Higher Biology Speciation. 2 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.

Higher Biology

Speciation

2

Speciation

By the end of this lesson you should be able to:

Explain what a species isKnow what is meant by a gene poolKnow what happens during speciationName the 6 stages leading to the development of a new speciesName 3 different isolating mechanismsKnow how the 3 sub-species of European wren haveevolved

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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. Mutation2. Natural selection3. Gene migration4. Non-random mating5. Genetic drift6. Chance

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How does a gene pool change?

1. MutationNew alleles appear & are reshuffled

during meiosis when chromosomes cross-over & are independently associated to each other.

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How does a gene pool change?

2. Natural selectionThe frequency of an allele increases

in a population if it provides a selective advantage.

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How does a gene pool change?

3. Gene migrationThis 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.

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How does a gene pool change?

3. Gene migrationHowever, continual gene flow

decreases the differences between the gene pools of populations.

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How does a gene pool change?

4. Non-random matingThis 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)

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How does a gene pool change?

5. Genetic driftThis tends to occur in small

populations- small populations isolated from each other can vary greatly from each other.

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How does a gene pool change?

6. ChanceChanges to an allele frequency can

occur due to random loss.e.g. an individual possessing a certain

allele my die or fail to reproduce.

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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

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Water creates a difficult barrier to cross

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Stages in Speciation

geographical

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Deserts are hostile environments

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Stages in Speciation

ecological

e.g. changes in temperature, humiditypH, 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 organsOR different courtship behaviourOR individuals no longer attracted to each otherOR pollination/fertilisation fails

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Stages in Speciation

Stage 3 Random mutations in each sub-

population 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 sub-

group 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 isKnow what is meant by a gene poolKnow what happens during speciationName the 6 stages leading to the development of a new speciesName 3 different isolating mechanismsKnow how the 3 sub-species of European wren haveevolved