1. Evolution of Populations

2. Five factors that can lead to evolution
1. Genetic drift

3. 2. Gene flow

4. 3. Mutation

5. 4. Sexual selection

6. 5. Natural selection

7. Gene flow: the movement of alleles between populations.
Gene flow occurs when individuals join new populations and reproduce.
Lots of gene flow: similar populations
Limited gene flow: higher chance of new species
bald eagle migration

8. Genetic drift: change in allele frequencies due to chance.
Genetic drift: small populations more affected
a. Bottleneck effect
occurs when an event drastically reduces population size.

9. Example: In the 1800’s, northern elephant seals were overhunted
Example: In the 1800’s, northern elephant seals were overhunted. The population was reduced to about 20 individuals. Hunting has ended, and there are now about 100,000 seals. However, the population has little genetic variation.

10. B. Founder effect: genetic drift that occurs after start of new population

11. Genetic drift has negative effects on a population.
less likely to have some individuals that can adapt
harmful alleles can become more common

12. Sexual Selection: occurs when certain traits increase mating success.
How? Females prefer males that possess certain traits.

13. There are two types of sexual selection.
intrasexual selection: competition among males
intersexual selection: males display certain traits to females

14. Evolution and fitness

15. Reproductive isolation: can occur between isolated populations.
members of different populations cannot mate successfully
Speciation is the rise of two or more species from one existing species.

16. Reproductive isolation can be caused by
Geographic isolation
physical barriers divide population

17. Geographic isolation

18. 2. Temporal isolation
timing of reproductive periods prevents mating

19. 3. Behavioral isolation
includes differences in courtship or mating behaviors
Example: female fireflies only respond to light patterns of males of their own species

20. History of Life

21. Fossils can form in several ways.
Permineralization occurs when minerals carried by water are deposited around a hard structure.

22. Trace fossils record the activity of an organism.

23. Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

24. Preserved remains form when an entire organism becomes encased in material such as ice.

25. Specific conditions are needed for fossilization.
Only a tiny percentage of living things became fossils.

26. What type of fossil is this?
Arizona - World’s largest collection of petrified wood
What type of
fossil is this?
PETRIFIED WOOD – These trees thrived in a sub tropical forest ecosystem million of years ago. When they fell they were covered by volcanic ash that seeped into their cells. Over millions of years the ash crystallized into a silica-quartz composite that gives it the “stone-like” quality.

27. Relative dating estimates the time during which an organism lived.
It compares the placement of fossils in layers of rock.
Scientists infer the order in which species existed.

28. Radiometric dating uses decay of unstable isotopes.
Isotopes are atoms of an element that differ in their number of neutrons.
neutrons
protrons

29. Radiometric dating uses decay of unstable isotopes.
Isotopes are atoms of an element that differ in their number of neutrons.
A half-life is the amount of time it takes for half of the isotope to decay.

30. Several sets of hypotheses propose how life began on Earth.
There are two organic molecule hypotheses.
Miller-Urey experiment
electrodes
heat source
amino acids
water
“atmosphere”
“ocean”
meteorite hypothesis

31. Microbes have changed the physical and chemical composition of Earth.
The oldest known fossils are a group of marine cyanobacteria.
prokaryotic cells
added oxygen to atmosphere
deposited minerals

32. Eukaryotic cells may have evolved through endosymbiosis.
Endosymbiosis is a relationship in which one organism lives within the body of another.
Mitochondria and chloroplasts may have developed through endosymbiosis.