1. Evolution and Population GENETICS

2. Changes in evolution occur in populations, not individuals
Population Genetics
Population Genetics
Changes in evolution occur in populations, not individuals

3. entire collection of genes in a population allele frequency
Population Genetics
Basic Vocaulary
gene pool
entire collection of genes in a population
allele frequency
number of times an allele appears in a gene pool
genetic equilibrium
gene pool which is not changing in allele frequencies
a population at genetic equilibrium is not evolving

4. Evolution and Population Genetics
For a population to evolve, there must be some form of change genetically.
What are some things that cause change in the gene pool of a population?

5. 4 Basic Evolutionary Mechanisms
Mutation
Migration
Genetic drift
Natural selection

6. Mutation introduces of new alleles into gene pool

7. How Mutation Causes Change
A mutation (change in DNA code) could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population.
Causes of mutations?

8. Migration
When individuals of one population move and join a new population

9. How Migration Causes Change
Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.

10. The movement of alleles from one population to another
Population Genetics
gene flow
The movement of alleles from one population to another
this can change the allele frequency of both populations

11. Genetic Drift random change in allele frequency over time

12. Causes of Genetic Drift
1.The Bottleneck Effect
Genetic drift that occurs after an event greatly reduces the sizes of a population
Numbers of individuals in population are greatly reduced
Loss of diversity

13. Causes of Genetic Drift
2. The Founder Effect
Genetic drift that occurs after a small number of individuals colonize a new area
Gene pool very different from the larger population

14. Problems with Genetic Drift
Loss of genetic diversity
Less likely for some individuals to adapt to a changing environment
Lethal and/or harmful alleles carried by heterozygotes and become more common in gene pool

15. Natural Selection
Organisms that are better adapted to the environment survive and reproduce
For larger populations natural selection is the significant factor which causes changes in allele frequency

17. Types of Natural Selection
Directional- selection for one extreme
Disruptive- selection for both extremes- against the “middle”
Stabilizing- selection for the middle- against the extremes

18. Types of Natural Selection
1. Stabilizing Selection
selection against extremes, favors the average

19. Types of Natural Selection
2. Directional Selection
selection against one extreme, favors other extreme

20. Types of Natural Selection
3. Disruptive Selection
selection against average, favors both extremes

21. Hardy-Weinberg Equilibrium
Genotype frequencies remain constant in a population as long as certain conditions are met
Frequencies can be predicted
Identifies 5 conditions that must be met in order for a population to be in equilibrium
Populations in equilibrium are not evolving= in Hardy-Weinberg Equilibrium

22. Hardy-Weinberg Equilibrium
Very large population (no genetic drift)
No emigration or immigration (no gene flow)
No mutations (no new alleles added)
Random Mating (no sexual selection)
No natural selection (all traits are equal)

23. Why Use Hardy-Weinberg?
Real populations rarely ever meet all 5 conditions!
Why do you think we use the Hardy-Weinberg model?

24. Genotype Frequencies p2 + 2pq + q2 = 1 p= frequency of dominant allele
q= frequency of recessive allele
p+q = 1 Why?
What does p2 equal?
What does 2pq equal?
What does q2 equal?

25. Example
In a population of fish fork tails are dominant over smooth tails.
You have 1000 fish total in this population.
640 of them have forked tails.
360 of them have smooth tails.
What are the genotype frequencies?

26. Example q2= 360 smooth-finned fish out of 1000 total
To find q, take the square root of 0.36= 0.6
Find P with the equation p + q = 1
So = 0.4
Now we have p= 0.4 and q = 0.6 (allele frequencies)

27. Example Now we have p= 0.4 and q = 0.6 (allele frequencies)
Calculate the genotype frequencies:
p2 = 0.42 = 0.16 = 16% TT
q2 = 0.62 = 0.36 = 36% tt
2pq= (2)x(0.4)x(0.6) = 0.48 = 48% Tt

28. Evolution of a Species speciation
the production of two or more species from one original population

29. What Causes Speciation?
1. Geographic Isolation
physical barrier which separates populations

30. What Causes Speciation?
2. Reproductive Isolation
groups can no longer sexually reproduce
ex: behavior, mating patterns, physical differences

31. Speed of Speciation 1. Gradualism
species evolve at a slow constant rate

32. Speed of Speciation 2. Punctuated Equilibrium
rapid significant changes over a short time

33. Patterns in Evolution 1. Adaptive Radiation
new species develop from a single common ancestor

34. Patterns in Evolution 2. Divergent Evolution
new species develop from a single common ancestor

35. Patterns in Evolution 3. Convergent Evolution
different species develop similar traits

36. Patterns in Evolution 4. Co-evolution
different species develop traits as a result of a close relationship with the other species

37. Two Types of Evolution
Microevolution: a change in gene frequency within a population.
Ex. Changes is a beetle population over a short period of time.
Ex. Antibacterial resistance
Macroevolution: evolution above the species level. Large Scale!
(Patterns, Speciation)
Ex. Changes in all beetle populations over a long time
Ex. Origin of mammals