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Lecture 7

BIOL 215 Lecture Notes - Lecture 7: Diploblasty, Parazoa, Notochord

Biology (Sci)
Course Code
BIOL 215
Neil Price

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BIOL215 Lecture 7 Notes
What caused the Cambrian Explosion as discussed in class:
Abundant mutations
Climax change
Breakup of land masses, though the time period is still too early
A Cambrian "Explosion?":
How did so many body plans arise and why have so few, if any, arisen since the Early Cambrian?
There were only 35 animal phyla in the body plan
Adaptive radiation? Maybe there were too highly specialized
too specialized upon appearance in the fossil record to have originated in the Cambrian
Explosion: origin and radiation occur together
Geological conditions (Snowball theory)
Rising oxygen levels
Predator-prey relationships
Molecular Clock: origin first, radiation later
Large body size
Acquired skeletons - availability of CaCO3
Consider how accurate the fossils are
Radiation facilitated by:
Highly conserved developmental genes
Of 1.2 billion (fossils - 500 million) years of animal evolution, modern humans have been on the planet
only 200,000 years
Scientists discovered the genes that control development and that these genes are highly conserved
across all animals. It turns out that the genes found in fruit flies are shared across all animals
An example is PAX6 which is the gene that code for eye development. However, as we see with flies,
humans, and frogs, we all have different eyes, as such, we know that PAX6 eyeless gene is highly
conserved but will evolve independently
Developmental change and evolution:
Gene regulation has emerged as a central mechanism explaining developmental and evolutionary
Jacob referred to evolution as bricolage (tinkering), a term that rightly places the emphasis on
modification of existing genes. You don't change the physical structure of the gene but rather the
regulatory region of the gene to affect the turning on or off of the gene
Without changing the physical structure of the gene, you can start changing where the gene gets
turned on and off
Understand homeobox genes and see Figure 12A/B/C to understand expression of Hox genes
Plants, fungi and animals are the three kingdoms of multicellular organismLand plants are known to
have evolved from organisms similar to some living green algae
Many of the adaptations of land plants reflect the transition from water to land
Fungi are not simple plants but a sister group of animals
Animals: a story of ingestion:
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