1. Set up Cornell Notes on pg. 23
Topic: Other Mechanisms of Evolution: Genetic Drift
Essential Question:
How does gene flow affect neighboring populations?
Would a population of 10 individuals or 100 individuals be more vulnerable to genetic drift. Why?
11.3 Other Mechanisms of Evolution:
Genetic Drift
2.1 Atoms, Ions, and Molecules
How does gene flow affect neighboring populations?
Draw a “Picture Tree Map” on pg.22 describing the two processes through which genetic drift can occur

2. 11.3 Other Mechanisms of Evolution
Objectives
8 c: Students know the effects of genetic drift on the diversity of organisms in a population.

3. 11.3 Other Mechanisms of Evolution
KEY CONCEPT Natural selection is not the only mechanism through which populations evolve.

4. Gene flow is the movement of alleles between populations.
11.3 Other Mechanisms of Evolution
Gene flow is the movement of alleles between populations.
Occurs when individuals join new populations and reproduce
Its alleles become part of that new population’s gene pool
The alleles are removed from its former population
Increases genetic variation in the receiving population!
Population 1 in Florida
Population 2 in Maine

5. 11.3 Other Mechanisms of Evolution
Leaving population #1
Joining population # 2
2 miles away

6. 11.3 Other Mechanisms of Evolution
Gene flow keeps neighboring populations similar.
The less gene flow that occurs, the more genetically different the two populations will become
Low gene flow increases the chance that two populations will evolve into different species.

7. 11.3 Other Mechanisms of Evolution
If I asked you to randomly pick 100 flowers from this field what percentage of each color would you expect to pick?
What if I asked you to choose 10?
Would it always be 50/50?
NO! You could pick 90 red and 10 pink. Unlikely, but it could happen.
1000 pink and 1000 red flowers in the population

8. 11.3 Other Mechanisms of Evolution
Genetic drift is a change in allele frequencies due to CHANCE and causes a LOSS of genetic diversity *It is most common in small populations
Generation # Generation #2

9. 11.3 Other Mechanisms of Evolution
Genetic Drift Activity:
You are working with a very small population of rabbits
6 Rabbits in total- 3 white and 3 black
Over each generation, you should see the genetic diversity decrease over time due to random mating

10. 11.3 Other Mechanisms of Evolution
There are two types of Genetic Drift:
1. Bottleneck Effect
2. Founder Effect
Effects of Genetic drift:
Populations lose genetic variation
With little variation, a population is less likely to have some individuals that will be able to adapt to a changing environment
Any lethal alleles may be carried in the population by heterozygous individuals, and become more common in the gene pool due to chance alone

11. 11.3 Other Mechanisms of Evolution
On pg. 22 create a Picture Tree map on the two types of Genetic Drift
Genetic Drift
Bottleneck Effect Founder Effect
Define/
explain .
Real Life Example .
Real Life Example
Define/
explain
PICTURE
PICTURE

12. 11.3 Other Mechanisms of Evolution
A population bottleneck event can lead to genetic drift.
It occurs when an event drastically reduces population size.
Original population
The bottleneck effect is genetic drift that occurs after a bottleneck event. Leaves very little genetic variation

13. 11.3 Other Mechanisms of Evolution
Genetic Drift: Bottleneck Effect: Northern Elephant Seals
During the 1800s the over hunting of Northern Elephant seals reduced the population to about 20 individuals
The 20 seals did not represent the genetic diversity of the original population
Since hunting stopped, the population has grown to over 100,000
However the population has little genetic diversity

14. 11.3 Other Mechanisms of Evolution
The founder effect is genetic drift that occurs after the start of new population.
It occurs when a few individuals start a new population

15. 11.3 Other Mechanisms of Evolution
Genetic Drift: Founder Effect: The Amish of Lancaster PA
Amish communities founded in N. America by small #s of migrants from Europe
Amish in PA have a high rate of Ellis-van Creveld Syndrome
This dwarfism is rare in other human populations, but more common in Amish populations
Can trace it back to one of the community’s founding couples

16. Set up Cornell Notes on pg. 25
Topic: 11.3 Other Mechanisms of Evolution: Sexual Selection
Essential Question:
How can mating have an important effect of the evolution of populations?
Traits that increase mating success are not always adaptive for the survival of the individual (Red or blue feathers). How can these traits evolve if it makes them easily spotted by predators?
11.3 Other Mechanisms of Evolution: Sexual Selection
2.1 Atoms, Ions, and Molecules
How can mating have an important effect of the evolution of populations?
Traits that increase mating success are not always adaptive for the survival of the individual (Red or blue feathers). How can these traits evolve if it makes them easily spotted by predators?

17. 11.3 Other Mechanisms of Evolution
Mating can have an important effect on the evolution of populations
Both sexes benefit from having offspring that survive

18. Sexual selection occurs when certain traits increase mating success.
11.3 Other Mechanisms of Evolution
Sexual selection occurs when certain traits increase mating success.
Sexual selection occurs due to higher cost of reproduction for females.
males produce many sperm continuously
females are more limited in potential offspring each cycle
* This makes females choosy about mates!

19. 11.3 Other Mechanisms of Evolution
There are two types of sexual selection.
intrasexual selection: competition among males
Ex: head butting of Bighorn sheep
intersexual selection: males display certain traits to females
Ex: Male peacocks fanning out their tails

20. Sexual Selection Video Notes:
Which trait increases mating success?
It is intrasexual or intersexual selection?
Vogelkop Bowerbird:
Hummingbird:
Red deer:
Capercaillie:
Ibex:
Mudskipper:

21. Sexual Selection of Guppies
In books on page 339
Read the example
Complete the 3 questions about the guppy tail size experiment on pg. 24 in your I.N.B.