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

PRACTICE WITH CLADOGRAMS

PRACTICE WITH CLADOGRAMS

PRACTICE WITH CLADOGRAMS

MORE PRACTICE

FINALLY!!!