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2009 EVOLn. 2 SUMMARY
(a)
1
Explain the relationship between classification and phylogeny.
1. Classification = Binomial system (Linnaeus)
 Naming & grouping organisms into meaning sets or divisions on basis
of their common characteristics
 Binomial
system………………………………………………………………………..
2. Phylogeny
 Study of diversity of organisms with the goal of determining the
phylogeny or evolutionary history or a group of organisms
 stresses common ancestry and degree of structural differences among
divergent groups
3.
CLADISTICS
 arranges taxa in a type of phylogenetic tree called cladogram
 use of shared derived characteristics to classify organisms
 primitive character) = one that is present in the common ancestor and
all members of a group
 derived character = one that is found only in a particular line of
descent
RECENT
A
B
C
Descendents
Unique ancestor to C
Common ancestor to B & C
Shared history to B & C
Speciation event
PAST
 Characters used in cladistics can include morphology, physiology,
behaviour and DNA
 Clade = grouping that includes a common ancestor and all its
descendents
 In contrast, a paraphyletic group consists of an ancestral species and
some but not all its descendants
 A polyphyletic group includes taxa with different ancestors.
 Cladists are guided by the principle of parsimony
2009 EVOLn. 2 SUMMARY
2
 the minimum number of assumptions is the most logical
Explain how homology (ANATOMY; EMBROLOGY; MOLECULAR) –
support Darwin’s theory.
(b)

Homology refers to fundamental similarity in characteristics that occurs
due to descent from a shared ancestry.
o These characters are altered in its decedents over time as they face
different environmental conditions.

Analogy (homoplasy). Analogous structures may have similar functions
but are based on vastly different structures that are not derived from a
common ancestor. E.g. fins of fish & dolphin
o These characters are altered in its decedents over time as they face
similar environmental conditions.
1.
Vertebrate forelimb / pentadactyl limb
 Evolutionarily related species may possess homologous structures that
have been modified in ways that allow them to be used differently by
each species.
 In some cases, such structures are no longer needed and degenerated
to non-functional vestigial structures.
 (humerus) is attached to (ulna & radius), several small carpals,
metacarpals, attached to five digits
 Modified to flippers in dolphins; wings in bats, digging in moles,
grasping in primates
 Organisms having vestigial structures share a common ancestry with
organisms in which the structure is functional.
 When selection forces that keep the structure in functional condition is
no longer present, the structure may degenerate over many
generations.
2.
EMBRYOLOGY
 The more closely related organisms are, the longer the embryological
development remains similar
 Pharyngeal gill slits link phylogeny of humans to fishes;
 post anal tail link man to fish reptiles birds
 Notochord retained as vertebral discs link humans to chordates
3.
MOLECULAR

At the molecular level, certain characteristics are found in all living
cells, suggesting all living species are derived from a common
ancestor.
-
All living species use DNA to store information.
-
RNA molecules are used to access that information.
-
Proteins are the functional products of most genes.
2009 EVOLn. 2 SUMMARY
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-
All species that use oxygen have similar proteins that together
make up an electron transport chain and an ATP synthase.
-
Nearly all organisms can metabolise glucose via the glycolytic
pathway.
 In addition, species that are closely related tend to have DNA or RNA
sequences, amino acid sequences that are more similar to each other
than to those distantly related.
 E.g. p53 protein that plays a role in preventing cancer.
 E.g. amino acid sequence in beta haemoglobin protein, cytochrome c
(c)
How do biogeography & the Fossil record support evolutionary
deduction based on homology
Biogeography is the study of the geographical distribution of extinct and
modern species.
Biogeography shows that unique species found on islands and other remote
areas have arisen because the species in these locations have evolved in
isolation from the rest of the world.
1.
ISLAND BIOGEOGRAPHY e.g. Darwin’s finches
 Ancestor = mainland ground finch
 On the Galapagos, finches diversified in absent of other bird species 
no competition form other forms. [ref to Evoln. 1 summary]
 Adapted to diverse niches available
 Mainland  these habitats occupied by different species birds present
2.
CONTINENT BIOGEOGRAPHY e.g. Australian marsupials
 Marsupials found in Australia, south America Australia
 Arose before placentals
 Diversified and adapted to all niches because of lack of competition by
placentals
 Australia separated by ocean from other continents where placentals
were found due to continental drift.
Convergent evolution
 To an astonishing degree, Australian marsupials resemble placental
mammals living in other continents. They are the result of convergent
evolution - similar forms from different ancestry having evolved in
different isolated areas because of similar selective pressures in
similar environments
3.
CONTINENT DRIFT
 The drifting apart of landmasses splits up organisms by the
development of oceanic barriers, isolating descendent populations,
which then evolve to form new taxa. (This is an example of allopatric
speciation. Ref. to Evolution Pt.1)
2009 EVOLn. 2 SUMMARY
4.
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FOSSIL RECORD
Fossils are relics or impressions of extinct organisms preserved in rock.
Are highly suggestive of evolution from common descent as they show:
 older forms are simpler than newer forms;
 The number of species increases with time


