Types of mutation
Point mutations
Change in a single DNA nucleotide
Substitution
Insertion
Deletion
Block mutation
Changes to a segment of a chromosome
Deletion
Duplication
Inversion
Translocation
Aneuploidy
Changes in number of chromosomes
2
Point mutations - substitution
A change in a single base can have dramatic phenotypic
effects
eg. Sickle Cell Anaemia
A change in a base will alter the codon transcribed
So an entirely different amino acid could be added to a protein
chain
AAA = Lysine
AAU = Asparagine
Alternatively, seeing as multiple codons code for a single amino
acid, it could have no effect at all
AAG = Lysine
3
Point mutations insertion / deletion
Can have far more dramatic effects than a substitution
A new nucleotide is inserted in to or deleted from an existing gene
sequence
AUG CCU GGA GUA
met pro glyval
AUG CAC UGGAGU A
met his trp ser
This is called a shift in the reading frame
4
Block mutations
The rearrangement of entire blocks of code in a gene
Normal
Deletion
Segment lost
Duplication
Inversion
Translocation
5
Aneuploidy
Please examine the following karyotype, chromosomes are in
numerical order
This individual has 3 copies of chromosome 21.
A condition known as Trisomy 21 or Down Syndrome
6
Evolution
changes over time
Evolution
There are currently ~30 million species on the planet and many
times more than this that have existed at some time in the
past
Evolution is only a theory in the same sense as atomic theory or
the theory of general relativity
It is based on the same solid scientific data as any other
established truths (ie. gravity)
Development of evolutionary theory
Erasmus Darwin
Father of Charles Darwin
Believed that all living things were derived from a single common
ancestor
...but could not suggest a mechanism for how this could have
ocured
Development of evolutionary theory
John Baptiste Lamarck
Believed that acquired characteristics could be inherited by the
next generation
Through the use or disuse of structures, an organisms appearance
could change over time
Development of evolutionary theory
Charles Darwin &
Alfred Russel Wallace
Developed the current accepted theory of evolution via natural
selection
Could not describe a mechanism of inheritance, even though their
work was preceded by that of Gregor Mendel
How old is the Earth?
According to James Usshers biblical calculations the earth is
approx. 6000 years old (created on the evening of 23 October 4004
BC)
Clair Pattersons accurate and reliable dating of an iron meteorite
places the age of the Earth closer to 4500 million years
old.
The relative age of rocks
The age of rocks can be expressed in relative or absolute
terms
The rule of superposition states that the relative age of a
stratigraphic layer of rock can be determined by being aware of the
order in which these layers were deposited
The relative age of rocks
The rule of correlation states that the relative age of rocks can
be determined by the presence of indicator fossils
These are of short-lived species of which existed at a known period
in the earths pre-history
The absolute age of rocks
Radiometric dating is based on the decomposition of particular
unstable elements found in the rock layers.
The absolute age of rocks
Each element has a known half-life, ie the time taken for 50% of
the mass of the unstable parent element to decompose to a stable
daughter element.
The absolute age of rocks
As the daughter element is usually a gas, one cannot determine the
original mass of the parent element from the remaining mass.
The unstable element exists in set ratios with its stable isotope.
ie 0.012% of Potassium found in feldspar is P-40, so the original
amount of potassium can be determined by the mass of the stable
P-39.
Specific dating method are useful only for rocks containing the
particular unstable element, and only if the half-life is of
appropriate length.
Eg. Carbon-14 dating, with a half life of 5730 years is not usesul
for material older than 60,000 years.
The absolute age of rocks
Electron spin resonance is useful for organic material 50,000
500,000 years old
When materials are buried, they accumulate high energy electrons at
a particular rate.
These electrons are returned to a ground state by exposure to fire
or sunlight.
So we are able to determine how long it has been since the
electrons in the material were in a ground state, and therefore how
long they have been buried.
Evidence of evolution
The fossil record
Transition fossils
Comparative biochemistry
Comparative anatomy
Bio-geographic distribution
The fossil record
A very small percentage of individual organisms are fossilised, the
conditions have to be perfect.
