1.1: Natural selection is a major mechanism of evolution 1. NATURAL SELECTION

Transcription

1 Domain 1: Evolution

2 1.1: Natural selection is a major mechanism of evolution 1. NATURAL SELECTION

3 Charles Darwin

4 Pre-Darwin Lyell: Geology, Uniformitarianism! very old earth. Malthus: Exponential Population Growth LaMarck: Evolution. Inheritance of acquired characteristics (wrong, but still evolutionary)

5 The Voyage of the HMS Beagle

6 Natural Selection Observation 1: Variation

7 No two organisms are completely alike.

8 Observation 2: Reproduction

9 And overproduction

10 Inference 1: Differential fitness in the environment due to variations.

11 The struggle for existence

12 Inference 2: Over the span of geological time (billions of years), inheritance of adaptations will lead to evolution of the population.

13 Fundamental Conclusions 1. To develop the diversity of life seen on the Earth today, the Earth has to be incredibly old. 2. If organisms evolve from pre-existing organisms, then all organisms should share a universal common ancestor

14 tree thinking

15 Unsettled by Darwin 1. Origin of Life 2. Origin of species 3. Nature of variation/inheritance

16 1.1: Natural selection is a major mechanism of evolution 2. THE MODERN SYNTHESIS

17 The Modern Synthesis Connects Darwinian evolution to genetics and modern understanding of inheritance.

18 Where Traits come from: Trait

19 Variation comes from Mutation Mutation: A change in a DNA sequence. Happens spontaneously and unavoidably.

20 Mutations create alleles Alleles: Different versions of the genes for a trait.

21 Evolution Defined: Evolution: Changes in allele frequencies over time.

22 Ex. Galapagos Finches Grant and Grant: Studied the finch population on an isolated island in the Galapagos. Measured the beak dimensions of all birds on the island every year for decades.

23 Connected changes in beak dimensions to fluctuations in the environment (precipitation, seed sizes)

24 Evolution Misconception Alert! Misconception: Individuals evolve. Evolution is a population level phenomenon. Individuals DO NOT evolve! The evolution of a population emerges from the individual fitness of members of that population. As they survive and reproduce or not, the frequencies of alleles in the next generation will change accordingly.

25 1.2: Natural selection acts on phenotypic variations in populations. 1. HOW NATURAL SELECTION WORKS.

26 Genotype The alleles that an individual has for a particular trait. 2 Types: Homozygous: Two copies of the same allele. Heterozygous: Two copies of different alleles for each trait.

27 Phenotype The trait that an individual shows. Genotype determines Phenotype!

28 Alleles control the production of proteins and proteins determine traits. Trait

29 Dominant & Recessive Some alleles ( dominant ) will control phenotype over other alleles ( recessive ) when both are present. Ex. Eye color (simplified) Two alleles: B (dominant) and b (recessive) Two phenotypes: Brown eyes and blue eyes

30 Eye Color Genetics: 3 possible genotypes: BB Bb bb Homozygous Heterozygous Homozygous Dominant Recessive 2 possible phenotypes: Brown eyes Blue eyes Heterozygotes have BROWN eyes.

31 Evolution Misconception Alert! Misconception: Dominant = better Dominant alleles are NOT better than recessive alleles Dominant and recessive have nothing to do with their effect on fitness. They only refer to how they contribute to phenotype expression.

32 Phenotype and Fitness Different phenotypes will be more or less fit, depending upon the requirements of the environment. Fitness : Ability to contribute genes to the next generation (reproduction). The environment determines fitness.

33 Fitness changes with the environment

34 Ex. Pesticide Resistance

35 Human Impact on Variation Humans are able to impact variation in other organisms by controlling which individuals are able to reproduce. Artificial selection: When reproductive success is determined by human requirements

36 Ex. Dog Breeds

37 Ex. Food Crops

38 1.3: Evolutionary change is also driven by random processes. 1. OTHER EVOLUTIONARY FORCES

39 Genetic Drift Random, non-selective, changes in allele frequency due to chance. Has a larger effect on smaller populations, since each individual is more of the total alleles.

40 Founder Effect The descendants of a small, founding population have different allele percentages than the population the founders came from.

