1. Higher Biology
Speciation

2. 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

3. 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.

4. Species What is a species?
Read page 130 of Torrance if you can’t remember!

5. What is meant by a Gene Pool?
The total of all the different genes in a population is the gene pool.

6. 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.

7. How does a gene pool change?
Any changes to gene frequency will change the gene pool.
These include:
Mutation
Natural selection
Gene migration
Non-random mating
Genetic drift
Chance

8. How does a gene pool change?
Mutation
New alleles appear & are reshuffled during meiosis when chromosomes cross-over & are independently associated to each other.

9. How does a gene pool change?
Natural selection
The frequency of an allele increases in a population if it provides a selective advantage.

10. 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.

11. How does a gene pool change?
Gene migration
However, continual gene flow decreases the differences between the gene pools of populations.

12. 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)

13. How does a gene pool change?
Genetic drift
This tends to occur in small populations- small populations isolated from each other can vary greatly from each other.

14. 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.

15. 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.

16. Stages in Speciation There are 6 stages. Stage 1
A large interbreeding population of one species exists- sharing the same gene pool.

17. Stages in Speciation Stage 2
A barrier separates the population into 2 isolated sub-populations.
Barriers can be:
geographical
ecological
reproductive

18. Stages in Speciation
geographical
This canyon is isolated by mountains

19. Stages in Speciation geographical
Different terrains on neighbouring mountains

20. Stages in Speciation geographical.
geographical
Water creates a difficult barrier to cross

21. Stages in Speciation .
geographical
Deserts are hostile environments

22. Stages in Speciation e.g. changes in temperature, humidity
ecological
e.g. changes in temperature, humidity
pH, salinity, altitude

23. 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

24. 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)

25. Stages in Speciation Stage 4
Different selection pressures act on each sub-population depending on local conditions like:
Climate
Predators
Disease.

26. 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.

27. 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.

28. 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!

29. Stages in Speciation

30. European Wren
Explain how the 3 sub-species of wren have evolved, with reference to:
Isolation
Mutation
Natural selection
Future speciation

31. Practice Questions
Torrance:
Page 136 TYK Q2
Pages AYK Q1-5

32. 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