1. Mechanisms (Features) of Evolution
What is needed for Natural Selection to occur?

2. Evolution of Populations
Population: A particular species in one area
By focusing on evolution of populations, we define evolution on the smallest scale (microevolution)
Because:
Individuals do not evolve
Populations are isolated from others of their own species; keeps gene pool from being manipulated by outside traits
Allele frequencies can be monitored over generations
Allele: traits passed on from parents (You have two alleles for each trait, one from each parent)
Changing allele frequencies point to an evolving population

3. Genetic Variation The most important factor needed for NS to occur
Random Mutations in DNA
Mutation cannot be silent or non-beneficial to reproductive success of individual
Mutation must occur in cell line that produces gametes
Less limiting in plants and fungi as many cell lines produce gametes
Mutations produced in somatic cells die with individual

4. Genetic Variation The most important factor needed for NS to occur
Random Mutations in DNA
This is likely how vertebrates evolved
Invertebrates have a gene called the Hox complex that direct the major development of body parts during fetal (embryological) development
520 million years ago a duplication of the Hox complex may have provided genetic material associated with the first vertebrates
A second duplication (leading to 4 Hox complexes in current vertebrates) points to a linear evolution of these genes

5. Hox Gene Evolution

6. Genetic Variation The most important factor needed for NS to occur
Sexual Reproduction (only in organisms that reproduce in this manner)
Shuffles genetic material in individuals to contribute variability to population
Crossing over during Meiosis – happens during synapsis in which homologous chromosomes touch, exchanging chromatids and ensures that specific variation of traits do not have to be inherited together
Independent Assortment – homologous chromosomes from each parent do not have to all line up on one side of metaphase plate; ensures that parental DNA is shuffled in offspring creating genetic variability
Random Fertilization – each gamete produced has a unique combination of parental DNA and fertilized at random; ensures variability of offspring with each combination of gametes

7. Genetic Variation The most important factor needed for NS to occur
Asexual Reproduction – creates offspring that are genetically identical to parents
Advantageous only when environment is stable

8. Genetic Variation
How can asexually reproducing organisms be genetically variable?
Random Mutations in DNA
Mutation cannot be silent or non-beneficial to reproductive success of individual
Mutation must occur in cell line that produces gametes
Horizontal Gene Transfer: transfer of genes between organisms in a manner other than traditional reproduction
Transformation
Transduction
Conjugation

9. Genetic Variation
How can asexually reproducing organisms be genetically variable?
Bacterial Transformation: Direct uptake of DNA from environment by bacteria through cell wall
Can occur naturally in some bacteria but has to be induced in others
E.coli Lab

10. Genetic Variation
How can asexually reproducing organisms be genetically variable?
Bacterial Transduction: Uptake of DNA through viruses known as bacteriophages
Bacteriophage: virus that infects bacteria
Happens naturally; once virus takes over bacterial cell, new viruses have bacterial DNA incorporated into them; those viruses then go onto infect other bacteria and are more readily accepted by the bacteria because of the recombinant DNA
Now commonly used in gene therapy to insert therapeutic DNA or siRNA into cells

11. Bacterial Transduction

12. Genetic Variation
How can asexually reproducing organisms be genetically variable?
Bacterial Conjugation: transfer of genetic material (DNA or RNA) between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells

13. Bacterial Conjugation

14. Genetic Variation
Genetic Drift: Chance events that alter the allele frequencies of a population with no regard to how trait is related survival
Not considered NS
Example: You stepping on a large population of green bugs; trait has nothing to do with survival, just an oops
Extreme drift can lead to:
Founders Effect
Bottleneck Effect

15. Genetic Variation
Founders Effect: A few individuals become isolated from original population; allele frequency may differ from original population
Not necessarily a negative effect unless frequency reflects less variation

16. Genetic Variation
Bottleneck Effect: A dramatic reduction in population size that may not be representative of allele frequencies original population
Generally reduces genetic variation
Can lead to endangerment of species
Example: Cheetahs
Two Bottlenecking Events: Ice age (100,000 years ago) and extreme hunting and poaching (100 years ago)
So genetically similar that tissue grafts are never rejected between unrelated cats (less than 1% genetic variation)

17. Genetic Variation
Gene Flow: Transfer of alleles into or out of a population due to movement of fertile individuals or gametes
Not considered NS
Introduced alleles would change frequencies of next generation
Transferred alleles can be both beneficial and damaging to the survival of population
Reduces variation between populations of different geographic locations
Example: HUMANS! Much more mobile than previous generations; much less variation based on geographic location

18. Relative Fitness - Competition
Variation doesn’t matter unless organism that is passing on traits is in some way improving its chances of reproductive success
Competition for Limited Resources
Food
Space
Mates
Survive long enough to have offspring
Interactions with environment such as coloration or symbiotic relationships with other organisms

19. Relative Fitness - Competition
Sexual Selection: Form of natural selection in which certain individuals are more likely to obtain mates
Intrasexual selection: individuals compete with member of the same sex for mate
More often occurs in males, but can occur in females
Intersexual selection: mate choice; individuals are choosy in selecting mates
Often it is females choosing males based on behavior or appearance
Results in sexual dimorphism

20. Overall Requirements for NS to Occur
Reproduction
Heredity (ability to pass on heritable traits)
Variation of traits in the population
Relative Fitness of members of the population