1. Speciation occurs through changes in allele frequencies in a population's gene pool over many generations, driven by factors like natural selection, genetic drift, and geographic isolation of populations.
2. Reproductive isolating mechanisms like temporal, ecological, behavioral, and mechanical barriers prevent interbreeding between species and maintain genetic integrity of gene pools.
3. Adaptive radiation and divergent evolution describe how a single ancestral species can evolve into many new species adapted to different ecological niches or environments through natural selection.
Phylogeny
1
`
http://biology-forums.com/gallery/33_14_08_11_11_21_00_15201243.jpeg
Outline:
Introduction to Phylogeny
Lab Explanation
Lab Time!!
2
You’re going to look at the changes in organisms through time, in the image here the Top of the tree is today
http://elephant.elehost.com/About_Elephants/Stories/Evolution/ancestry.gif
Phylogeny:
The evolutionary development and diversification of a species, or group of organisms, or of a particular feature (characteristic) of an organism
All organisms can be classified
3
Phylogeny is the evolutionary development and diversification of a species
This allows us to classify and identify all organisms
All organisms are connected by the passage of genes along the branches of the phylogenetic Tree of Life
http://tolweb.org/tree/learn/concepts/ConceptsImg/LeavesAndAncestors.jpg
Classification:
Classification of organisms = Taxonomy
There are three main Domains:
Bacteria
Archaea
Eukaryotes
Which two are the
most similar?
4
The classification of organisms is called taxonomy
It is based on distinguishing characteristics
There are 3 Domains, Bacteria, Archaea, and Eukaryotes, which we belong to.
Which two seem to be the most similar?
Carl Linnaeus:
Developed modern taxonomical system
Hierarchical system of classification
General
Specific
Do
KEEP
POND
CLEAN
OR
FROGGY
GETS
SICK
5
So who came up with all of this?
Carl Linnaeus, developed the hierarchical system of classification
It goes: Domain, Kingdom, Phylum, Subphylum, Class, Order, Family, Genus, Species
It starts with the most commonly shared characteristics to species specific characteristics
And can be remembered by the following rhymes, my favorite is
Keep Pond Clean Or Froggy Gets Sick
http://www.icr.org/i/articles/af/linnaeus_found_wide.jpg
http://savannahthecell.weebly.com/uploads/1/3/4/0/13403173/443151711.jpg
6
Now coming back to the three Dominans, which two are most closely related based on their genetics?
Here you can see looking at the tree of life, based on their genetics, the Archaea are more closely related to the Eukaryotes.
Taxonomy of Art:
Kingdom
Phylum
Class
Order
Family
Genus
species
But you’re not going to look at genetics in class today, instead you will be looking at physical characteristics to classify different organisms and then specifically with fish.
I’m going to start off with something that will hopefully be more relatable to you, looking at the a classification of music.
So we start in the Domain of Art, within art there are three kingdoms…
7
Phylogenetic Tree:
Taxonomic classifications reflect phylogeny
Phylogeny Evolutionary History of Organism
Species with similar characteristics have a common ancestor
Greater resemblance, more recent divergence
8
This classification system reflects the evolutionary history of an organism, which is phylogeny.
Taxonomy and Phylogeny are very closely related.
Each species can be traced bac ...
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2. D.2.1 Define allele frequency and gene pool
al·lele fre·quen·cy gene pool
Allele frequency is the proportion Noun: The total collection of
of all copies of a gene that is different alleles in an interbreeding
made up of a particular gene population.
variant (allele).
Example
Say if a recessive allele h made up
2% of the total in a human …then the dominant allele H
population… would make up 98%.
The frequency for h would be expressed as 0.02 and for H 0.98
Recessive allele frequency + dominant allele frequency = 1
(for characteristics determined by two alleles)
http://www.flickr.com/photos/limowreck666/171979083/
3. D.2.2 State that evolution involves a change in allele frequency in a population’s gene pool over
a number of generations
New combinations of
alleles lead to new
phenotypes that can
then be selected for or
against by the
environment.
