Transcript Systematics: The Science of Biological Diversity II

Phylogeny
• Phylogeny- the
evolutionary relationships
among organisms.
– Natural classification.
• Phylogenetic tree- a
treelike diagram that
represents a hypothesis of
the evolutionary history of
a species or group of
related organisms.
Tree of Life- Universal Evolutionary Tree
Hominid Evolutionary Tree
Tree of Homo sapiens L.
Tree Terminology
Phylogenetic Groups
Phylogenetic trees
• Cladogram
– Slanted
– Rectangular
• Phylogram- shows
divergence distances
between taxa.
Slanted
Rectangular cladogram
Phylogram
Chondracanthus exasperatus
Chondracanthus spinosus
Chondracanthus squarrulosus
Cladistics
• Cladistics- a method of
organizing organisms on the
basis of synapomorphic
characters.
– Characters- morphological,
chemical, developmental, and
molecular.
• Homologous characters- features of
different species that are similar
because they were inherited from a
common ancestor.
– Outgroup- a closely related taxon
outside the group that is being
analyzed.
– Node- the branching point on a
tree.
Molecular Characters (Data)
Lynn Margulis (1938-)
• In 1967 proposed the endosymbiotic theory
as the origin of mitochondria.
• Symbiosis in Cell Evolution.
– Included chloroplast evolution.
Endosymbiotic Theory and the
Evolution of Chloroplasts
• Photosynthetic eukaryotes and their chloroplasts evolved from
the engulfment of a cyanobacterium by a protozoan.
– A phagocytotic protozoan took up a cyanobacterium into a food vesicle.
– Instead of being digested, the cyanobacterium was retained as an
endosymbiont.
– The protozoan provided the alga with protection, a stable environment,
and mineral nutrients.
– The cyanobacterium produced carbohydrates for the protozoan.
– The cell wall of the cyanobacterium was lost through evolutionary
selection.
– Food vesicle membrane= outer chloroplast membrane.
– Plasma membrane of cyanobacterium= inner chloroplast membrane.
Support for the Endosymbiotic Theory
• Chloroplasts are about the same
size as cyanobacteria.
• Evolve oxygen in photosynthesis.
• 70S ribosomes.
• Chlorophyll A is the primary
photosynthetic pigment in
cyanobacteria and plants.
• Circular prokaryotic DNA
without histones.
• Glaucophyta
Endosymbiosis in Vorticella and Chlorella