1. Population Genetics
Ch 17 and Ch 18.2

2. Genes and Variation
Combine Darwin’s theory of Natural Selection with Mendel’s studies on genetics.
Which phenotype will be more often expressed in a population?
For example why might the black coat show up more in a population than the brown?

3. Which moth is more likely to survive due to the theory of Natural Selection?

4. How would happen to the black moth’s population here?
Natural selection never acts on genes. Why?

5. The organisms that have phenotypes that are better suited to their environment, will produce more offspring.
Organisms more adapted to their environment, can pass these traits onto their offspring.

6. Populations and Gene Pools
Population – a group of individuals of the same species that mate and produce offspring.
Gene pool- consists of all the genes (different alleles), found in that population.
Allele frequency – the number of times an allele occurs in a population

7. Evolution, in genetic terms involves a change in the frequency of alleles in a population over time. Populations evolve, not individuals.

8. Some alleles affect the species ability to survive.

9. Determing Allele Frequency
You have a population of 25 mice. How many alleles for coat color are found in this population?

10. Allele Frequencies of Different Blood types

11. Location of O Blood type globally

12. Location of A blood type globally

13. Location of B blood type globally

14. Sources of Genetic Variation
Mutations
Genetic Recombination in Sexual Reproduction
Crossing over
Lateral Gene Transfer
Bacteria swapping plasmid DNA

15. What determines the number of phenotypes for a given trait?
Single gene trait
Absence or presence of a band on shells
Polygenic traits
Over 180 genes help code for height
How many alleles are found in each example?

16. How does Natural Selection Work?

17. Pesticide Resistance

18. What changes Allele Frequencies besides Natural Selection?

19. Genetic Drift
Random change in an allele frequency in small populations. (Change is not caused by Natural Selection)
Genetic Bottlenecks – change in allele frequency after a dramatic reduction in size of the population
Disaster such as disease

20. Potato Famine in Ireland
Irish poor grew one variety of potatoes called lumpers, which were harvested in the fall.
Airborne fungus wiped out the crop in September of 1845 and wiped out the potato crops for the next 6 years.

21. Genetic Drift
The Founder Effect – allele frequencies change as a result of the migration of a small group of a population.

22. Finches on G. Islands
Random loss of alleles; leads to reduced genetic variation
Smaller population that changed from the original population found on South America.

23. Allele frequency in a Population
A population that does not evolve should have allele frequencies that do not change in a population – Genetic Equilibrium
Hardy-Weinberg Principle – allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change.
Used to make predictions about allele frequencies in populations. (Similar to what Mendel did with offspring)

24. What factors would cause a change in allele frequency?
Five conditions that affect genetic equilibrium
Nonrandom mating
Sexual Selection – genes that are used for selection of a mate, are not longer in equilibrium
Small Population Size
Genetic drift has a greater chance of affecting small populations. Why?
Immigration and Emigration
Addition and removal of alleles from a population

25. Factors that affect genetic equilibrium? (cont.)
Mutations
New alleles are introduced into gene pool
Natural Selection
A allele makes the organisms better able to survive, genetic equilibrium will be disrupted. More organism will show up with the better adapted trait over time.

26. How do you determine allele frequency using Hardy-Weinberg?
Hardy-Weinberg Equation
p2 +2pq + q2 = 1
q represents the frequency for the recessive allele (a)
P represents the frequency for the homozygous dominant allele (A)
pq represents the frequency for heterozygous (Aa)

27. Solving allele frequency with Hardy-Weinberg Equation
Remember that p + q = 1
Always solve for q first and then p. Why?
Example. In a population of mice, the recessive brown coat has an allele frequency of .36.
We need to solve for q represents q2. Why?
To Solve for q take the √ of .36
q =
How would you solve for p? (Remember p+q =1)
How would you determine the allele frequency for heterozygous?

28. Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Calculate the following: The frequency of the recessive allele. The frequency of homozygous dominant individuals The percentage of butterflies in the population that are heterozygous.
Take sq rt. of .4 (.63) to find q = .37 for P Bb = 2pq 2 X .37 X .63 = .47 or 47% P2 = .372 = .14

29. In the U.S., 16% of the population is Rh-, due to a homozygous recessive pair of alleles From this data determine: a. The frequency of the recessive allele         b. the frequency of the dominant allele         c. The percentage of homozygous dominants and percentage of heterozygotes in the population.

