1
Q
Some mechanisms of evolution
A
- mutation
- Genetic drift
- Natural selection
- Sexual selection
- Gene flow
2
Q
Mutation
A
- ultimate source of all genetic variation
- change the genetic code which generates new alleles, which may change amino acid sequence or gene expression, which may have phenotypic effects
3
Q
Mutation - Deleterious
A
- decrease fitness (survival and reproductive success)
- average mutation reduces fitness by about 2% per generation
4
Q
Mutation - Benefits
A
- few beneficial mutations are likely to be of small effect
- most things are fairly good at surviving so helpful mutations mostly just tweak things
- “Hopeful monster” are rare - “beneficial mutations
5
Q
Genetic Drift
A
- causes random changes in allele frequency
- Calculate frequency by adding up # of one types of alleles and dividing by total # of alleles
- Evolution happened but it was completely random
- is stronger in smaller populations (can be seen in computer simulations)
- Eventually half the population will fix for the allele and the other half will fix for the other allele, if there are 2 alleles in total
6
Q
“Quantitative” genetic variation
A
- Traits influenced by multiple gene (polygenic)
- usually influenced by environmental conditions
- typically leads to continuous variation (most alleles have a continuous distribution)
- changes in allele frequency at multiple genes underlie genetic changes in quantitative traits
7
Q
Two complementary ways of looking at evolutionary change
A
- changes in allele frequency
- changes in mean values of quantitative traits
8
Q
Natural Selection (quantitative traits)
A
Darwin’s and Wallace’s insight
- All organisms have the potential for exponential growth and yet most populations remain relative stable in the # of individuals: this implies high mortality in nature
- traits vary among individuals
- traits influence survival
- traits are heritable
9
Q
Natural selection (prediction)
A
- traits that improve survival should increase in frequency (or size) through time
- Darwin used domestic breeds (pigeons) as an example of the power of the selection
- Ex. Ecological changes caused by 1976 Daphne Major drought (seed abundance decreased, average seed size and hardness increased)
G. Fortis (bird) - Approximately 90% of all individuals died during this drought
- used a capture-measure-mark-resight method to view birds
- See whether the beak size influenced survival (were the birds with longer beaks recaptured?)
- Certain traits influenced the survival of birds (individuals with larger/deeper beaks were more likely to survive, traits are heritable: relationships btwn beak size of parents and offspring)
- Weak sizes were larger in the next generation
- Selection and evolution are highly variable
10
Q
Sexual selection
A
Intra-sexual: male-male competition
Inter-sexual female choice (widow birds)
11
Q
Why do male mosquitofish have such long gonopodia?
A
Natural and sexual selection often act in opposition to each other
- It aids in sneaky copulations and it impresses females
- So then why isn’t it longer? It is a real drag/causes drag
12
Q
Gene flow
A
- movements of gene among populations
- tends to oppose the divergent nature of natural selection
- exchanging individuals btwn the 2 selections line of Drosophila would reduce their divergence