41 Ex. Amish Populations and polydactyly

42 Bottleneck Effect The survivors of a catastrophic decrease in a population may have a different allele frequency than the pre-bottleneck population

43 Ex. Modern Cheetahs are all genetically similar due to 2 bottlenecks

44 Gene Flow Movement of alleles due to immigration and emigration

45 Example: Modern Human Migration

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47 Sexual Selection Persistence of traits that signify fitness and aid in reproduction

48 Ex. Peacocks are male.

49 Can be intersexual or intrasexual

50 Evolution Misconception Alert! Misconception: Evolution is random. Evolution is a change in allele frequency in a population. That change involves random forces (ex. Genetic drift) and selective processes (ex. Natural selection).

51 1.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics. 1. EVIDENCE OF EVOLUTION

52 Geological Evidence: Radiometric dating: Used to date geological formations and fossils. Establishes chronological history of Earth, and establishes Earth s age at ~4.5 billion years.

53 Fossil Record: Establishes History of life on Earth.

54 Living organisms resemble fossilized forms.

55 Transitional Fossils: Show evolutionary progression between groups Ex. Tiktaalik

56 Anatomical Evidence Similarities and differences in the anatomy (morphology) of organisms. Vestigial structures: structures that have lost their primary adaptive purpose Ex. Whale hind-limbs

57 Homologous structures: Structures present in a common ancestor, which have diverged during evolution. Ex. Vertebrate limbs

58 Analogous structures: Structures that have evolved multiple times in different lineages to fill similar adaptive needs. Ex. Wings

59 Chemical Evidence Similarities and differences in DNA and protein sequences.

60 Chemical evidence has been used to establish the evolutionary relatedness ( phylogeny ) of all life on Earth

61 Mathematical Modeling: Computational analysis: The ability to analyze large amounts of chemical sequence data to establish evolutionary relationships among organisms. Hardy-Weinberg Theory: The ability to quantify the amount of evolutionary change from generation to generation.

62 1.5 Organisms share many conserved core processes and features that evolved and are widely distributed among many organisms today 1. EVIDENCE OF COMMON ANCESTRY

63 The Universal Genetic Code

64 Common Metabolic Pathways Ex. Glycolysis

65 Cellular Morphology Note: Not to scale. Prokaryotic Cell: Animal-like eukaryotic cell: Plant-like eukaryotic cell:

66 Endosymbiosis

67 1.4: Biological evolution is supported by scientific evidence from many disciplines, including mathematics. 2. MATH SKILLS: HARDY-WEINBERG THEORY

68 What is Hardy Weinberg Theory? Equations that enable us to determine how much a population is evolving from generation to generation. Hardy-Weinberg equilibrium : Refers to an idealized, non-evolving population. Five characteristics:

69 Characteristics of a non-evolving population: 1. Large size (no genetic drift) 2. Random mating (no sexual selection) 3. Stable environment (no natural selection) 4. No immigration/emigration (no gene flow) 5. No mutations. No real population is in HW equilibrium.

70 Hardy-Weinberg Equations For a trait controlled by two alleles, where p is the dominant allele and q is the recessive allele: Gene Frequency: p + q = 1 Genotype Frequency: p 2 + 2pq + q 2 = 1

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72 Sample Problem In pea plants, the allele for purple flowers is dominant to the allele for white flowers. If 99% of the plants in the population have purple flowers, determine the percentage of heterozygotes in the population.

73 Uses of HW Theory To determine how a population is evolving from generation to generation. To help to determine which evolutionary pressures are affecting a population more/less.

74 1.6: Phylogenetic trees and cladograms are graphical representations (models) of evolutionary history that can be tested. 1. PHYLOGENY

75 Cladograms Diagrams that group items together based on the number of common characteristics. 1. Determine number of shared characteristics. 2. Arrange items as a tree showing most commonality possible

76 Phylogenetic Tree A cladogram that represents evolutionary relationships. Use two types of data: 1. Shared Derived Characters: Physical traits that represent evolutionary history (homologous structures). 2. DNA/Protein sequence Data: Differences in sequences accumulate as species evolve away from each other.

