1. Ch. 16 Evolution of Populations

2. Variations and Gene Pools
Gene pool – consists of all genes, including all the different alleles, that are present in a population.
Relative frequency – the number of times that the allele occurs in a gene pool, compared with the number of times other alleles for the same gene occur.

3. Variations and Gene Pools

4. Sources of Genetic Variation
The 2 main sources of genetic variation are mutations & the genetic shuffling that results from sexual reproduction.

5. Single-Gene & Polygenic Traits
The # of phenotypes produced for a given trait depend on how many genes control the trait.
Single-gene trait - controlled by a single gene, that
has 2 alleles
Ex.) Widow’s Peak

6. Single-Gene & Polygenic Traits
Polygenic traits - trait controlled by 2 or more genes
Ex.) Height in humans

7. Evolution as Genetic Change
Evolutionary fitness can be viewed as an organism’s success in passing genes to the next generation.
Evolutionary adaptation can be viewed as any genetically controlled trait that increases an individual’s ability to pass along its genes.

8. Evolution as Genetic Change
NS never acts directly on genes.
NS can only affect which individuals survive & reproduce, & which do not.
Also, remember that it is populations, not individual organisms, that can evolve over time.

9. NS on Single-Gene Traits
NS on single-gene traits can lead to changes in allele frequencies & thus to evolution.

10. NS on Polygenic Traits
NS can affect the distributions of phenotypes in any of 3 ways:
-directional selection
-stabilizing selection
-disruptive selection

11. NS on Polygenic Traits
Directional Selection - occurs when individuals at 1 end of the curve have higher fitness than individuals in the middle or at the other end.

12. NS on Polygenic Traits
Stabilizing selection - occurs when individuals near
the center of a curve
have higher fitness
than individuals at
either end.

13. NS on Polygenic Traits
Disruptive selection - when individuals at the upper & lower ends of the curve have higher fitness than individuals near the middle.

14. Genetic Drift
Genetic drift – random change in allele frequencies that occurs in small populations.
Founder effect - situation in which allele frequencies change as a result of the migration of a small subgroup of a population.

15. Genetic Drift

16. Evolution vs. Genetic Equilibrium
Hardy-Weinberg Principle-allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change.
Genetic equilibrium - when allele frequencies remain constant, the population will not evolve.

17. Evolution vs. Genetic Equilibrium
5 conditions are required to maintain genetic equilibrium:
-random mating
-large population
-no movement into/out of pop.
-no mutations
-no NS

18. Overuse of Antibiotics
People may be overusing antibiotics.
Doctors may prescribe them for diseases which they are not effective.
This wide use of antibiotics has caused many bacteria to evolve resistance to antibiotics.

19. The Process of Speciation
Speciation - formation of a new species
The gene pools of 2 populations must become separated for them to become new species.

20. Isolating Mechanisms
As new species evolve, populations become reproductively isolated from each other.
Reproductive isolation - when members of 2 populations can’t interbreed & produce fertile offspring

21. Isolating Mechanisms
Behavioral isolation - when 2 populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies that involve behavior
Ex.) Birds with different mating songs

22. Isolating Mechanisms
Geographic isolation - 2 populations are separated by geographic barriers like rivers, mountains, or bodies of water
Ex.) Squirrels split by Colorado River

23. Isolating Mechanisms
Temporal isolation - when 2 or more species reproduce at different times
Ex.) Orchids releasing pollen on
different days

24. Testing NS in Nature

25. Speciation in Darwin’s Finches
Speciation in the Galapagos
finches occurred by:
founding a new population
geographic isolation
changes in the new population’s gene
pool
reproductive isolation
ecological competition

26. Patterns of Evolution
Macroevolution - large-scale evolutionary patterns & processes that occur over long periods of time
6 important topics in macroevolution are:
extinction
adaptive radiation
convergent evolution
coevolution,
punctuated equilibrium,
changes in developmental genes

27. Patterns of Evolution Extinction:
More than 99% of all species are now extinct
It usually happens for a reason; species compete for resources, & environments change
Some species adapt & survive, others become extinct

28. Patterns of Evolution
Adaptive radiation - when a single species has evolved, through NS, into diverse forms that live in different ways
Ex.) Darwin’s Finches

29. Patterns of Evolution
Convergent evolution - when unrelated organisms begin to resemble one another
It has occurred in both plants & animals
Ex.) Swimming animals

30. Patterns of Evolution
Coevolution - when 2 species evolve in response to changes in each other over time
Ex.) Orchid has long spur with nectar in its tip, a Hawk moth has equally long feeding tube that allows it to feed on the nectar

31. Patterns of Evolution
Punctuated equilibrium - a pattern of long, stable periods interrupted by brief periods of more rapid change