1. Evolution of Populations
AP Biology
Crosby High School

2. Modern Evolutionary Synthesis
Modern Synthesis
Emphasize importance of population as evolutionary unit
Natural selection most important mechanism of evolution
Gradualism explains large changes from accumulated small changes
Population Genetics
Emphasizes extensive genetic variability
Recognized quantitative characteristics

3. Pop. Gen. Terminology
Population: local group of individuals belonging to the same species
Species: group of populations whose individuals have potential to interbreed and produce fertile offspring
Gene Pool: total aggregate of genes in population at any given time
Fixed gene pool: all individuals homozygous for an allele

4. Hardy-Weinberg Assumptions Equations Very large pop. Size No migration
No net mutations
Random mating
No natural selection
Equations
p + q = 1
p2 + 2pq + q2 = 1

5. Causes of Microevolution
Genetic Drift
Bottleneck Effect
Results from disasters and leads to little variability
Founder Effect
Huevos a doce
Natural Selection
Moths
Gene Flow
Migration
Mutation

6. Bottleneck Effect

7. Genetic Variation w/in Populations
Polymorphism
More than one form of a characteristic
Not quantitative traits
Measuring Genetic Variation
Gene Diversity
% Heterozygous
Humans: 14%
Nucleotide Diversity
% Difference in nucleotides of two individuals
Humans: 0.1%

8. Genetic Variations Btw. Populations
Geographic Variations: Result from different environments
Cline: Graded change in a trait along geographic axis

9. Genetic Variation Mutation Sexual Recombination Diploidy
Balanced Polymorphism
Heterozygote advantage
Sickle Cell carriers are advantageous
Frequency-dependent Selection
Two species affect each others evolution

10. Fitness
Evolutionary: relative contribution an individual makes to the gene pool
Darwinian: Contribution an individual makes to the gene pool of the next generation relative to the contributions of another individual
Relative: Contribution of genotype to the next generation compared to other genotypes

11. Relative Fitness Most favored genotype set to a value of 1
Less favored genotypes are given values based on how much offspring they produce
If they produce 80% as many offspring as the most favored genotype then Relative fitness = 0.8
Sterile individuals have relative fitness of 0.0

12. Modes of Selection
Directional Selection: common during periods of environmental change or migration
Diversifying Selection: favors both extremes over the intermediate genotype
Stabilizing Selection: Acts against the extremes keeping the status quo
Birth weight (3-4 kg)

13. Modes of Selection

14. Sexual Selection Benefits of sex
Sexual Dimorphism: Difference in appearance between the sexes
Intrasexual Selection: Direct competition between males of the same sex
Rams
Intersexual Selection: Individual of one sex are choosy in selecting a mate
Peacocks

15. Nobody’s Perfect Evolution is limited by historical contraints
Adaptations are often compromises
Not all evolution is adaptive
Selection can only edit existing variations