Chapter 20- Introduction to Biological Diversity- Phylogeny

• What are the major mechanisms of evolution?

  natural selection, mutation, genetic drift, gene flow, sexual selection (non-random mating), and artificial selection (humans choose alleles)
• What is the source of all new variation?

  mutations
• At what level of biological organization does evolution occur?

  population; same species, same location/ place, and same time
• Compare microevolution and macroevolution.

  microevolution: small changes, like different dog breeds

  macroevolution: speciation, changes so big that there are now multiple species
• systematics: a scientific discipline focused on classifying organisms and determining their evolutionary relationships
• taxonomy- a scientific discipline focused on naming organisms
• Binomial (2 names) Nomeclature:

  1. genus- capitalize
  2. species- lowercase
  3. underline/ italicize the whole name
• domain- eukarya
• kingdom- animalia
• phylum- chordata
• class- mammalia
• order- carnivora
• family- canidae
• genus- canis
• species- canis lupus
• subspecies- canus lupus familiaris
• Evolution: change in genetic composition of a population from generation to generation/ descent with modification
• Phylogeny (Tree of Life): organization of evolution changes/ ancestors in a tree
• Phylogenies are hypotheses.

  • constantly tested and updated as new data is used to increase reliability
  • don't tell us order of evolution
  • branches are most important
  • trying to understand where organisms came from
  • hypothesis is testable and for how we think evolution has occurred for a population
  • created by Darwin
• taxon (taxa): group of organisms, each individual can be a taxon
• sister taxa: taxa that are closely related and share a common ancestor
• nodes: show common ancestors, every node has 2 evolutionary lineages
• Structures of two or more groups are more likely to be homologous if:

  • fossil evidence indicates that the common ancestor had the same characters
  • the structure are complex and many elements are similar
  • the genes in two organisms share many portions of nucleotide sequence
• • analogous characteristics NOT useful in building phylogenetic trees
  • ONLY use homologous traits
• Maximum parsimony: simplest explanation of how a group of organisms came to be

  • the phylogenetic tree that requires the fewest evolutionary events (fewest number of evolutionary changes) is the most likely and most efficient
• Limitations of Phylogenetic Trees:

  • phylogenetic trees show patterns of descent, not phenotypic similarity
  • phylogenetic trees do not indicate when species evolved or how much change occurred in a lineage
  • it should not be assumed that a taxon evolved from the taxon next to it (think of sister taxa/ common ancestors)
• Clades: should be monophyletic; group of organisms should all be descendants of common ancestor like a family
• monophyletic group: ALL descendants included and no EXTRAS
• paraphyletic group: common ancestor and SOME descendants, 1 or 2 missing from the group
• polyphyletic group: descendants that DONT share a recent common ancestor
• convergent evolution: when species evolve to have similar traits due to similar environmental pressures
• outgroup: a group from an evolutionary lineage that is closely related to but not part of the group that we are studying (the ingroup)
• shared ancestral character: a character found in both the outgroup and the ingroup
• shared derived characters: characters that are unique to the ingroup
• character matrix: used to compare members of the ingroup with each other and the outgroup in an attempt to determine which characters were derived at various branch points in the evolutionary history
• character: a heritable feature that can be described or defined for an organism which can also be used to infer phylogenetic relationships
• • pay attention to branch length and the corresponding scale
  • scale can indicate time
  • in some cases, branch length doesn't matter, but if a scale is present, branch length MATTERS
• Constructing a Phylogenetic Tree:

  • phylogenies are inferred using information about the morphology, genes, and biochemistry of living organisms, and NOT only looking at physical traits
  • organisms with similar morphologies or DNA sequences are likely to be more closely related than organisms with different structures of sequences
• homologous characters: similarities between 2 groups because of inheritance or shared ancestry

  • ex: twins, as they inherited traits from their parents
• analogous: 2 groups that share similarities because of their environment, convergent evolution

  • ex: two best friends, probably similar due to their environment