1. Ch 16 Evolution of populations

2. Crash Course: Population Genetics

3. 16-1 Genetic equilibrium
Population genetics: study of evolution from a genetic point of view
Basically how populations of a species evolve
But what is a population?
Group of members of the same species living in the same area

4. Sources of genetic variation
Three main sources
Mutations: any change in sequence of DNA
Replication mistakes
Radiation/environmental causes
recombination: reshuffling of genes
Random pairing of gametes

5. Bell curve Many traits in nature show trends like this
Phenotype continuum
# of individuals with that trait

6. Number of phenotypes produced depends on how many genes control that trait
Single gene traits- have two alleles
Two distinct phenotypes

7. Polygenic traits- controlled by two or more genes
Results in multiple phenotypes

8. frequency (of an allele)- number of times alleles occur in a gene pool
Gene pool- all genes, including all different alleles, that are present in a population
frequency (of an allele)- number of times alleles occur in a gene pool
Percentage
Genetic definition of evolution?
Change in relative frequency of alleles in a population over time

9. Phenotype frequency
How often a specific phenotype is observed in a population
Can be written mathematically
Frequency = # indiv. w/a particular phenotype
total # of indiv. in population

10. Hardy-Weinberg equilibrium
When evolution is not occurring
Allele frequencies remain the same
In order for evolution to not occur, certain conditions must be met.

11. Evolution Versus Genetic Equilibrium
Hardy-Weinberg principle = Genetic Equilibrium
Random Mating – Equal opportunity to produce offspring
Large Population – Genetic Drift does not effect Allele Frequency
No Movement into or out of Population – The gene pool must be kept together (no new alleles)
No Mutations – Mutations cause new forms of alleles changing the frequency
No Natural Selection – All genotypes must have equal probability of surviving.

12. Hardy-Weinberg equilibrium
Allele frequency equation
p + q = 1
p = frequency of dominant allele
q = frequency of recessive allele
Together, they make 100% of alleles for a gene in that population
If p = 34%, what is q?
If q = 19%, what is p?
0.66
0.81

13. Hardy-Weinberg equilibrium
Genotypic frequency equation
p2 + 2pq + q2 = 1
p2 = homozygous dominant frequency
2pq = heterozygous frequency
q2 = homozygous recessive frequency
If p = .46, what is p2?
If p = .12, what is q2?
If q =.31, what is 2pq?
0.2116
0.0144
0.4278

14. 16-2 Disruption of genetic equilibrium
Mutation
Occur at a relatively constant rate over time
Can be sped up when exposed to mutagens
Gene flow: process of genes moving from one population to another
Immigration: moving into a population
Emigration: moving out of a population

15. Genetic Drift Alleles can become rare by chance
Over time a series of chance occurrences can cause an alleles to become common in a population
Effects of genetic drift are more dramatic with small population size
Founder effect: change in allele frequencies as a result of migration of a small subgroup of a population

16. Genetic Drift Section 16-2 Sample of Original Population Descendants
Founding Population A
Founding Population B

17. Genetic Drift Section 16-2 Sample of Original Population Descendants
Founding Population A
Founding Population B

18. Genetic Drift Section 16-2 Sample of Original Population Descendants
Founding Population A
Founding Population B

19. Nonrandom mating
Sexual selection: tendency of individuals to choose a mate with certain traits.
Common in birds
Peacock display
Tropical birds of paradise - Papua New Guinea
The amazing Lyrebird - Australia

20. Natural selection
Natural selection on a single gene traits can lead to changes in allele frequencies
Natural selection on polygenic traits
3 possible effects
Directional selection
Stabilizing selection
Disruptive selection

21. Directional selection
When individuals at one end of curve have higher fitness than individuals in the middle or the other end

22. Stabilizing selection
When individuals near the middle have higher fitness than the individuals at either end

23. Disruptive selection
When individuals at upper and lower ends have higher fitness than individuals near the middle

24. 16-3 Formation of Species
As new species evolve, populations become reproductively isolated from each other
Reproductive isolation: when two members of populations cannot interbreed and produce fertile offspring
Separate gene pools

25. Isolation Mechanisms Geographic Isolation:
- separation of animals in a specific region
- formation of river, canyon, mountain

26. Isolation Mechanisms Behavioral Isolation:
- differences in courtship or reproductive
behaviors
-meadowlark songs
Temporal isolation:
-two or more species reproduce at different times
-orchids

27. Formation of species
Allopatric speciation: when species arise from geographic isolation
Different places

28. Reproductive isolation
Prezygotic isolation: premating isolation
Species may live
in different places
Reproduce at different times
Have different mating behaviors
Postzygotic isolation: postmating isolation
Hybrids may be weak
Hybrids may be sterile

31. Sympatric speciation
Sympatric speciation: when two subpopulations become isolated while living in the same area

32. Rates of speciation
Gradualism: speciation at gradual and regular rate

33. Punctuated equilibrium: periods of sudden, rapid change followed by periods of littelchange