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Teacher's Notes
Mechanisms
of Evolution
Grades: 11-12
Duration: 28 mins
Summary of Program
Evolution is the gradual change that can be seen
in a population’s genetic composition, from one
generation to the next. The three main
mechanisms of evolution include:
1.
Genetic Drift
2.
Mutation, and
3.
Natural Selection
The first part will concentrate on Genetic Drift
with the use of a model to demonstrate its
effect on small and large populations. An
example will also be used to explain how Genetic
Drift can lead to the formation of new biological
species over a long period of time. Then models
of Mutation and Natural Selection will be
demonstrated and the results carefully tabulated
and analyzed. Examples of particular populations,
which have likely evolved through each
mechanism, will also be highlighted.
1.
Genetic Drift
A population is a group of interbreeding
organisms of the same species. There is great
variation within any population due to each type
of gene being present in different forms and
frequencies. The collection of all the different
types of genes in a population is known as a
gene pool. From generation to generation,
changes in the gene pool will occur due to
chance leading to the disappearance of
particular forms of a gene. This phenomenon is
called Genetic Drift and it occurs more quickly
when the population is small. Since this process
is due to chance, the loss of a particular gene
from a population’s gene pool is completely
random. This means that two different
populations of a certain species living in close
proximity yet isolated from each other (e.g..
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geographical barrier) may produce different
results. The long-term outcome of Genetic
Drift occurring in these two populations can
be the formation of a new biological species.
This is known as speciation.
2.
Mutation
Mutations are changes that can occur in
individuals DNA. They may result from a
deletion, transposition or duplication of a part
of the DNA, or a substitution of one or more
nucleotides in the molecule. Most mutations
occur randomly and spontaneously, and
generally have no effect on the organism’s
survival. However, other types of mutations
include those that are:
a)
deleterious, which have a varying,
negative effect on an organism’s survival
b)
lethal, where organism’s do not live long
enough to reproduce, and
c)
advantageous, which increases the
organism’s chances of survival.
Mutations are generally regarded as the main
driving force for evolutionary change.
3.
Natural Selection
In any organism a particular gene will occur in
pairs (one from each parent) called alleles.
Alleles may confer favourable characteristics
to the organism making it more likely to
survive and reproduce in a particular
environment. This means that these alleles
are more likely to be present in greater
numbers in the next generation. In contrast,
an organism that has inherited less favourable
alleles for a particular environment will be less
likely to survive and reproduce. These alleles
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will eventually diminish from the population
with time. This interaction between an
organism and its environment results in
changes in the population’s gene pool from
generation to generation, leading to
evolution. This process was introduced by
Charles Darwin in 1838 and is known as
Natural Selection.
Humans have been manipulating the process
of selecting “favourable” characteristics for
the purpose of breeding crops and animals.
For example, traits for sweetness in fruit and
size in animals are often specifically selected
and carefully bred into succeeding
generations. This is called artificial selection.
The smaller the population size, the quicker
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the desired outcome is reached.
Pre-Video Work
1.
Students can write their own definition
for what they understand evolution to
mean. Collect a variety of responses
from the students and use them to
formulate a formal definition for the
class to incorporate into their work.
2.
Visit the library with your class and
instruct students to research two
contributors to the theory of evolution
and briefly describe their ideas (e.g..
Charles Darwin, Jean Baptiste Lamarck,
Georges Cuvier, Louis Agassiz, Alfred
Russel Wallace).
3.
Have a ‘Pop Quiz’ with the class or
simply discuss the meaning of the
following terms, population, genes, gene
pool, and species.
4.
Read the questions on the student work
sheet with the class to familiarize them
with the work to be completed. It is
advised that students carefully view the
video first to give it their full attention
and then attempt the questions during a
second viewing.
5.
Revise work on mutations by discussing
the following terms, chromosome, gene,
allele, DNA, nucleotide, base pair, amino
acid, mutation, DNA replication, and
protein synthesis (transcription and
translation). Alternatively, students
could be asked to write a paragraph
about mutations using the above terms.
6.
Visit the library to research
diseases/disorders caused by
different types of mutations.
Students could either
a) be given the name of a particular
condition to work on and be
asked to determine the category
of mutation that it belongs to
along with its effects on the
individual and possible treatment,
or else,
b) choose their own disorder to
research from a pre-determined
category.
This will eliminate students all
researching the same disease. A
brief presentation could then be
given to the class.
