Phylogeny and Systematics Part 6 Phylogeny and Systematics

Phylogeny and Systematics (Part 6) Phylogeny and Systematics (Making “Trees of Life”) AP Biology Ms. Day

Macroevolution • studies focus on change that occurs at or above the level of species ▫ The origin of taxonomic groups higher than species level How does this occur? • Evolution of new traits (novelties) • mass extinctions • Open adaptive zones (divergent evolution)

Intro to Phylogenetics • https: //highered. mheducation. com/sites/98340 92339/student_view 0/chapter 23/animation__phylogenetic_trees. html

Phylogeny What is phylogeny? • The evolutionary history of a group of organisms • Systematics attempts to reconstruct phylogeny, by analyzing evolutionary relatedness ▫ Use morphological and biochemical similarities • Molecular systematics uses DNA, RNA and proteins to infer evolutionary relatedness. • Different tools are used to reconstruct phylogenies called phylogentic trees.

Making Evolutionary “Trees”: Illustrating Phylogeny 2 Methods 1. Cladistics = BRANCHES NOT TIME RELATED ▫ sorts primitive and shared derived characteristics ▫ based on evolutionary relationships Makes cladograms

Let’s review in groups…

Cladograms have clades • A clade within a cladogram ▫ a group of species that includes an ancestral species and all its descendants • Cladistics ▫ the study of resemblances among clades

Cladistics • Each branch is called a clade https: //www. youtube. com/w atch? v=46 L_2 RI 1 k 3 k

WHY?

2. Phenetics = BRANCHES ARE TIME RELATED ▫ based on overall similarity (morphology) without regard for evolutionary relationships based on how similar organisms look REMEMER: Organisms can develop similar features through converent evolution **Creates phylograms

• Each branch point ▫ Represents the divergence of two species Leopard Domestic cat Common ancestor

• “Deeper” branch points ▫ Represent progressively greater amounts of divergence; more closely related Wolf Leopard Common ancestor Domestic cat

More changes here length of a branch reflects # of genetic changes that have taken place in a particular DNA sequence in that lineage

• Currently, scientists use ▫ Morphological (anatomy), biochemical, and molecular comparisons to show evolutionary relationships in “trees” Obtained through fossil studies, DNA technology and current organisms

Molecular systematics

Not all Similarities Represent Common Ancestry • Homologous structures indicate shared common ancestry ▫ Homologous structures are therefore evidence of divergent evolution • Analogous structures are similar in function but not in evolutionary history ▫ Analogous structures are evidence of convergent evolution It is not always easy to sort homologous from analogous structures

Analogous Structures

How to Make a Trees: Hypotheses

• https: //ccl. northwestern. edu/simevolution/obonu/cladogra ms/Open-This-File. swf • A shared primitive character ▫ a homologous structure that is shared by all groups you are trying to define • A shared derived character ▫ A new evolutionary trait unique to a particular clade(s)/branch

Outgroups vs. Ingroups • Outgroup ▫ Species or group of species that is closely related to the ingroup ▫ Distinguishes between shared primitive and shared derived characteristics ▫ Closely related to ingroup • Ingroup ▫ the various species we are studying

A Cladogram What is the shared primitive characteristic? Notochord

• http: //www. cengage. com/biology/discipline_co ntent/animations/cladogram_construction. html • http: //www. wwnorton. com/college/biology/evo lution/ch/04/animations. aspx

Phylograms and cladograms trees are JUST hypotheses Which is the most parsimonious tree? • the best hypothesis which requires fewest evolutionary changes Parsimony does not always work, nature does not always take the simplest course