Transcript Speciation - eduBuzz.org

Higher Biology
Speciation
Speciation
By the end of this lesson you should be
able to:
Explain what a species is
Know what is meant by a gene pool
Know what happens during speciation
Name the 6 stages leading to the development of a
new species
Name 3 different isolating mechanisms
Know how the 3 sub-species of European wren have
evolved
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Introduction



Speciation is the evolutionary process
leading to the formation of a new species.
Populations first need to be isolated from
each other so that gene pools can diverge.
The isolated populations develop different
characteristics & eventually will no longer be
able to breed with each other.
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Species
What is a species?
Read page 130 of Torrance if you can’t
remember!
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What is meant by a Gene Pool?

The total of
all the
different
genes in a
population is
the gene pool.
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What is meant by a Gene Pool?


As long as the population is large and
mating is random then the gene pool is
considered stable.
Gene frequency is the frequency of
occurrence of an allele of a gene in a
population.
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How does a gene pool change?
Any changes to gene frequency will change the
gene pool.
These include:
1.
Mutation
2.
Natural selection
3.
Gene migration
4.
Non-random mating
5.
Genetic drift
6.
Chance
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How does a gene pool change?
Mutation
New alleles appear & are reshuffled
during meiosis when chromosomes
cross-over & are independently
associated to each other.
1.
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How does a gene pool change?
Natural selection
The frequency of an allele increases in a
population if it provides a selective
advantage.
2.
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How does a gene pool change?
Gene migration
This is when alleles move between
populations by individuals arriving
from a different population &
breeding.
These individuals could have a different
gene pool and so introduce new alleles
into the population.
3.
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How does a gene pool change?
Gene migration
However, continual gene flow decreases
the differences between the gene
pools of populations.
3.
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How does a gene pool change?
Non-random mating
This increases the number of homozygous
individuals (but does not change the
frequency of the alleles)
Inbreeding is a common form of this.
In humans this can increase the chances of the
offspring inheriting a disease caused by a
homozygous recessive genotype (e.g. cystic
fibrosis or sickle cell anaemia)
4.
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How does a gene pool change?
Genetic drift
This tends to occur in small populationssmall populations isolated from each
other can vary greatly from each
other.
5.
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How does a gene pool change?
Chance
Changes to an allele frequency can occur
due to random loss.
e.g. an individual possessing a certain
allele my die or fail to reproduce.
6.
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How does a new species arise?



Speciation is the formation of a new
species.
Evolution is the mechanism by which
speciation occurs and involves changes
to the genotype & phenotype.
These changes enable the organism to
better exploit the environment.
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Stages in Speciation
There are 6 stages.
Stage 1
 A large interbreeding population of
one species exists- sharing the same
gene pool.
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Stages in Speciation
Stage 2
 A barrier separates the population
into 2 isolated sub-populations.
Barriers can be:
geographical
ecological
reproductive
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Stages in Speciation
geographical
This canyon
is isolated
by
mountains
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Stages in Speciation
geographical
Different
terrains on
neighbouring
mountains
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.
Stages in Speciation
geographical
Water
creates a
difficult
barrier to
cross
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.
Stages in Speciation
geographical
Deserts are
hostile
environments
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Stages in Speciation
ecological
e.g. changes in temperature, humidity
pH, salinity, altitude
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Stages in Speciation
reproductive
e.g. different populations are fertile
at different times of the year.
OR changes to sexual organs
OR different courtship behaviour
OR individuals no longer attracted to each other
OR pollination/fertilisation fails
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Stages in Speciation
Stage 3
 Random mutations in each subpopulation give rise to new variation
within each group (but not shared by
both groups)
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Stages in Speciation
Stage 4
 Different selection pressures act on
each sub-population depending on
local conditions like:



Climate
Predators
Disease.
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Stages in Speciation
Stage 4
 Natural selection affects each subgroup in a different way, by favouring
the alleles that allow the individuals
to better exploit their environment.
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Stages in Speciation
Stage 5
 Over a very very long time……
Stages 3 & 4 cause the two gene pools to
become so altered that the groups
become genetically distinct &
isolated.
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Stages in Speciation
Stage 6
 If the original barrier is removed, the
two sub-populations are no longer able
to interbreed (since their
chromosomes are no longer able to
form homologous pairs).
 There are now 2 separate distinct
species.
 Speciation has occurred!
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Stages in Speciation
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European Wren
Explain how the 3 sub-species of wren
have evolved, with reference to:
 Isolation
 Mutation
 Natural selection
 Future speciation
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Practice Questions
Torrance:
 Page 136 TYK Q2
 Pages 137-8 AYK Q1-5
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Speciation
Can you do it?
Explain what a species is
Know what is meant by a gene pool
Know what happens during speciation
Name the 6 stages leading to the development of a
new species
Name 3 different isolating mechanisms
Know how the 3 sub-species of European wren have
evolved
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