1. Natural Selection EU 1.A: Change in the genetic makeup of a population over time is evolution

2. Natural Selection is a Major Mechanisms of Evolution Darwin’s Theory of Natural : ◦There is variation within a population. ◦Competition for limited resources results in differential survival. ◦Individuals with more favorable phenotypes are more likely to survive and produce more offspring, thus passing traits to subsequent generations

3. Evolutionary Fitness Fitness = Reproductive Success

4. Natural Selection Depends on Genetic Variation Genetic Variation is essential for the survival of a species in a changing environment Sources of Variation ◦Mutation ◦Sexual Reproduction  Segregation – Anaphase 1  Independent Assortment – Metaphase 1  Crossing Over – Prophase 1  Random Fertilization

5. Favored Phenotypic Variation Some phenotypic variations significantly increase or decrease fitness of the organism and the population ◦Sickle Cell anemia ◦DDT resistance in insects ◦Antibiotic resistance in bacteria

6. Environmental Impact Environments can be more or less stable or fluctuating, and this affects evolutionary rate and direction; different genetic variations can be selected each generation. ◦Peppered Moth  Bernard Kettlewell vindicated by Michael Majerus  8 February 2012 as "Selective bird predation on the peppered moth: the last experiment of Michael Majerus.“ ◦Global warming and flowering times in Thoreau's Concord: a community perspective.  “Using a subset of 43 common species, we determined that plants are now flowering seven days earlier on average than they did in Thoreau's times.” Miller-Rushing & Primack, Ecology. 2008 Feb;89(2):332-41 http://www.ncbi.nlm.nih.gov/pubmed/18409423 Ecology. http://www.ncbi.nlm.nih.gov/pubmed/18409423

7. Adaptation Genetic variation that is favored by selection & is manifested as a trait that provides an advantage to an organism in a particular environment

8. Other Influences Evolution (especially in small populations) can be influenced by: ◦Genetic drift – chance events causing changes in allele frequency  Founder effect  Bottleneck effect ◦Mutations ◦Human Impact  Artificial selection  Loss of genetic diversity  Overuse of antibiotics

9. Hardy-Weinberg Equilibrium Conditions: ◦Large population size ◦Absence of migration ◦No net mutations ◦Random mating ◦Absence of selection Rarely are these conditions met…

10. Hardy-Weinberg Equilibrium Mathematical approach to calculate allele frequency, providing evidence for the occurrence of evolution in a population ◦p + q = 1 ◦p 2 + 2pq + q 2 = 1 ◦p = frequency of dominant allele ◦q = frequency of recessive allele ◦p 2 = frequency of homozygous dominant ◦2pq = frequency of heterozygous ◦ q 2 = frequency of homozygous recessive

11. Hardy-Weinberg Equilibrium Example: A fruit fly population has a gene with two alleles A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg Equilibrium, what proportion of the flies carry both the A1 and the A1 alleles? ◦What is given?  p or q (this problem doesn’t tell you enough to know which for sure) ◦What are you finding?  2pq (so it doesn’t matter if you are given p or q – the answer is still the same – 0.42)

12. Graphical Analysis A second mathematical approach to calculate changes in allele frequency provides evidence for evolution.