Download Processes that Cause Evolution

Population Genetics & Evolution
Warm-up
What are the 3 ways that sexual reproduction
produces genetic diversity? Why is this
important for evolution?
Warm-up
At which level does natural selection at—
individuals or populations?
At which level does evolution act—individuals or
populations?
Vocab
• Gene pool: all of the alleles for
all genes in all the members of
the population
– What’s in the gene pool for the beetles?
– Can calculate allele and frequencies
• Fixed allele: all members of a population only
have 1 allele for a particular trait
– The more fixed alleles a population has, the
LOWER the species’ diversity
– Example of a fixed allele in the beetle population…
Hardy-Weinberg Theorem
Hardy-Weinberg Theorem: The allele and genotype
frequencies of a population will remain constant from
generation to generation
…UNLESS they are acted upon by certain forces
Equilibrium = allele and genotype frequencies
remain constant
Conditions for Hardy-Weinberg equilibrium
1.
2.
3.
4.
5.
No mutations.
Random mating.
No natural selection.
Extremely large population size.
No gene flow.
If at least one of these conditions is NOT met, then the
population is EVOLVING!
Microevolution vs Macroevolution:
• Microevolution: A change in allele frequencies
in a population over generations. Creates
changes (adaptations) that are confined to a
particular gene pool or population.
• Macroevolution: Occurs over geologic time
above the level of the species. The fossil
record reflects macroevolution. It results from
microevolution taking place over many
generations and helps define taxa.
Minor Causes of Evolution:
#1 - Mutations
– Rare, very small changes in allele frequencies
#2 - Nonrandom mating
– The idea that mating is NOT random! (females are
“choosy”)
•
•
https://www.youtube.com/watch?v=KW8GX2n4qbY
https://www.youtube.com/watch?v=L54bxmZy_NE
Minor Causes of Evolution:
#1 - Mutations
– Rare, very small changes in allele frequencies
#2 - Nonrandom mating
– Affect genotypes, but not allele frequencies
Major Causes of Evolution:
• Natural selection, genetic drift, gene flow (#3-5)
Major Causes of Evolution
#3 – Natural Selection
– Individuals with variations better suited to
environment pass more alleles to next generation
4- Genetic drift – a change in allele
frequencies due to chance, not natural
selection.
• Usually occurs in smaller
populations cut off from
main population. (No gene
flow)
• Reduces genetic variation.
Genetic Drift: allele frequencies “drift”
away from original population’s.
The smaller a population, the more
vulnerable it is to genetic drift.
• How might this affect
endangered species?
The Bottleneck Effect – when a population has
been dramatically reduced, and the gene pool is
no longer reflective of the gene pool of the
original population.
Founder effect – when a small number of
individuals colonize a new area; new gene
pool not reflective of original population
The Fugate family Kentucky's Troublesome CreekExtra credit 
Reduction of genetic variation within a
given population can increase the
differences between populations of the
same species.
The Serval from Africa, the
Canada Lynx from N. America
and Margay from S. America
Michael
Major Causes of Evolution
#5 – Gene Flow (migration)
– Movement of fertile
individuals between
populations
– Gain/lose alleles
– Reduces genetic differences
between populations
(slows down speciation)
Gene flow
Conditions for Hardy-Weinberg equilibrium
1.
2.
3.
4.
5.
No mutations.
Random mating.
No natural selection.
Extremely large population size.
No gene flow.
If at least one of these conditions is NOT met, then the
population is EVOLVING!
Crash Course Review
• https://www.youtube.com/watch?v=WhFKPa
RnTdQ
• (1:04 – 4:45)
Model 1
Model 2