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      • TOPIC 1: CELL BIOLOGY >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of Cells
        • 1.3 Membrane Structure
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        • 1.5 Origin of Cells
        • 1.6 Cell Division
      • TOPIC 2: MOLECULAR BIOLOGY >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and Lipids
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        • 2.5 Enzymes
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        • 3.1 Genes
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        • 4.1: Species, Communities and Ecosystems
        • 4.2 Energy Flow
        • 4.3 Carbon Cycling
        • 4.4 Climate Change
      • Topic 5: Evolution and Biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural Selection
        • 5.3 Classification and Biodiversity
        • 5.4 Cladistics
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        • 6.1 Digestive System
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5.4 Cladistics

5.4 Syllabus
Picture

U1. A clade is a group of organisms that have evolved from a common ancestor.

-Over time species evolve and split to from new species. This process can occur repeatedly with some highly successful species leading to a large group of organisms that share a common ancestor. 
-These groups of species evolved from a common ancestor, that have shared characteristics is called a clade is method of classifying organisms into groups of species called clades. 
  • Each clade consists of an ancestral organism and all of its evolutionary descendants
  • Members of a clade will possess common characteristics as a result of their shared evolutionary lineage
  • Branch points in the tree represent the time at which two taxa split from each other
  • The degree of divergence between branches represent the differences that have developed between the two taxa since they diverged
​

U2. ​Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.

-All organisms use DNA and RNA as genetic material and the genetic code by which proteins are synthesized is universal. This shared molecular heritage means that base and amino acid sequences can be compared to ascertain levels of relatedness. 
-Over the course of millions of years, mutations will accumulate within any given segment of DNA. 
-Sometimes determining which species are part of certain clade is difficult. The most accurate evidence is derived from amino acid sequences of certain proteins. 
  • ​Phylogeny = the evolutionary history of a taxonomic group, often shown in a phylogenetic tree
  • Mutations in DNA occur with predictable rates
  • Differences can be used as a molecular clock to develop phylogeny 
  • DNA nucleotide sequences
  • Protein amino acid sequences
​

U3. ​Sequence differences accumulate gradually so there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor.

-Differences in nucleotide base sequences in DNA, and therefore amino acid sequences in proteins, accumulate gradually over long periods of time
  • Differences accumulate at roughly constant and predictable rate
    • ​  Therefore, the number of differences can be used as a clock
    • To measure the time since two divergent groups shared a common ancestor
  • However, variations are partly due to mutations
    • Which are unpredictable chance events
    • So there must be caution in interpreting data
​

U4. ​Traits can be analogous or homologous.

-Analogous characteristic: Structures with a common function, but a different evolutionary origin
  • Example: Dolphin fins and Shark fins
-Homologous characteristics: Structures that have common evolutionary origin, even if they have different functions
  • Example: Dolphin forelimbs and human arms
​

U5. ​Cladograms are tree diagrams that show the most probable sequence of divergence in clades.

-Cladograms are tree diagrams where each branch point represents the splitting of two new groups from a common ancestor. Each branch point (node) represents a speciation event by which distinct species are formed via divergent evolution. 

-Cladograms show the probable sequence of divergence and hence demonstrate the likely evolutionary history of a clade. The fewer the number of nodes between two groups the more closely related they are expected to be. 

-The strength of cladistics is that the comparisons are objective, relying on morphological and molecular homologies

-The weakness of cladistics is that molecular differences are analyzed on the basis of probabilities. 
  • Improbable events occasionally occur, making the analyses wrong
​

U6. ​Evidence from cladistics has shown that classifications of some groups based on structure did not correspond with the evolutionary origins of a group or species.

-Historically, classification was based primarily on morphological differences (Structural characteristics). Closely related species were expected to show similar structural features, indicating common ancestry. However, there are two key limitations to using morphological differences as a basis for classification: 
  • Closely related organisms can exhibit very different structural features due to adaptive radiation (Pentadactyl limb)
  • Distantly related organisms can display very similar structural features due to convergent evolution 

-In many cases, cladograms have confirmed existing classification, as expected, since both are based on phylogeny
-In some cases, cladograms can be difficult to reconcile with traditional classifications 
  • Nodes can be placed at any point
  • Making the fit of taxa to the cladogram arbitrary

