Lecture 14 - Evo devo Flashcards
How is the developmental process different in drosophila and grasshoppers and why might this be the case?
Drosophila-embryo, interphases, adult (through metamorphic process)
Grasshopper - hatches as a mini fully formed grasshopper, no metamorphosis, just grows in size
Why different strategies - Feeding
- in drosophila, early maggots are not competing for food with the adult, can feed themselve -> successful and can feed as soon as they hatch and are not competing
- in grasshopper nymph eats the same food as the adult -> still successful because the timing of the stages mean that it takes the grasshopper to 5-6 days to get to the feeding stage
How do frogs exploit the timing of developmental events?
- development of Eleutherodactylus use elimination of the larval stage and rapid development to adult
- look after eggs more carfully
- these hatch into mini adults
- leads to rapid development of the frog, miss the tadpole stage
How has the timing of developmental events changed over time in Mexican axolotyl?
prolonged larval stages with delayed sexual maturity = Neoteny
What stage of embryonic development is likely to be common to distant ancestors of vertebrates and why?
- shared stage after neurulation and the formation of the somites
- due to hox gene expression
- lots of comminality in the ancestry of vertebrates in particular stages of embryogenesis
What genes/proteins are involved in the development of the basic body plan in arthropods and vertebrates, where the dorsoventral axis is inverterd?
- Chordin = dorsal specifier in vertebrates, related to Sog = ventral specifier in Drosophila
- BMP-4 = vertberate ventral specifier, related to Dpp = specifies dorsal
-patterned by the same patterning mechanism
How does hox gene expression pattern different body plans?
-although conserved, lead to dramatically different evolutionary outcomes due to small changes in expresion e.g. grasshopper verses crustacean
-Grasshopper has different appendage to crustacean due to different sequential and separate expression of hox genes ->
=Grasshopper has different hox gene expression temporally and spacially
=crustaceans express all the hox genes at the same time and have multiple limbs with same plan but different function
-Crustaceans hox genes have same expression domains leading to uniform segments
-Grasshoppers have distinct segments due to the combinatorial hox gene experssion
How are the body plans of insects and crusaceans homolgous to one another?
Insects and crustaceans are a distinct group of arthropods evolved from a common arthropod ancestor
- Thorax and abdomen of grasshopper may be homolgous to the entire thoraxof the shrimp
- genital segments are homologous
differences due to different developmental strategy which is acheived through simple change in hox gene expression
What are the differences in the patterning of axes between vertebrates and arthropods?
-switch of the dorsal ventral axis
-inversion of initial developmental pattern
-specification of patterning is by same genes in different organisms
=>
-chordin and sog -> dorsal (vertebrates) and ventral (invertebrates)
-BMP-4 and DPP -> ventral (vertebrates) and dorsal (invertebrates)
How is timing crucial in limb development?
some structures are grown longer than others
e. g.
- many patterning mechanisms are conserved between the human arm, bat wing and a horse leg (can see common structures)
- but the digits are grown for different times so end up as different lengths
What is the growth pattern of the horse leg?
- digits have been reduced over time, third digit become ‘hoofed’, others have become redundant
- overall increase in size
- forelimbs now better suited to running
- underlying part of the skeletal elements are maintained
- faster growing regions get proportionally larger
What have changes in patterning and differential growth led to in mammals?
Diversification of mammalian limbs
-but the underlying pattern of skeltal elements maintained
How do the drosophila wing and the chick wing bud show evolutionary conservation of patterning?
Drosophila wing
-double layer of epithelial tissue
Chick wing bud
-mesenchymal cone surrounded by ectoderm
Appear to have little similarity
HOWEVER
-equivulent genes pattern equivilent regions in these different structures
-in ancient common ancestor, patterning mechanism established by changing the development via timing and through new interactions and downstream targets
-although the growth in these structures have evolved over time, the basic patterning still present (specifically the interacting circuit (axes and positional values) remain to specify different appendages
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