77 Ex. Vertebrate Phylogeny.

78 Ex. Complete Phylogeny

79 Phylogenetic Tree Construction 1. Determine similarities among organisms (character table works well). 2. Arrange organisms in a tree diagram showing simplest possible evolution. Maximum parsimony: All else being equal, a trait is assumed to evolve once and be present in all descendants

80 SKILL: Create a tree- Selected Vertebrates Character Table: Animal Opposable Thumb 4-chamber heart Amniotic egg lungs Spinal column Chimpanze e Mouse Turtle Frog Fish Lamprey

81 Trees are Hypotheses Continual revision: As more data is gathered, the phylogenetic relationships among organisms are continually revised. Role of computers: Computer analysis is needed to determine the similarities in large amounts of DNA/ protein sequence information.

82 1.7: Speciation and extinction have occurred throughout the Earth s history. 1. SPECIATION CONCEPTS

83 What is a species? Biological Species : A group of organisms that are capable of successfully reproducing. It s testable, but simplistic. And it is limited in application.

84 Speciation Rate Gradualism: species are the product of slowly accumulating, small evolutionary changes. Punctuated equilibrium: species undergo long periods of very little change, followed by rapid, large evolutionary changes.

85 Ex. Major Extinctions.

86 One species evolves in to many species that occupy open niches. Adaptive Radiation Ex. Lake Cichlids, Mammals, Galapagos Finches.

87 1.8: Speciation may occur when two populations become reproductively isolated from each other. 1. SPECIATION PROCESS

88 Reproductive Isolation Speciation occurs when a population can no longer interbreed with any other population. Allopatric: Happens due to physical separation. Sympatric: Happens while occupying the same area.

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90 Species Barriers Pre-Zygotic: Physical Temporal Behavioral Mechanical Chemical Post-Zygotic: Reduced Viability Reduced Fertility Hybrid Breakdown

91 Ex. Mules

92 Ex. Apples

93 Ex. Fruit Fly Food Speciation.

94 1.9 Populations of Organisms Continue to Evolve 1. ONGOING EVOLUTION OF ORGANISMS

95 Evolution is Ongoing Evolution continues to happen. Ex. Pesticide Resistance

96 Ex. Rock Pocket Mouse

97 Analysis of Evolution Mathematical modeling (e.g. HW Equilibrium) and genetic analysis can be used to investigate evolution as it occurs in real-time over generations.

98 1.10: There are several hypotheses about the natural origin of life on Earth, each with supporting scientific evidence. 1. ORIGIN OF LIFE

99 Origin Hypotheses Hypotheses must be testable. Many thoughts about the origin of life are not testable. Two major hypothesis for life on Earth. 1. Panspermia: Life from extraterrestrial life. 2. Abiogenesis: Life from non-life. Requires 4 major milestones to occur.

100 1. Development of Biological Molecules

101 2. Development of Proto-cells

102 3. Information Molecule Evolution

103 4. Reproduction

104 The RNA World A Hypothetical pre-dna state of life. Based on RNA s dual ability to store information AND catalyze reactions.

105 Evolution of Metabolism Heterotroph Hypothesis : Glycolysis! Photosynthesis! Aerobic Cellular Respiration.

106 Endosymbiosis Prokaryote! Eukaryote

107 Multicellularity Multicellularity opens previously inaccessible niches. Many organisms have unicellular and multicellular stages of their life cycles.

108 History of Life on Earth

109 1.11: Scientific evidence from many different disciplines supports models of the origin of life. 1. EVIDENCE FOR THE ORIGIN OF LIFE

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111 Geology Radioisotope Dating: Allows estimates of events during evolutionary history.

112 ~65 70 mya

113 Ex. Banded Iron Formations

114 Ex. Fossil Fuels

115 Miller-Urey Experiments Simulated Early Earth conditions (no O 2 ). Created Simple Biological Molecules

116 Commonalities among all organisms suggests common ancestry. It is the simplest explanation for the evidence. DNA Stores Information in all cells on Earth.

117 The Genetic Code is universal in all cells

118 Glycolysis is universal in all cells

119 All life is organized into cells These cells contain fundamental structural similarities Note: Not to scale. Prokaryotic Cell: Animal-like eukaryotic cell: Plant-like eukaryotic cell:

120 A Universal Phylogenetic Tree

121 Image Credits All images taken from wikimedia commons. Exceptions slide 23: Image from Grant & Grant, Slide 96: Image and Diagram from M. Nachman