Conditions could include sickle cell
anaemia, phenylketonuria, Down’s
Syndrome, haemophilia, Tay-Sachs
disease, Huntington’s disease,
colour-blindness, Duchenne muscular
dystrophy, Aniridia tumour, Wilms’
tumour, dwarfism, albinism.
7.
Ask students to write a paragraph
about the main idea behind Natural
Selection. Students are encouraged
to discuss their understanding of
Natural Selection with the class.
CREDITS
Writer/Producer
Arthur Tanaka
On-line Editor
Dominique Fusy
Photography
Peter Beeh
Graphics/Editor
Rowena Crowe
Sound
Phillip Mcguire
Dominique Fusy
Consultant/Teachers Notes
Vanesssa Hutchinson
Executive Producers
John Davis
Corinna Klupiec
Thanks to
Mark Tanaka
University of NSW
Copyright
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Student Worksheet:
Part 1 - Genetic Drift
1.
What is heredity?
2.
Who described how heredity works?
3.
What word did he use for the term ‘gene’?
4.
How do bacteria and eukaryotes differ?
5.
What is an allele?
6.
How did the two students in the demonstration ensure random mating would occur between the organisms they were
studying?
7.
What assumptions are made in this demonstration?
8.
Describe the results obtained from this demonstration?
9.
Describe a ‘population bottleneck’.
10. Where can population bottlenecks occur in nature?
11. What happened when the demonstration was repeated with a larger population?
12. How is Genetic Drift used a genetic tool?
13. Define speciation and how it can occur.
14. Why does Madagascar have so many different varieties of Lemurs?
15. Genetic Drift occurs _____________ in small populations and _____________ in larger populations.
16. Genetic Drift occurs _____________ in isolated populations and _____________ in non-isolated populations.
17. Populations living close to each other, but isolated from each other may drift into
becoming _____________ species over a very long time, through Genetic Drift.
Activities following the video
1.
Students can repeat the experiments for themselves. Half the class can examine the effect of Genetic Drift on large populations
and the other half, small populations. Between each group comparisons can be made about which genes have gone extinct.
This can highlight the random nature of Genetic Drift.
2.
Have students discuss in terms of Genetic Drift how it could be possible in nature for two different populations of the same
species living close by to diverge into two different species over time. Discussion can be guided towards the effects of different
types of isolation (eg. reproductive isolation, geographical isolation, genetic isolation).
Research Task
1.
In this video, two members of the Prosimian group of Primates, the Lemur’s of Madagascar and the Lorises of India, were used
as an example of populations that have experienced Genetic Drift. Use secondary sources to research another species that has
undergone this process.
Student Worksheet:
Part 2 - Mutation and Natural Selection
1.
Define mutation.
2.
Give an example of the effect of mutation.
3.
Name 4 types of mutations.
4.
A ____________ mutation has no effect on the survival of the organism.
5.
The number of ____________ mutations far outweigh the ____________, ____________ or ____________ mutations in
any single organism.
6.
Mutation is the ultimate source of genetic ____________.
7.
Evolution needs ____________.
8.
Mutation acts in opposition to ____________ ____________ by increasing variation.
9.
Name the organism that Darwin studied on the Galapagos Islands.
10. It is through Natural Selection that ____________ changes occur in a population.
11. Selection occurs when one ____________ is favoured over another by the environment.
12. Define adaptation.
13. How was Natural Selection modelled in the demonstration.
14. In a ____________ population, the effect of Natural Selection may take a long time to manifest.
15. In a small population what force can overpower the effect of Natural Selection?
16. What effect has Natural Selection had on fish and the fishing industry?
17. What effect has Natural Selection had on bacteria?
18. How have humans used Natural Selection to their advantage? Give examples of its use.
Activities following the video
1.
Students can design and conduct their own demonstration to model Natural Selection. It may involve using counters of varying
colours of which one may be better able to camouflage into a particular surface (eg. the grass, earth or if you wish to remain in
the classroom a coloured mat could be used).
2.
Discuss the effects that Genetic Drift, Mutation and Natural Selection have on genetic variation. Students can also discuss the
benefits of variation within a population.
Research Task
1.
In this video, the decrease in the size of fish caught by the fishing industry and the increased resistance of bacteria to
antibiotics, were discussed as examples of Natural Selection. Students are to use secondary sources to research their own
example of the effect of Natural Selection upon a population. Students may work in pairs to collect and present their
information to the class.