This leads to
evolutionary change in
the species
5. D.2.3 Discuss the definition of the term species
Ecological species
There are many definitions, A set of organisms adapted to a particular set
of resources, called a niche, in the
here are five! environment.
Genetic species
Based on similarity of DNA of individuals or populations. Having a common gene pool.
Evolutionary species
A group of organisms that shares an ancestor; a lineage that maintains its
integrity with respect to other lineages through both time and space. At some
point in the progress of such a group, some members may diverge from the main
population and evolve into a subspecies.
Lots to discuss if you get a
Cladistic Species question about this!
A group of organisms that shares an ancestor; a lineage that maintains its
integrity with respect to other lineages through both time and space. At some
point in the progress of such a group, members may diverge from one another:
when such a divergence becomes sufficiently clear, the two populations are
regarded as separate species. (This differs from the Evolutionary definition in
that the parent species goes extinct when two new species are recognised).
Breeding Species
Two organisms that are able to reproduce naturally to produce
fertile offspring of both sexes.
http://en.wikipedia.org/wiki/Species
6. The genetic definition is most widely
used and works well for most
multicellular organisms
The following 4 slides outline the
exceptions:
…is anything ever simple in Biology?
7. Hors
d’oeuvre?
It could be (ahem)
physically impossible
for members of the
same species to mate.
Therefore they are
genetically isolated.
http://www.flickr.com/photos/lepetitblonde/2247963815/
8. 1 : Lesser Black-backed Gull
2 : Siberian population Black-backed gull
3 : Heuglin's gull
4 : Birula's Gull
5 : East Siberian Herring Gull
6 : American Herring Gull
7 : Herring Gull
Ring Species:
Adjacent populations
can interbreed but the
populations at the “end
of the line” cannot.
1 and 7 cannot
produce offspring. So
close…
…and yet
so far :’(
http://commons.wikimedia.org/wiki/File:Ring_species_seagull.svg
9. Hybrids are usually infertile and can not produce offspring together,
for example the mule (63 chromosomes): a cross between a Male Why are 63
horse (64 chromosomes) and a female donkey (62 chromosomes) chromosomes a
problem when
The liger is a hybrid cross between a male Panthera leo (lion), and a female reproducing?
Panthera tigris (tiger) and is denoted scientifically as:
Panthera tigris × Panthera leo.
The tiglon is a hybrid cross between a female Panthera leo
…conversely… (lion), and a male Panthera tigris (tiger) and is denoted
scientifically as: Panthera leo × Panthera tigris.
Ligers and tiglons sometimes
produce offspring when mated
back with a parent species
e.g. The hybrid of a male lion
and a female tiglon is a li-tiglon!
MADNESS!!
http://xkcd.com/419/
10. The genetic definition
only applies to sexually Rats!
reproducing organisms
and doesn’t apply to
single-celled organisms
http://www.flickr.com/photos/microagua/3721497804/
11. Additionally:
Fossil remains can’t tell us whether
species were able to interbreed or
produce viable offspring so
palaeontologists tend to use the
cladistic definition
http://www.flickr.com/photos/bruce_mcadam/1393218574/
12. D.2.4 Describe three examples of barriers between gene pools
The circumstances preventing different species from
interbreeding are known as reproductive isolating mechanisms
13. Temporal isolation
Pinus radiata (Monterey Pine)
MAX Pinus attenuata (Knobcone pine)
Pollen Production
J F M A M J J A S O N D
Month
Pinus radiata and Pinus attenuata are prevented from hybridising because
they have separate pollination times.
They can be made to hybridise by pollinating them manually.
*Random fact: The Monterey pine is at risk in it’s native range but
is one of the most common plantation trees in the world. If you
see a pine forest in Australia or NZ, it is probably Pinus radiata
http://www.flickr.com/photos/alancleaver/4293345631/
14. Ecological isolation
The two species are in the same area, but live in different habitats
I love me
some
CaCO3 in
my soil
Blechhh!
