1. Evolution of Populations
Chapter 11

2. Warm Up 1/30 & 1/31
Explain how the terms trait, gene, and allele are related.
What is genetic drift and what types of populations are affected?
Give an example of an isolating mechanism which could result in speciation.

3. KEY CONCEPT A population shares a common gene pool

4. Genes and Variation
Gene pool - all the genes that exist within a population

5. Genetic variation in a population increases the chance that some individuals will survive
Genetic variation leads to phenotypic variation.
Phenotypic variation is necessary for natural selection.
Genetic variation is stored in a population’s gene pool.
made up of all alleles in a population
allele combinations form when organisms have offspring

6. Allele frequencies measure genetic variation
Allele frequencies measure genetic variation. measures how common allele is in population can be calculated for each allele in gene pool

7. Genes and Variation
Relative (allelic) frequency - the percentage of a particular allele in a gene pool.

8. KEY CONCEPT Populations, not individuals, evolve.

9. Natural Selection in Populations
Natural Selection- In nature, unequal ability to survive and reproduce... Survival of the fittest.
Natural Selection ACTS ON PHENOTYPE but influences genotype (thus, allelic frequency)
Artificial Selection- Mankind selects for desired traits. Also known as “selective breeding”

10. Artificial Selection

11. Over time, the zebra herd becomes faster as the slower zebra (and their genes) are removed from the population… survival of the fittest Darwin’s Theory = Evolution by means of natural selection

12. ADAPT OR DIE!
Camouflage- organisms blend-in with surrounding environment
Mimicry- species copy another to insure their own survival
NatGeo

13. Natural Selection effects Genetic Change in Populations
Natural Selection has three affects on phenotype distribution
Directional Selection
Stabilizing Selection
Disruptive Selection

14. Normal Distribution of traits
A normal distribution graphs as a bell-shaped curve.
Phenotypes near the
middle range tend to
be most common.
Examples- height and
weight

15. Directional Selection
This type of selection favors phenotypes at
one extreme of a trait’s range.
An extreme phenotype that was once rare becomes more common.
Ex. Drug resistant bacteria

16. Directional Selection
Directional Selection- Individuals on one end of a curve are “better fitted” than the middle or other end
Peccaries naturally choose to consume those
cactus plants with the fewest spines As a result,
at flowering time there are more cacti with
higher spine numbers; thus, there are more of
their alleles going into pollen, eggs, and seeds
for the next generation.

17. Stabilizing Selection
Stabilizing selection favors the intermediate phenotype.
Selection against both extremes decreases the genetic diversity of a given population.

18. Stabilizing Selection
Stabilizing Selection- Individuals near center of a curve are “better fitted” (have highest fitness) than both ends
Peccaries are consuming the low-spine
number plants, and the insects are killing
the high-spine-number plants. As these
gene combinations are removed from the
cactus gene pool, there is less and less
variety possible in subsequent
generations.

19. Disruptive Selection
This type of selection occurs when both extreme phenotypes are observed.
Individuals with the intermediate type are selected against.
By favoring both extreme phenotypes, disruptive selection can lead to the formation of a new species.

20. Disruptive Selection
Disruptive Selection- Individuals at upper and lower ends are “better fitted” than the ones in the middle
Years of collecting have left their toll on
the roadside cacti. In this environment, it is
maladaptive to be good looking and have
a reasonable number of spines. Low
spine-number plants are not picked
because they don't "look right", and high
spine-number varieties are left alone
because they are too hard to pick.
Gradually, the gene pool changes in favor
of the two extreme spine number types.

