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 species1. ____________- Each creature has a “made to order” body plan

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

Human arm

Seal limb

Bird wing

Bat wing

Each implied a “___________”

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

Pre- 1990- many invertebrate biologists thought that the reconstruction of relationships among phyla was an ________________

Ernst __________- fused embryology and evolutionConcluded- Each organisms evolved as a terminal

addition to latest stage, with humans being the final stage

A typical phylogeny- Pax6 involved in eye development

Pax6

Pax6

1990s- ________ could be developed •Combined use of 1) new ___ analysis programs, 2) data on ____ gene similarities and 3) advanced _________ programs

Fig. 22.1

Predict two ancestral groups of most eukaryotes from one split- ____________ (e.g mouse) and __________ (e.g. drosophila)

Mouse Pax6 gene expressed in Dros. imaginal leg disc results in _______

Evidence

3. ___ genes are used by insect and mammals to dictate anterior/posterior axis

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 __________

Problem- No fossils of earlier creatures have been found

Expect ancestral creature would have __________________ genes

figure 22.2

Identify several genes which have ____________ in diverse creatures

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

Broad changes in Hox gene regulation

Subtle changes in Hox gene regulation

changes in Hox gene number

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

Reason?- Forelimbs develop __________ to the Hoxc-6 expression, but Hoxc-6 is expressed throughout organism, thus specifying _____

Insert Fig. 22.9

Some fossil snakes have _______ but no _________

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 _________

Insert figure 22.13

The Wnt pathway is used by diverse organisms:

Drosophila C.Elegans Xenopus

Fig. 22.13

Modularity

• How can development change when it is do finely tuned??

1. Through ____________- one module can change it’s time of expression relative to another modulee.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”

Possibilities

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 co-opted (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 SynthesisEarly 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

History

Problems with the Modern Synthesis1. 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