Burial needs to be very rapid in alkaline or oxygen poor water or
soil.
Fossilised bone, teeth, shells, etc, are considered direct
evidence.
Footprints, teeth marks, coprolites (fossilised dung), etc are
considered indirect evidence.
The fossil record
The fossil record details the evolution of horses over time.
All its ancestors have since ceased to exist, but members of the
genus Equus persist.
This includes numerous species of horses, donkeys and
zebras
Transitional fossils
Every current species evolved from an extinct but previously
successful ancestor, so it is logical that there must have been
transitional species in between.
A prime example is the transitional fossil between birds and
dinosaurs
Archaeopteryx
Comparative anatomy
Fossils bearing homologous structures as their origin can be traced
to a common ancestor.
The same cannot be done with analogous structures (independently
developed for a similar purpose (eg. bats wing and flys wing)
Mammalian
forelimb
Knee
Ankle
Toe
Toenail
Homologous structures in locomotion
Comparative anatomy
Vestigial structures will also give clues to an animals origin. A
disused structure will take a long to to completely dissappear (eg.
nestigial hind limbs in whales)
Homeotic genes may prevent the development of disused structures in
adults but evidence of these structures can still be found in
embryos (eg. Non-functional gill slits in terrestrial vertibrates
(some reptiles, birds and mammals comparative
embryology.
Comparative biochemistry and genetics
Evolution predicts that the more similar two species are, the more
biochemical and genetic similarities there will be.
It is already curious that all species share the same amino acid
building blocks for proteins
As well as the same sucleotide building blocks for DNA
The protein, haemoglobin
Fish
Goose
Human
Worm
Pig
Molecular studies
Amino acid sequence studies
The tables below represent the number of differences in amino acid
subunits in a) the chain of haemoglobin and b)cytochrome C
a)
b)
DNA Hybridisation
DNA from two species is mixed and cut by restriction enzymes to a
length of ~500 bp
Heat is applied to separate the strands
Solution is cooled to allow single strands from each species to
hybridise to each other.
Heat is again gradually applied, hybrid strands with a higher
degree of complementarity will have a higher melting (separation)
point than strands with a lower degree of
complementarity.
DNA hybridisation
Data obtained for primates using DNA hybridisation
Data can be calibrated using the fossil record and used to create a
phylogenic tree of inferred evolutionary relationships.
Other techniques
Comparison of DNA sequences
Greater understanding from comparing entire genome instead of
single genes
Comparison of chromosomes
Can compare with regard to number and banding pattern
Carried out via karyotype analysis
Led to the discovery that chimpanzee chromosomes #12 and #13 fused
to form the human chromosome #2,
Biogeographic distributions
Evolutionary perspective
If all the Earths creatures were created then why arent similar
species found in similar environments around the world?
Australian desert dwelling animals should display greater
similarity with African desert dwelling animals rather than
Australian rainforest dwellers, yet it is the other way
around!
Biogeographic distributions the expectations
1. native species in different isolated regions will be
distinctive, having evolved from different ancestral species
This can be seen in any island including Australia.
Species display distinct features, often found only in that
particular location
Biogeographic distributions the expectations
2. modern species native to a given region will be more similar to
species that lived in that region in the geological past than to
modern species living in a distant region with similar
environmental conditions
This can be seen in the fossil record
There are far greater similarities found between current and
prehistoric Australian fauna than with animals found in other
countries
Biogeographic distributions the expectations
3. the same ecological niche in different isolated regions will be
occupied by different species (that are descended from different
ancestral species that once lived in that region).
A distinct ecological niche is that of ant eating mammals.
They exist around the world but bear greater similarity to their
geographical ancestors than to each other
The molecular clock
Used to calculate evolutionary distance between two current
species
This evolutionary distance represents the time (in millions of
years) since they diverged from a common ancestor.
A protein is selected and the number of differences in the amino
acid sequence between two species is recorded
Table of amino acid differences in the haemoglobin protein (by
percentage)
The molecular clock
Changes in AA sequences have been discovered to change at a steady
rate
If accurate data on the time of emergence for one or two species
exists in the fossil record, the clack can be calibrated
The calibrated clock converts relative data in to absolute
data
The data
Time scale of clock must be adjusted as large % differences are an
underestimate due to amino acids being changed, and then changed
again.