-In some cases, cladograms radically alter existing classifications
  • For example, birds are grouped within a clade including dinosaurs 
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  • Home
  • IB STUDY MATERIALS
    • Psychology SL/HL >
      • Tips & Guide
      • Biological Approach >
        • Brain and Behaviour
        • Hormones and Pheromones
        • Genetics and Evolution
        • HL Animal Research
      • Sociocultural Approach >
        • Individual and the group
        • Cultural Origins
        • Cultural Influences
        • HL Globalization
      • Cognitive Approach >
        • Cognitive Processing
        • Reliability of Cognitive Processes
        • Emotion and Cognition
        • HL Digital World
      • B. Human Relationships >
        • Personal Relationships
        • Group Dynamics
      • D. Developmental >
        • Developing as a Learner
        • Developing an Identity
      • Studies >
        • Biological Approach
        • Sociocultural Approach
        • Cognitive Approach
        • B. Human Relationships
        • D. Developmental
    • Chemistry SL/HL >
      • Tips & Guide
      • All Vocab Definitions
      • ALL EQUATIONS
      • Unit 1,2 & 12
      • Unit 3 &13
      • Unit 4 &14
      • Unit 5,6,7 & 15,16,17
      • Unit 8 & 18
      • Unit 9 & 19
      • Unit 10 & 20
      • Unit 11 & 21
      • Option D: Medicinal Chemistry >
        • D.1 PHARMACEUTICAL PRODUCTS AND DRUG ACTION
        • D.2 Aspirin and penicillin
        • D.3 Opiates
        • D.4 pH Regulation of the Stomach
        • D.5 Antiviral Medications
        • D.6 Environmental impact of some medications
        • D.7 Taxol- A Chiral Auxiliary Case Study
        • D.8 Nuclear Medicine
        • D.9 Drug Detection and Analysis
    • Biology SL >
      • Tips & Guides
      • TOPIC 1: CELL BIOLOGY >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of Cells
        • 1.3 Membrane Structure
        • 1.4 Membrane Transport
        • 1.5 Origin of Cells
        • 1.6 Cell Division
      • TOPIC 2: MOLECULAR BIOLOGY >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and Lipids
        • 2.4 Proteins
        • 2.5 Enzymes
        • 2.6 Structure of DNA and RNA
        • 2.7 DNA Replications, Transcription and Translation
        • 2.8 Cell Respiration
        • 2.9 Photosynthesis
      • Topic 3: Genetics >
        • 3.1 Genes
        • 3.2 Chromosomes
        • 3.3 Meiosis
        • 3.4 Inheritance
        • 3.5 Genetic Modification and Biotechnology
      • Topic 4: Ecology >
        • 4.1: Species, Communities and Ecosystems
        • 4.2 Energy Flow
        • 4.3 Carbon Cycling
        • 4.4 Climate Change
      • Topic 5: Evolution and Biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural Selection
        • 5.3 Classification and Biodiversity
        • 5.4 Cladistics
      • Topic 6: Human Physiology >
        • 6.1 Digestive System
        • 6.2 The blood system
        • 6.3 Defense against infectious disease
        • 6.4 Gas Exchange
        • 6.5 Neurons and Synapses
        • 6.6 Hormones, Homeostasis and Reproduction
    • Physics SL >
      • Must-have Resources
      • Full Study Resources
      • Other Resources
      • Tips & Guide
      • IA, Lab Report
      • Topic 1: Measurements & Uncertainties
      • TOPIC 2: MECHANICS
      • TOPIC ​3: THERMAL PHYSICS
      • Topic 4: Waves
      • Topic 5: Electricity & Magnetism
      • Topic 6: Circular Motion & Gravitation
      • Topic 7: Atomic, Nuclear, & Particle Physics
      • Topic 8: Energy Production
      • Option D: Astrophysics
    • Geography SL/HL >
      • Tips & guide
      • Unit 1: Changing population
      • Unit 2: Global climate—vulnerability and resilience
      • Unit 3: Global resource consumption and security
      • Unit 4: Power, Places and Networks
      • Unit 5: Human Development and Diversity
      • Unit 6: Global Risks and Resillience
      • Option A: Freshwater
      • Option B: Ocean and Coastal Margins
      • Option C: Extreme Environments
      • Option E: Leisure, tourism and sport
    • Business SL/HL(pending) >
      • Tips & guides
      • Unit 1: Business Organization and Movement >
        • 1.1 Nature of Business
        • 1.2 Types of Organizations
        • 1.3 Organizational objectives
        • 1.4 Stakeholders
        • 1.5 External Environment
        • 1.6 Growth and evolution
      • Unit 2: Human Resource Management >
        • 2.1 The functions and evolution of human resource management
        • 2.2 Organizational structure
        • 2.3 Leadership and management
        • 2.4 Motivation
      • Unit 3: Finance and Accounts >
        • 3.1 Sources of Finance
        • 3.2 Costs and Revenues
        • 3.3 Break-even analysis
        • 3.4 Final accounts
        • 3.5 Profitability and liquidity ratio analysis
        • 3.7 cash flow
      • Unit 4: Marketing >
        • 4.1 The role of marketing
        • 4.2 Marketing Planning
        • 4.4 Market Research
        • 4.5 The four ps
        • 4.8 E-commerce
      • Unit 5: Operations Management >
        • 5.1 The role of operations Management
        • 5.2 Production methods
        • 5.4 Locations
    • Economics SL/HL (pending) >
      • Tips & guides
      • MICROECONOMICS >
        • 1.1 Competitive Markets: Demand and Supply
      • macroeconomics
    • Chinese B SL >
      • Oral Example
    • Extended Essay (EE) >
      • General Tips
      • Physics EE
    • Internal Assessment (IA) >
      • General Tips
    • Theory of Knowledge >
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    • Other notes >
      • Topic 1: Measurements and Uncertainties
      • Topic 2: Mechanics
      • Topic 3: Thermal Physics
      • Topic 4: Waves
      • Topic 5: Electricity and Magnetism
      • Topic 6: Circular Motion and Gravitation
      • Topic 7: Atomic, Nuclear and Particle Physics
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      • Option D: Astrophysics
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  • our warm advice
    • academic advice!
    • Toxic Productivity
    • Finding Your Balance
    • Giving Up
    • YOLO?
    • Are grades important
    • Danger of Quotes
    • How to Destress
  • About us