Experimental Evolution Flashcards
(44 cards)
what are the three methods of studying evolution?
- fossil data
- genome sequencing
- experimental evolution
how can we study evolution through fossil data?
- traditionally at macroevolution level use fossil records
- if evolution is slow and steady we’d expect to see the entire transition from ancestor to descendent in the fossil record
- can see the evolution of organisms
what are the limitations of fossil data?
- fossil records are often incomplete and not all organisms form fossils
- they only form in specific conditions
- eg if they dont have a skeleton wont get a fossil
how can we study evolution through genome sequence data?
- genomics is a rapidly expanding field
- good at showing genetic relatedness between organisms
- can build phylogenetic trees to show relatedness
what are the limitations of genome sequence data?
- cant be used to establish causality
how can we study evolution through experimental evolution?
- replaying tape of life real-time
- use of labatory or controlled field manipulations to investigate evolutionary processes
- usually makes use of an organims with rapid generation times and small physical size (eg microbes)
what are the limitations of experimental evolution?
it would take to long to observe evolution in large multicellular organisms - occurs too slowly
what are the stages of phase 1 of experimental evolution: selection experiment?
- start with a single bacterial clone and replicate to get a genetically uniform base
- expose to certain selection pressures
- need a control population
- grow in a test tube and every 24hrs transfer a small subset of the population to a new medium
- new mutations will be introduce
- could be fitter than the ancestral bacteria
- selection acts on mutations
- can store some bacteria from each stage -80degrees
what are the stages of experimental evolution phase 2: compare changes in fitness?
- measure adpatation, done first at phenotypic level
- compare the evolved population to the ancestral or controlled population
- use direct competition to assess fitness
- 1:1 mix and compare
- see which increases in frequncy
- can then sequence genes and find mutations underlying the changes
what does experimental evolution combine?
the fossil record and sequence genomes together in a controlled lab experiment
what is the LTEE?
- long term evolution experiment
- 12 replicate populations adapting to glucose
- 1% transferred to fresh media every day and samples stored at around -80 degrees
- experiment has lasted around 30 years
- fitness measured bin direct competition against ancestral bacterial strain
- followed by genome sequencing
what are some key factors affect the rate and trajectory of evolution?
- genetic variation
- mutations
what does genetic variation provide?
raw material for selection
what are the key factors in generating mutations in bacteria?
- de novo mutations (new mutations)
- recombination (eg HGT)
how is antibiotic resistance an example of genetic variation?
- initial population, only a couple are resistant
- initiate selection process (most are killed but the resistant survive)
- resistance increase in frequency
what are the sources of mutations?
- HGT, resistant plasmids can move between bacteria
- mutations as bacterial replication can have a lot of errors
what are the 3 key factors in the emergence of potentially benefecial de novo mutations?
- mutation rate
- mutation supply rate
- generation time
what is mutation rate?
the frequency of new mutations in a single gene or organism over time
why do viruses have higher mutation rates than eukaryotes?
RNA is less stable than DNA
what is mutation supply rate?
rate of adaptation as a function of the relative mutation supply rate (ie population size * mutation rate)
what is the mutation supply rate in larger populations?
- larger population has more mutations appearing as there is more cell division which means there is more chances for error
what does an increase in mutation rate speed up?
evolution
what does the increase in the mutation rate for a small population do?
increases evolution
what effect does mutation rate have on large populations?
none
