Lecture 07 Tuesday March 25 2008
Homology
- common ancestry
- convergent evolution
for example wings
- arthropods and insects are the only species to have developed wings
- arthropods developed frame rodents
- 7 steps to get to the bat - bat is deeply imbedded evolutionary wise to mammals
- it doesn't have close relatives that fly
- when you see an anomalous trait deeply imbedded within the phylogeny
- when considering parsimony it is clear that the simpler solution would for the trait of wings to have occurred within the phylogeny rather than the majority of species loosing wings
- common ancester: the common ancestor did not have wings
- the wing structure of birds and bats are not homlogous
analgous
- convergence of function but independently derived
- still talking about wings
- evidence
- wings are analogous, but the bones are homologous
- using the forearm as a wing was a novelty arrived at independently
Enter Molecular Biology
- wingless gene in fruit flies - studied significantly even before micbio
- wingless was a popular molecule found all over the place
- responsible for not just making wings but segments in general
- a popular evolutionary gene
- but the name stuck
+
- fringe
- Distilliss
- genes are conserved in evolution and used in lots of different places
- embryonic buds or disks that turn in to chick and insect wings were suprisingly similar
- Dorsal ventral sides - back looks different from the front
- distilliss and fringe were very important in dorsal ventral variation
- some genes have the function of interacting with different molecules
- gene actoris has a specific region - it shows homologous to actoris
- you can usually take a limb gene from a mouse and save a fruit fly
fruit fly bones
- anterior posterior - fore arm biceps
- same protein as in fruit flys was found in mammals
- this was initially strange when approaching genetics from the one gene one protein hypothesis
- this was because the protein coded for bones but fruit flies don't have bones
- But off course molecules and proteins are a tool kit that can serve many functions
- this did not prevent early scientists from thing there was a deep homology
eyes
- 7 8 hundred cuticular lenses - made of skin cells
- vertibrates have their eyes developed from nerve or brain tissue
- sephlipodes - squid, octopus - molesques - thye have eyes like human eyes - single lense with retina
- the difference is that the photoreceptor faces backward - light has to go through a lot of tissue
- in octopus the light comes through and immediately hits the photorecptor
- in humans light hits the back of the photo receptor and passes through the pigmints
- all animals with eyes look for food, move quickly, actively search out food - a hunting strategy
- image forming eyes vs. light sensors
- these vision forming eyes were associated with a hunting strategy and arose independently
What genes are associated with sight?
- eyeless mutation
- mutations in mice - no iris forms
- eyeless was homologous to a gene in mice that destroyed the iris
- a mutation in one gene caused both eyeless and irisless - pax 6
- eyes seem to be convergently evolved
this paradox has to be resolved the same genes are able to destroy a trait
Old Genes for New Eyes
- ancient genes - some invented before animals were (pax 6)
- combines molecular basis of development and formational structure with homology and convergent evolution
- all genes are homologous but the structures they make are not homologous
- you can have bone homology without wing homology
April 10th
page revision: 2, last edited: 26 Mar 2008 13:40