• Mutation - the ultimate source of all genetic variation
• Recombination - shuffles existing alleles
• Selection - different alleles and genotypes have different fitness. Frequencies change with time
• Migration - introduces alleles and genotypes into populations
• Drift - results in the loss of alleles from populations
Mutation and the fluctuation test
A population is:
• a group of individuals of the same species from which the next generation is drawn. (Often included is that members of the same population occupy the same locality and ecological niche.)
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
Effect of strong selection
See: Kent Holsinger’s web site, Univ. Connecticut
See: Kent Holsinger’s web site, Univ. Connecticut
Consider a population that is:
• Haploid• Asexual (no recombination)• Not subject to any kind of selection
1
2
3
4
5
1
Random numbers:1 3 1 4 3
Individuals
Generations
1
2
3
4
5
1 2
Random numbers:3 4 3 5 1
Individuals
Generations
1
2
3
4
5
1 2 3
Random numbers:5 3 5 4 4
Individuals
Generations
1
2
3
4
5
1 2 33 4
Random numbers:5 1 5 1 3
Individuals
Generations
1
2
3
4
5
1 2 33 44 5
Random numbers:2 3 1 3 2
Individuals
Generations
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
Not all individuals leave behind descendants.
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
Present individuals have a common ancestor.
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
Present individuals have a common ancestor.
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
Present individuals have a common ancestor.
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
Present individuals have a common ancestor.
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
Present individuals have a common ancestor.
For any pair of individuals, what is the chance of a common ancestor in the generation immediately preceding?
Answer: 1/N
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
For any pair of individuals, what is the average time back to the most recent common ancestor?
Answer: N generations
1
2
3
4
5
1 2 33 44 55 6
Individuals
Generations
For any pair of individuals, what is the average number of mutational events separating them?
Answer: 2Nwhere is theRATE of mutation per gene (or per nucleotide) per generation.