GE CLST 70B Lecture 9: Week 5-Adaptation

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GE 70B Evolution of the Cosmos and Life: Adaptation
I. Adaptation
A. A trait that has been selected for that is beneficial in a particular environment
1. beneficial=increases fitness=allows reproduction of more offspring
B. Always builds on older traits
1. Evolution tinkers with what is already there
2. Exaptation: a trait that was already there was adapted
C. Constraints:
1. Phylogenetic history- ancestors
2. Developmental history- ontogeny
3. Biomechanics- physics
4. Ecology- there are only a few ways to do the same job
5. Available variation-combination of the above
D. An example of adaptation in bacteria
1. Bacteria were grown in broth which contained a compound called citrate
2. Normally, E. coli bacteria can only process citrate without oxygen, due to
the citT gene
3. The better adapted strain evolved an ability to process citrate in an
aerobic environment. How?
a) The adaptation arose as a result of a mutation to a segment of a
genome that contains the citT gene. The citT gene got copied
and the new copy went under a different promoter, which works
under aerobic environments so now it could process citrate in the
presence of oxygen
b) Gene duplication is often the fuel for adaptation
II. Gene Trees
A. Allow us to see the evolution of changes in genome
B. HOX genes
1. Set up basic axes of body orientation
a) anterior/posterior
b) dorsal/ventral
c) medial/lateral
2. highly conserved-the same throughout a lot of organisms
3. Colinear on genome- they are near each other in the sequence
4. Flies and us
a) Humans have the same HOX genes as flies, but humans have
four sets of the same genes in a fly due to duplication events
(1) Accounts for our more complex body plan
5. They are regulatory genes- they control other genes
a) DNA binding transcription factor- they turn on the various genes
that control the axes
b) HOX genes are called HOX genes bc they have the homeobox is
a particular conserved DNA sequence that codes for the
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