The molecular clock
Caution is advised when using data as it is not without its
problems
The rate of change with regard to amino acid sequences has been
found to be different for different species.
Also the rate of change (per amino acid) is not the same for all
proteins
Patterns of evolution
Divergent evolution
Convergent evolution
Parallel evolution
Co-evolution
Divergent evolution
An ancestral species can give rise to multiple new species (from
different founder populations)
These new species will adapt to the individual environments in
which they live and may eventually look quite different to each
other
The ancestral species is gradually replaced in all locations by its
more competitive evolutionary product
American hares
These two species evolved from a more generalised hare, but to two
very different environments
Snowshoe hare
Lepusamericanus
Alpine regions
Black-tailed jack rabbit
Lepuscalifornicus
Desert regions
Adaptive radiation
Adaptive radiation will occur when an ancestral species will give
rise to multiple evolutionary products, all evolving to suit a
different environment
Eg. Darwins Galapagos finches
Convergent evolution
The result of unrelated organisms developing similar features due
to similar environmental conditions.
The resulting structures will serve similar purposes but will have
had completely separate evolutionary origins.
Eg both Arctic and Antarctic fish (unrelated) have developed
glycoproteins that act as a natural anti-freeze. These are produced
by totally different genes.
Example #1 the opposable digit
The primate thumb was formed by one of the 5 digits in the forelimb
migrating down towards the wrist.
This evolutionary development is shared by all monkeys, apes and
humans (due to it being present in a common ancestor)
In a completely separate evolutionary incident, koalas had two
of their five digits migrate down towards the wrist
The original 5 forward-facing digits were present in the common
ancestor of virtually all mammals
The panda started with the original 5 digits and then a 6th
digit developed from the radial sesamoidbone in the list
enlarging.
This phenomenon of similar environmentally induced requirements
resulting in simillar morphological developments is called
convergent evolution
Well developed sagittal crest
An African mammal of Order Carnivora
Spotted Hyena
An Australian mammal of Order Dasyuromorphia
Tasmanian devil
Well developed sagittal crest
An African mammal of Order Carnivora
Spotted Hyena
An Australian mammal of Order Dasyuromorphia
Tasmanian devil
Parallel evolution / Co-evolution
Occurs when two species have such a close interaction that they
steer each others evolution in a particular direction.
A good example is flowers and insects, their physical forms are
uniquely adapted to maximise their benefit from thei interaction
with each other.
eg. flowers produce pheromones to attract insects
eg. insect mouth parts adapt to the shape of flowers
Speciation
The result of time and the necessity to adapt to changing
environmental conditions
Phyletic evolution 1 species evolving in to a new form
Branching evolution 1 species gives rise to two or more unique
forms
Allopatric speciation The result of members of the original
population becoming geographically isolated
Evolution: gradual or intermittent
Darwins theory states that evolution is the result of gradual
changes accumulating over time.
Gould & Eldridge proposed the theory of Punk Ekk(Punctuated
Equilibrium)
Long periods will pass with no changes occurring
When the appropriate conditions arise, change occurs at a rapid
pace
The adapted species quickly replace those less suited to the new
environment
The fossil record appears to lend some support to this
theory
Extinction
Can occur as a result of:
Loss of habitat / food
Competition / predation
Can be as the result of a catastrophic event. The asteroid that is
believed to have hit Mexicos Yukutan Peninsula 65 mya wiped out 70%
of the species that nhabited the earth at that time
The asteroid would have been 10-20km in diameter, causing a crater
180km wide
The death toll
Humans have been responsible for the vast majority of the worlds
recent extinctions
In the last 200 years, Australian species account for 50% of the
worlds extinctions
What do these names mean to you?
The last 10 large animals we lost
Comparitive genomics
Advancing technology now gives is the ability to sequence and
compare the entire genomes of organisms rather than individual
genes.
Computers are required to compare these vast quantities of genetic
code
This graph displays various species % of alignment with the human
genome