1. More on Natural Selection Bio Standard 8a, 7a, b, and c
How Does Evolution Occur?
More on Natural Selection
Bio Standard 8a, 7a, b, and c

2. Genetics Orgs differ by DNA they possess.
DNA: code that forms your traits.
DNA makes up genes- set of instructions for one trait.
Chromosomes carry the genes.
Some traits are dominant (shows up in offspring) or recessive (doesn’t show).
DNA

3. Chromosomes

4. Genotype and Phenotype
Genotype: genes/DNA that an org contains for a trait.
Phenotype: observable/physical traits of an individual.
Natural selection works on phenotypes, what org looks like.

5.  Survival of the Fittest.
Darwin’s Natural Selection
States that individs whose characteristics are well-suited to the environment will survive.
 Survival of the Fittest.
                                        

6. Variation among individuals
To Work…
Populations have:
Variation among individuals

7. 2) Pop. size had to increase

8. 3) Traits Are Passed on to Offspring

9. To Work..4) Struggle for Survival

10. Peppered Moth Story: Natural Selection Example
England: 2 types of moths (same species): black and white.
White: abundant, black: rare.

12. Peppered Moth Story: Natural Selection Example
Trees the moths lived on were whitish colored.
Predatory birds could only see dark moths to eat.
 Huge white moth pops.

15. Then, the Industrial Revolution happened…

16. Coal was burned…created soot…

17.  Trees lined with soot…

18. SO…Now who is best fit for this environment??

19. Black moths now camouflaged w/ trees.
Black moths  abundant, passed on genes to offspring.

20. Survival of the fittest!
Natural selection works on an individual’s phenotype (physical features), not its genotype (DNA)

21. Types of Natural Selection
1) Stabilizing Selection: Selective pressures select against the 2 extremes of a trait.
Ex: it is better to be average!

22. Types of Natural Selection
2) Directional selection: one extreme of the trait experiences selection against it.
Ex: giraffes w/ short necks

23. Types of Natural Selection
3) Disruptive selection: Selection pressures act against individuals in the middle of the 2 extremes of the trait.
Ex: it’s not good to be average

24. Peppered Moth Virtual Lab