Ch. 14 Evolution

Mutation

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

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

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.

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.

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.

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

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

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

Echidna (Australia)
Giant anteater (South America)
Aardvark (Africa)
Pangolin (South-East Asia)

The Molecular Clock

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

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