1. Population Genetics http://www. youtube. com/watch
Population Genetics Bozeman ..7:39min.

2. The Gene Pool
Members of a species can interbreed & produce fertile offspring
Species have a shared gene pool
Gene pool – all of the alleles of all individuals in a population

3. The Gene Pool Different species do NOT exchange genes by interbreeding
Different species that interbreed often produce sterile or less viable offspring e.g. Mule

4. Populations A group of the same species living in an area
No two individuals are exactly alike (variations)
More Fit individuals survive & pass on their traits

5. Modern Evolutionary Thought…Genes

6. Modern Synthesis Theory
Combines Darwinian selection and Mendelian inheritance
Population genetics - study of genetic variation within a population
Emphasis on quantitative characters (height, size …)

7. Modern Synthesis Theory
1940s – comprehensive theory of evolution (Modern Synthesis Theory)
Introduced by Fisher & Wright
Until then, many did not accept that Darwin’s theory of natural selection could drive evolution
S. Wright
A. Fisher

8. Modern Synthesis Theory
TODAY’S theory on evolution
Recognizes that GENES are responsible for the inheritance of characteristics
Recognizes that POPULATIONS, not individuals, evolve due to natural selection & genetic drift
Recognizes that SPECIATION usually is due to the gradual accumulation of small genetic changes

9. Microevolution of Species

10. Microevolution
Changes occur in gene pools due to mutation, natural selection, genetic drift, etc.
Gene pool changes cause more VARIATION in individuals in the population
This process is called MICROEVOLUTION
Example: Bacteria becoming unaffected by antibiotics (resistant)

11. 5 Causes of Microevolution
1. Genetic Drift
- the change in the gene pool of a small population due to chance
2. Natural Selection
- success in reproduction based on heritable traits results in selected alleles being passed to relatively more offspring (Darwinian inheritance)
- Cause ADAPTATION of Populations
3. Gene Flow
-is genetic exchange due to the migration of fertile individuals or gametes between populations

12. Causes of Microevolution
4. Mutation
a change in an organism’s DNA
Mutations can be transmitted in gametes to offspring
5. Non-random mating
- Mates are chosen on the basis of the best traits

13. 1. Genetic Drift

14. Factors that Cause Genetic Drift
Bottleneck Effect
a drastic reduction in population (volcanoes, earthquakes, landslides …)
Reduced genetic variation
Smaller population may not be able to adapt to new selection pressures
Founder Effect
occurs when a new colony is started by a few members of the original population
May lead to speciation

16. Loss of Genetic Variation
Cheetahs have little genetic variation in their gene pool
This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age

18. Founder’s Effect

19. 2. Natural Selection…3 modes of Nat. selection.

20. Polygenes
A gene which interacts with other polygenes to produce a quantitative phenotypic effect on a character. Ex height and blood in humans.
These genes lead to different modes of natural selection favoring some traits in a population.
“Polygenic Inheritance”..3:03 min.

21. Modes of Natural Selection
1.Directional Selection
Favors individuals at one end of the phenotypic range
Most common during times of environmental change or when moving to new habitats
2. Disruptive selection
Favors extreme over intermediate phenotypes
Occurs when environmental change favors an extreme phenotype

22. Directional Selection

23. Disruptive Selection

24. Modes of Natural Selection
3.Stabilizing Selection
Favors intermediate over extreme phenotypes
Reduces variation and maintains the cureent average
Example: Human birth weight

26. “Examples of Natural Selection”..8 min.
Natural Selection..Disruptive, Directional,Stabilizing. 3:03min.
“Examples of Natural Selection”..8 min.

27. 3. Gene Flow….Variations in Populations

28. Geographic Variations
Variation in a species due to climate or another geographical condition
Populations live in different locations
Example: Finches of Galapagos Islands & South America

30. Heterozygote Advantage
Favors heterozygotes (Aa)
Maintains both alleles (A,a) instead of removing less successful alleles from a population
Sickle cell anemia
> Homozygotes exhibit severe anemia, have abnormal blood cell shape, and usually die before reproductive age.
> Heterozygotes are less susceptible to malaria

31. Sickle Cell and Malaria

33. Other Sources of Variation
4.Mutations
In stable environments, mutations often result in little or no benefit to an organism, or are often harmful
Mutations are more beneficial (rare) in changing environments  (Example:  HIV resistance to antiviral drugs)
5. Genetic Recombination
source of most genetic differences between individuals in a population

34. Coevolution

35. Hardy-Weinberg Principle

36. The Hardy-Weinberg Principle
Used to describe a non-evolving population.
Shuffling of alleles by meiosis and random fertilization have no effect on the overall gene pool. 
 Natural populations are NOT expected to actually be in Hardy-Weinberg equilibrium.

37. The Hardy-Weinberg Principle
Deviation from Hardy-Weinberg equilibrium usually results in evolution
Understanding a non-evolving population, helps us to understand how evolution occurs
                        .

38. 5 Assumptions of the H-W Principle
Large population size - small populations have fluctuations in allele frequencies (e.g., fire, storm).
No migration - immigrants can change the frequency of an allele by bringing in new alleles to a population.
No net mutations - if alleles change from one to another, this will change the frequency of those alleles

39. 5 Assumptions of the H-W Principle
Random mating - if certain traits are more desirable, then individuals with those traits will be selected and this will not allow for random mixing of alleles.
No natural selection - if some individuals survive and reproduce at a higher rate than others, then their offspring will carry those genes and the frequency will change for the next generation.

40. Traits Selected for Random Mating

41. The Hardy-Weinberg Principle
The gene pool of a NON-EVOLVING population remains CONSTANT over multiple generations (allele frequency doesn’t change)
The Hardy-Weinberg Equation: 
               1.0 = p2 + 2pq + q2
 Where:
p2 = frequency of AA genotype
2pq = frequency of Aa
q2 = frequency of aa genotype

42. The Hardy-Weinberg Principle
Determining the Allele Frequency using Hardy-Weinberg: 
              
1.0 = p + q
 Where:
p = frequency of A allele
q = frequency of a allele

43. Allele Frequencies Define Gene Pools
500 flowering plants
480 red flowers
20 white flowers
320 RR
160 Rr
20 rr
As there are 1000 copies of the genes for color,
the allele frequencies are (in both males and females):
320 x 2 (RR) x 1 (Rr) = 800 R; 800/1000 = 0.8 (80%) R
160 x 1 (Rr) + 20 x 2 (rr) = 200 r; 200/1000 = 0.2 (20%) r

46. HARDY – WEINBERG PRINCIPLE..4:39 MIN