BG2

Question 1

Aristotle homology

Answer 1

distinguished between analagous and those that were ‘the same without qualification’.
- stimualted by enquiry into origin of cephalopod and vertebrate brain

Question 2

renaissance homology

Answer 2

peirre belon

noticed simlarities between human and avian skeletons

Question 3

idealistic homology

Answer 3

richard owen in the 19th century, founder of the NHM,

archetypal vertebrate, from which all vertebrate arose - fanciful and failed when tested against embryology

Question 4

darwins homology

Answer 4

same by virtue of common descent

Question 5

modern homology defintion

Answer 5

character are homologous when the genetic info required to specify them is similar by descent.

Question 6

homoplasy in Algae Eaters

Answer 6

Homoplasy:
Galapagos marine iguana, Lake Tanganyika/Malawi cichlids and russian periwinkle all have flexible rasping stalked teeth like structures with multiple cusps.
snail = radula.
convergent evolution for algal feeders, most efficent method of algal scarping.

Question 7

evidence for homology

Answer 7

1. structural similarity
2. fossils
3. embryology
4. genetic programme

Question 8

Structural evidence for homology of the mammalian middle ear

Answer 8

homologous to reptilian jaw
* same blood vessels and nerves involved in both
Quadrate -> incus
Articular -> malleus
Stapes -> stapedial cartilage.

Question 9

fossil evidence for homology of mammalian middle ear

Answer 9

in the synapsid reptile can see jaw bones have become smaller and been translated further and further into the middle ear

Question 10

embryological evidence for homology of mammalian middle ear

Answer 10

incus and malleus of mammals and quadrate and articulate of reptiles all develop from first pharyngeal pouch and stapes and stapedial cartilage develop from the second

1. early in vertebrate development neural crest cells migrate out of the newly formed dorsal neural tube.
2. NC forms a series of pharyngeal pouches.
   - — In mammals the incus and malleus develop from the first pharyngeal pouch, in reptiles the quadrate and articulate bones do.
   - — in mammals stapes develops from second pharyngeal pouch and in reptiles stapedial cartilage does.

Question 11

Haekel on homology

Answer 11

ontogeny recapitulate phylogeny

** development of an organism expresses all the intermediate forms of its ancestors throughout evolution.

Question 12

ontogeny recapitulate phylogeny in mammalian middle ear

Answer 12

mallus can be see to remain attached to the jaw cartilage until late in development.

Question 13

what are the different eye types

Answer 13

Vertebrates and cephalopods: lens eyes

Arthropod and Annelid: compound eye

Question 14

Pax6 KO mutations

what is pax6

Answer 14

pax6 = TF found in metazoan eyes`

Aniridia: lack iris in humans, cant regualte size o pupils due to pax6 mutation,
eyeless drosophila: mutations in pax6

Question 15

Pax6 overexpression drosophila

Answer 15

cause ectopic eye formation

Question 16

are eyes homologous

Answer 16

all metazoan eyes are descended from a CA structure, a simple photorecepto specified by Pax6. general mechanism is maintained.
but eyes are not homologous
homology should be considered as degree of homology

Question 17

Gene regulatory network for eye formation

Answer 17

pax6 is one commponent of network of TFs involved in eye specification.
vertebrates and insects both have GRNs of TFs that regulate eye development.
Topology of network differs but similar TFs are involved.

Question 18

Homology of sine occulus and optx2

argument for homology

Answer 18

sine occulus gene in drosophila have two mammalian homologs six1 and six2, however these dont work in eyes but earlier in sensory placade.
mammalian homologs of another drosophila gene: optix have been found that work in the eye: six3/6

some argue that differences are evidence against eye homology other argue differences due to divergence.

Question 19

Describe the relevance of thr GRN for limb formation for dung beetle horns

Answer 19

insects have a GRN that regulates limb formation

in dung beetles, this GRn have been clearly co-opted for use in horns.

Question 20

evidence for cooption of leg genes in dung beetles

Answer 20

clone homologs of Drosophila genes from dung beetles and look for their expression patterns.
found dung beetle horns are made using leg genes: hth, n-exd, dac, DII

Question 21

what is DII

Answer 21

distalous
controls proximal distal limb growth in insects,
loss causes loss of outgrowth of limb.

Question 22

what does investigating genetic programmes for homology allow us to do

Answer 22

refine our notion of how structures are built when begin to attend to underlying genetic info.