UNITY & DIVERSITY: WHAT’S THE RELATIONSHIP? CLADISTICS.

U N I T Y & D I V E R S I T Y: W H AT ’ S T H E R E L AT I O N S H I P ?

CLADISTICS

WHAT ARE CLADISTICS & TAXONOMY?

• Cladistics: Method of hypothesizing how one organism is related to another. • Taxonomy: system of naming/classifying species• Taxon: the name of a group or a single organism

WHAT’S A CLADOGRAM?

• Cladogram: a graphic organizer showing the relationship between organisms

WHAT’S THE EVIDENCE?

• Scientists base their hypotheses on shared characteristics, called a homologous feature

Ex. Forelimbs of four-legged animals

3 BASIC ASSUMPTIONS

1. All organisms are related by a common ancestor

3 BASIC ASSUMPTIONS

2. There is a branching (splitting in two) pattern of relationships

3 BASIC ASSUMPTIONS

3. Change in characteristics occurs over time

METHODOLOGY“HOW-TO” OF CLADISTICS

1. SAME CLADE

• The organisms you are organizing must all be part of the same clade, or “branch”

• Which color represents a clade?

2. DETERMINE THE FEATURES

• Taxa do not overlap • Decide if each taxon has the characteristics or

not

vertebra + + + + + + +

Boney skeleton - + + + + + +

4 limbs - - + + + + +

Amniotic egg- - - + + + +

hair - - - + + + +

Egg w/ shell - - - - - + +

3. GROUP BY FEATURES

• Species go on the ends of branches

• Nodes are common ancestors

• Features are labeled

VOCABULARY

• Shared (primitive) trait: a characteristic that was present in the common ancestor• Derived trait: a characteristic that is different

from the common ancestor• Outgroup: shares a common ancestor, but is the

least related in the clade

• What is an example of a shared trait?

• What is an example of a derived trait?

• Which is the outgroup?

4. RULE OF PARSIMONY

• If there are multiple possible cladograms, the simplest one (with the least number of changes) is best.

READING TREESHOW TO READ A CLADOGRAM

STRATEGY

• Look for the most recent common ancestor (nodes) • More recent ancestors will be “higher”• Older ancestors will be “lower”• Don’t read “along the tips”

PRACTICE WITH CLADOGRAMS

MORE PRACTICE

FINALLY!!!

UNITY & DIVERSITY: WHAT’S THE RELATIONSHIP? CLADISTICS.

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