1. Ch. 16- Genetics of Evolution

2. What you will learn today…
How do we measure genetic variation in a population?
Why is genetic variation in a population important?
What are the sources of genetic variation in a population?

5. GET YOUR NOTES OUT!! What determines a heritable trait?
DNA
(gene)
Observed trait
mRNA
protein
translation
transcription
protein function
(enzyme activity)
Therefore, if traits vary in a population, then the
genes (alleles) must vary in the population!

6. How do we measure genetic variation in a population?
Gene Pool- Total genetic information available in a population (all the alleles that are present). Allele (Relative) Frequency- The percentage of an allele in the gene pool. Tells you whether a given allele is common or rare (%)

7. New Vocab
Population – group of individuals of the same species that interbreed
Gene Pool – all genes (including all alleles) present in a population
Relative Frequency – number of times an allele occurs in a gene pool
Because members of a population interbreed, they share a common group of genes called a gene pool

8.
(4:28)

9. 4 Conditions for Natural Selection:
Variation: Individuals in a population are not identical to each other.
Inheritance: Traits are passed to offspring; traits have a genetic basis
Environmental population limits: Environmental limiting factors prevent all individuals from surviving to reproduce; some die young.

10. Environmental selection:
Individuals in the population with more favorable (advantageous) traits are the ones that survive to reproduce.
Individuals without advantageous traits die before reproducing.
These factors result in a change in the average trait of the population… Biologists call this EVOLUTION!

11. 1. VARIATION
Members of a population have traits similar to the average trait of the entire population, but they are not identical.
YOUR TURN: Using height as an example,
sketch a graph to represent the statement above.
Mean (average) height
First clarify the statement, then reveal “your turn” assignment.
Discuss with students what type of graph would be best- (frequency distribution)
Reveal axes as a hint while students sketch a graph on their notes sheet.
Finally, reveal what the completed sketch should look like
Frequency
Height (cm)

12. 2. INHERITANCE DNA determines the traits of individuals
Individuals inherit DNA from their parents
This causes the traits of the offspring to resemble the traits of the parents
DNA
mRNA
protein
trait

13. 3. ENVIRONMENTAL POPULATION LIMITS
For all species, if every individual born into a population were to reproduce, the population would grow exponentially
Population
Make note to students that these graphs have different axes than the other graphs we have been examining.
Time

14. 3. ENVIRONMENTAL POPULATION LIMITS
Environmental factors (limiting factors) prevent the majority of individuals from surviving to reproduce
Population
Make note to students that these graphs have different axes than the other graphs we have been examining.
Time

15. 4. SELECTION
Individuals without advantageous traits die before reproducing.
Individuals with advantageous traits survive to reproduce.
Again, make note the labeling of the axes
Frequency
die without reproducing
These individuals
These individuals
survive to reproduce
Characteristic

16. Populations change, not individuals
The “average” characteristic or other measure of the population changes over generations
average, 1st gen.
average, 2nd gen.
average, 3rd gen.
average, 50th gen.
Frequency
die without reproducing
These individuals
die without reproducing
These individuals
These individuals
survive to reproduce
Characteristic

17. The environment is the selective force behind evolution
The environment determines what characteristics are “favorable”
Because the environment changes over time, the characteristic that is more favorable for a population changes
Therefore, characteristics of the population change, or evolution occurs
Questions for discussion

18. What do these all have in common (what are they all trying to do
PBS evolution Library:
Peacock video:
Human mate choice:

19. A population with variation in traits…
Grey
White
Tall ears
Short ears

20. ...is caused by variation in alleles
Grey allele = G
White allele = g
Tall ear allele = T
Short ear allele = t
T t
G G
t t
G g
T T
G g
t t
g g
t t
G g
t t
G G
T t
g g
t t
G g

21. How do we measure genetic variation in a population?
Grey allele = G
White allele = g
Tall ear allele = T
Short ear allele = t
8 / 16 = 50% G
T t
G G
t t
G g
T T
G g
t t
g g
8 / 16 = 50% g
t t
G g
t t
G G
4 / 16 = 25% T
T t
g g
t t
G g
12 / 16 = 75% t
“Gene Pool”

22. Allele Frequency
It is usually expressed as a proportion or a percentage, and describes the amount ofgenetic diversity at the individual, population, or species level.
Example: assuming that in a human population, there are 100 individuals. Since each of them would have two alleles for a particular character (one allele inherited from the father, the other allele from the mother), the total number of genes in this population is 200 (=100 x 2).
If out of the 100 individuals, there are 30 homozygous for the dominant trait (AA), 50 are heterozygous (Aa), and the remaining 20 are homozygous for the recessive trait (aa). Therefore, the total number of dominant genes in the population is (30 x 2) + (50 x1) = 110. [That is, (30 x 2) from the 30homozygous (AA) plus (50 x1) from the 50 heterozygous (Aa)] Thus, the frequency of the dominant trait (A) is (110/200) = 0.55 or 55%. Similarly, the total number of recessive genes in the population is (20 x 2) + (50 x 1) = 90. [That is, (20 x 2) from the 20 homozygous (aa) plus the (50 x 1) from theheterozygous (Aa)] The frequency of the recessive trait (a) is (90/200) = 0.45 or 45%.

