1. THE EVOLUTION
OF POPULATIONS

2. Individuals are selected, but populations evolve
Species
Gene pool
Population genetics
Modern synthesis

3. Population distribution
Fir populations Not totally isolated, interbreeding may occur
Eastern U.S.
People mobile, but more likely to choose mate locally

4. ALLELE FREQUENCIES Gene pool – all alleles in a population
Diploid organisms – 2 alleles at each locus
Two or more alleles in a population – each has a relative frequency (proportion)
Population = 500 organisms = ? alleles
320 homozygous dominant = ? alleles
160 heterozygous = ? alleles
20 homozygous recessive = ? alleles

7. HARDY - WEINBERG p + q = 1 p2 + 2pq + q2 = 1
p = frequency of dominant allele
q = frequency of recessive allele
PKU 1/10,000 births; q2 = ?

8. Hardy-Weinberg Equilibrium
Very large population
No migration
No net mutations
Random mating
No natural selection
No genetic drift

9. Causes of Microevolution
Evolution is a generation-to-generation change in a population’s frequencies of alleles.
Genetic Drift – a change in a population’s allele frequencies due to chance
bottleneck effect: drastic reduction in population size
founder effect: new colony, not representative of the larger population
Natural Selection – allele frequencies in offspring generation different than parental due to differential reproductive success

10. GENETIC DRIFT

11. BOTTLENECK EFFECT

12. GENE FLOW: genetic change due to migration, tends to reduce differences between populations.
Gene flow & Human Evolution
MUTATION: a change in an organism’s DNA

13. VARIATION WITHIN POPULATIONS Quantitative characters
- vary along continuum
Discrete characters
- either/or
Polymorphism
- 2+ forms represented
- applies to discrete characters
Gene diversity
- average % heterozygous loci
Nucleotide diversity
- about 0.01% in humans

14. GEOGRAPHIC VARIATION
Clinal variation

15. GEOGRAPHIC VARIATION
Madeira: 2 mouse populations separated by mountains
Squirrel populations & the Grand Canyon

16. BALANCED POLYMORPHISM
DIPLOIDY – recessive alleles cannot be selected for/against in heterozygotes
BALANCED POLYMORPHISM
Heterozygote advantage: malaria & sickle cell anemia
Frequency dependent selection: survival & reproduction of 1 morph declines if that phenotype becomes too common
NEUTRAL VARIATION

17. HETEROZYGOTE
ADVANTAGE

18. FREQUENCY DEPENDENT SELECTION IN HOST/PARASITE RELATIONSHIP

19. Modes of selection

20. Directional selection

21. DIVERSIFYING SELECTION
Intermediate selected against – inefficient at cracking both size seeds

22. Sex: 2 fold disadvantage

23. Sexual Selection Sexual dimorphism: secondary sex characteristics
Intrasexual selection: direct competition among same sex individuals
Intersexual selection: mate choice, individuals of one sex (usually female) are choosy in selecting mates