Chapter 25 Phylogeny and Systematics. Macroevolution Attempts to explain how major adaptive...
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Transcript of Chapter 25 Phylogeny and Systematics. Macroevolution Attempts to explain how major adaptive...
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