1. Mechanisms of Evolution

2. Is this population evolving?
What do you think?
Is this population evolving?

3. This population is NOT evolving
Genetic Equilibrium - Population in which allelic frequency does NOT change over generations,
i.e. population is NOT evolving

4. Connecting Darwin & Mendel
Darwin’s Handicap ~
Mendel’s work
Two gaps in Darwin’s thinking:

5. Two Main Sources of Genetic Variation
1) Mutations 2) Gene Shuffling

6. 1) Mutations
Any change in a sequence of DNA.
Caused by mistakes during replication or environmental factors such as radiation or chemicals.

7. Mutations can be beneficial, harmful, or harmless

8. 2) Gene Shuffling
~ Mixing of genes during the production of gametes in meiosis

9. How Does Variety Arise? Video
2) Gene Shuffling
Recombination as homologous chromosomes move independently during meiosis
Crossing over: the exchange of genetic material during prophase I
How Does Variety Arise? Video

10. Gene Pool & Allelic Frequency
Gene Pool: Entire collection of all the alleles in a population
Allelic Frequency: The number of times an allele appears in the gene pool

11. Gene Pool & Allelic Frequency
Gene Pool: 12 green alleles and 8 brown alleles
Allelic Frequency of green: 12/20
Allelic Frequency of brown: 8/20

12. Evolution vs. Genetic Equilibrium
Occurs when ALL of the following conditions are met:
Random Mating: All members of the population must have an equal opportunity to produce offspring
Large Population: To prevent genetic drift
No Migration
No Mutations
No Natural Selection
NOTE: These conditions DO NOT exist in nature

13. Evolution is the change in allele frequency
Occurs in one of three ways:
Gene Flow
Genetic Drift
Natural Selection

14. Evolution is the change in allele frequency
Remember…evolution occurs
Over time
In populations…NOT individuals
On phenotypes

15. 1) Gene Flow ~ The movement of alleles into or out of a population
Can increase or decrease genetic variation

16. 2. Genetic Drift Random change in allelic frequencies due to chance.
Decreases genetic variation

17. Types of Genetic Drift
Founder Effect ~ A small group of individuals colonize a new habitat

18. Types of Genetic Drift
Bottleneck ~ a sharp reduction in the size of a population due to environmental events (flooding, earthquake, etc.)

19. 3) Natural Selection Can increase or decrease genetic variation
~ Most common source of evolutionary change
Can increase or decrease genetic variation
3 types

20. Main Mechanisms of Evolution Video