Chapter 26 Phylogeny and Systematics

Tree of Life Phylogeny – evolutionary history of a species or group - draw information from fossil record - organisms share genes, metabolic pathways, and structural proteins with close relatives Systematics – analytical approach to understanding diversity and relationships of organisms both present and past - molecular systematics – uses comparisons of DNA and RNA to infer relationships between genes and genomes

Fossil Record Sedimentary are richest source of fossils - compressed layers form strata Fossil record is a sequence of fossils that have accumulated in strata - detailed account of biological change over a vast scale of geologic time Drawbacks: - substantial but incomplete chronicle of change - many fossils were destroyed by other processes - biased in favor of species that existed for a long time, or have hard shells, skeletons

Convergent Evolution Analogy – describes similarities of two species that are a product of convergent evolution rather than descent from common ancestor *environmental pressures and natural selection produce similar adaptations in organisms from different lineages Ex: Australian mole vs. North American mole

Analogous vs. Homologous Bat wings would logically be associated with birds Actually forelimb structure is closer to cats Bat wing is homologous to many mammals but analogous to bird wing- different ancestors Homoplasies- (Greek for mold the same way) – analogous structures that evolved independently More points of resemblance between two organisms means more homology, less analogy

Morph & Molecular Homology Homology is tool used to connect similarities among organisms in their bone structure and functions DNA sequences can be used to show common link also - possible to large divergence morphologically but small molecular divergence

Molecular Homology Systematics can match and realign segments to show similarities

Phylogenetic Systems Taxonomy – ordered division of organisms into categories based on sets of characteristics that assess similarities and differences - developed in 1748 by Carolus Linnaeus 2 phylogenetic systematics: 1.Binomial nomenclature 2.Hierarchical Classification

Binomial Nomenclature Established to avoid ambiguity when communicating about various organisms - two word format of scientific name - Genus (capitalized and italicized) – depicts species association - Specific epithet (lower case italicized) – unique species within genus Ex: Panthera pardus Canis familiaris

Hierarchical Classification Groups organisms into increasingly broad categories Domains - became an accepted entity in the 1990’s from over 20 years of research by Dr. Carl Woese and his associates. based on evidence of a third kind of single celled organism

Linking Classification and Phylogeny Phylogenetic trees – depict hypothesis about evolutionary relationships -branching is hierarchical -constructed from series two way branch points -branch points represent divergence of two species from common ancestor -sequence of branching does not describe age existence of species

What Darwin never knew…

Cladistics Analysis of how species are grouped. Cladogram is the diagram used to depict patterns of shared characteristics

Cladistics Monophyletic – consists of ancestral species and all its descendants Paraphyletic – consists of ancestral species and some of descendants Polyphyletic – groups several species but lacks common ancestor

Shared and Derived Characters Clade represents group of species within the phylogenetic tree Shared primitive (ancestral) characters – characteristic shared beyond the taxon Shared derived characters – evolutionary novelty unique to a particular clade Ex: backbone is homologous to mammals and vertebrates (SPC), but hair is only to unique to mammalian clade not all vertebrates(SDC)

Phylograms Phylogram – present information about the sequence of events relative to one another - length of branch reflects the number of changes that have taken place in DNA sequence of that lineage -traces the rate of evolution

Ultrametric Tree Ultrametric trees – present information about the actual time given events occurred - place branch point in context of geologic time Ex: traces humans and bacteria to common ancestor 3 billion years old

Genome History Duplication is the most important mutation that indicates evolutionary change because it increases the number of genes Orthologous genes – homologous genes passed in a straight line from one generation to the next, but have ended in different gene pools because of speciation - can only diverge after speciation Ex: B hemoglobin gene between mice and humans Paralogous genes – result from duplications and have more than one copy in the genome - can diverge while in the same gene pool Ex: olfactory receptor gene 350 in human : 1000 in mice

Molecular Clocks Molecular clock – measures the absolute time of evolutionary change based on some genes and other regions of genomes appear to evolve at constant rates - used to date divergence of a species Drawbacks: 1. may not be accurate because DNA changes may be favored over another 2. may favor direction selection 3. attempts to use clocks beyond time span of fossil record has high level of uncertainty

Origin of HIV Molecular clock traced the origin back to viruses that descended from nonhuman hosts like chimpanzees or other primates Samples of viral sequence can date back to an epidemic in 1959, strain HIV -1 M From that strain researchers concluded that the true first exposure could have come from 1930’s. (Possibly 1910)