1. Title of Notes: Evolution of Populations
p. 38, 39, & 40 RS

2. Population Genetics
In genetic terms, evolution is any change in the allele frequency (relative frequency) of alleles in a population
Sexual reproduction can produce many different phenotypes, but it does not change the relative frequency of alleles in a population. Think of deck of cards.
Gene pool- all the combined genetic material of all of the members of a given population.
Allele frequency- the number of each allele is a fraction of all of the genes for a particular trait. (pg. 394)
1.36

3. Single Gene and Polygenic Traits
Single gene trait is controlled by one gene
Widows peak
Freckles
Dimples
Roll tongue
Taste PTC
Polygenic traits are controlled by many genes.
Body stature
Eye color
Height
Natural Selection on Single Gene traits can lead to changes in allele frequencies…evolution

4. Natural Selection on Polygenic Traits
Natural selection can affect the distributions of phenotypes in 3 ways.
Directional selection
Disruptive selection
Stabilizing selection
Microevolution: a change in the allele frequency of a species or
population

5. Directional Selection
Directional Selection occurs when a individual at one end of the curve have a higher fitness than individuals in the middle or at either end.
What is a phenotype and what are some examples?
Ie. Peppered moth

6. Example of Directional Selection

7. Disruptive Selection
Disruptive selection occurs when an environmental change makes it unfavorable to have a medium phenotype. You need an extreme one.

8. Stabilizing Selection
When individuals near the center of the curve have higher fitness than individuals at either end of the curve.

9. Draw the 3 Graphs on left side of p. 38 notebook
directional
disruptive
Draw the 3 Graphs on left side of p. 38 notebook
stabilizing

10. Hardy Weinberg Principle
If a population is not evolving, the allele frequencies in the population remain stable.
This constant state of allele frequency is called genetic equilibrium.
It states that, under specific conditions, allele frequencies in a population remain constant from generation to generation. If specific conditions are not met, genetic equilibrium in interrupted and the population may evolve.

11. Maintaining Genetic Equilibrium
5 conditions:
1. No natural selection
2. Random mating
3. No migration
4. No significant mutations.
5. Very large population

12. Hardy-Weinberg equations for population with 2 alleles at a locus (but only works if one assumes random mating):
Generation 1
p + q = 1
Frequency A allele
Frequency of a allele
p2 + 2 pq + q2 = 1
Generation 2
Frequency of AA genotype
Frequency of Aa genotype
Frequency of aa genotype

13. Genetic Drift
Genetic Drift is the random change in allele frequencies in a population due to chance events, such as natural disasters or migration. (Would genetic drift have a greater impact on smaller or larger populations?)
“Bottlenecking” is when genetic drift occurs after a random population reducing event.
The more variation, the easier it is to survive because they can adapt better.

14. An example is the Cheetah.

15. Bottleneck Effect Example
Example of Genetic Drift
Results from a drastic reduction in population like the hunting of the Cheetah
Cheetah

16. (2:55 genetic drift video)
Founder effect
Allele freq. change as a result of the migration of a small subgroup of population.
Will the new population become different or more like the parent population?
Due to chance
(2:55 genetic drift video)

17. Speciation
It can occur when members of a population become isolated from each other. (possibly from earthquakes.)
Once two populations are reproductively isolated, they are considered separate species.
Speciation is the evolution of one or more species from a single ancestor species.

19. Allopatric Speciation
Aka. Geographical Isolation
Physical barrier ( continental split, rise in sea level, formation of mountain range, advance of glacier, change in habitiat) prevents gene flow between populations of a species
Archipelago hotbed of speciation
Allopatric Speciation

20. Allopatric Speciation in the Grand Canyon

21. Behavioral Isolation
Two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies.

22. Temporal Isolation Two or more species reproduce at different times.
Orchid releasing pollens on different days, they can’t pollinate each other.

23. Speciation in Darwin’s Finches
Speciation in the Galapagos finches occurred by:
1. Founding of a new population.
Geographic isolation
Changes in new population’s gene pool
Reproductive isolation
Ecological competition

24. Evolution does not occur in a set direction
Evolution builds on what already exists, so the more variety there is, the more there can be in the future.
However, evolution does not necessitate long-term progress in a set direction.

25. Rate of Evolution
Gradualism- theory that new species evolve as the genomes of two populations differentiate over enormous spans of time.
(Small genetic changes occur slowly within a population.)
Punctuated equilibrium- theory that populations remain genetically stable for long period of time, interrupted by brief periods of repaid genetic change.
Rapid genetic changes in a population can result in the evolution of new species.

26. Graduated vs. Punctual

27. Mechanisms of Evolution
Divergent Evolution- when isolated populations of a species evolve independently. It occurs when geographic barriers separate population members or when a small group leaves an original population.
Ex: polar bears and brown bears
Convergent Evolution-occurs when natural selection has produced analogous adaptations in response to similar environment between different species.
Ie. Maned Wolf and Serval Cat
Eat same, legs same, ears same.

28. Coevolution
Species that interact closely often adapt to one another in a process called coevolution.
What does the prefix co- mean?
Ex:
Predatory birds and mimicry of butterflies
Parasites and hosts
Plant-eating animals and the plants they eat
Plants and the animals that pollinate them.

29. Adaptive Radiation
Adaptive Radiation is the evolution of many diversely adapted species from one common ancestor. It usually occurs on an isolated island.
ie. Finches that Darwin studied all came from common ancestor, but had different beaks for the kind of food they ate.