Welcome to AP Biology Saturday Study Session Cladistics Begin the session with a brief review of how to interpret phylogenetic trees/cladograms. The short free response questions will help students brush up on drawing phylogenetic trees/cladograms.

Phylogenetic trees/cladograms illustrate speciation and relatedness of any two groups (taxa) Remind students that the branching pattern often matches how taxonomists have classified groups of organisms. Emphasize that phylogenetic trees are constantly being revised due to new knowledge and better computational tools.

A clade includes a common ancestor and all of its descendants Monophyletic

Organisms which share a more recent common ancestor are more closely related Taxa Time Nodes/Common Ancestors Use this tree to review taxa (tips) and nodes (common ancestors).

Cladograms can be drawn in any orientation = = Trees can be drawn in any orientation without changing their meaning with regard to shared ancestry.

Branches can rotate and still represent the same phylogeny The common ancestor remains the same.

Sister taxa share an immediate common ancestor Outgroup is less closely related to the other organisms Outgroup Polytomy signifies that evolutionary relationships among the taxa are not yet clear.

Parsimony = the simplest explanation with fewer evolutionary events is more likely

Clue: less closely related to the other organisms Question 1 a Clue: less closely related to the other organisms This is a good slide to review ancestral and derived traits. The original shared trait is termed the ancestral trait and the trait found in the newly evolved organism is called the derived trait.

Question 2 c Clues:

a Clue: fish have gills Question 3 Ask students to predict what characters are represented by the remaining letters. The next slide has the answers.

D C B A

Clue: find the most recent common ancestor Question 4 b Clue: find the most recent common ancestor

Clue: independently from other mammals Question 5 d Clue: independently from other mammals Heart is an example of a homologous structure inherited from a common ancestor.

Homologous structures indicate common ancestry Homologous structures are any features shared by two or more species that are inherited from a common ancestor.

Vestigial structures are special types of homologous structures Vestigial structures are homologous structures that lost their original function.

Molecular homologies indicate common ancestry Molecular biology shows that closely related organisms have similar DNA sequences and similar amino acid sequences.

b Question 6 Clue: +/– CHARACTER A - Turtle B - Horse C - Wolf D - Cat E - Leopard Hair – + Carnivorous Retractable Claws Mammary glands Ability to purr Backbone Remind students that + indicates the presence of the character and – indicates the absence of a character.

A B C E D

Clue: similar environments Question 7 c Clue: similar environments

Convergent Evolution The ability to glide through the air evolved independently in these two distantly related mammals. When species share features due to convergent evolution, these features are analogous and do not reflect common ancestry.

Remind students one last time that only homologous structures support common ancestry. Analogous structures should not be used in establishing phylogenies.

Math Grid In The correct answer: 266 million years ago Solution: 17.7 x 15 = 265.5 The nearest whole number is 266.

Short Free Response 1 3 points possible Released 2014 Question 2a Phylogenetic trees and cladograms can represent traits that are either lost or derived due to evolution.

Short Free Response 2 4 points possible Released 2009 Question 3b