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Notes: Genetic Drift
Learning Objectives:
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Describe how and when mutations happen
Analyze data on genetic drift
Explain how genetic drift affects variation in populations
What have we learned about evolution so far?
• Evolution is change in the traits of a population over time
• Natural selection is the mechanism of evolution, and it acts on an
organism’s phenotype
• Evidence of evolution comes from the fossil record, DNA and
proteins, comparative anatomy, and embryology
• Isolation can lead to speciation. The major types of isolation are
geographic, behavioral, temporal, and reproductive
• Variation within a species increases the probability that some
members of the species will survive
• A great diversity of species increases the chance that at least
some organisms will survive great changes in the environment
Review: Mutations
Mutations are changes in DNA _____________________________ or
chromosome structure that can change the
_____________________________ produced by an organism. Mutations
can result in different _____________________________.
How do mutations occur? Do mutations ever stop happening?
Write the answers in your notes now.
Mutations produce _____________________________ within species.
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Vocabulary
1. _____________________________: different forms of a gene
2. _____________________________: how often something happens
3. _____________________________ _____________________________: the percentage of alleles for
a specific trait within a gene pool
3. _____________________________: to enter into a new population
4. _____________________________: to exit a population
5. _____________________________ _____________________________: change in allele frequency in
a population
6. _____________________________ _____________________________: when allele frequencies
change as a result of the migration of a small subset of a population out of the group
7. _____________________________ _____________________________: when a population
experiences a large decrease in the number of individuals
Genetic Drift
In _____________________________ populations, an _____________________________ can become
more or less common in the gene pool simply by _____________________________ chance,
rather than by _____________________________ _____________________________. The smaller a
population is, the greater the chance that this kind of random change in allele
_____________________________ will happen. This random change in allele frequency is
called _____________________________ _____________________________.
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Genetic Drift: Key Point
In small _____________________________, individuals that carry a particular
_____________________________ may have more _____________________________ than other
individuals just by _____________________________ _____________________________. Over time,
several random chance events like this can cause an allele to become
_____________________________ in a population.
Answer in your notes now: After genetic drift occurs, will there be more or less
variation in the population? Why?
The Founder Effect
The _____________________________ _____________________________ is a
specific type of genetic drift. The founder effect can be seen
when a few individuals _____________________________ out of a
population and start a new population with a different
_____________________________ _____________________________ than the
original population.
The Founder Effect: Ellis-van Creveld Syndrome
The founder effect can be seen in the _____________________________
population in Eastern Pennsylvania. This population was
founded by about _____________________________ German
immigrants. One couple in this founding population, Samuel
King and his wife, each carried an _____________________________ for
a rare _____________________________ genetic disorder called Ellisvan Creveld syndrome and passed it onto their children.
This syndrome causes short stature, _____________________________, and
several other abnormalities. Since the members of this population
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only have _____________________________ with _____________________________
members of the _____________________________ population, no new
genetic _____________________________ is being introduced. Now, the
_____________________________ of people in this Amish community with
Ellis-van Creveld syndrome is much _____________________________ than
the percentage of people with the disease in the rest of the United
States.
Population Bottlenecks
A _____________________________ _____________________________ is
when a population becomes much
_____________________________ due to
_____________________________ events (earthquakes, fires,
floods, droughts, etc) or due to
_____________________________ _____________________________ such as
excessive hunting, habitat destruction, and poaching. When a
population becomes much smaller, the amount of
_____________________________ _____________________________ is also
reduced. This reduction in variation also reduces the
chances that the population will survive. Some populations
that experience bottlenecks go extinct.
Population Bottleneck in Cheetahs
About 10,000 years ago - because of _____________________________
_____________________________ - all but one species of the cheetah became
_____________________________. With the drastic reduction in their numbers,
close relatives were forced to breed, and the cheetah became
genetically inbred, meaning all cheetahs are closely related. When
_____________________________ looked at the amount of genetic
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_____________________________ in cheetahs, they found that they have much less variation
than other mammals. The _____________________________ in cheetahs has led to low
survival rates, and greater _____________________________ to disease. Inbred
animals suffer from low genetic diversity. This means cheetahs do not
have the ability to _____________________________ to sudden changes in the
environment, such as disease _____________________________, and have
unusually high susceptibility to certain viruses. For example, if a virus
gets into a healthy population of leopards, not every animal dies; only
some do, because leopards are genetically _____________________________.
But if every animal is genetically the same, like the cheetah, and one
gets infected, all of them may become infected and _____________________________.
Because of their low genetic diversity, a deadly virus could kill all of the worlds' wild
cheetahs instead of just the susceptible animals. 
Question for YOU!
Write the answer in your notes now:
What is the major difference between the founder effect and the bottleneck effect?
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