1. Population Genetics and Speciation
Chapter 16
Population Genetics and Speciation
Mrs. Stewart
Honors Biology
Central Magnet School

2. Bell Work
List the evidence (at least 3) that supports the theory of evolution.

3. Standard / Objective
CLE Explain how genetic variation in a population and changing environmental conditions are associated with adaptation and the emergence of new species.

4. Variation of Traits Within a Population
Variations in the genotypes of a population arise by:
mutation – changes in genes that occur either naturally or influenced by environment
Passed to offspring if occurs in gametes
Recombination – reshuffling of alleles (chromosomes) and crossing over during meiosis
random pairing of gametes – organisms produce large numbers of gametes, so the union of a particular pair is strictly by chance.

5. The Gene Pool
The total genetic information available in a population is called the gene pool.

6. Allele Frequency
Allele frequency is the number of times an allele occurs in the gene pool
This is in comparison to how often the other alleles occur too

7. Relative Allele Frequencies
determined by dividing the total number of a certain allele by the total number of alleles of all types in the population
Expressed as a percentage or a decimal.

8. Example: I do B = Black b = brown What are the allele frequencies?
Total = 50
B = 20/50 = .40 or 40%
b = 30/50 = .60 or 60%

9. Example: We do .60 .40 B = black b = white 12 How many B? _________
What is the allele frequency of B?
What is the allele frequency of b?
.60 12
How many B? _________
How many b? _________
Total # of alleles for fur color? _________________
.40 8 20

10. Example: You do
Half of the population of four o’clocks has red flowers, and half has white flowers. What is the frequency of “r” allele?

11. Predicting Phenotype
Phenotype frequency is equal to the number of individuals with a particular phenotype divided by the total number of individuals in the population.

12. Phenotype Frequency

13. Evolution is any change in the relative frequency of alleles in a population.
Populations, not individual organisms, can evolve over time.

14. Hardy Weinberg Genetic Equilibrium
Due to sexual reproduction, phenotypic frequencies may change over time.
Does that mean the allele frequencies change too?
Unless acted upon by an outside force (perhaps a changing environment), the answer is no.

15. The Hardy-Weinberg Genetic Equilibrium
Allele frequencies in the gene pool do not change unless acted upon by certain forces.
Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable.

16. What factors affect the allele frequencies in a gene pool?
Factors to keep H.W. equilibrium:
Lack of mutations
No immigration or emigration
Ideally large population size
Individuals mate randomly
Selection does not occur

17. Calculating using the Hardy Weinberg equation
Dominant allele frequency = p
Recessive allele frequency = q
p + q = 1
p2 +2pq+ q2 = 1

18. Exit Ticket M.socrative.com Room: stewart348
Final question: How does immigration or emigration affect allele frequencies in a gene pool?

19. Darwin’s Finches

21. Five conditions under which evolution may take place
Genetic mutations
Gene flow
Genetic drift
Nonrandom mating
Natural selection.

22. Mutation
Mutations are changes in the DNA.

23. Gene Flow
Emigration and immigration cause gene flow between populations and can thus affect gene frequencies.

24. Genetic Drift
Genetic drift is a change in allele frequencies due to random events.
Genetic drift operates most strongly in small populations.

25. Nonrandom Mating
Mating is nonrandom whenever individuals may choose partners.
Sexual selection occurs when certain traits increase an individual’s success at mating.
Sexual selection explains the development of traits that improve reproductive success but that may harm the individual.

26. Natural Selection Three general patterns Stabilizing Selection
favors the formation of average traits.
Disruptive Selection
favors extreme traits rather than average traits.
Directional Selection
favors the formation of more-extreme traits.

28. The Concept of Species Biological species concept
a species is a population of organisms that can successfully interbreed but cannot breed with other groups

29. Isolation and Speciation
Geographic Isolation
Results from the separation of population subgroups by geographic barriers.
Allopatric Speciation
Speciation due to separation of subgroups of a population
Reproductive Isolation
Results from the separation of population subgroups by barriers to successful breeding.
Sympatric Speciation
Reproductive isolation within the same geographic area

30. Allopatry vs Sympatry

31. Reproductive isolation: Monkeyflower

32. Reproductive isolation

33. Rates of Speciation Gradualism Punctuated equilibrium
species undergo small changes at a constant rate.
Punctuated equilibrium
new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.