Acidic soils
are more my
thing
Viola arvensis Viola tricolor
http://www.flickr.com/photos/annetanne/3035068940/ http://www.flickr.com/photos/carinemily/644052381/
15. Behavioural isolation
Animals exhibit courting behaviour (song,
dance etc.) or release pheremones to
attract mates. Individuals are only attracted
to, and will only mate with, members of the
opposite sex who perform the appropriate
ritual or release the correct chemical.
Yo! I don’t like
your music!
Its like,
totally
mutual!
http://www.flickr.com/photos/nrk-p3/2333221093/ http://www.flickr.com/photos/rowelbg/2895578034/
16. Mechanical isolation
Animal example:
Different species of bush baby (Galago) have particular shapes for their genitalia
and they are physically incapable of copulation*.
It is like a
lock and
key.
She says “We’re
not a good fit”.
In plants, mechanical isolation occurs What is that
when different species have different supposed to
pollinators that are not able to service mean?
the flowers of other species
*Take care when Googling “Bush baby genitalia”!
http://www.flickr.com/photos/joachim_s_mueller/4113758487/
18. D.2.5 Explain how polyploidy can contribute to speciation
So far you’ve learnt that cells contain two homologous sets of chromosomes.
Well….. that isn’t always the case.
It goes on:
Pentaploid
Hexaploid
Septaploid
Octaploid
Etc.
up to:
84-ploid and 1260
chromosomes
Ophioglossum reticulatum
A small fern.
The incredible thing is that this plant is
able to carry out meiosis accurately with
1260 chromosomes to divvy up
http://commons.wikimedia.org/wiki/File:Haploid,_diploid_,triploid_and_tetraploid.svg
19. How it happens:
Remember: Self
When non-disjunction occurs fertilisation
during meiosis in humans, an
individual can end up with an extra
chromosome or missing
chromosomes.
E.g. An extra chromosome 21
means Downs syndrome (see 4.2.4)
Total non-disjunction, is when one of the
two cells produced during Meiosis I gets
all of the chromosomes. The other cell is
not viable and is reabsorbed.
This results in two (2n) daughter cells
from meiosis instead of the usual four (n)
daughter cells.
See animation
http://commons.wikimedia.org/wiki/File:Polyploidization.svg
20. Few polyploid organisms exist in the animal kingdom.
Can you think of the reasons why not?
Animal polyploid species include salamanders, goldfish and
salmon.
However, polyploidy is a great source of speciation amongst plants.
Polyploidy often leads to
increased size, resistance to
disease and overall vigour.
Many plants used by humans are
polyploid. Including cereal crops
like wheat.
Polyploid crops generally have
bigger fruits, seeds and storage
organs
21. Two versions of Polyploidy:
• Autopolyploidy*
• Allopolyploidy
*This is not autopolyploidy
http://www.flickr.com/photos/leapkye/3224058317/
22. Autopolyploidy (Auto = “self”)
• Autopolyploids are polyploids with multiple chromosome
sets derived from a single species as described a couple of
slides ago.
• Autopolyploids form following fusion of 2n gametes
• Autopolyploidy can be induced in plants using colchicine, a
chemical extracted from the autumn crocus.
• Autopolyploids with odd ploidys eg triploid or pentaploid
have trouble reproducing sexually WHY?
• That does not stop them from being good crops if they can
be propagated asexually
23. Allopolyploidy (Allo = “different”)
Allopolyploids come about when a sterile F1 hybrid doubles all of its
chromosomes and becomes fertile.
For example, Triticale is the hybrid of
wheat (Triticum turgidum) and rye
+ = (Secale cereale). It combines sought-
after characteristics of the parents, but
the initial hybrids were sterile until
doubling of the number of
Wheat Rye Triticale
chromosomes occurred
Remember the poor sterile mule with 63
chromosomes?
