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Set up Cornell Notes on pg.
23
•Topic: Other Mechanisms
of Evolution: Genetic Drift
•Essential Question:
1. How does gene flow
affect neighboring
populations?
2. Would a population of
10 individuals or 100
individuals be more
vulnerable to genetic
drift. Why?
11.3
OtherIons,
Mechanisms of Evolution:
2.1 Atoms,
and
Molecules
Genetic
Drift
1. How does gene flow affect
neighboring populations?
2. Draw a “Picture Tree Map” on
pg.22 describing the two
processes through which
genetic drift can occur
11.3 Other Mechanisms of Evolution
Objectives
8 c: Students know the effects of
genetic drift on the diversity of
organisms in a population.
11.3 Other Mechanisms of Evolution
KEY CONCEPT
Natural selection is not the only mechanism through
which populations evolve.
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
11.3 Other Mechanisms of Evolution
Leaving population #1
Joining population # 2
2 miles away
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.
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
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 #1
Generation #2
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
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
11.3 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
• .
• .
• .
• .
• .
• .
• Real Life
Example
• Real Life
Example
PICTURE
PICTURE
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
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
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
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
Set up Cornell Notes on pg.
25
•Topic: 11.3 Other
Mechanisms of Evolution:
Sexual Selection
•Essential Question:
1. How can mating have an
important effect of the
evolution of populations?
2. 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
OtherIons,
Mechanisms of Evolution:
2.1 Atoms,
Sexual
Selection
and Molecules
1. How can mating have an
important effect of the
evolution of populations?
2. 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
Mating can have an important effect on the evolution of
populations
• Both sexes benefit from having offspring that survive
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!
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
Sexual Selection Video Notes:
• Which trait increases mating success?
• It is intrasexual or intersexual selection?
• Vogelkop Bowerbird:
• Hummingbird:
• Red deer:
• Capercaillie:
• Ibex:
• Mudskipper:
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.