SPECIATION
1.3 Genome: (c) iv Speciation
From the Arrangements
Speciation is the generation of new biological species by evolution. A species
is a group of organisms capable of interbreeding and producing fertile
offspring, and which does not normally breed with ot her groups.
The importance of geographical barriers in allopatric speciation. The
importance of behavioural or ecological barriers in sympatric speciation.
The formation of hybrid zones in regions where the ranges of closely related
species meet.
Teacher’s notes
Activity 1
As an introduction show students the The facts of evolution – speciation (9
minutes):
http://www.liveleak.com/view?i=9d6_1267560644
You can also download this from YouTube (you may prefer to do this since
there are some suspect adverts on the web page) . As the class watch it get
everyone to take notes. The narrator’s voice is clear and relatively slow,
which is ideal for note taking.
(The video clip mentions hooded and carrion crow hybridisation and
salamander hybridisation zones. Make sure you emphasise that a species is a
group of organisms that can interbreed and produce fertile young.)
As soon as the video is finished pair the students up and give them 5 minutes
to compare notes and write down bits they missed. Repeat this process again
and perhaps a third time if you think it necessary. For homework get students
to redraft their notes into a final version.
It is important that you make clear from the beginning what you are
demanding from the students and what processes they will have to go through
to deliver their final report.
UNIT 1, PART (III) GENOME (H, BIOLOGY)
© Learning and Teaching Scotland 2011
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SPECIATION
Activity 2
The following link takes you to a pdf file that contains three activities which
relate to evolution. In particular ‘The evolution of a DNA sequence over
time’ activity ties in well with this section of the course. All three activities
are pitched at the right level, building on previous knowledge of DNA
sequences and protein synthesis. Furthermore, there is an excellent set of
instructions contained in the document to get students started.
http://www.asm.org/images/MDA-PDF/mda-evolutionofdnabwpdf.final.pdf
The activity is also useful in that it addresses several of the components of
Darwin’s theory of evolution through natural selection. There are three
separate activities, one regarding sequence change over time, one regarding
selective pressure on sequences and one regarding divergence over time.
Activity 3
Print off or display the two diagrams on allopatric and sympatric speciation.
A data projector would be ideal.
Working in pairs, give students a copy of the worksheet ‘Allopatric
speciation’, a sheet of A3 or poster paper, scissors and glue. The instructions
are given in the textbox at the foot of the sheet. Once the students have
completed the task choose two or three groups who have a different layout in
their poster and get them to explain to the rest of the class why they presented
the information the way they did.
Activity 4
This is a mix and match activity based on Torrance ’s Higher Biology, which
was written for the previous Arrangements. (The chapter and page numbers
have been included to help students navigate through the relev ant sections of
the book. These could easily be deleted to leave this as a stand -alone
activity.)
Activity 5
This is based on students researching sympatric speciation. Guidance is given
so that suitable examples can be used to illustrate the phenomenon. You may
wish to use the diagrams as a way of introducing the topic and comparing it
to allopatric speciation.
This activity could be used within the classroom but would make an ideal
homework task. Students could be asked to present their work to the cla ss as
a talk or as a poster.
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UNIT 1, PART (III) GENOME (H, BIOLOGY)
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SPECIATION
‘On the other hand, ‘we may feel sure that any variation in the least degree injurious would be rigidly destroyed.
This preservation of favourable variations and the rejection of injurio us variations, I call natural selection.’
Charles Darwin (1859) on the origin of species by the means of natural selection
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SPECIATION
Student activities
Allopatric speciation
Learning objectives
By completing this exercise you will know what allopatric speciation
involves. You will appreciate why geographical barriers pla y an important
role in this type of speciation. Allopatric speciation is the evolution of new
species in populations that are geographically isolated from one another .
Species
generally give
rise to fertile
offspring.
Isolation of a
group of
individuals due
to mountain
ranges, oceans
or migration.
Species are
populations
within which
genes are free
to mix by
interbreeding.
New or
favourable
alleles are
passed onto
the next
generation.
Less welladapted
organisms fail
to pass on
their alleles to
the next
generation.
Best adapted
survive
(survival of the
fittest).
Over time and
many
generations
different
characteristics
begin to
emerge.
Environmental
selection
pressures are
different for
each group.
Genetic
differences,
due to
mutations in
the separated
populations,
begin to
accumulate.
Individuals
within a
population
may not be
able to
compete as
well as others.
Starting off
with one
population, a
common gene
pool.
The original
environment
may be very
different from
the isolated
area.
Geographical
barriers
prevent
interbreeding
of populations.
Healthiest or
best
individuals
will be the
most likely to
breed.
New
phenotypes
gradually
appear in the
population.
Genetic drift
(random
mutations/
differences)
occurs
independently.
