Chapter 26 Bio

Classification of Organisms

  • Taxon: a named group of organisms

  • Taxonomy: the science of classifying and naming organisms

  • Systematics: the science of classification of organisms and evolutionary relationships between organisms

  • Phylogeny: evolutionary history of a species or related groups

  • Phylogenetic Tree: branching diagram that represents a hypothesis about the evolutionary history of a group of organisms

  • Phylogenetics: study of the reconstruction of evolutionary relationships among organisms

  • Genus and species make up binomial nomenclature

  • Family: group of related genera

  • Order: group of related families

  • Class: group of related orders

  • Phylum: group of related classes

  • Kingdom: related phyla

  • Domain: highest level of classification

Phylogenetic Trees

  • Shows common ancestry and evolutionary history of groups of organisms

  • Parts of phylogenetic trees:

    • Common ancestor

    • Evolutionary lineage

    • Ancestor in the lineage

    • Sister taxa

Binomial Nomenclature

  • Biologists use a hierarchical binomial system for classifying organisms (binomial nomenclature)

Tree Terminology

  • Taxa/tips: individual species

  • Node: represent ancestor shared by specific groups of taxa

  • Branch: represents evolutionary lineage

  • Root: common ancestor of all taxa in tree

  • Outgroup: related to all species but not part of group of interest

  • Sister Taxa: two taxa that share a more recent common ancestor with each other than with any other taxon

Phylogenetic Terminology

  • Groups of Organisms:

    • Monophyletic (clade): includes most recent common ancestor and all descendants (occur at each node)

    • Paraphyletic: includes most recent common ancestor but not all descendants

    • Polyphyletic: does not include most recent common ancestor

  • Cladistics: approach to systematics that uses common ancestry to classify organisms

Shared Traits

  • Homology: “homo” = same; “ology” = study of

  • Analogy: phenotypic and genetic similarities without shared ancestry, due to convergent evolution

  • Convergent Evolution: occurs when similar environmental pressures and natural selection produce similar (analogous) adaptations in organisms found in different evolutionary lineages

  • Homologous Traits: similarities shared due to ancestry

  • Analogous Traits: similarities shared due to convergent evolution

  • Shared Ancestral Character: shared trait that originated in the ancestor of the taxa

  • Shared Derived Character: trait shared by all members of the taxa but not the ancestor of the taxa

  • Synapomorphy: trait shared by all members of the taxa but not the ancestor of the taxa

Parsimony

  • Maximum Parsimony: assumes that the most likely tree is the one that requires fewest evolutionary events

  • If Homologous

    • 1 origin of trait and 5 losses

  • If Analogous:

    • 2 origins and 0 loses

Synapomorphies

  • Synapomorphies: homologous trait that is shared among certain species and is similar because it was modified in a common ancestor

Outgroups

  • Outgroups: group of organisms that is outside of the monophyletic group under consideration but closely related to that group. Can be used to infer the ancestral states of characters

Phylogenetic Branch Lengths

  • Can be proportional to time and genetic changes

  • Maximum Likelihood: identifies tree most likely to have produced a given set of DNA based on probability rules about how DNA changes over time

    • Compares many trees and identifies trees that require fewest evolutionary changes

Phylogenetic Trees as Hypotheses

  • Phylogenetic Bracketing: predicts that features shared by two closely related groups will be present in their ancestor and all its descendants

Organisms Evolutionary History

  • DNA that codes for rRNA changes slowly

    • Can be used to investigate relationships between species that diverged millions of years ago

  • mtDNA evolves rapidly

    • Can be used to investigate relationships between closely related species and even within species

Trees Can Be Built With Molecular Data

  • Sequence DNA

    • Whole genome

    • Genes of interest

  • Align DNA sequences and compare differences

  • Build trees that minimize mutations (maximum parsimony)

Gene Duplications and Gene Families

  • Gene Duplications: increase the number of genes in the genome and provide opportunities for evolutionary change

  • Gene Families: groups of related genes within an organism’s genome

  • Orthologous Genes: homology is the result of speciation

    • Same gene, different species

  • Paralogous Genes: homology is the result of gene duplication

    • Same species, different gene

Molecular Clock

  • Molecular Clock: used to estimate the absolute time of evolutionary change, allows us to date phylogenetic trees built with genetic data

Classification of Life

  • Eukaryotes

    • Domain Eukarya - plants, fungi, animals

  • Prokaryotes

    • Domain Archaea

    • Domain Bacteria