HORSES
o The earliest form of the horse were small (the
size of dogs), with short legs and broad feet.
Had low crown teeth
o Features adapted to wooded habitats, browsing
on leaves and herbs and escaping predators by
dodging through the forest vegetation.
o
Modern horses evolved to open grasslands.
Increased in size, toe reduction and high crown
tooth.
o
He increase in size and changes in foot structure
allowed horses to escape predators and travel
great distances in search of food. Changes in horse teeth are
consistent with a shift in diet from tender leaves to grasses that need
more chewing.
Transitional Fossils link older fossils to modern species
 Archaeopteryx – intermediate between dinosaurs and birds
 Jaws with teeth, long bony tail, gait link it to carnivorous dinosaurs
 wings with feathers link it to birds
(d)
Advantages of molecular (nucleotide; aa sequences) methods in
classification
1.
All known life is based on nuclei acids thus studies involving any types
of taxa can use DNA sequence data.
2.
They can be used to compare species so phylogenetically distant that
they share very few morphological similarities.
3.
They are objective and quantitative. Molecular character states are
unambiguous (e.g. A, C, G and T)

May be used to measure degree of relatedness quantitatively
4.
Amino acid sequences for many proteins and nucleotide sequences for a
rapidly increasing number of genomes can be accessed from large
electronic databases and used for comparative study and classification.
5.
Offers an enormous set of characters to be studied. Each nucleotide
position can be considered a character and each organism has millions to
billions of nucleotide positions.
6.
Molecular data are easily converted to numerical form and hence are
amenable to mathematical and statistical analysis.
7.
avoid pitfalls of convergent evolution.
2009 EVOLn. 2 SUMMARY
(e)
5
Explain how recessive alleles may be preserved in a natural population
1. Diploidy
 Recessive alleles which are less favourable are propagated in
hetrozygote condition
2.
Heterozygote advantage e.g. sickle cell
 Presence of plasmodium causes rbc to rupture stopping life cycle
 Cystic fibrosis – malfunction of Cl- transport protein – lungs, digestive
system; maintain water equilibrium in cells
-
3.
Higher survival to diarrhoea
Inbreeding
 When relatives mate  higher chance of homozygosity of recessive
alleles
(f) Describe the neutral theory of molecular evolution
1.
MOLECULAR CLOCK
 neutral mutations occur at a relatively constant rate thus they can act
as a molecular clock
 gene sequences of the species accumulate independent mutations
after they have diverged from each other; a longer period after
divergence allows for a greater accumulation of mutations.
 Because the relationship between Nucleotide differences in
homologous genes between pairs of species and time is linear we can
predict when a pair of species have diverged from each other
2.
NEUTRAL THEORY
Kimura’s neutral theory of evolution states that most genetic variation (in
a population) is due to the accumulation of neutral mutations (at the
molecular level). These mutations have attained high frequencies in a
population via genetic drift.
 Neutral mutations involve changes in genotypes that do not affect the
phenotype of the organism.
 nucleotide substitutions are more prevalent in the third base than in the
first or second base.
 Mutations in the third base are often neutral because they do not
change the amino acid coded for.
 In contrast mutations at the first or second base are more likely to be
harmful than beneficial and tend to be eliminated from a population.
 When mutations do change the coding sequence, they are more likely
to involve conservative substitutions. E.g., the difference between two
alleles of a given gene may be the replacement of a nonpolar amino
acid with another nonpolar amino acid. This change is less likely to
affect protein function.

Favourable mutations are rare, and detrimental mutations are likely
to be eliminated from a population by natural selection.
Darwin vs. Neutral theory
2009 EVOLn. 2 SUMMARY
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Darwin: Genetic variation in a population is the result of natural selection.
Natural selection selects for the fittest phenotypes thus beneficial
alleles get established in the population.
Neutral theory: Genetic variation in a population is due the accumulation of
neutral mutations. These mutations get established in the population
by genetic drift.
Kimura agreed with Darwin that natural selection is responsible for
adaptive changes in a species during evolution.