Pre-Tutorial Assignment #2 BIOL 336 Section 202 Cassandra Chan ...
Pre-Tutorial Assignment #2 BIOL 336 Section 202 Cassandra Chan 60463080 th January 18 , 2013 1. No, because the population genetics definition of evolution is the change in allele frequencies observed in a population over generations. An individual alone cannot undergo “evolution” under this definition. 2. “The Hardy-Weinberg theorem is a null model of evolution.” This phrase means that the H-W theorem is a model that predicts what expected allele frequencies should be when a population is not undergoing evolution (i.e. no evolutionary mechanisms are occuring). 3. Assumption of the H-W model
Evolutionary mechanism
Population infinitely large
Drift
All genotypes equally likely to survive and reproduce
Selection
No alleles enter or leave population via migration Gene flow No mutations
Mutation
4. Evolution can occur if one or more of these assumptions are not met. 5. “Random mating” is mating between individuals in a population with respect to the alleles at their genetic locus of interest.
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6. a) Population size = 4 shows some simulations' allele frequencies fixate or disappear.
Population size = 40 shows less simulations' allele frequencies fixate or disappear.
Population size = 400 show no simulations' allele frequencies fixate or disappear.
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b) As population size increases, allele frequencies of new generations tend to remain more consistent with allele frequencies from previous generations. c) Over time (i.e. over generations), all allele frequencies change relatively drastically; some reach fixation and some disappear. d) In small populations, time to fixation or loss of an allele is relatively short. In large populations, time to fixation or loss of an allele is relatively long. e) We need to run a simulation several times to get the general idea because there is greater deviation in smaller than infinite populations. In infinite populations, under all the same conditions, the system would be under Hardy-Weinberg equilibrium and so allele frequencies would not change (i.e. all simulations would be the same).
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Evolutionary mechanism
Population infinitely large
Drift
All genotypes equally likely to survive and reproduce
Selection
No alleles enter or leave population via migration Gene flow No mutations
Mutation
4. Evolution can occur if one or more of these assumptions are not met. 5. “Random mating” is mating between individuals in a population with respect to the alleles at their genetic locus of interest.
1
6. a) Population size = 4 shows some simulations' allele frequencies fixate or disappear.
Population size = 40 shows less simulations' allele frequencies fixate or disappear.
Population size = 400 show no simulations' allele frequencies fixate or disappear.
2
b) As population size increases, allele frequencies of new generations tend to remain more consistent with allele frequencies from previous generations. c) Over time (i.e. over generations), all allele frequencies change relatively drastically; some reach fixation and some disappear. d) In small populations, time to fixation or loss of an allele is relatively short. In large populations, time to fixation or loss of an allele is relatively long. e) We need to run a simulation several times to get the general idea because there is greater deviation in smaller than infinite populations. In infinite populations, under all the same conditions, the system would be under Hardy-Weinberg equilibrium and so allele frequencies would not change (i.e. all simulations would be the same).
3