Healthiest or
best
individuals
will be the
most likely to
breed.
Different
mutations arise
in different
populations.
Mutations
give rise to
different
phenotypes.
Individuals
within a
population
may become
better at
exploiting
their
environment.
Mutations
occurring in
each
population will
be different.
Usually a good
correlation
with the
phenotype
(underlying
new alleles)
and the
environment.
Members of the
different
populations
may become so
distinct that
they can no
longer breed.
Often
isolated
populations
are very
small.
Evolution
occurs and
new
biological
species are
formed.
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UNIT 1, PART (III) GENOME (H, BIOLOGY)
© Learning and Teaching Scotland 2011
SPECIATION
What to do
Your teacher may show you a diagram on allopatric and sympatric speciation.
Working in pairs, cut out each box and decide which statements are closely
related.
Lay out the statements in the order which tells the story of allopatric
speciation. If it helps, stick the statements onto a sheet of poster paper and
make little drawings to help clarify your thoughts.
There are some statements that are very similar, but you must use them all.
Be prepared to explain why you grouped the statements as you did.
Can you explain how variation occurs and why it is important?
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SPECIATION
Speciation (chapters 18–20, p130–151)
Keyword (page number)
Definition
Gene pool (130)
The rate at which an allele occurs in a
population
Gene frequency (130)
The frequency of particular alleles
increases following a selective
advantage after an environmental
change
Natural selection (130)
The formation of new species
(usually many from a few)
Genetic drift (130)
A group of similar organisms that are
capable of producing fertile young
Species (130)
A device that splits a population,
isolating the two subpopulations and
preventing interbreeding and gene
exchange
Barrier (131)
When a small group of a species
becomes isolated and after several
generations becomes distinctive since
the frequency of certain alleles has
changed
Speciation (130)
All the alleles in a population of
interbreeding individuals
Evolutionary tree (134)
Evidence gained from rocks allowing
evolutionary trees to be constructed
Fossil record (134)
The role an organism plays within a
community
Niche (134)
The evolution of a group of closely
related organisms (common ancestor)
along several different lines by
adapting over a long period of time to
a wide variety of environments
Adaptive radiation (139)
A time line of evolution showing
common ancestors and groups of
closely related species
Rewrite the table properly, placing the correct definition with its keyword.
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UNIT 1, PART (III) GENOME (H, BIOLOGY)
© Learning and Teaching Scotland 2011
SPECIATION
The table should look like this:
Key word (page number)
Definition
Gene pool (130)
All the alleles in a population of
interbreeding individuals
Gene frequency (130)
The rate at which an allele occurs in a
population
Natural selection (130)
The frequency of particular alleles
increases following a selective
advantage after an environmental
change
Genetic drift (130)
When a small group of a species
becomes isolated and after several
generations becomes distinctive since
the frequency of certain alleles has
changed
Species (130)
A group of similar organisms that are
capable of producing fertile young
Barrier (131)
A device that splits a population,
isolating the two subpopulations and
preventing interbreeding and gene
exchange
Speciation (130)
The formation of new species
(usually many from a few)
Evolutionary tree (134)
A time line of evolution showing
common ancestors and groups of
closely related species
Fossil record (134)
Evidence gained from rocks allowing
evolutionary trees to be constructed
Niche (134)
The role an organism plays within a
community
Adaptive radiation (139)
The evolution of a group of closely
related organisms (common ancestor)
along several different lines by
adapting over a long period of time to
a wide variety of environments
UNIT 1, PART (III) GENOME (H, BIOLOGY)
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SPECIATION
Sympatric speciation
Learning objective
You should know the definition of sympatric speciation and by carrying out
the research activity be able to give at least two examples of this type of
evolution.
You should know that there are likely to be behavioural or ecological barriers
in place to prevent gene exchange within a given area. Behavioural barriers ,
such as breeding patterns or rituals, and ecological barriers, such as food
availability, may operate in sympatric speciation. Sympatric speciation is the
evolution of new species in populations tha t live in the same geographic area.
Sympatric speciation is where new species evolve from a single species
whilst inhabiting the same geographic region. The areas may overlap or be
within the same boundary.
The above definition raises the question of how speciation can occur within a
population of interbreeding individuals.
Find out what sort of ecological and behavioural barriers lead to speciation
within the same geographical area. Clearly explain what the selection
pressures are and how this affects the phenotype of the emerging new species.
The medium ground finch, cichlid fish and apple maggot flies of North
America would make a good starting point (eg type ‘ground finch and
sympatric speciation’ into your search engine.
Present your findings in a written report of no more than one page. Labelled
diagrams with accompanying explanations are acceptable.
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UNIT 1, PART (III) GENOME (H, BIOLOGY)
© Learning and Teaching Scotland 2011