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▼ Biology 1020 - Fall 2006 Lecture outlines
▼ Lecture 1 - Biodiversity, evolution and natural selection
▼ Introduction, Biodiversity, Taxonomy
• We will be covering a broad range of organisms
• we need some understanding of structure, which requires learning
some morphology and terminology.
• structures that distinguish groups of organisms perform particular
functions for the organisms,
• coping with the complexity of organismal diversity has always been
an overwhelming task.
▼ Biodiversity
▶ Biodiversity - what does it mean?
▶ Just how many organisms are there out there?
▼ history of the view of diversity
• even the first “scientific” classification systems are hierarchical,
with mutually exclusive categories
▶ Aristotle (384-322 BC)
▶ Linnaeus (1707-1778)
• where do species come from?
▶ Darwin’s analogy • Darwinian thinking results in us looking at diversity using an
evolutionary tree as an organizational framework
▶ examples of tree thinking
• Descent with modification
▼ Darwin (1809-1882)
• naturalist on the Beagle (1831-1836)
▼ numerous observations - Galapagos
• recent volcanic origin
• most species were unique
• most were similar to species in South America
• finches showed diversity based on different islands and different
habitats
▼ His theory of evolution
• Descent with modification
• Propinquity - nearness of relationship; kinship;
• Why are species similar to each other ? - propinquity of descent
• Why are they different from one another? - Natural Selection
▼ Natural selection
▶ differential reproductive success
▶ selection occurs through interaction between the environment and
genetic variability among individuals within the population
▶ The product of natural selection is adaptation
• Neo-Darwinism - the incorporation of genetics into the theory (1930s)
• definition of evolution: ‘any change in genetic makeup in a population
over time’
• our main purpose is to use an understanding of evolution to help in the
construction and interpretation of evolutionary trees
• evolutionary trees are based on divergence (speciation) resulting in
branches
▼ Lecture 2 - Natural Selection and Speciation
▶ Darwin’s finches again
▼ reproductive isolation leads to divergence
• as mentioned last time, the lack of migration among islands means
that changes that occur in one population via selection, drift or
whatever means, cannot be passed on to another population
• when this occurs the populations diverge
• as time passes and more differences accumulate, speciation may
occur; i.e. even if the two populations were in contact again, they
would not interbreed
• divergence in the tree is then thought to represent a speciation
event.
▼ Biological species concept
• members have the potential to interbreed in nature and produce
viable fertile offspring but are unable to produce viable, fertile
offspring with members of other populations
▼ Kinds of reproductive barriers
▶ Prezygotic
▶ Postzygotic
▼ modes of speciation
▶ Allopatric speciation
▶ Sympatric speciation
▼ Lecture 3 - Phylogeny
▼ text slides
▼ Construction of phylogenetic trees
• 1. Choose a group to study
• 2. Decide the outgroup
• 3. Choose characters
• 4. Polarize characters.
• 5. Score the characters.
• 6. Construct the most parsimonious
▼ The principle of Parsimony
• based on the idea that evolution proceeded by a smaller rather
than a larger number of events
▼ Similarity Differences define group types
▼ paraphyletic groups
• ancestral homologies (symplesiomorphies)
▼ monophyletic groups
• derived homologies (synapomorphies)
▼ polyphyletic groups
• analogies (homoplasy)
▼ The three groups can also be defined by what they include
▼ monophyletic groups
• common ancestor and all of its descendants
▼ paraphyletic groups
• common ancestor and some of its descendants
▼ polyphyletic groups
• common ancestor is excluded from the group
• if there is one true evolutionary history experienced by organisms on
earth, there there is one true evolutionary tree that reflects that history.
How can we determine what that tree is?
▼ Phylogenetic (Cladistic) methods.
▼ the branches of the tree show two aspects of evolution
▶ anagenesis
▶ cladogenesis
▶ determining the branching points
• Principle of parsimony
▼ symplesiomorphies (ancestral homologies) versus synapomorphies
(derived homologies)
• only synapomorphies show relationship
▶ symplesiomorphies show no evidence of relationship
▼ homology and analogy
• shared derived characters are homologies; they are present in
the common ancestor; ancestral characters are homologies
▶ parallelisms or convergences are analogies; they are not similar
due to common descent
▼ organisms can then be similar for three reasons
• synapomorphies (derived homologies)
• symplesiomorphies (ancestral homologies)
• homoplasy or analogies (Convergences/parallelisms)
▼ we then can therefore think of three different kinds of groups
▶ monophyletic groups
▶ paraphyletic groups
▶ polyphyletic groups
• only monophyletic groups reflect the branching pattern of the tree.
They are therefore considered the most useful.