Imagine if we could somehow induce sperm and
ova with 126 chromosomes
Voila! The mule born would be fertile.
Of course, it would need to be done a couple of
times to get a few mules to breed together
http://en.wikipedia.org/wiki/File:Wheat,_rye,_triticale_montage.jpg http://jonathanturley.org/2009/03/01/a-happy-mule/
24. D.2.6 Compare allopatric and sympatric speciation
Allopatric speciation (Allo = “different”, patric = “fatherland”)
This arises when a species is subject to geographic isolation.
This can occur when a population is split by:
• A river
• A mountain range Gene flow is cut off between the two split
• A desert populations and they can evolve in different
• A road directions (See animations below)
• The sea etc.
Remember
Darwin’s
finches?
http://commons.wikimedia.org/wiki/File:Darwin%27s_finches_by_Gould.jpg
25. Once the populations have been
separated into two gene pools they
can diverge through natural selection
or through random genetic drift
http://upload.wikimedia.org/wikipedia/commons/b/b6/Random_sampling_genetic_drift.gif
26. Allopatric speciation of Drosophila
in the lab
Even when the “geographic barrier”
is removed, the populations are still
genetically isolated
27. Sympatric speciation (Sym = “same”, patric = “fatherland”)
The formation of two or more descendant
species from a single ancestral species all
occupying the same geographic location.
Whether it actually happens is still contested.
Find a pair of species that are thought to have diverged by sympatric speciation
http://etc.usf.edu/clipart/2200/2288/salamander_1.htm
29. D.2.7 Outline the process of adaptive radiation
Starting with a recent single ancestor, this process results in the speciation
and phenotypic adaptation of an array of species exhibiting different
morphological and physiological traits with which they can exploit a range
of divergent environments.
Wikipedia
Think Darwin’s finches (AGAIN!)
They originated from a population of an ancestral species that flew or were blown to the
Galapagos islands from mainland South America.
They colonised the islands and (while geographically isolated) evolved via natural selection
to have beaks that suited the types of food available on their islands.
Their beaks are
homologous structures in
that they have evolved
from a common structure
to have different functions.
30. D.2.8 Compare convergent and divergent evolution
What do humans,
octopi and box
jellyfish have in
common?
http://www.flickr.com/photos/jlambus/2303592201/
31. We all have complex
camera* eyes.
They evolved
independently in
organisms only very
distantly related.
They are an example
of convergent
evolution
Complex eyes
have evolved 50 to
100 times!
*Camera means ‘room’
32. Convergent evolution describes the acquisition of
the same biological trait in unrelated lineages.
Other (random!) examples include:
- Penguins in the southern hemisphere
and Auks in the northern hemisphere
both use wings as flippers Little Auk
- Echolocation in bats, toothed whales
and shrews to capture prey. It even http://commons.wikimedia.org/wiki/File:AlleA
evolved independently twice
amongst the bats
- Super strong jaws on different
genuses of ants (Trapjaw )
- Flight/gliding in birds, pterosaurs,
bats, insects and flying fish!
Little Penguin
http://commons.wikimedia.org/wiki/File:Little_penguin_Eudyptula_minor.jpg
33. I’m including this image
because I mentioned bats
twice on the last slide and
bats are awesome!
*
*Whatever he’s saying, its ultrasonic
http://www.flickr.com/photos/furryscalyman/673915993/
34. Features that come about by convergent evolution are known as
analogous structures
http://www.flickr.com/photos/sniffette/6705872/
http://www.flickr.com/photos/volk/1038089969/
http://www.flickr.com/photos/jaybock/4006029348/
http://www.flickr.com/photos/martynr/76538849/sizes/o/in/photostream/
35. Divergent Evolution is another way of saying adaptive radiation (D.2.7).
As natural selection acts on two or more species that have arisen from a
common ancestor, they become phenotypically different.
