1. Allele Frequencies

2. Introduction Darwin proposed natural selection
Certain traits get passed on
Genetics = change in allele frequencies to cause evolution
Genetic Factors + Natural selection =
Mutations
Gene flow
Genetic drift
Founder effect
Bottle neck
Nonrandom mating

3. Natural selection
Increase or decrease in allele frequencies due to impact of environment

4. Mutations
Introduction of new alleles that may provide a selective advantage
Most mutations are deleterious
“causing harm”

5. Gene Flow Describes movement of individuals between populations
Removal of alleles from population (emigration)
Introduction of alleles to population (immigration)

6. Genetic Drift Random increase or decrease of alleles 2 types:
Due to chance
Usually when populations are small
Associated with flipping a coin
2 types:
Founder effect
Bottleneck

7. Founder Effect
Allele frequencies in a group of migrating individuals differ from their population origin
Ex. Germans Amish community possessed allele for polydactylism
200 years of reproductive isolation = over 8,000 in population had polydactylism (exceeding number of cases around the world)
Amish Community in Pennsylvania
Polydactylism = more than 5 fingers and toes

9. Bottleneck Population’s dramatic decrease in size
Catastrophe, predation, disease, etc.
Small population becomes severely vulnerable

10. Nonrandom Mating Individuals choose mates based on particular traits
Can occur when mates choose only nearby individuals
Certain, selected traits passed to next generation
2 main examples:
Inbreeding
Sexual selection

11. Inbreeding
Individuals mate with relatives

12. Sexual Selection
Females choose males based on attractive appearance or behavior

13. Sources of Variation in Populations
Must be variation for natural selection
Types:
Mutations
Sexual reproduction
Diploidy
Outbreeding
Polymorphism

14. Mutations Provide raw material for new variation
Rearranging existing alleles in new combinations
Invent alleles that have never existed in gene pool
Ex. antibiotic and pesticide resistance

15. Sexual Reproduction
Creates individuals with new combinations of alleles
Genetic recombination
Crossing over
Independent assortment
Random joining of gametes
Crossing over – exchange DNA between non-sister chromatids
Independent assortment – metaphase I making random combinations of maternal and paternal chromosomes
Random joining of gametes – fertilization contributes to diversity of gene combinations in zygote

16. Diploidy Presence of 2 copies of each chromosome in a cell
Recessive allele
Stored for future generations

17. Outbreeding Mating with unrelated partners
Increase possibility of mixing different alleles and creating new allele combinations

18. Balanced Polymorphism
Maintenance of different phenotypes in population
1 phenotype may provide best adaptation
Alleles for advantageous traits increase
Alleles for disadvantageous traits decrease
Heterozygote advantage = resistance to malaria
Hybrid vigor = hybrid of corn = resistance to disease and produce larger corn ears
Minority advantage = least common phenotypes have advantage

19. Neutral Variation Not all variation has selective value
Fingerprint patterns are neutral variation = everyone has different fingerprints
Most cases, environment determines whether variation is neutral or selective
Monocultures
Overuse of antibiotics

20. Monocultures
No genetic variation due to agriculture
Potato famine

21. Overuse of Antibiotics
Reduces variation in bacterial populations by eliminating individuals susceptible to disease
Non-susceptible bacteria increase
Domination of the population
New outbreaks of diseases (harder to destroy)