• some of our system is still based on overall similarity (or difference)
rather than strict cladistic methodology
▼Lecture 4 Origin of Life (26) Prokaryotes (27) Origin of Eukaryotes (28)
▼ text slides
▼ Characteristics of prokaryotes
•no true nucleus - no organelles
•size varies - 1 - 5 um
•shape varies, most are unicellular, for some its not too clear
(Cyanobacteria)
•cell wall of peptidoglycan for Eubacteria
•some have a capsule; some have pili (Fig 27.4)
•motility – various methods
•metabolic diversity is greater among prokaryotes than
•reproduction via binary fission - no true sexual reproduction
eukaryotes
▼The characteristics of Eukaryotes
• membrane bound nucleus
• mitochondria, chloroplasts internal membrane system
• cytoskeleton
• flagella with 9+2 organization
• chromosomes
• meiotic life cycles (sex)
▼ The endosymbiotic theory for the origin of Eukaryotes
•mainly chloroplasts and mitochondria
•chloroplasts are descended from cyanobacteria
•mitochondria from aerobic heterotrophs
•endosymbiotic relationships still exist today
▼ Evidence for the Endosymbiotic theory
• inner membranes of organelles are similar to prokaryote
membranes
• organelles replicate in a similar fashion to prokaryotes
• circular DNA, not associated with histones, like prokaryotes
• possess components that allow DNA transcription and
translation
• possess ribosomes that are more similar to prokaryotic
ribosomes
• molecular systematic evidence (rRNA sequence data) also
supportive
▼ Implications for the Evolution of Eukaryotes
There are unlikely to be intermediates in the evolution of
organelles
The possibility of continued endosymbiosis means there could
be possible horizontal transfer across branches of the
phylogeny.
e.g. Photosynthetic eukaryotes might be
polyphyletic
▼ Origin of Life
• the age of the earth is estimated at 4.5 billion years
• 3.5-1.7 billion years ago - prokaryotes and aqueous
environments
▶ evidence for life
• how did life originate?
▼ properties of life
• Heredity - reproduction
▶ Metabolism - controlled reactions and growth
• cellular structure - membranes
▶ all three of these properties depend on long chain molecules polymers (made up of monomers)
• Miller’s studies were the first to show the formation of monomers
▼ anaerobic conditions (like in the primitive atmosphere) promote
polymer formation - some perhaps requiring a clay surface
• the formation of short RNA strands can also occur
spontaneously
• replication using existing RNA as a template has also been
demonstrated (for short strands)
• RNA can also act as an enzyme and therefore promote its own
replication (Fig. 26.7)
▼Prokaryotes (Chapter 27)
▶the origins of metabolism
•Table 27.2 compares Archaea, Bacteria, Eukarya
▶Ecology of Prokaryotes
▼Origins of Eukaryotes
•as complexity increased, compartmentalization of processes within
cells was one solution (multicellularity, and complex prokaryote
community interactions were others)
▶ compartmentalization could have arisen in 1 of 2 ways
▶ structures that needed to arise
▼
Endosymbiotic Theory (Fig. 28.2)
• mainly chloroplasts and mitochondria
• chloroplasts are descended from cyanobacteria
▶ mitochondria from aerobic heterotrophs
• endosymbiotic relationships still exist today so hypothesizing
them is not a leap
▶evidence for the hypothesis
▼
Implications for Phylogeny
▼ Lecture #5 - Diploidy, Life Cycles, Multcellularity
▼ Sexual Reproduction
• if the ancestral prokaryote had one copy of DNA in its cell, then
by outgroup comparison, the ancestral eukaryotic cell would be
haploid
▶ how did diploidy arise?
▶ temporary co-existence of the two cells may have had an
advantage under some circumstances
▶ how does the new cell divide?
• Chlamydomonas life cycle - Fig. 28.31 - know this life cycle
▼ multicellularity
▶ how did it evolve?
▶ a division of labour or specialization of cell types is possible after
aggregation
▶ not unique to eukaryotes
• evolved many times in eukaryotes
▶ why did it evolve in some lineages and not in others?
▶ life cycles of multicellular organisms
▼ Lecture #6 - Unicellular Protista
▶ Introduction to aqueous light environment
▼ Diplomonads and Parabasala
▶ DIplomonads have two nuclei and no mitochondria(Giardia is an
example)
▶ Parabasalids include Trichomonas (pathogen of humans)
▼ Euglenozoa (flagellates)
▶ Euglenids
▶ Kinetoplastids
▼ Alveolata
▶ Dinoflagellates (Fig. 28.10 - photo)
▶ Apicomplexans
▶ Ciliates (e.g. Paramecium)
▶ Stramenopila
▶ Amoebozoa (Table 28.1)
▶ Chlorophyta
▼ Lecture #7 - Complex (multicellular) Protista
▼text slides
▼ Rhodophyta
• accessory pigments (phycobilins) impart red colour
• floridean starch as a storage product
• cell wall of cellulose and sulfated polysaccharides
• no flagellated types
• mostly marine -tropical and sub-tropical
• mostly filamentous (even parenchymatous types)
• pit connections exist between cells
• many parasitic types
▼ Stramenopila
▼ Oomycota (water molds)
• large aquatic group with some terrestrial pathogens
▶ characters
▶ reproduction (Figure 28.14) - know the life cycle (gametic
meiosis)
▼ Phaeophyta - brown algae
▶ Characters
• reproduction (Fig. 28.21) - know the life cycle (sporic
meiosis)
▼ Rhodophyta
▼ characters
▶ reproduction
▶ light and photosynthesis
▶ Dulse as food
▼ Chlorophyta
• characters already discussed
• many species
• pyrenoid and eyespot in some motile forms
▶ morphological types
▶ widespread
▶ how to divide them??
▶ cell division types
▶ stoneworts and brittleworts (charophyceaen algae)