Chapter 22 Developmental mechanisms of Evolutionary Change is

Chapter 22 Developmental mechanisms of Evolutionary Change • “_____” is a recent term used to describe the merging of the developmental genetic approach to ______ 1800 s- Two major views concerning the origin of species 1. ______- 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 Each implied a “______”

Darwin (1850 s) extended these ideas to “descent with modification” with _______ as the driver Late 1800 s- 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 ________

1990 s- ____ 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 Pax 6 gene expressed in Dros. Pax 6 imaginal leg disc results in _______ Pax 6 Fig. 22. 1 A typical phylogeny- Pax 6 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 pax 6 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. Myo. D (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 1 st 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” 1950 s- 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 1970 s-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. 1990 s-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