Chapter 25

Phylogeny and Systematics

Macroevolution

• Attempts to explain how major adaptive characteristics came into existence

• These characteristics would be the basis for creating new taxa above the species level– Individual unit of classification system• Ex: Kingdom

Phylogeny • The evolutionary

history of a species or group of related species

• Constructed through fossils, DNA/RNA/ protein analysis

Systematics• Study of biodiversity

in an evolutionary context

• Uses taxonomy to trace phylogeny

• Classifies organisms based on evolutionary history

Fossil Formation• Fossils are formed in

sedimentary rock• Organisms die, then

sediments are deposited on top of them

• Older fossils on bottom of strata; newer ones in top strata

Incomplete Record• Organisms don’t always

die in locations favoring fossil formation

• Lots of organisms don’t make fossils

• Some fossils may never be discovered due to location

Mass Extinctions

• Mass extinctions punctuated by major geological and climatic events– Permian– Pangaea– Cretaceous

Systematics: Taxonomy

• Modern system of taxonomy invented by Linnaeus

• Sought to give binomial names to all organisms: Genus species naming convention

• Example: Homo sapiens

Hierarchy of Classification

• Groups organisms from most broad to most specific categories

Example

Cladistics and Phylogeny• Cladistics: study of

relationships among organisms shown by common characteristics not found in ancestral group

• Cladogram: diagram showing relationships among organisms

Constructing a Cladogram: Step 1

• Sort homology from analogy:–Homologous

structures–Analogous structures:

do not have common ancestry; different structure, same function

Constructing a Cladogram: Step 2

• Identify shared primitive characters:–Not limited to group

being studied (e.g. backbone)

• Identify shared derived characters:–Characteristics

unique to clade (hair in mammals)

Constructing a Cladogram: Step 3

• Outgroup comparison– The ingroup is what’s being studied– The outgroup is what you compare ingroup to

• Identify characteristics to study• Make a data matrix• Make the cladogram

Cladogram

DNA Sequences• Genome sequencing

allows us to study DNA sequences of organisms to observe change over time

• Sequence alignments generated with computers

Amino Acid Sequences

• Similarities in DNA sequences lead to similarities in AA sequences as well

• Gaps are present due to mutations

Molecular Clocks

• Based on observation that some genomic regions evolve at constant rates• DNA or proteins can be compared

and the number of sequence differences is proportional to time passed since branching occurred

Example of Molecular Clock: Cytochrome C