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KEY
Evolution: Population Genetics Guided Notes
Population Genetics:
• Evolution occurs at the population level, not the individual. Genes are the raw
material for evolution.
Modern Synthesis Ideas:
• Combines Darwin's original theory of evolution with new evidence from other fields of
study
Mechanisms of Evolution
1. Genetic Drift:
• any change in the gene allele frequencies that is due to chance.
• it has the greatest effect in small populations due to the small gene pool size.
Accidents, such as the one in the picture, occur in nature. How
might it cause evolution?
a. accidents might allow genetic drift and change in allele
frequencies
b. less-fit dark beetles are eliminated because of the
accident
c. accidents might increase the amount of mutations
d. more-fit dark beetles will reproduce faster and make a comeback
2. Founder Effect: (extreme example of genetic drift)
• decrease in genetic variation that occurs when a small part of a population becomes
isolated from the rest of the population.
• Example: Amish – polydactyly and dwarfism
3. Gene Flow:
• new genes entering the population and other genes leaving the population as
individuals randomly move (migrate) between populations
4. Nonrandom Mating:
• organisms usually mate with individuals in close proximity. This can lead to inbreeding
and a chance in allele frequency.
5. Natural Selection:
• acts to select the individuals best adapted for survival and reproduction. It acts on an
organism's phenotype, and changes allele frequencies.
Mutation:
• random change in genetic material
• balances natural selection by creating new alleles
Speciation:
• formation of a new species
• individuals of the same species share a common gene pool, and a genetic change occurs
in an individual and spreads throughout the population as it reproduces
• for a species to evolve into two new species, the gene pools of the two populations
must become separated.
• this means the populations must be reproductively isolated: the members of the two
populations can't interbreed and produce fertile offspring.
Reproductive Isolation Can Occur By:
1. Behavioral Isolation – two populations are capable of interbreeding but have different
courtship rituals or reproductive strategies that involve behavior.
2. Geographic Isolation – two populations are separated by geographic barriers. This can
result in separate gene pools.
Patterns of Evolution
1. Adaptive Radiation aka Divergent Evolution:
• occurs in relatively short time when one species gives rise to many new species in
response to creation of new habitat or other ecological change.
• Example: rise of the mammals after the extinction of dinosaurs.
2. Coevolution:
• species evolve in close relationship with other species – evolution of one affects the
other
• Example: can be mutually beneficial (both benefit), can be parasitic (one benefits and
takes, one is harmed)
3. Convergent Evolution:
• unrelated species evolve similar traits in different parts of the world
• occurs in ecologically similar environments that are geographically separate
Final Exam Practice Questions:
1. Which of the following CANNOT cause evolution?
a. genetic drift
b. non-random mating
c. gene flow
d. all can cause evolution
2. Natural selection tends to reduce variation in gene pools. What process serves to balance
natural selection by creating new alleles?
a. meiosis
b. sex
c. mutation
d. migration
3. Gene frequencies in a gene pool may shift randomly and by chance. This is called:
a. artificial selection
b. adaptive radiation
c. genetic drift
d. natural selection
4. Which of the following is true about mutations in population genetics?
a. mutations have no affect on allele frequencies
b. mutations play a significant role in changing allele frequencies
c. mutation plays a relatively insignificant role in changing allele frequencies
d. none of the above is correct
5. A decrease in genetic variation that occurs when an entire population descends from a
small number of individuals
a. founder effect
b. vestigial
c. natural selection
d. allele
6. What does speciation, the formation of one species from another, usually require?
a. human intervention
b. billions of years
c. reproductive isolation
d. all of the above
7. What is the importance of Modern Synthesis ideas of Evolution?
a. it completely contradicts everything Darwin said and supports Lamarck's theories
b. it shows how current humans are no longer evolving because they have reached
evolutionary perfection
c. it combines Darwin's original theory of evolution with new evidence from other fields
of study
d. it reveals all of Darwin's notes, showing his doubt in his theory
8. Five populations of deer exist within a single forest. As gene flow between these
populations increases, what will happen to the genetic makeup of these populations?
a. the populations will become more genetically unique
b. the populations will not change at all
c. the populations will become more genetically similar to one another
d. the genetic makeup of each population will remain roughly the same