Phylogeny and Systematics By: Ashley Yamachika

Biologists use systematics They use systematics as an analytical approach to understanding the diversity and relationships of organisms, both present-day and extinct

Systematists use morphological, biochemical, and molecular comparisons to infer evolutionary relationships Phylogenies are based on common ancestries inferred from fossil morphological and molecular evidence.

The Fossil Record Sedimentary Rocks… Are the richest source of fossils Are deposited into layers called strata Based on the sequence in which fossils have accumulated in such strata Fossils reveal characteristics that may have been lost over time

Radiometric Dating Measures the decay of radioactive isotopes in terms of half-life Half-life is the amount of time it takes for ½ the amount of a radioactive isotope to decay

Morphological and Molecular Homologies Phylogenetic history can be inferred from certain morphological and molecular similarities among living organisms Organisms that share very similar morphologies or similar DNA sequences Are likely to be more closely related than organisms with vastly different structures or sequences

Convergent Evolution occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms from different evolutionary lineages Analogous Structures or molecular sequences that evolved independently are also called homoplasies

Parallel Evolution When both descendants are similar in a particular respect, evolution is defined as parallel if the ancestors considered were also similar, and convergent if they were not

Divergent Evolution  The diversification of an ancestral group into two or more species in different habitats is called divergent evolution.  When it involves the formation of a large number of species to occupy different niches is called an adaptive radiation.

Phylogenetic systematics connects classification with evolutionary history Taxonomy Is the ordered division of organisms into categories based on a set of characteristics used to assess similarities and differences.

Binomial Nomenclature Is the two-part format of the scientific name of an organism Was developed by Carolus Linnaeus The binomial name of an organism or scientific epithet Is latinized Is the genus and species

Hierarchical Classification Panthera pardus Panthera Felidae Carnivora Mammalia Chordata Animalia Eukarya Domain Kingdom Phylum Class Order Family Genus Species Panthera pardus Panthera Felidae Carnivora Mammalia Chordata Animalia Eukarya Domain Kingdom Phylum Class Order Family Genus Species Panthera pardus Panthera Felidae Carnivora Mammalia Chordata Animalia Eukarya Domain Kingdom Phylum Class Order Family Genus Species

Systematists depict evolutionary relationships In branching phylogenetic trees

Phylogenetic systematics informs the construction of phylogenetic trees based on shared characteristics A cladogram Is a depiction of patterns of shared characteristics among taxa A clade within a cladogram Is defined as a group of species that includes an ancestral species and all its descendants Cladistics Is the study of resemblances among clades

Clades Valid Clade is monophyletic Valid Clade is monophyletic Signifying that it consists of the ancestor species and all its descendants Signifying that it consists of the ancestor species and all its descendants Paraphyletic Clade Paraphyletic Clade Is a grouping that consists of an ancestral species and some, but not all, of the descendants Is a grouping that consists of an ancestral species and some, but not all, of the descendants

Phylograms In a phylogram The length of a branch in a cladogram reflects the number of genetic changes that have taken place in a particular DNA or RNA sequence in that lineage

Orthologous genes Are genes found in a single copy in the genome Can diverge only once speciation has taken place Paralogous genes Result from gene duplication, so they are found in more than one copy in the genome Can diverge within the clade that carries them, often adding new functions

Neutral Theory states that Much evolutionary change in genes and proteins has no effect on fitness and therefore is not influenced by Darwinian selection And that the rate of molecular change in these genes and proteins should be regular like a clock

Eubacterial Most numerous organisms on earthMost numerous organisms on earth Earliest life forms (fossils date 3.5 billion years old)Earliest life forms (fossils date 3.5 billion years old) Microscopic prokaryotes (no nucleus nor membrane-bound organelles)Microscopic prokaryotes (no nucleus nor membrane-bound organelles) Have only one circular chromosomeHave only one circular chromosome Have small rings of DNA called plasmidsHave small rings of DNA called plasmids Most are unicellularMost are unicellular Found in most habitatsFound in most habitats Main decomposers of deadMain decomposers of dead organisms so recycle nutrients Some cause diseaseSome cause disease