Classification and Cladistics

(IB Topic A3.2 – AHL only)

Essential Idea(s): Traditional taxonomy classifies organisms based on evolving relationships, but also presents some challenges. Cladistics offers an alternative by using shared characteristics and molecular data, allowing enhanced insight into evolutionary history.

Unit Length: 3 AHL Lessons

Guiding Questions

◊ What tools are used to classify organisms into taxonomic groups?

◊ How do cladistic methods differ from traditional taxonomic methods?

Materials:

Self-Teaching Slides (AHL)	Quizlet Vocab Set
	Notes Template (AHL)

IB Statement(s) and Objective(s)
A3.2.1: Need for classification of organisms State the need for a classification system Explain why biological classification is a continuous process A3.2.2: Difficulties classifying organisms into the traditional hierarchy of taxa Define taxonomy List the hierarchy of taxa, from largest to smallest List the three domains of life State the two groups of prokaryotes Draw a tree diagram to illustrate the evolutionary relationship between organisms of the three domains List the four kingdoms of eukaryotes NOS Concept: A fixed ranking of taxa (kingdom, phylum, etc) is arbitrary because it does not reflect the gradation of variation NOS Concept: Cladistics offers an alternative approach to classification using unranked clades. Define clade, cladistics, and cladogram Identify members of clades given a cladogram A3.2.3: Advantages of classification corresponding to evolutionary relationships Explain why the ideal classification system follows evolutionary relationships Define phylogenetics A3.2.4: Clades as groups of organisms with common ancestry and shared characteristics Outline the relationship between time, evolutionary relationships and biological sequences (nitrogenous base or amino acid) Outline the criteria used for organizing organism into clades Outline the use of morphological traits in cladistics A3.2.5: Gradual accumulation of sequence differences as the basis for estimates of when clades diverged from a common ancestor Outline the use of a “molecular clock” to determine time since divergence between two species Outline the limitations of a molecular clock A3.2.6: Base sequences of genes or amino acid sequences of proteins as the basis for constructing cladograms Explain the rationale for using DNA base sequences or amino acid sequences as the basis for constructing cladograms NOS Concept: Different criteria for judgment can lead to different hypotheses Define parsimony Use parsimony analysis to select the most probable of 2 cladograms A3.2.7: Analyzing cladograms Define the terms root, node, and terminal branch in the context of cladistics Analyze a cladogram based on a mutations in a gene A3.2.8: Using cladistics to investigate whether the classification of groups corresponds to evolutionary relationships Outline the reason and evidence for the reclassification of the figwort family NOS Concept: Scientific knowledge claims may eventually be falsified A3.2.9: Classification of all organisms into three domains using evidence from rRNA base sequences Explain the reclassification of prokaryotic cells in 1977

IB Statement(s) and Objective(s)

A3.2.1: Need for classification of organisms

State the need for a classification system
Explain why biological classification is a continuous process

A3.2.2: Difficulties classifying organisms into the traditional hierarchy of taxa

Define taxonomy
List the hierarchy of taxa, from largest to smallest
List the three domains of life
State the two groups of prokaryotes
Draw a tree diagram to illustrate the evolutionary relationship between organisms of the three domains
List the four kingdoms of eukaryotes
NOS Concept*: A fixed ranking of taxa (kingdom, phylum, etc) is arbitrary because it does not reflect the gradation of variation
NOS Concept*: Cladistics offers an alternative approach to classification using unranked clades.
Define clade, cladistics, and cladogram
Identify members of clades given a cladogram

A3.2.3: Advantages of classification corresponding to evolutionary relationships

Explain why the ideal classification system follows evolutionary relationships
Define phylogenetics

A3.2.4: Clades as groups of organisms with common ancestry and shared characteristics

Outline the relationship between time, evolutionary relationships and biological sequences (nitrogenous base or amino acid)
Outline the criteria used for organizing organism into clades
Outline the use of morphological traits in cladistics

A3.2.5: Gradual accumulation of sequence differences as the basis for estimates of when clades diverged from a common ancestor

Outline the use of a “molecular clock” to determine time since divergence between two species
Outline the limitations of a molecular clock

A3.2.6: Base sequences of genes or amino acid sequences of proteins as the basis for constructing cladograms

Explain the rationale for using DNA base sequences or amino acid sequences as the basis for constructing cladograms
NOS Concept*: Different criteria for judgment can lead to different hypotheses
Define parsimony
Use parsimony analysis to select the most probable of 2 cladograms