It gives rise to homologous structures, features that now look different
or have a different purpose for each species that has evolved
37. Divergent evolution Convergent evolution
Time
Parent species Parent Parent
(common ancestor) species species
38. D.2.9 Discuss ideas on the pace of evolution including gradualism and punctuated evolution
Phyletic Gradualism, as
the name suggests, is the
idea that evolution
occurs at a slow-but-
steady pace.
Punctuated Equilibrium is
the idea that, for most of the
time, species are stable. But
every now and then there is
a disruptive event that
prompts rapid change.
The slope of the line indicates rate of change.
• Vertical lines = little/no change
• Horizontal lines = very rapid change
39. Gradualism is the older idea.
Darwin is one of the
originators of the concept,
borrowing from his friend
Charles Lyell.
Darwin recognised however
that not all species evolve at
the same rate all of the time
"I think case must be that one generation should
have as many living as now. To do this and to have as
many species in same genus (as is) requires
extinction . Thus between A + B the immense gap of
relation. C + B the finest gradation. B+D rather
greater distinction. Thus genera would be formed.
Bearing relation" (next page begins) "to ancient
types with several extinct forms" http://commons.wikimedia.org/wiki/File:Darwin_tree.png
40. Punctuated equilibrium was first proposed
by palaeontologists Niles Eldredge and
Stephen Jay Gould in 1972. They were the
first to suggest that species did not
change for long periods of time but were
in stasis until events punctuated
(disrupted) the equilibrium (balance)
Richard Dawkins is a prominent critic of the theory
TOK: Find out more:
• What evidence are the two theories based on?
• Gould (deceased) and Dawkins have both become
popular writers. How does this affect the weight of
their opinion:
• In the scientific community?
• In the wider community?
http://www.flickr.com/photos/ideonexus/4022727065/
http://www.flickr.com/photos/mrccos/288136783/sizes/m/in/photostream/
41. Revisiting the tree for punctuated
equilibrium it should be noted that the
“sudden” speciation events are only
sudden in terms of geological time. They
would still take many generations and
possibly thousands of years.
The periods of stasis may be
explained by stabilising selection
The punctuation could be
explained by
directional selection or
disruptive selection
42. You should be able to understand and interpret these diagrams.
Practise sketching them.
The downward facing arrows indicate selection pressure against individuals
with that morphology
Stabilising Directional Disruptive
Before
After
All images CC Andrew Colvin
43. Darwin’s Finches (again!) are an example of disruptive selection
A B
Short-beaked birds (A) and long-beaked birds (B) were able to exploit different
food sources and this selection pressure led to the evolution of two species
http://www.flickr.com/photos/kookr/2917861361/
44. Lake Turkana (Kenya,
Ethiopia) contains several
species of snails that have
a fossil record showing The periods of change
long periods with little coincide with times
change followed by when the water level of
sudden change the lake dropped and it
(punctuated equilibrium) became a series of
smaller lakes.
What happens then?
http://en.wikipedia.org/wiki/File:Lake_turkana_satellite.jpg
45. That’s right: geographic isolation
Smaller gene pools are
more susceptible to
directional selection
By the time lake levels
So evolution of the recovered and the
isolated populations may populations were
be faster than when they united, isolating
were one big happy gene mechanisms were in
pool place that prevented
hybridisation
46. After each extinction event, the number of genera has bounced back
Phanerozoic_Biodiversity.svg
47. The K/T extinction event (250 MA at the
Cretaceous-Tertiary boundary) wiped out
over half the genera, including most of
the dinosaurs.
A layer of iridium has been found in
sediments laid down at that time all over
the globe. Iridium is in higher
concentrations in meteorites than on
Earth generally.
Therefore it is postulated that a large
meteor or comet hit the Earth and
caused the extinction.
Individuals in the species that survived could
move into the empty ecological niches and
directional selection led to rapid evolution
http://www.flickr.com/photos/53402955@N08/4928503884/in/photostream/
48. D.2.10 Describe one example of transient polymorphism
Darwin's finches…. Have little to do with this point (for a change!).
