BG22 Flashcards
Cichlids in African lakes
and radiations
Lake malawi = 500 spp. of cichlids have evolved from a single CA that lived 5mya.
Lake Tanganyika = CA lived 10mya
Lake victoria = more recent radiation
adaptive landscapes metaphore
combos of genes create adaptive landscapes
- shape of the adaptive landscape depends on the pattern of gene interaction for fitness.
additive gene action gives a simple landscape with a single peak, epistasis gives more complex.
selection usually pushes popualtions to the top of one adaptive hill
from here adaptive and potentially developmental constraints prevent movement to other adaptive landscapes.
smooth adaptive landscape
no epistasis
each new gene adds a set unit
bumpy landscape
positive epistasis
genes are only exceptionally more beneficial when expressed together.
rugged landscape
negative epistasis
genes are beneficial only if in particular combinations
adaptive landscape in baby survival
single peak landscape of birth and weight gestation period in human infacnts
as birth mass and gestation period increases so does survival to a point
after this survival begins to drop (baby too big for birth canal)
adaptive landscape gater snakes
two peaks can be observed in two predator related traits
- reverse wriggle to escape predators
- camouflage with stripes
* when both are present the adaptive landspace drops as survival is low
individually the landscape peaks for each trait
predictability of cancer
cancers can be thought of as evolutionary process = not developmental
individual cancers are their own evolutionary lineage
gliboblastoma gene sequences
- no gene is mutated in all tumours, large diversity at gene level, no gene is essential for progression.
- convergence can be seen at a pathway level, although half of the gliboblastoma mutations in TP53 itself, 83% have altered P53 signalling.
Lenskis experiment
expose. E. coli strains to low nutrient environment
- make 12 replicate e. coli populations from a single cell, serial transfer to new flask occured daily (~7 generation per day) to maintain exponential growth
- new supply of glucose every morning, runs out by afternoon
- samples frozen
characters monitored in lenskis
mean fittness and cell size
- fittness calculated against ancestral
results of lenski
continued for 50,000 generations and still goin
1 mil years to do same in humans
- fitness increased over generation but began to slow
at 10,000 generations
fitness selects for itself.
av. cell size increased up to 1200 then plateus.
- step like increase in both
parrallel evolution in lenskis
sequenced genomes of evolving popualtions at different generations
- identified many potentially causal muutations
- atleast some evolved in the other popualtion too = parallele = ascertainment bias (only looked for them as found elsewhere).
massively replicated thermal evo experiment
al bennet
- lenskis colleague studied thermal adaptation in bacteria.
- evolved 115 lines of lenskis e.coli for 3k generations at 42 degrees
MRTE results
sequened and looked for co-variance between mutation and effects
- few strains shre exactly the same mutations
- homogeneity increases up the hierachy (fraction of shared alleles increase from point mutation, mutation, gene, operon, functional unit etc)
- ** only 33% of strains shared hits in the same functional unit.
- two groups of strains in multilocus space
- suggests adaptive landscape with two peaks