23. Why is genetic variation in a population important?
A gene pool without much variation limits a species’ ability to further evolve.
Evolution- change over time in the gene pools of a species
If populations do not change (adapt) to their environment, they may become extinct.

24. Sources of genetic variation
SEXUAL REPRODUCTION
Meiosis – one allele is passed on from each parent (recall that sperm and eggs are haploid cells, each containing half the necessary genetic information).
Random fertilization – only one of the millions of sperm involved in mating will fertilize the egg.
The randomness of sexual reproduction explains why siblings can look so different.

25. Crossing over during meiosis

26. Sources of genetic variation
MUTATION
A change in DNA sequence.
New DNA sequence = new allele of a gene.
Many mutations produce genes that are harmful (e.g. Huntington’s disease)
Some mutations produce genes that are neutral (neither helpful nor harmful)
Very, very few mutations produce genes that are advantageous, beneficial

27. Mutations add new alleles to the gene pool
Mutations add new alleles to the gene pool. That is, they increase the variety of alleles in the population.

28. Deck of Cards Analogy
Deck is Gene Pool – It contains all possible alleles for the next generation.
Drawing cards picks the alleles that are inherited by the next generation.
Shuffling of the deck is sexual reproduction.
Adding new cards to the deck is mutation.
(Mutation is rare, but shuffling happens each time a new generation is produced)

29. Natural Selection
Individuals with advantageous genes survive to reproduce and pass on these genes to their offspring.
Individuals without advantages genes do not survive to reproduce, and these genes do not get passed on in the population.

30. Conclusion Mutation does NOT cause evolution
it is only a source of variation (just one of the factors required for natural selection)
Natural selection determines if the allele frequency will change within a population.
Change in allele frequency = EVOLUTION
Explain the change in allele frequency in the peppered moth population.

32. Kerosene Karl- Changes in Allelic Frequency

33. Allele Frequency example
Figure 16-2, pg work out the frequency of each allele.
Sample Population
Frequency of Alleles
allele for brown fur, b
allele for black fur, B
48% heterozygous black, Bb
16% homozygous black, BB
36% homozygous brown, bb
Population = mice
Gene Pool – all possible genes/alleles for coat color
Relative frequency of each allele
20 alleles are black (40%), 30 alleles are brown (60%).

34. What is evolution?
Evolution is any change in relative frequency of alleles in a population (NOT IN AN INDIVIDUAL!!)

35. Sources of Genetic Variation
Mutations
Mistakes in replication
Radiation or chemicals in environment
Gene Shuffling
Assortment of chromosomes
Crossing over
Mutation – change in DNA sequence
don’t always affect phenotype
some affect fitness; other’s don’t
Gene Shuffling – during meiosis
independent assortment of chromosomes from each parent
23 pairs of chromosomes can produce 8.4 million different combinations of genes
sexual reproduction is major source of variation within population – can produce many different phenotypes but does NOT change relative frequency of alleles

36. Single-Gene Trait
Variation in single gene traits lead to only two distinct phenotypes
Frequency of phenotype determined by frequency of alleles
100 80 60 40 20
Frequency of Phenotype (%)
The number of phenotypes produced for a given trait depends on how many genes control the trait
Widow’s peak
No widow’s peak
Phenotype

37. Frequency of Phenotype
Polygenic Trait
Trait controlled by 2 or more genes
Many possible genotype and phenotype possibilities
Bell shaped curve typical of polygenic traits
Frequency of Phenotype
Phenotype (height)

38. CHECK POINT
What are the main sources of heritable variation in a population?
Mutations and Gene Shuffling
How is evolution defined in genetic terms?
Evolution is any change in relative frequency of alleles in a population
What determines the numbers of phenotypes for a given trait?
The number of genes that control the trait

39. Natural Selection on Polygenic Traits
Directional Selection
Low mortality,
high fitness
High mortality, low fitness
Food becomes scarce
Individuals at one end of curve have higher fitness
Range of phenotypes shifts

40. Natural Selection on Polygenic Traits
Individuals near center of curve have highest fitness
Keeps center of curve at same position and narrows graph
Stabilizing Selection
Low mortality,
high fitness
High mortality,
low fitness
Selection against both extremes keeps curve narrow and in same place
Percentage of Population
Birth Weight

