1. Natural Selection
Garielle Wagnac

2. So…….what is natural Selection?
Who knows?

3. Natural Selection……… It’s a process Causes evolution to occur
Beneficial traits inherited become more common in consecutive generations
Causes evolution to occur
Happens because of adaptation

4. Yes, Natural Selection favors individuals!
BUT WHICH?!?!

5. Reproductive Success
Likelihood of an individual contributing fertile offspring to the next generation
Traits favorable to reproductive success
Two categories of traits
Characteristics organisms better adapted
Traits associated with reproductive success

6. Principles of Natural Selection
Allele variation due to mutation (may alter function of protein)
Some alleles enhance reproductive success
Beneficial alleles more likely to survive
Allele frequency change through natural selection

7. How do you measure reproductive success?
FITNESS
likelihood that a genotype will contribute to gene pool of next generation compared to other genotypes
Mean Fitness
average reproduction success of members
*as mean increases, so does natural selection of organisms

8. AA produces 5 offspring
Aa produces 4 offspring
aa produces 1 offspring

9. Natural Selection Paths
There are 4!
Natural Selection Paths

10. Directional Selection
Individuals at one extreme of phenotypic range have greater reproductive success in a particular environment
Arise from?
New allele added
Expose to change in environment

11. Stabilizing Selection
Favors individuals with intermediate phenotypes an selects against those with extreme phenotypes
Tends to decrease genetic diversity

13. Diversifying (Disruptive) Selection
Favors the survival of two or more different genotypes that produce different phenotypes
Likely to occur in populations that occupy heterogeneous environments

15. Balancing Selection
Type of natural selection that maintains genetic diversity
Balanced polymorphism occurs
2+ alleles kept in balance of each other
Can happen by…….

16. Negative frequency-dependent selection Heterozygote Advantage
Balancing Selection
Negative frequency-dependent selection
Heterozygote Advantage
Phenomenon where heterozygotes have a higher fitness than the corresponding homozygotes
Fitness of a genotype decreases when its frequency becomes higher!

19. NOW YOU KNOW EVERYTHING ABOUT NATURAL SELECTION!
At least, I hope so!
NOW YOU KNOW EVERYTHING ABOUT NATURAL SELECTION!