharyngula/2008/08/01/hh_inactive.jpg
• Sharks are earliest
creatures with fins and
an inner skeleton
• Randy Dahn found a
shark Sonic Hedgehog
– Activated at same time in
development as in
chickens
– Like chickens, activated in
patch of tissue at end of fin
– When injected with vitamin
A, mirror-image fin
• Shark rods look alike,
inserted mouse Sonic
Hedgehog
– Rods looked different and
responded by proximity to
Sonic Hedgehog
Photos from: http://www.elasmoresearch.org/education/shark_profiles/profileimages/heterod/h_spine.gif and
http://www.nature.com/nature/journal/v445/n7125/images/nature05436f2.0.jpg
Citations
Neil Shubin. Your Inner Fish, a Journey
into the 3.5-Billion-Year History of the
Human Body. New York. ISBN: ISBN 13: 978-0-375-42447-2.