30. Allele W for white wool is dominant over allele w for black wool
Allele W for white wool is dominant over allele w for black wool. In a sample of 900 sheep, 891 are white and 9 are black. Estimate the allele frequencies in this sample. For w: For W: For Ww:

31. In a given population, only the "A" and "B" alleles are present in the ABO system; there are no individuals with type "O" blood or with O alleles in this particular population. If 200 people have type A blood, 75 have type AB blood, and 25 have type B blood, what are the allele frequencies of this population (i.e., what are p and q)?
To calculate the allele frequencies for A and B, we need to remember that the individuals with type A blood are homozygous AA, individuals with type AB blood are heterozygous AB, and individuals with type B blood are homozygous BB. The frequency of A equals the following: 2 x (number of AA) + (number of AB) divided by 2 x (total number of individuals). Thus 2 x (200) + (75) divided by 2 ( ). This is 475/600 = = p. Since q is simply 1 - p, then q = or

32. Speciation is the formation of a new species
Speciation is the formation of a new species. A species is a population whose members can interbreed and produce fertile offspring.
How does one species become two?
When populations become reproductively isolated, they can evolve into two separate species. Reproductive isolation can develop in a variety of ways, including behavioral isolation, or geographic isolation.

33. Isolating Mechanisms
Reproductive isolation occurs when a population splits into two groups and the two populations no longer interbreed. When populations become reproductively isolated, they can evolve into two separate species.

34. Behavioral Isolation
Behavioral isolation occurs when two populations that are capable of interbreeding develop differences in courtship rituals or other behaviors.

35. Why would this cause speciation?
Geographic isolation occurs when two populations are separated by geographic barriers such as rivers, mountains, or bodies of water.
An example: Kaibab squirrel is a subspecies of the Abert’s squirrel that formed when a small population became isolated on the north rim of the Grand Canyon.
Why would this cause speciation?
Separate gene pools formed. Genetic changes were not passed on two both groups.

36. Testing Natural Selection in Nature
What did the Grants’ scientific investigation show about Galápagos finches? (pages )
Founder effect – allele frequencies change as a result of the migration of a small subgroup of a population.
Variation within a species increases the likelihood that the species can adapt and survive environmental change.

37. Testing Natural Selection in Nature
Darwin hypothesized that the Galápagos finches had descended from a common ancestor.
He proposed that natural selection shaped the beaks of different bird populations as they became adapted to eat different foods.

38. A Testable Hypothesis
Peter and Rosemary Grant from Princeton University realized that Darwin’s hypothesis rested on two testable assumptions:
For beak size and shape to evolve, there must be enough heritable variation in those traits to the material for natural selection.
research found that there was a lot of diversity
Differences in beak size and shape must produce differences in fitness.

39. Natural Selection
The Grants’ data showed individual finches with different-sized beaks had different chances of surviving drought. When food was scarce, individuals with the largest beaks were more likely to survive.
The Grants observed that average beak size in that finch population increased dramatically over time.

40. What is a current hypothesis about Galápagos finch speciation?
Founders Arrive
Many years ago, a few finches from South America—species M—arrived on one of the Galápagos islands.
Because of the founder effect, the allele frequencies of this founding finch population could have differed from those in the South American population.

41. Geographic Isolation
Over time, GI and NS enabled the island finch population to evolve into a new species – Species A.
These species (A) crossed to another island.
As a result we have two populations who are geographically isolated.

42. Changes in Gene Pools
Over time, populations on each island adapted to local environments.
Natural selection could have caused two distinct populations to evolve (A and B), each characterized by a new phenotype.

43. Behavioral Isolation
Over time, populations on each island adapted to local environments.
A few birds (B) come back to main island, but since they have evolved differently, they don’t mate with each other.
We now have two distinct species.

44. Competition and Continued Evolution
Birds that are most different from each other have the highest fitness. More specialized birds have less competition for food. Over time, species evolve in a way that increases the differences between them, and new species may evolve (C, D, and E).
This process could have produced the `13 different finch species found today.