22. Other mechanisms of Evolution
Natural selection is not the only mechanism through which populations evolve 3 other mechanisms of Evolution: Gene Flow Genetic Drift Sexual Selection

23. Gene flow – movement of alleles into or out of a population
Immigration – new alleles move IN
Emigration – alleles move OUT

24. Genetic drift - change in allelic frequencies by chance
Ex: sudden extinction of a dominant species; small populations most affected

25. Genetic drift is a change in allele frequencies due to chance.
Genetic drift causes a loss of genetic diversity It is most common in small populations.
A population bottleneck can lead to genetic drift.
It occurs when an event drastically reduces population size.
The bottleneck effect is genetic drift that occurs after a bottleneck event.

26. The founding of a small population can lead to genetic drift.
It occurs when a few individuals start a new population.
The founder effect is genetic drift that occurs after start of new population

27. Sexual selection occurs when certain traits increase mating success.
Sexual selection occurs due to higher cost of reproduction for females.
males produce many sperm continuously
females are more limited in potential offspring each cycle

28. Genetic equilibrium - when alleles stay the same from generation to generation
The Hardy Weinberg Principle: Allele frequencies will remain constant under five conditions
Random Mating
Large Population
No movement (immigration or emigration)
No Mutations
No Natural Selection: equal change of survival

29. 5 Factors that can lead to evolution
Genetic Drift
Gene Flow
Mutation
Sexual Selection
Natural Selection

30. Genetic drift changes allele frequencies due to chance alone

31. Gene flow moves alleles from one population to another

32. Mutations produce the genetic variation needed for evolution.

33. Sexual selection selects for traits that improve mating success.

34. Natural selection selects for traits advantageous for survival

35. KEY CONCEPT New species can arise when populations are isolated
The isolation of populations can lead to speciation
speciation - evolution of a new species .
Reproductive isolation can occur between isolated populations
Populations can become isolated in several ways:
1. Behavioral
2. Geographic
3. Temporal

36. 1. Behavioral Isolation: Two populations
1. Behavioral Isolation: Two populations capable of breeding but cannot because of courtship rituals

37. 2. Geographic Isolation: Two populations are separated by geographic barriers
Ex: Rivers, Oceans, Mountains
3. Temporal Isolation: Two or more populations reproduce at different times

38. Patterns of Evolution Extinction
Divergent Evolution (adaptive radiation)
Convergent Evolution
Coevolution

39. 1.Extinction
Why do species go extinct?

40. Extinction
Natural selection, climate changes, and catastrophic events have caused 99 percent of all species that have ever lived to become extinct.
Mass extinctions – caused by continents moving, sea level changing, volcano eruptions, large meteors

41. Predict what each ecosystem will look like after the event.
Catastrophic
Event
Catastrophic
Event

42. Question
When a mass extinction happens, what do you think will happen next?

43. Divergent Evolution (adaptive radiation)
Divergent evolution – natural selection causes 1 species to evolve into many species with many different adaptations (homologous structures)
After mass extinctions, many environments will be open for inhabitation
Species will migrate to that area and new environmental pressures will cause the population to change over time
This is also known as Adaptive Radiation

44. Adaptive Radiation in honeycreepers

45. ---DIVERGENT EVOLUTION---
Evidence of Evolution
Homologous structures - similar structures found in related organisms that are adapted for different purposes.
Ex: human arm and bat wing or whale flipper
---DIVERGENT EVOLUTION---
the process of two or more related species becoming more and more dissimilar.

46. Homologous structures  Divergent evolution

47. Convergent Evolution
Convergent Evolution – when unrelated organisms come to resemble one another (analagous structures)

48. ---CONVERGENT EVOLUTION---
Analogous structures - structures found in unrelated organisms that have a similar function but may be structurally different
Ex: bird wing and insect wing
---CONVERGENT EVOLUTION---
independent evolution of similar features in species of different lineages

49. Analogous structures  Convergent evolution

50. Coevolution
When 2 species evolve in response to one another

51. Coevolution can occur in competitive relationships, sometimes called evolutionary.

54. Speciation occurs in patterns
Punctuated equilibrium: species show little evolutionary change for millions of years, followed by periods of rapid speciation
Gradualism- Species evolve slowly, over long periods of time.