Download Phylogenetic Trees: Common Ancestry and Divergence

Phylogenetic Trees: Common
Ancestry and Divergence
1B1: Organisms share many conserved core processes and features that evolved and are
widely distributed among organisms today.
1B2: Phylogenetic tress and cladograms are graphical representations (models) of evolutionary
history that can be tested.
2D2: Homeostatic mechanisms reflect both common ancestry and divergence due to
adaptations in different environments
Shared Characteristics of Life
• Three main domains:
• Bacteria – prokaryotic – single celled, no nucleus
• Archaea – prokaryotic – single celled, no nucleus – closer relation to
eukaryotes – determined by looking at the rRNA (ribosomal RNA)
• Eukaryotes – contain a nucleus and other membrane bound organelles
• All three domains share:
• Same type of genetic material: DNA and or RNA
• Central Dogma: DNAmRNAchain of amino acids (aka protein)
• Metabolic pathways: ATP is the energy coinage for all three domains
• Cellular Respiration: Glycolysis, Kreb Cycle, Oxidative Phosphorylation (aka Electron
Transport Chain)
Shared Characteristics of Eukaryotes
• Endomembranes:
• Nucleus: contains the genetic material (DNA)
• Endoplasmic Reticulum: transports proteins to Golgi Complex
• Golgi Complex: packages, sorts, transports proteins
• Organelles:
• Mitochondria
• Ribosomes
• Chloroplast (only in plant cells)
• Linear Chromosomes
Phylogeny
• The evolutionary history of a species or group of species
• To construct a phylogeny biologists use systematics
• A discipline focused on classifying organisms and determining their evolutionary
relationships
• Systematists use data ranging from fossils, molecules (proteins), and genes
(DNA, mDNA, rRNA) to infer evolutionary relationships
• Info is used to construct a tree of life
• Tree continues to be refined as additions information becomes available
• Phylogenetic Tree: a branching diagram that shows the evolutionary history
of a group of organisms; represents a hypothesis
Terminology of a Phylogenetic Tree
• Branch point: represents the divergence of two evolutionary lineages from a
common ancestor
• Taxon (plural, taxa): think of it as describing the species level on a phylogenetic
tree
• Sister taxa: group of organisms that share an immediate common ancestor and
hence are each other’s closest relatives
• Rooted: brand point represents the last common ancestor of all the taxa in the
three
• Polytomy: branch point from which more than two descendant group emerge;
indicates the evolutionary relationships among the descendant taxa are not
yet clear
• Clade: is a group of organisms that consists of a common ancestor and all its
lineal descendants
How to read a phylogenetic tree
What We Can and Cannot Learn from
Phylogenetic Trees
• Sequence of branching in a tree does not indicate actual ages of the
particular species
• No assumptions should be made about when particular species
evolved or how much genetic change occurred in each evolutionary
lineage
• Cannot assume a taxon on a phylogenetic tree evolved from the taxon
next to it  we can only infer sister taxa shared a common ancestor
Morphological and Molecular Homologies
• Similarities due to shared ancestry are called
homologies
• Two main types:
• Morphological homology – similar structures due to a
common ancestor
• Genetic homology – similar DNA sequences due to a
common ancestor
Partner Share
• Will the morphological homologies match the
genetic homologies? In other words – if there is
a structural change will there be a genetic
change and vice versa?
• If the morphological homology and genetic
homology do not match then which one is more
reliable when constructing a phylogenetic tree?
Sorting Homology from Analogy
• Morphological divergences between related species can be
great and their genetic divergences small (or vice versa)
• Analogy – similarity due to convergent evolution
• Convergent evolution – occurs when similar environmental
pressures and natural selection produce similar (analogous)
adaptations in organisms from different evolutionary
lineages
• Ex: Bat wing is analogous, not homologous, to a bird’s wing
• Both organisms evolved wings; however, they came from different
common ancestors
Pair Share
•Explain the difference between
homology and analogy. Explain
why distinguishing between the
two is critical when constructing
an Phylogenetic Tree
Shared characters are used to construct
phylogenetic trees
• In constructing a tree the first step is to distinguish
homologous features from analogous features
• Second biologist place species into groups of clades
• Clade: an ancestor species and all of its descendants
• Monophyletic – consists of an ancestral species and ALL of its
descendants
• Paraphyletic – consists of an ancestral species and SOME of its
descendants
• Polyphyletic – consists of taxa with more than one ancestral
species
Shared Ancestral and Shared Derived
Characters
• Shared ancestral character – characteristic that is
shared by ALL the ancestors in the taxon including the
shared common ancestor
• Shared derived character – characteristic that is not
shared by the common ancestor but appeared later in
the evolutionary sequence
Inferring Phylogenies Using Derived
Characters
• Outgroup: a species from and evolutionary lineage that is known to
have diverged before the lineage being studied
• Ingroup: a group of species whose evolutionary relationship we seek
to determine
• By comparing members of the ingroup to each other and to the
outgroup, we can determine which were derived at the various
branch points
Let’s Practice
With the
person sitting
next to you
use the data
table to
construct a
phylogenetic
tree
2D2: Homeostatic mechanisms reflect both
common ancestry and divergence due to
adaptations in different environments
• Homeostatic mechanisms:
• Osmoregulation: process by which organisms control solute concentrations
and balance water gain and loss
• For physiological systems to function properly, the relative concentrations of water and
solutes must be kept within fairly narrow limits
• Ions such as sodium and calcium must be maintained at concentrations that permit
normal activity of muscles, neurons, and other body cells
• Excretion: breakdown of nitrogenous molecules releases ammonia, a very
toxic compound, the process of eliminating the nitrogenous waste
• Thermoregulation
• Digestive Mechanisms
• Circulatory