1. Lesson Overview
17.1 Genes and Variation

2. OBJECTIVES: Define evolution in genetic terms.
Identify the main sources of genetic variation in a population.
State what determines the number of phenotypes for a trait.

3. Genetics Joins Evolutionary Theory
Heritable traits are controlled by GENES!!!!
Changes in GENES / CHROMOSOMES result in VARIATION!!!!
Genotype  combination of alleles it carries; produces a phenotype
Phenotype  all physical, physiological, and behavioral characteristics
Natural selection acts directly on PHENOTYPE, not genotype.
Ex. Some individuals have phenotypes that are better suited to their environment, so they will survive and reproduce, passing on more copies of their genes to the next generation.

4. Populations and Gene Pools
group of individuals of the same species that mate and produce offspring.
gene pool
all the genes, including all the different alleles for each gene, that are present in a population
Ex. B = black fur and b = brown fur
The relative frequency of an allele is studied in gene pools
Number of times a particular allele occurs in a gene pool compared with the number of times the other allele appears in the gene pool
Ex. How many times does B appear versus b????

5. Ex. this diagram shows the gene pool for fur color in a population of mice.

6. Populations and Gene Pools
Evolution is any change in the relative frequency of alleles in the gene pool of a population over time.
Natural selection acts on POPULATIONS not INDIVIDUALS.

7. Mutations
Mutations
Can produce changes in genotypes, and therefore phenotypes
May or may not affect fitness (some are lethal and some are beneficial)
Can affect evolution ONLY if the mutation is heritable (passed from generation to generation)  must be in the egg or sperm cell

8. Single-Gene Traits single-gene trait
a trait controlled by only one gene
Have only 2 or 3 distinct phenotypes
Most common forms are dominant or recessive

9. Polygenic Traits Polygenic traits
traits controlled by two or more genes
Each gene has two or more alleles  leads to MANY possible genotypes and phenotypes
Ex. AaBBccDd …..for height

10. 17.2 Evolution as Genetic Change in Populations
Lesson Overview
17.2 Evolution as Genetic Change in Populations

11. OBJECTIVES:
Explain how natural selection affects single-gene and polygenic traits.
Describe genetic drift.
Explain how different factors affect genetic equilibrium.

12. Natural Selection on Single-Gene Traits
Can lead to changes in allele frequencies and then leads to evolution
Ex. Deer Population 

13. Natural Selection on Polygenic Traits
Can affect the range of phenotypes and hence the shape of the bell curve
Results in:
Directional Selection
Stabilizing Selection
Disruptive Selection

14. Directional Selection
occurs when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end.
The range of phenotypes shifts to one extreme of the bell curve

15. Stabilizing Selection
occurs when individuals near the center of the curve have higher fitness than individuals at either end.
Narrows the overall bell curve, but keeps the center of the curve at its current position

16. Disruptive Selection Disruptive selection
occurs when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle
acts against individuals of an intermediate type and can create two distinct phenotypes

17. Genetic Drift
An allele becomes more or less common simply by chance or a random change in allele frequency
Occurs in small populations

18. Genetic Bottlenecks bottleneck effect
change in allele frequency following a dramatic reduction in the size of a population
Ex. After a natural disaster

19. The Founder Effect founder effect
occurs when allele frequencies change as a result of the migration of a small subgroup of a population

20. Evolution Versus Genetic Equilibrium
When a population’s allele frequencies remain the same…..NO EVOLUTION TAKES PLACE.
Due to:
Large populations
Less likelihood of genetic drift
No mutations
No new alleles are introduced into the population
Lack in Random Mating
Some species prefer to mate with others having specific traits
No Movement into or out of a Population
no alleles flow into or out of the gene pool to change frequencies
No Natural Selection
All phenotypes have equal likelihood of survival and reproduction

21. 17.3 The Process of Speciation
Lesson Overview
17.3 The Process of Speciation

22. OBJECTIVES:
Identify the types of isolation that can lead to the formation of new species.
Describe the current hypothesis about Galapagos finch speciation.

23. Isolating Mechanisms Speciation
formation of a new species (population whose members can interbreed and produce fertile offspring)
Due to:
Reproductive Isolation
Behavioral Isolation
Geographic Isolation
Temporal Isolation

24. Reproductive Isolation
occurs when a population splits into two groups and the two populations no longer interbreed.
Can result in evolution of two separate species

25. Behavioral Isolation Behavioral isolation
when two populations that are capable of interbreeding develop differences in courtship rituals or other behaviors.

26. Geographic Isolation Geographic isolation
occurs when two populations are separated by geographic barriers
Ex. Rivers, mountains, bodies of water

27. Temporal Isolation Temporal isolation
two or more species reproduce at different times
Ex. Species of orchids….flowers that last only one day and must be pollinated on that day to produce seeds…..if they bloom on different days, they cannot cross-pollinate.

28. Testing Natural Selection in Nature
Darwin hypothesized that the Galápagos finches had descended from a common ancestor.
Natural selection shaped the beaks of different bird populations as they became adapted to eat different foods.

29. Founders Arrive
Many years ago, a few finches from South America—species M—arrived on one of the Galápagos islands 
founder effect
allele frequencies of this founding finch population could have differed from those in the South American population

30. Geographic Isolation
Populations on one island will separate to other islands due to competition for resources

31. Changes in Gene Pools
Over time, populations on each island adapted to local environments.
Natural selection could have caused two distinct populations to evolve (A and B), each characterized by a new phenotype.

32. Behavioral Isolation
When species B returns to its previous island, behaviors for mating may have changes to prevent reproduction with species A

33. Competition and Continued Evolution
Birds that are most different from each other have the highest fitness.
More specialized birds have less competition for food.
Over time, species evolve in a way that increases the differences between them, and new species may evolve (C, D, and E).