L9 Flashcards
Timeline of evolution
1900s
- Neo-Darwinian evolution
1920s-1930s
-Mathematics of gene frequencies
1945
- Attempts to bring palaeontology back into the fold
1953
- Crick and watson unravel DNA
1960s
- Genetic code established
1970s
- Technological innovation enables manual DNA sequencing
1980s
- Technological innovation enables identification of genes and gene function
1990s
- Automated DNA sequencing
2000s
- Whole genome sequencing and evo-devo research
Palaeogenomics - Amber fossils
- As soon as an organism dies it becomes infested with microbes (internal and external) that contaminate DNA
- DNA breaks down very quickly in the presence of water and/or air
- Theoretical DNA could only be observed from more recent fossils
Major and rapid advances in the last decade:
- Most of the genome of the woolly mammoth has been sequenced
- We even know the nuclear gene for coat-colour polymorphism
- We now know that the mammoth was more closely related to Asian rather than African elephant and the two diverged 6-7 million years ago
- Neanderthals DNA has been sequenced
- T-rex protein sequences obtained from bone-derived collagen
Molecular taxonomy
- Entire genomes can be analyzed
- Fossils along with living specimens can be made into a phylogeny
- Fossils show unknown character combinations
Molecular biogeography
- Multiregional vs out-of-Africa hypothesis
- multiregional describes long divergence time ago whereas out of Africa does not
Molecular clocks
- Calculates divergence time
- Tends to work for shallow dates but not very old dates
- Because the genome doesn’t evolve at a constant rate eg during adaptive radiations
In all cases fossils are incorporated into these analyses either to:
- Reflect evolutionary history (long extinct organisms and traits)
- Provide and calibrate a time dimension
Case stud: radiation of birds
- Birds evolve from small agile, feathered theropod dinosaurs by at least the Upper Jurassic
- Traits evolve sequentially
- Birds are neither common or diverse with the skies ruled by the pterosaurs
- Many lose ability to fly
- Still have other primitive characters
Did the KT boundary wipe out dinosaurs…. or were there modern birds in the cretaceous period?
- Mot much evidence for modern birds in the cretaceous
- Two major radiations, after KT and meioscene
Pterosaurs become extinct, birds appear to diversify as the Neognathae radiate. The vast majority of living birds are Neognathae with 8,500 species in 140 families
Did the neognathae evolve after the KT mass extinction and fill the ecological vacuum left by pterosaur extinction?
-Depends on fossils used to calibrate
Did the neognathae have a long cretaceous history but they were simply rare and not very diverse?
Evidence from:
Fossils
Phylogenetic analysis
Molecular clocks
Developmental genetics
- Ability to identify genes and look at their function
- Turning genes off and on
- Can look at past character combinations
- Speed of genome evolution
Hox genes
- Can work out how evolution worked
- Hox gene locations can be calculated
- How hox genes form segmentations in different groups can be calculated