A3.2.7: Analyzing cladograms

Define the terms root, node, and terminal branch in the context of cladistics
Analyze a cladogram based on a mutations in a gene

A3.2.8: Using cladistics to investigate whether the classification of groups corresponds to evolutionary relationships

Outline the reason and evidence for the reclassification of the figwort family
NOS Concept*: Scientific knowledge claims may eventually be falsified

A3.2.9: Classification of all organisms into three domains using evidence from rRNA base sequences

Explain the reclassification of prokaryotic cells in 1977


Activities: ⓟ = podcast / ⍰ = inquiry 5 / ⓦ = Write it / Ӕ = The academy / Ⓡ = Read it
Lab! ⓟ/ⓦ: Marine Mammals, Caffeine Evolution, and Cladistics (👭👭👭 / 👭👭👭 [half class vs. half class]) You live in a time where little more than a screen and some internet access enables you to answer some pretty deep, significant evolutionary questions, like: How and when did humanity’s favorite rereational drug first evolve in plants? or… Did marine mammals evolve from a single ancestor who returned to the ocean? This technically isn’t a virtual lab – you’re actually using the same tools as real-life geneticists to answer these questions. As a class, split into 2 groups and have a race: Follow the instructions for either group to construct a phylogenic tree to answer the questions above. The first group with both an accurate answer AND an accurate phylogenic tree…wins. Lab! ⓟ/ⓦ/Ӕ/⍰: Exploring Lizard Phylogeny with DNA (💁 [written] / 👭 [podcast only] max 3) Jump into the Caribbean to see how anole lizards have been evolving to local climates for millions of years. *Complete Module 2* of this virtual lab – you may answer the accompanying questions either as a podcast or a written assignment. Alternatively, you can come up with your own inquiry questions, and treat this as an inquiry task. Work your way through this document as you go. You might need the following documents to complete your module: DNA Sequences of various anoles Use the steps on this page to construct a cladogram from genetic information Lab! ⓟ/ⓦ: T-Rex Phylogeny (Cookbook Lab) (💁 [written] / 👭 [podcast only] max 2) This is probably as close to Jurassic Park as you’ll realistically ever get. By sequencing the collagen (a bone protein) from Tyrannosaurus Rex fossils, we can compare the genetic amino acid sequence of these famous dinosaurs to living organisms (including humans). It’s a fairly hefty cookbook lab (meaning there are a lot of steps to follow), but it’s kind of cool — find out who the closest living relative to the T-rex is. Have a discussion about the lab and the ways it connects to this unit – use the questions at the end of the lab for some inspiration. Here’s the lab Here’s the collagen sequences of various animals (you’ll compare the t-rex sequences to these) Lab! ⓟ/ⓦ: Figwort Reclassification (💁/ 👭 max 2) Retrace the steps of figwort reclassification. Find out the original criteria used to sort all the figworts into a single family, then see some of the genetic evidence that changed all of that. Complete all sections as instructed, including the questions on the final slides — then submit to G. Classroom. [Source: Lab and slides from biologyforlife.com] Ӕ: The Academy: Cladistics (💁) Create a Khan Academy-style video to explain cladistics and classification. Go here for some inspiration from Sal Khan himself. Try to cover as many points as possible from Topic A3.2. ⓡ/ⓟ/ⓦ (+NOS link): Move over, DNA: Ancient Proteins are Starting to Reveal Humanity’s History (💁) Where did humans actually come from? We still don’t know the answer to our distant ancestors, and new discoveries (such as the Dragon Man discovered in China in 2021) are constantly adding pieces to the puzzle. New techniques in amino acid sequencing are helping to solve the puzzle. Read about the way this rising science is changing the search, and come up with some good questions to discuss this topic and link it to the content from this week. Here are some suggested questions to get you going: How has genetic sequencing and cladistics enabled us to better understand where we come from? How can proteins be used to create phylogenetic trees (cladograms)? How have recent discoveries with this method changed the story of where humans originated? What species are currently suspected to be the closest ancestral relatives to humans? How does the search for humanity’s origins serve as an example of the Nature of Science, particularly regarding how science theories can change over time? After reading the article, what do you think is in store for the future search for humanity’s ancestry? When do you think we’ll know for sure who our ancestors really were?