1. Population Genetics Chapter 11 The study of allele frequencies in populations

2. Reminder: 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

3. Reminder:Speciation Formation of new species
One species may split into 2 or more species
A species may evolve into a new species
Requires very long periods of time

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

5. What causes populations of organisms to EVOLVE???

6. There are 5 factors that can lead to or cause EVOLUTION!!!
1. Genetic Drift
2. Natural Selection
3. Gene Flow
4. Mutation
5. Sexual Selection
(non-random mating)

7. see chapter 11.3 Causes of Evolution Genetic Drift-
the change in the gene pool of a small population due to chance

8. Factors that Cause Genetic Drift
Bottleneck Effect
a drastic reduction in population about 10,000 years ago
Reduced genetic variation
Smaller population have a hard time adapting

9. Factors that cause Genetic Drift Founder’s Effect Genetic drift that occures after a small number of individuals colonize a new area

10. Causes of Evolution 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

11. Causes of Evolution: Gene Flow
Changes in the gene pool of a population because of the introduction of genes from another population by migration.
Example: the gene pool in southeast Asia was changed when U.S. Soldiers had children with Vietnamese women during the Vietnam war.

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

13. Having a lot of genetic variation within a population is GOOD. Chap 11

14. The Gene Pool Chapter 11.1
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

15. Allele Frequencies
Different combinations of alleles in a gene pool can be formed when organisms mate and have offspring.
The Allele Frequency is the measure of how common a certain allele is in the population.
Allele Frequency = the number of times an allele occurs
the total number of alleles for that gene

16. Let’s calculate the allele frequency for:
You have a population of mice. There are 30 mice total and 15 mice are black (BB), 10 mice are brown (Bb) and 5 mice are white (bb).
What is the allele frequency of B?
What is the allele frequency of b?
You can track the frequency of an allele over time to see the changes in populations

17. Answer this!!
If a certain trait’s allele frequency is 100%, describe the genetic variation of that allele in the population.

18. 2 main sources for variation in allele frequencies
1. Mutation
2. Recombination through Meiosis
Q? Why aren’t mutations in somatic cells sources of genetic variation??

19. Evolution Through Natural Selection Modes of Natural Selection
1. Directional Selection
Favors individuals at one end or the other end of the phenotypic range
Most common during times of environmental change or when moving to new habitats
example, colored animals like mice.
At times black is favored, other times white is favored

20. Modes of Natural Selection
2. Disruptive selection
Favors both extremes over intermediate phenotypes
Occurs when environmental change favors an extreme phenotype
Can be a pathway for species formation WITHOUT geographic isolation

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

23. How does Natural Selection Affect Allele Frequency??
1. Mutations provide the raw material on which natural selection acts
2. Evolution depends on variations because it is the only way that differences among organisms are created
3. Acts on Populations not individuals by changing the % of alleles in the population

24. How Do New Species Occur? ISOLATION!!!!! (nobody likes to be alone!!)

25. New Species Evolve in Patterns:
Convergent Evolution: Different species must adapt to similar environments. Evolution towards SIMILAR characteristics in UNRELATED species.
ex: Dolphin/Shark
Divergent Evolution: Closely related species evolve
In different directions. Evolution towards
DIFFERENT characteristics in RELATED species.
ex: Kit fox/Red fox
Co-Evolution: When 2 or more different species evolve in response to changes in the other.
ex: Acacia plant/ants

26. Repeating Patterns of Speciation Throughout the history of EARTH
Punctuated Equilibrium A pattern of BURSTS of evolutionary activity followed by long periods of stability. EX:
Adaptive Radiation
The diversification of one ancestral species into many descendent species.
EX: mammals

28. Genetic Variations, (changes in allele frequencies) within Populations creates Evolution of Species!!