Instead, the peppered moths (Biston betularia) are the best known example
Polymorphism is the existence of two or more different forms
of a species Poly = “many” morphism = “shapes”
Prior to 1840 peppered moths in Britain were light grey with dark spots
to blend in with the grey lichen that grew on the trees in their habitat
http://www.flickr.com/photos/wildhastings/4720082589/
49. The first dark variant was
reported in 1848 and by
1895 most of them were
black.
The term industrial
melanism was coined.
Soot and acid rain from
the burning of coal
changed the colour or
the trees that the moths
rested on.
Directional selection did
the rest.
http://www.flickr.com/photos/naturalhistoryman/817332984/
50. Before long the majority were
dark.
This situation reversed after 1956
when Britain instituted the clean
air act. Less coal was burnt and
most trees returned to their
original colour.
Now in polluted areas most
moths are dark and in rural areas
most moths are light.
They are not distinct species
because they still interbreed.
The theory that natural selection
due to predation was the cause
of these changes has been
confirmed experimentally by
Dr HBD Kettlewell
51. D.2.10 Describe sickle cell anaemia as an example of balanced polymorphism
Sickle cell anaemia occurs when a single-base mutation in the gene that
codes for haemoglobin causes the amino acid valine to be produced in a
particular spot rather than glutamic acid.
Valine is non-polar, unlike glutamic acid,
and this causes the mutant variety of
haemoglobin (haemoglobin S) to crystallise
at low concentrations of oxygen.
This in turn pulls the red blood cell into a
sickle shape. It is less able to carry oxygen
and can get stuck in small capillaries,
causing blockages, pain and damage.
Homozygous individuals (HbS HbS) are
subject to a debilitating condition and have
a shortened life expectancy
52. On the brighter side, while individuals who are heterozygous (HbA HbS) will have
some mutant haemoglobin. They can lead normal lives. As a benefit, they are
resistant to malaria as the plasmodium parasite that causes it is not able to use
sickle cells to reproduce.
Individuals that are homozygous normal (HbA HbA) have no sickle cells
and no resistance to malaria.
Historical distribution of malaria Distribution of the sickle cell trait
53. HbA HbA
Haemoglobin: Normal
RBCs: Normal
Heterozygous: Heterozygous: O2 Capacity: Normal
Sickle cell trait Sickle cell trait Malaria resistance: None
HbA HbS
Haemoglobin:
A S A S 50% normal, 50% mutant
RBCs: Usually normal, sickle
when [O2] low
A A A S A S S S O2 Capacity: Mild anaemia
Malaria resistance: Moderate
HbS HbS
Haemoglobin: mutant
RBCs: Sickle
O2 Capacity: Severe anaemia
Malaria Resistance: High
Homozygous: Heterozygous: Homozygous:
‘Normal’ Sickle cell trait Sickle Anaemia
25% chance 50% chance 25% chance http://en.wikipedia.org/wiki/File:Autorecessive.svg
54. This is an example of balancing selection and balanced polymorphism
People who are homozygous for sickle cell are severely anaemic
and have less chance of surviving to reproduce.
Likewise individuals homozygous for normal haemoglobin are likely
to contract malaria and are less likely to survive.
Heterozygous individuals have what
is termed heterozygote advantage.
They are the most likely to survive
and reproduce.
Therefore both alleles are
maintained in the population
http://en.wikipedia.org/wiki/File:Plasmodium.jpg
http://en.wikipedia.org/wiki/File:Sicklecells.jpg
http://commons.wikimedia.org/wiki/File:Simple_balance_scales-01.jpg
55. Hypotheticals:
France has the greatest number of sickle cell sufferers in Europe because
of immigration from its former African and Caribbean colonies.
What do you expect will happen to the sickle cell allele in France over
time given:
1. no more immigration,
2. modern medicine,
3. and the absence of malaria?
What do you expect will happen to the sickle cell allele in West Africa over
time if:
• We eradicate malaria?
Or
• We develop medication that helps all sickle cell sufferers live
normally