41. Natural Selection on Polygenic Traits
Disruptive Selection
Largest and smallest seeds become more common
Population splits into two subgroups specializing in different
seeds.
Low mortality,
high fitness
Number of Birds
in Population
Number of Birds
in Population
High mortality,
Low fitness
Beak Size
Beak Size
Individuals at upper and lower ends of the curve have higher fitness than individuals in the middle
Selection acts strongly against individuals of the intermediate type

42. Genetic Drift Random change in allele frequency by chance
Occurs in small populations
Founder effect – allele frequencies change as a result of migration of subgroup of population A a
1st (26)
.62
.38
3rd (28)
.30
.70
4th (30)
.37
.63
5th (32)
.52
.48
6th (28)
.34
.66
In small populations, an allele can become more or less common simply by chance
Genetics controlled by laws of probability – works in large population not always in small population
In small populations, individuals that carry a particular allele may leave more descendents than others just by chance. Over time a series of chance occurrences of this type can cause an allele to become common in a population
May occur when a small group of individuals colonize new habitat

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

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

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

46. Hardy-Weinberg Principle- Are there any conditions when evolution DOES NOT happen?
States that allele frequencies remain constant (genetic equilibrium) unless one or more factors cause them to change
No change in allele frequency of population = no evolution in population
To clarify how evolutionary change operates, scientists often find it helpful to determine what happens when no change takes place.
Are there any conditions under which evolution will not occur?

47. Mechanisms for Evolution
Random genetic drift
Gene flow
Non-random mating
Mutation
Natural selection

48. 5 Conditions of Genetic Equilibrium- 1 or more of these must happen in order for evolution to occur
Random Mating
Equal chance of passing on alleles to offspring
Large Populations
Genetic drift less likely to occur
No Movement In or Out of Population
New members might bring new alleles
Random mating ensures that everyone has an equal chance of passing on their alleles. In natural populations, mating is rarely completely random- species select mates with traits they want. Nonrandom mating means genes for those selected traits are NOT in equilibrium, but are under strong selection pressure.
Genes drifting “in and out” of a large population will have less of an effect on the gene pool of a small population.
In new individuals come n, new alleles will too- the gene pool will change.

49. 5 Conditions of Genetic Equilibrium
No Mutations
New alleles may be introduced
No Natural Selection
All genotypes must have equal chance of survival and reproduction
4. Genes mutate = allele frequencies will change.
5. No phenotype must have selective advantage over the others.

50. Speciation Speciation = formation of new species
Species = group of organisms that breed with one another and produce fertile offspring
As new species evolve, populations become reproductively isolated from each other
Members of same species share same gene pool
Genetic change that occurs in one individual can spread through the population
Gene pools must become separated for speciation to occur
When two population cannot interbreed and produce fertile offspring, reproductive isolation has occurred

51. Speciation

52. Isolating Mechanisms (lacewing interactive)
Behavioral Isolation
Differences in courtship rituals or other reproductive strategies
Geographic Isolation
Two populations separated by geographic barrier such as rivers, mountains or bodies of water
Temporal Isolation
Two or more species reproduce at different times of the day or year

53. Behavioral Isolation
Behavioral Isolation is when two populations can share the same habitat but their different behaviors prevent them from breeding together. For example, some organisms within a population will not breed with another organism if it doesn’t have the same mating rituals. For the birds in the picture, the mating ritual in the left differs from the mating ritual on the right, and if a bird (even though they look the same) tries to present the ritual between the two variations, the female will not breed with them.

54. Geographic Isolation

55. Temporal Isolation
Temporal Isolation occurs when two organisms have different breeding times. This is separation in time. For example, flowers bloom at different times of year, and therefore will not cross pollinate. In this way, two species can be reproductively isolated, yet live side-by-side.

56. Reproductive Isolation
results from
Isolating mechanisms
which include
Behavioral isolation
Temporal isolation
Geographic isolation
produced by
produced by
produced by
Behavioral differences
Different mating times
Physical separation
which result in
Independently evolving populations
which result in
Formation of new species

57. Speciation of Darwin’s Finches
Founders Arrive
Separation of Populations
Changes in the Gene Pool
Reproductive Isolation
Ecological Competition
Continued Evolution

58. Speciation in the Andes (Ecuador)
Hummingbird video
Explain the hypothesis presented by the scientists profiled in this segment to explain the process of speciation in hummingbirds and possibly other species.
How does this hypothesis differ from the traditional view that speciation often requires geographic separation of populations?
Why were the researchers collecting blood from the populations they studied? Discuss at least two possible analyses that could be performed on those samples and, identify at least two different questions that might be answered with sufficient data.

59. Could Gamera ever happen in real life???!! If so, how?