anatomical characters important in systematics -
data typically only available for extinct organisms
deciding number of independent
character differences
DNA sequence data - changes at
several sites might be likely to evolve in
concert to preserve function
DNA sequences must be aligned so
homologous sites can be compared
homoplasy is common
data set may yield several different phylogenetic
estimates that are equally as good
unwise to rely on particular phylogenetic
estimate if other hypotheses imply just a few
extra evolutionary changes
try to get more data on other
characters instead
process of evolution often
erases traces of prior
evolutionary history
is studied taxa diverged long ago or evolved very
rapidly many characteristics will have diverged so
much that homologous characters difficult to discern
eg teeth useful for determining relationships
between many mammals but can't use to assess
relationship of toothless anteater
earlier synapomorphies erased from
DNA sequences by multiple
substitutions occurring at a site
evidence of common ancestry lost if
mutation occurs at site multiple times, eg
A to C then C to G
more likely for same substitution to
occur in parallel in different lineages as
time passes
convergent evolution & successive substitutions cause
amount of sequence divergence between taxa to level off
rapidly evolving DNA sequences
useful for phylogenetic analyses
of taxa that diverged recently
slowly evolving sequences
required to assess
relationships among taxa that
diverged in distant past
some lineages diverge so rapidly little
opportunity for ancestors of each
monophyletic group to evolve distinct
synapomorphies
ADAPTIVE RADIATION
evolutionary radiation associated
with marked adaptive diversification
EVOLUTIONARY RADIATION
episode of significantly
sustained excess of
cladogenesis over extinction
CLADOGENESIS
splitting of lineage into 2 or
more descendant lineages
HYBRIDISATION
offspring from interbreeding from 2
different populations or species
usually transfers genes
between populations or species
HORIZONTAL /
LATERAL GENE
TRANSFER
usually incorporates just a few genes of one
species into the genome of another species
(contrasts to hybridisation)
very important in evolution of bacteria - responsible
for providing genes for antibiotic resistance
usually through viruses (natural) or
genetic modification (human
intervention)