Transcript Genetic Drift

Mechanisms of Evolution
Notes
June 2, 2016
I. Mechanisms of Evolution
A. Natural Selection
B. Sexual Selection / Non-random mating
C. Mutation
D. Gene Flow: movement of alleles between
populations
1. Example: When organisms migrate into a
new population
E. Genetic Drift- reduces population size
1. Bottleneck effect
2. Founder effect
II. Genetic Drift
A. Refers to changes in the allele
frequencies of a gene pool due to
chance (random)
1. Not due to natural selection
B. Genetic Drift Example
1. A population of 10 frogs includes 3 red frogs,
5 light green frogs, and 2 dark green frogs.
2. By chance, the three red frogs die and only
the green frogs reproduce and pass on their
genes. The allele frequencies of the next
generation’s gene pool may be completely
different from previous generation.
Genetic Drift
Natural Selection vs. Genetic Drift
C. Types of Genetic Drift
1. Bottleneck Effect
a. Occurs when an event causes a significant
percentage of the population or species to be
killed or otherwise prevented from
reproducing
b. Often caused by natural disasters or human
interference
c. Population is reduced by 50% or more
d. Reduces population’s ability to adapt to
changes in environment
Bottleneck Effect Model
Types of Genetic Drift (cont.)
2. Founder Effect
a. Occurs when a few individuals found a
colony and only a fraction of the total genetic
diversity of the original gene pool is
represented
b. Alleles that are carried by the founders is
due to chance (from their parents)
Founder Effect (cont.)
c. Example: Amish population
1. Isolated religious sect that descended from a
few German ancestors
2. As many as 1 out of every 14 people carry a
recessive allele for unusual form of dwarfism
(affects only lower arms & legs) and/or allele
for polydactylism (extra fingers)
a.
In non-Amish population, only 1 in 1,000 has this
allele
What term would best describe the
picture below?
Founder Effect
2. Bottleneck Effect
3. Mutation
4. I need help with this.
25%
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Newly
Established
Population
Original Population
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What term would best describe the
picture below?
25%
1. Founder effect
25%
2. Bottleneck effect
25%
3. Natural selection
25%
4. I need help with this.
The frequency of a particular recessive allele in a
population of chipmunks is .3
The frequency of the dominant allele in this same
population is:
0%
1. .3
5%
2. .6
95%
3. .7
0%
4. 1
You have determined the frequency of the
dominant allele in a population. Over the next two
generations, the frequency of this allele does not
change. Which factors below must be true in order
to maintain this equilibrium?
14%
1. Random mating
14%
2. Large population size
3. No natural selection
14%
4. No gene flow
14%
5. No mutations
14%
6. All of the above
14%
7. None of the above
14%
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