Transcript Chapter 22 Developmental mechanisms of Evolutionary Change

Chapter 22 Developmental mechanisms
of Evolutionary Change
• “__________” is a recent term used to describe
the merging of the developmental genetic
approach to ____________
1800s- Two major views concerning the origin of species
1. ____________- Each creature has a “made to order” body plan
Human arm
2. ______________- Most organisms use
modifications of a few body plans to adapt
to an environment
• Human hand, bat
wings and seal flipper
are modifications of
same basic plan
Each implied a “___________”
Seal limb
Bird wing
Bat wing
Darwin (1850s) extended these ideas to “descent with
modification” with _____________ as the driver
Late 1800s- E.B. _______ and F. R. _______ show that in
diverse creatures the same organs arose from the same
embryonic structures
Ernst __________- fused embryology and evolution
Concluded- Each organisms evolved as a terminal
addition to latest stage, with humans being the final stage
Pre- 1990- many invertebrate biologists thought that the
reconstruction of relationships among phyla was an
________________
1990s- ________ could be developed
•Combined use of 1) new ___ analysis programs, 2) data on
____ gene similarities and 3) advanced _________ programs
Predict two ancestral groups of most eukaryotes from one split____________ (e.g mouse) and __________ (e.g. drosophila)
Evidence
Mouse Pax6 gene
expressed in Dros.
Pax6
imaginal leg disc
results in _______
Pax6
Fig. 22.1
A typical phylogeny- Pax6 involved in eye development
Problem- No fossils of earlier creatures have been found
Instead, look for homologous genes that perform similar
functions in diverse phyla
1. Since ____ (and other eye genes) are used in all phyla with
eyes, predict that the _________ creature would have pax6
2. ________ exists in insects and mammals and is required for
heart development in both, predict that the ancestor creature
would have __________
3. ___ genes are used by insect and mammals to dictate
anterior/posterior axis
Expect ancestral creature would have __________________ genes
Identify several genes which have ____________ in diverse creatures
figure 22.2
3. Hox genes are used by insect and mammals to dictate
anterior/posterior axis
How could different phyla emerge if hox genes are used for all?
a. Changes in Hox-responsive elements of downstream genes
Butterfly has ______ instead of ______ (as in
drosophila) because a hox gene (Ubx) fails to regulate
expression of certain ____________ genes
changes in Hox
gene number
Broad changes
in Hox gene
regulation
Subtle changes
in Hox gene
regulation
Changes in
regulation of
downstream
genes
b. Changes in Hox gene expression patterns between ___________
Some snakes (pythons and boas) have rudimentary pelvic
girdles and femurs, but most have none
Some fossil snakes have _______ but no _________
Reason?- Forelimbs develop __________ to the Hoxc-6
expression, but Hoxc-6 is expressed throughout organism,
thus specifying _____
Insert Fig. 22.9
CHICK
PYTHON
c. Changes in hox number
•
Sponges have ____ hox genes, insects have ______
•
Earliest vertebrates have ______ hox clusters
•
The majority of genes hox genes have no
_____________ hox genes in drosophila
Signal transduction pathways in axis formation are also _________
The Wnt pathway is used by diverse organisms:
Drosophila
C.Elegans
Xenopus
Insert figure 22.13
Fig. 22.13
Modularity
• How can development change when it is do
finely tuned??
Possibilities
1. Through ____________- one module can change
it’s time of expression relative to another module
e.g. neoteny- sex organs mature while body remains ________
2. Through ___________- one module grows at
different ______relative to another module
• E.g. the whale’s upper jaw grows rapidly and
forces the nose to the top – a “blow hole”
3. Through __________________________________
e.g. MyoD (muscle factor), hox genes
TGF-B, Wnt factors all share homology
within a family
Predict- One gene was ______ and ______,
allowing for new functions to arise
4. Through _________- Preexisting units
(structures or individual proteins) can be coopted (recruited for new ___________)
e.g. engrailed is used to 1st to specify ________, then to
specify ___________, then later for anterior-posterior
positioning of _______________.
The New Evolutionary Synthesis
History
Early 1900- Hypothesis that ____________________________
This is clearly _____________- organisms do not
simply run the course of less-evolved creatures then
become “specialized”
1922- Ontogeny ___________ phylogeny (Walter Garstang)
“The first bird was hatched from a reptiles egg”
1950s- The ______________________
Diversity arises from random mutations, and
environment acts to select best fit phenotypes
Problems with the Modern Synthesis
1. Modern Synthesis predicts ________________But transition organisms are lacking in the fossil record
1970s-Gould and Stanley suggest __________________
•Evolution occurred quickly (over a few
_____________ generations then stabilized)
2. Modern Synthesis predicts ________________ is the result
of _________________ (accumulation of small mutations
How could hair vs feathers vs scales arise?
3. Modern synthesis predicts lack of genetic similarity in
distinct organisms
Now observe much homology, not in
structures, but in _______________________
4. 1990s-A new ___________________ - Includes
developmental genetics to explain evolution – “The
__________ of the fittest”
•Evolution is driven by modifications of
___________________ programs
Many believe that complex structures simply could not evolve
due to irreduccible complexity•The _________________
•The bacterial ______________
•The blood clotting ______________
Other say that developmental biology solves this
problem by “_____________” a pathway
Controversy will continue