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What are the four fundamental forces of evolution?
- 1. Natural selection
- 2. Mutation
- 3. Recombination
- 4. Random Drift
Name characteristics of natural selection.
- It's a population based phenomenon.
- Indiviuals are selected for or against.
- Populations evolve.
- Acts on phenotype.
Name characteristics of mutation.
- No genome can replicate without error so we have mutation.
- DNA and RNA are error prone.
- There are environmental mutagens (ex: UV Light).
- There are genetic mutagens (ex: transposable elements).
- Mutation can be directional (specific mutations can be more prevalent).
Name characteristics of recombination.
- Higher rates of recomb. allow selection to work more efficiently.
- Recombination allows the removal of deleterious mutations (BAD).
- Muller's Ratchet- no recombination = accumulation of deleterious mutations on chromosome until it dies out.
- Allows multiple beneficial mutations on the same chromosome.
What is Clonal Interference?
- In an asexual species beneficial mutations compete with eachother.
- In sexual species recombination can bring beneficial mutations onto the same chromosome.
Are recombination rates uniform across the genome? Why or why not?
No, they aren't. Recombination rates differ in males and females and different "hotspots" exist in different species in different amounts.
The efficiency of natural selection is different across the genome.
What is the "two-fold cost of sex"?
For a short period of time an asexual species grows twice as fast as a sexual species.
Name characteristics of Gentic drift.
- It's random change in allele frequencies over time due to finite sample size.
- An example is the founder effect (given a small number of individuals they'd be biased for certain traits or genes just because of chance).
Random Drift is strong in _______ populations. The average _____________ differ from the initial condition.
small ; does not
Wright Fisher Model of Drift
See binomial distribution in the first set of lecture notes, 1/20, page 9.
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